Merge "Add bp2build mode to soong_build."
diff --git a/Android.bp b/Android.bp
index e7a5de2..866ed25 100644
--- a/Android.bp
+++ b/Android.bp
@@ -75,6 +75,10 @@
     product_available: true,
     recovery_available: true,
     native_bridge_supported: true,
+    apex_available: [
+        "//apex_available:platform",
+        "//apex_available:anyapex",
+    ],
 
     arch: {
         arm: {
diff --git a/android/androidmk.go b/android/androidmk.go
index 7afc9de..42c5d00 100644
--- a/android/androidmk.go
+++ b/android/androidmk.go
@@ -12,6 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// This file offers AndroidMkEntriesProvider, which individual modules implement to output
+// Android.mk entries that contain information about the modules built through Soong. Kati reads
+// and combines them with the legacy Make-based module definitions to produce the complete view of
+// the source tree, which makes this a critical point of Make-Soong interoperability.
+//
+// Naturally, Soong-only builds do not rely on this mechanism.
+
 package android
 
 import (
@@ -36,8 +43,8 @@
 	ctx.RegisterSingletonType("androidmk", AndroidMkSingleton)
 }
 
-// Deprecated: consider using AndroidMkEntriesProvider instead, especially if you're not going to
-// use the Custom function.
+// Deprecated: Use AndroidMkEntriesProvider instead, especially if you're not going to use the
+// Custom function. It's easier to use and test.
 type AndroidMkDataProvider interface {
 	AndroidMk() AndroidMkData
 	BaseModuleName() string
@@ -63,37 +70,82 @@
 
 type AndroidMkExtraFunc func(w io.Writer, outputFile Path)
 
-// Allows modules to customize their Android*.mk output.
+// Interface for modules to declare their Android.mk outputs. Note that every module needs to
+// implement this in order to be included in the final Android-<product_name>.mk output, even if
+// they only need to output the common set of entries without any customizations.
 type AndroidMkEntriesProvider interface {
+	// Returns AndroidMkEntries objects that contain all basic info plus extra customization data
+	// if needed. This is the core func to implement.
+	// Note that one can return multiple objects. For example, java_library may return an additional
+	// AndroidMkEntries object for its hostdex sub-module.
 	AndroidMkEntries() []AndroidMkEntries
+	// Modules don't need to implement this as it's already implemented by ModuleBase.
+	// AndroidMkEntries uses BaseModuleName() instead of ModuleName() because certain modules
+	// e.g. Prebuilts, override the Name() func and return modified names.
+	// If a different name is preferred, use SubName or OverrideName in AndroidMkEntries.
 	BaseModuleName() string
 }
 
+// The core data struct that modules use to provide their Android.mk data.
 type AndroidMkEntries struct {
-	Class           string
-	SubName         string
-	OverrideName    string
-	DistFiles       TaggedDistFiles
-	OutputFile      OptionalPath
-	Disabled        bool
-	Include         string
-	Required        []string
-	Host_required   []string
+	// Android.mk class string, e.g EXECUTABLES, JAVA_LIBRARIES, ETC
+	Class string
+	// Optional suffix to append to the module name. Useful when a module wants to return multiple
+	// AndroidMkEntries objects. For example, when a java_library returns an additional entry for
+	// its hostdex sub-module, this SubName field is set to "-hostdex" so that it can have a
+	// different name than the parent's.
+	SubName string
+	// If set, this value overrides the base module name. SubName is still appended.
+	OverrideName string
+	// Dist files to output
+	DistFiles TaggedDistFiles
+	// The output file for Kati to process and/or install. If absent, the module is skipped.
+	OutputFile OptionalPath
+	// If true, the module is skipped and does not appear on the final Android-<product name>.mk
+	// file. Useful when a module needs to be skipped conditionally.
+	Disabled bool
+	// The postprocessing mk file to include, e.g. $(BUILD_SYSTEM)/soong_cc_prebuilt.mk
+	// If not set, $(BUILD_SYSTEM)/prebuilt.mk is used.
+	Include string
+	// Required modules that need to be built and included in the final build output when building
+	// this module.
+	Required []string
+	// Required host modules that need to be built and included in the final build output when
+	// building this module.
+	Host_required []string
+	// Required device modules that need to be built and included in the final build output when
+	// building this module.
 	Target_required []string
 
 	header bytes.Buffer
 	footer bytes.Buffer
 
+	// Funcs to append additional Android.mk entries or modify the common ones. Multiple funcs are
+	// accepted so that common logic can be factored out as a shared func.
 	ExtraEntries []AndroidMkExtraEntriesFunc
+	// Funcs to add extra lines to the module's Android.mk output. Unlike AndroidMkExtraEntriesFunc,
+	// which simply sets Make variable values, this can be used for anything since it can write any
+	// Make statements directly to the final Android-*.mk file.
+	// Primarily used to call macros or declare/update Make targets.
 	ExtraFooters []AndroidMkExtraFootersFunc
 
-	EntryMap   map[string][]string
+	// A map that holds the up-to-date Make variable values. Can be accessed from tests.
+	EntryMap map[string][]string
+	// A list of EntryMap keys in insertion order. This serves a few purposes:
+	// 1. Prevents churns. Golang map doesn't provide consistent iteration order, so without this,
+	// the outputted Android-*.mk file may change even though there have been no content changes.
+	// 2. Allows modules to refer to other variables, like LOCAL_BAR_VAR := $(LOCAL_FOO_VAR),
+	// without worrying about the variables being mixed up in the actual mk file.
+	// 3. Makes troubleshooting and spotting errors easier.
 	entryOrder []string
 }
 
 type AndroidMkExtraEntriesFunc func(entries *AndroidMkEntries)
 type AndroidMkExtraFootersFunc func(w io.Writer, name, prefix, moduleDir string, entries *AndroidMkEntries)
 
+// Utility funcs to manipulate Android.mk variable entries.
+
+// SetString sets a Make variable with the given name to the given value.
 func (a *AndroidMkEntries) SetString(name, value string) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -101,6 +153,7 @@
 	a.EntryMap[name] = []string{value}
 }
 
+// SetPath sets a Make variable with the given name to the given path string.
 func (a *AndroidMkEntries) SetPath(name string, path Path) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -108,12 +161,15 @@
 	a.EntryMap[name] = []string{path.String()}
 }
 
+// SetOptionalPath sets a Make variable with the given name to the given path string if it is valid.
+// It is a no-op if the given path is invalid.
 func (a *AndroidMkEntries) SetOptionalPath(name string, path OptionalPath) {
 	if path.Valid() {
 		a.SetPath(name, path.Path())
 	}
 }
 
+// AddPath appends the given path string to a Make variable with the given name.
 func (a *AndroidMkEntries) AddPath(name string, path Path) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -121,12 +177,15 @@
 	a.EntryMap[name] = append(a.EntryMap[name], path.String())
 }
 
+// AddOptionalPath appends the given path string to a Make variable with the given name if it is
+// valid. It is a no-op if the given path is invalid.
 func (a *AndroidMkEntries) AddOptionalPath(name string, path OptionalPath) {
 	if path.Valid() {
 		a.AddPath(name, path.Path())
 	}
 }
 
+// SetPaths sets a Make variable with the given name to a slice of the given path strings.
 func (a *AndroidMkEntries) SetPaths(name string, paths Paths) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -134,12 +193,15 @@
 	a.EntryMap[name] = paths.Strings()
 }
 
+// SetOptionalPaths sets a Make variable with the given name to a slice of the given path strings
+// only if there are a non-zero amount of paths.
 func (a *AndroidMkEntries) SetOptionalPaths(name string, paths Paths) {
 	if len(paths) > 0 {
 		a.SetPaths(name, paths)
 	}
 }
 
+// AddPaths appends the given path strings to a Make variable with the given name.
 func (a *AndroidMkEntries) AddPaths(name string, paths Paths) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -147,6 +209,8 @@
 	a.EntryMap[name] = append(a.EntryMap[name], paths.Strings()...)
 }
 
+// SetBoolIfTrue sets a Make variable with the given name to true if the given flag is true.
+// It is a no-op if the given flag is false.
 func (a *AndroidMkEntries) SetBoolIfTrue(name string, flag bool) {
 	if flag {
 		if _, ok := a.EntryMap[name]; !ok {
@@ -156,6 +220,7 @@
 	}
 }
 
+// SetBool sets a Make variable with the given name to if the given bool flag value.
 func (a *AndroidMkEntries) SetBool(name string, flag bool) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -167,6 +232,7 @@
 	}
 }
 
+// AddStrings appends the given strings to a Make variable with the given name.
 func (a *AndroidMkEntries) AddStrings(name string, value ...string) {
 	if len(value) == 0 {
 		return
@@ -177,6 +243,18 @@
 	a.EntryMap[name] = append(a.EntryMap[name], value...)
 }
 
+// AddCompatibilityTestSuites adds the supplied test suites to the EntryMap, with special handling
+// for partial MTS test suites.
+func (a *AndroidMkEntries) AddCompatibilityTestSuites(suites ...string) {
+	// MTS supports a full test suite and partial per-module MTS test suites, with naming mts-${MODULE}.
+	// To reduce repetition, if we find a partial MTS test suite without an full MTS test suite,
+	// we add the full test suite to our list.
+	if PrefixInList(suites, "mts-") && !InList("mts", suites) {
+		suites = append(suites, "mts")
+	}
+	a.AddStrings("LOCAL_COMPATIBILITY_SUITE", suites...)
+}
+
 // The contributions to the dist.
 type distContributions struct {
 	// List of goals and the dist copy instructions.
@@ -222,13 +300,32 @@
 	amod := mod.(Module).base()
 	name := amod.BaseModuleName()
 
+	// Collate the set of associated tag/paths available for copying to the dist.
+	// Start with an empty (nil) set.
 	var availableTaggedDists TaggedDistFiles
 
+	// Then merge in any that are provided explicitly by the module.
 	if a.DistFiles != nil {
-		availableTaggedDists = a.DistFiles
-	} else if a.OutputFile.Valid() {
-		availableTaggedDists = MakeDefaultDistFiles(a.OutputFile.Path())
-	} else {
+		// Merge the DistFiles into the set.
+		availableTaggedDists = availableTaggedDists.merge(a.DistFiles)
+	}
+
+	// If no paths have been provided for the DefaultDistTag and the output file is
+	// valid then add that as the default dist path.
+	if _, ok := availableTaggedDists[DefaultDistTag]; !ok && a.OutputFile.Valid() {
+		availableTaggedDists = availableTaggedDists.addPathsForTag(DefaultDistTag, a.OutputFile.Path())
+	}
+
+	// If the distFiles created by GenerateTaggedDistFiles contains paths for the
+	// DefaultDistTag then that takes priority so delete any existing paths.
+	if _, ok := amod.distFiles[DefaultDistTag]; ok {
+		delete(availableTaggedDists, DefaultDistTag)
+	}
+
+	// Finally, merge the distFiles created by GenerateTaggedDistFiles.
+	availableTaggedDists = availableTaggedDists.merge(amod.distFiles)
+
+	if len(availableTaggedDists) == 0 {
 		// Nothing dist-able for this module.
 		return nil
 	}
@@ -245,7 +342,7 @@
 		var tag string
 		if dist.Tag == nil {
 			// If the dist struct does not specify a tag, use the default output files tag.
-			tag = ""
+			tag = DefaultDistTag
 		} else {
 			tag = *dist.Tag
 		}
@@ -259,10 +356,10 @@
 		}
 
 		if len(tagPaths) > 1 && (dist.Dest != nil || dist.Suffix != nil) {
-			errorMessage := "Cannot apply dest/suffix for more than one dist " +
-				"file for %s goals in module %s. The list of dist files, " +
+			errorMessage := "%s: Cannot apply dest/suffix for more than one dist " +
+				"file for %q goals tag %q in module %s. The list of dist files, " +
 				"which should have a single element, is:\n%s"
-			panic(fmt.Errorf(errorMessage, goals, name, tagPaths))
+			panic(fmt.Errorf(errorMessage, mod, goals, tag, name, tagPaths))
 		}
 
 		copiesForGoals := distContributions.getCopiesForGoals(goals)
@@ -337,6 +434,8 @@
 	return generateDistContributionsForMake(distContributions)
 }
 
+// fillInEntries goes through the common variable processing and calls the extra data funcs to
+// generate and fill in AndroidMkEntries's in-struct data, ready to be flushed to a file.
 func (a *AndroidMkEntries) fillInEntries(config Config, bpPath string, mod blueprint.Module) {
 	a.EntryMap = make(map[string][]string)
 	amod := mod.(Module).base()
@@ -400,7 +499,9 @@
 			}
 		}
 
-		a.AddStrings("LOCAL_INIT_RC", amod.commonProperties.Init_rc...)
+		if !amod.InRamdisk() && !amod.InVendorRamdisk() {
+			a.AddStrings("LOCAL_INIT_RC", amod.commonProperties.Init_rc...)
+		}
 		a.AddStrings("LOCAL_VINTF_FRAGMENTS", amod.commonProperties.Vintf_fragments...)
 		a.SetBoolIfTrue("LOCAL_PROPRIETARY_MODULE", Bool(amod.commonProperties.Proprietary))
 		if Bool(amod.commonProperties.Vendor) || Bool(amod.commonProperties.Soc_specific) {
@@ -457,6 +558,8 @@
 	}
 }
 
+// write  flushes the AndroidMkEntries's in-struct data populated by AndroidMkEntries into the
+// given Writer object.
 func (a *AndroidMkEntries) write(w io.Writer) {
 	if a.Disabled {
 		return
@@ -477,6 +580,8 @@
 	return strings.Split(string(a.footer.Bytes()), "\n")
 }
 
+// AndroidMkSingleton is a singleton to collect Android.mk data from all modules and dump them into
+// the final Android-<product_name>.mk file output.
 func AndroidMkSingleton() Singleton {
 	return &androidMkSingleton{}
 }
@@ -484,6 +589,7 @@
 type androidMkSingleton struct{}
 
 func (c *androidMkSingleton) GenerateBuildActions(ctx SingletonContext) {
+	// Skip if Soong wasn't invoked from Make.
 	if !ctx.Config().KatiEnabled() {
 		return
 	}
@@ -494,6 +600,8 @@
 		androidMkModulesList = append(androidMkModulesList, module)
 	})
 
+	// Sort the module list by the module names to eliminate random churns, which may erroneously
+	// invoke additional build processes.
 	sort.SliceStable(androidMkModulesList, func(i, j int) bool {
 		return ctx.ModuleName(androidMkModulesList[i]) < ctx.ModuleName(androidMkModulesList[j])
 	})
@@ -586,6 +694,8 @@
 	}
 }
 
+// A simple, special Android.mk entry output func to make it possible to build blueprint tools using
+// m by making them phony targets.
 func translateGoBinaryModule(ctx SingletonContext, w io.Writer, mod blueprint.Module,
 	goBinary bootstrap.GoBinaryTool) error {
 
@@ -618,6 +728,8 @@
 	data.Target_required = data.Entries.Target_required
 }
 
+// A support func for the deprecated AndroidMkDataProvider interface. Use AndroidMkEntryProvider
+// instead.
 func translateAndroidModule(ctx SingletonContext, w io.Writer, mod blueprint.Module,
 	provider AndroidMkDataProvider) error {
 
@@ -664,6 +776,8 @@
 	return nil
 }
 
+// A support func for the deprecated AndroidMkDataProvider interface. Use AndroidMkEntryProvider
+// instead.
 func WriteAndroidMkData(w io.Writer, data AndroidMkData) {
 	if data.Disabled {
 		return
@@ -711,11 +825,14 @@
 		module.Os() == LinuxBionic
 }
 
+// A utility func to format LOCAL_TEST_DATA outputs. See the comments on DataPath to understand how
+// to use this func.
 func AndroidMkDataPaths(data []DataPath) []string {
 	var testFiles []string
 	for _, d := range data {
 		rel := d.SrcPath.Rel()
 		path := d.SrcPath.String()
+		// LOCAL_TEST_DATA requires the rel portion of the path to be removed from the path.
 		if !strings.HasSuffix(path, rel) {
 			panic(fmt.Errorf("path %q does not end with %q", path, rel))
 		}
diff --git a/android/androidmk_test.go b/android/androidmk_test.go
index 5d05d91..347b92e 100644
--- a/android/androidmk_test.go
+++ b/android/androidmk_test.go
@@ -35,6 +35,10 @@
 	data       AndroidMkData
 	distFiles  TaggedDistFiles
 	outputFile OptionalPath
+
+	// The paths that will be used as the default dist paths if no tag is
+	// specified.
+	defaultDistPaths Paths
 }
 
 const (
@@ -48,7 +52,14 @@
 	// If the dist_output_file: true then create an output file that is stored in
 	// the OutputFile property of the AndroidMkEntry.
 	if proptools.BoolDefault(m.properties.Dist_output_file, true) {
-		m.outputFile = OptionalPathForPath(PathForTesting("dist-output-file.out"))
+		path := PathForTesting("dist-output-file.out")
+		m.outputFile = OptionalPathForPath(path)
+
+		// Previous code would prioritize the DistFiles property over the OutputFile
+		// property in AndroidMkEntry when determining the default dist paths.
+		// Setting this first allows it to be overridden based on the
+		// default_dist_files setting replicating that previous behavior.
+		m.defaultDistPaths = Paths{path}
 	}
 
 	// Based on the setting of the default_dist_files property possibly create a
@@ -60,9 +71,22 @@
 		// Do nothing
 
 	case defaultDistFiles_Default:
-		m.distFiles = MakeDefaultDistFiles(PathForTesting("default-dist.out"))
+		path := PathForTesting("default-dist.out")
+		m.defaultDistPaths = Paths{path}
+		m.distFiles = MakeDefaultDistFiles(path)
 
 	case defaultDistFiles_Tagged:
+		// Module types that set AndroidMkEntry.DistFiles to the result of calling
+		// GenerateTaggedDistFiles(ctx) relied on no tag being treated as "" which
+		// meant that the default dist paths would be whatever was returned by
+		// OutputFiles(""). In order to preserve that behavior when treating no tag
+		// as being equal to DefaultDistTag this ensures that
+		// OutputFiles(DefaultDistTag) will return the same as OutputFiles("").
+		m.defaultDistPaths = PathsForTesting("one.out")
+
+		// This must be called after setting defaultDistPaths/outputFile as
+		// GenerateTaggedDistFiles calls into OutputFiles(tag) which may use those
+		// fields.
 		m.distFiles = m.GenerateTaggedDistFiles(ctx)
 	}
 }
@@ -77,6 +101,12 @@
 
 func (m *customModule) OutputFiles(tag string) (Paths, error) {
 	switch tag {
+	case DefaultDistTag:
+		if m.defaultDistPaths != nil {
+			return m.defaultDistPaths, nil
+		} else {
+			return nil, fmt.Errorf("default dist tag is not available")
+		}
 	case "":
 		return PathsForTesting("one.out"), nil
 	case ".multiple":
@@ -571,8 +601,6 @@
 					{
 						targets: ["my_goal"],
 					},
-					// The following is silently ignored because the dist files do not
-					// contain the tagged files.
 					{
 						targets: ["my_goal"],
 						tag: ".multiple",
@@ -587,6 +615,13 @@
 					distCopyForTest("default-dist.out", "default-dist.out"),
 				},
 			},
+			{
+				goals: "my_goal",
+				copies: []distCopy{
+					distCopyForTest("two.out", "two.out"),
+					distCopyForTest("three/four.out", "four.out"),
+				},
+			},
 		},
 	})
 
@@ -601,15 +636,23 @@
 					{
 						targets: ["my_goal"],
 					},
-					// The following is silently ignored because the dist files do not
-					// contain the tagged files.
 					{
 						targets: ["my_goal"],
 						tag: ".multiple",
 					},
 				],
 			}
-`, nil)
+`, &distContributions{
+		copiesForGoals: []*copiesForGoals{
+			{
+				goals: "my_goal",
+				copies: []distCopy{
+					distCopyForTest("two.out", "two.out"),
+					distCopyForTest("three/four.out", "four.out"),
+				},
+			},
+		},
+	})
 
 	testHelper(t, "tagged-dist-files-default-output", `
 			custom {
@@ -653,8 +696,6 @@
 					{
 						targets: ["my_goal"],
 					},
-					// The following is silently ignored because the dist files do not
-					// contain the tagged files.
 					{
 						targets: ["my_goal"],
 						tag: ".multiple",
@@ -669,6 +710,13 @@
 					distCopyForTest("default-dist.out", "default-dist.out"),
 				},
 			},
+			{
+				goals: "my_goal",
+				copies: []distCopy{
+					distCopyForTest("two.out", "two.out"),
+					distCopyForTest("three/four.out", "four.out"),
+				},
+			},
 		},
 	})
 
@@ -681,8 +729,6 @@
 					{
 						targets: ["my_goal"],
 					},
-					// The following is silently ignored because the dist files do not
-					// contain the tagged files.
 					{
 						targets: ["my_goal"],
 						tag: ".multiple",
@@ -697,6 +743,13 @@
 					distCopyForTest("dist-output-file.out", "dist-output-file.out"),
 				},
 			},
+			{
+				goals: "my_goal",
+				copies: []distCopy{
+					distCopyForTest("two.out", "two.out"),
+					distCopyForTest("three/four.out", "four.out"),
+				},
+			},
 		},
 	})
 }
diff --git a/android/arch.go b/android/arch.go
index df407d4..34f9b29 100644
--- a/android/arch.go
+++ b/android/arch.go
@@ -1337,17 +1337,6 @@
 		addTarget(BuildOs, *variables.HostSecondaryArch, nil, nil, nil, NativeBridgeDisabled, nil, nil)
 	}
 
-	// An optional host target that uses the Bionic glibc runtime.
-	if Bool(config.Host_bionic) {
-		addTarget(LinuxBionic, "x86_64", nil, nil, nil, NativeBridgeDisabled, nil, nil)
-	}
-
-	// An optional cross-compiled host target that uses the Bionic glibc runtime on an arm64
-	// architecture.
-	if Bool(config.Host_bionic_arm64) {
-		addTarget(LinuxBionic, "arm64", nil, nil, nil, NativeBridgeDisabled, nil, nil)
-	}
-
 	// Optional cross-compiled host targets, generally Windows.
 	if String(variables.CrossHost) != "" {
 		crossHostOs := osByName(*variables.CrossHost)
@@ -1437,53 +1426,6 @@
 	abi         []string
 }
 
-// getMegaDeviceConfig returns a list of archConfigs for every architecture simultaneously.
-func getMegaDeviceConfig() []archConfig {
-	return []archConfig{
-		{"arm", "armv7-a", "generic", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "generic", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a7", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a8", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a9", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a15", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a53", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a53.a57", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a72", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a73", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a75", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a76", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "krait", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "kryo", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "kryo385", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "exynos-m1", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "exynos-m2", []string{"armeabi-v7a"}},
-		{"arm64", "armv8-a", "cortex-a53", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "cortex-a72", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "cortex-a73", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "kryo", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "exynos-m1", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "exynos-m2", []string{"arm64-v8a"}},
-		{"arm64", "armv8-2a", "kryo385", []string{"arm64-v8a"}},
-		{"arm64", "armv8-2a-dotprod", "cortex-a55", []string{"arm64-v8a"}},
-		{"arm64", "armv8-2a-dotprod", "cortex-a75", []string{"arm64-v8a"}},
-		{"arm64", "armv8-2a-dotprod", "cortex-a76", []string{"arm64-v8a"}},
-		{"x86", "", "", []string{"x86"}},
-		{"x86", "atom", "", []string{"x86"}},
-		{"x86", "haswell", "", []string{"x86"}},
-		{"x86", "ivybridge", "", []string{"x86"}},
-		{"x86", "sandybridge", "", []string{"x86"}},
-		{"x86", "silvermont", "", []string{"x86"}},
-		{"x86", "stoneyridge", "", []string{"x86"}},
-		{"x86", "x86_64", "", []string{"x86"}},
-		{"x86_64", "", "", []string{"x86_64"}},
-		{"x86_64", "haswell", "", []string{"x86_64"}},
-		{"x86_64", "ivybridge", "", []string{"x86_64"}},
-		{"x86_64", "sandybridge", "", []string{"x86_64"}},
-		{"x86_64", "silvermont", "", []string{"x86_64"}},
-		{"x86_64", "stoneyridge", "", []string{"x86_64"}},
-	}
-}
-
 // getNdkAbisConfig returns a list of archConfigs for the ABIs supported by the NDK.
 func getNdkAbisConfig() []archConfig {
 	return []archConfig{
diff --git a/android/config.go b/android/config.go
index 04c9129..9882d55 100644
--- a/android/config.go
+++ b/android/config.go
@@ -54,28 +54,9 @@
 	isPreview: true,
 }
 
-// configFileName is the name the file containing FileConfigurableOptions from
-// soong_ui for the soong_build primary builder.
-const configFileName = "soong.config"
-
-// productVariablesFileName contain the product configuration variables from soong_ui for the
-// soong_build primary builder and Kati.
+// The product variables file name, containing product config from Kati.
 const productVariablesFileName = "soong.variables"
 
-// A FileConfigurableOptions contains options which can be configured by the
-// config file. These will be included in the config struct.
-type FileConfigurableOptions struct {
-	Mega_device       *bool `json:",omitempty"`
-	Host_bionic       *bool `json:",omitempty"`
-	Host_bionic_arm64 *bool `json:",omitempty"`
-}
-
-// SetDefaultConfig resets the receiving FileConfigurableOptions to default
-// values.
-func (f *FileConfigurableOptions) SetDefaultConfig() {
-	*f = FileConfigurableOptions{}
-}
-
 // A Config object represents the entire build configuration for Android.
 type Config struct {
 	*config
@@ -97,12 +78,8 @@
 type VendorConfig soongconfig.SoongConfig
 
 // Definition of general build configuration for soong_build. Some of these
-// configuration values are generated from soong_ui for soong_build,
-// communicated over JSON files like soong.config or soong.variables.
+// product configuration values are read from Kati-generated soong.variables.
 type config struct {
-	// Options configurable with soong.confg
-	FileConfigurableOptions
-
 	// Options configurable with soong.variables
 	productVariables productVariables
 
@@ -113,7 +90,6 @@
 	// purposes.
 	BazelContext BazelContext
 
-	ConfigFileName           string
 	ProductVariablesFileName string
 
 	Targets                  map[OsType][]Target
@@ -170,11 +146,6 @@
 }
 
 func loadConfig(config *config) error {
-	err := loadFromConfigFile(&config.FileConfigurableOptions, absolutePath(config.ConfigFileName))
-	if err != nil {
-		return err
-	}
-
 	return loadFromConfigFile(&config.productVariables, absolutePath(config.ProductVariablesFileName))
 }
 
@@ -384,7 +355,6 @@
 func NewConfig(srcDir, buildDir string, moduleListFile string) (Config, error) {
 	// Make a config with default options.
 	config := &config{
-		ConfigFileName:           filepath.Join(buildDir, configFileName),
 		ProductVariablesFileName: filepath.Join(buildDir, productVariablesFileName),
 
 		env: originalEnv,
@@ -439,9 +409,7 @@
 	targets[CommonOS] = []Target{commonTargetMap[CommonOS.Name]}
 
 	var archConfig []archConfig
-	if Bool(config.Mega_device) {
-		archConfig = getMegaDeviceConfig()
-	} else if config.NdkAbis() {
+	if config.NdkAbis() {
 		archConfig = getNdkAbisConfig()
 	} else if config.AmlAbis() {
 		archConfig = getAmlAbisConfig()
@@ -864,11 +832,6 @@
 	return c.Targets[Android][0].Arch.ArchType
 }
 
-func (c *config) SkipMegaDeviceInstall(path string) bool {
-	return Bool(c.Mega_device) &&
-		strings.HasPrefix(path, filepath.Join(c.buildDir, "target", "product"))
-}
-
 func (c *config) SanitizeHost() []string {
 	return append([]string(nil), c.productVariables.SanitizeHost...)
 }
@@ -1321,6 +1284,14 @@
 	return Bool(c.productVariables.EnforceProductPartitionInterface)
 }
 
+func (c *config) EnforceInterPartitionJavaSdkLibrary() bool {
+	return Bool(c.productVariables.EnforceInterPartitionJavaSdkLibrary)
+}
+
+func (c *config) InterPartitionJavaLibraryAllowList() []string {
+	return c.productVariables.InterPartitionJavaLibraryAllowList
+}
+
 func (c *config) InstallExtraFlattenedApexes() bool {
 	return Bool(c.productVariables.InstallExtraFlattenedApexes)
 }
diff --git a/android/config_test.go b/android/config_test.go
index 68f68a0..7bfc800 100644
--- a/android/config_test.go
+++ b/android/config_test.go
@@ -78,11 +78,6 @@
 	if err != nil {
 		t.Errorf(err.Error())
 	}
-
-	validateConfigAnnotations(&FileConfigurableOptions{})
-	if err != nil {
-		t.Errorf(err.Error())
-	}
 }
 
 func TestMissingVendorConfig(t *testing.T) {
diff --git a/android/csuite_config.go b/android/csuite_config.go
index a5b1533..bf24d98 100644
--- a/android/csuite_config.go
+++ b/android/csuite_config.go
@@ -44,7 +44,7 @@
 			if me.properties.Test_config != nil {
 				entries.SetString("LOCAL_TEST_CONFIG", *me.properties.Test_config)
 			}
-			entries.AddStrings("LOCAL_COMPATIBILITY_SUITE", "csuite")
+			entries.AddCompatibilityTestSuites("csuite")
 		},
 	}
 	return []AndroidMkEntries{androidMkEntries}
diff --git a/android/defs.go b/android/defs.go
index 631dfe8..f5bd362 100644
--- a/android/defs.go
+++ b/android/defs.go
@@ -15,6 +15,7 @@
 package android
 
 import (
+	"fmt"
 	"strings"
 	"testing"
 
@@ -97,7 +98,7 @@
 	// content to file.
 	writeFile = pctx.AndroidStaticRule("writeFile",
 		blueprint.RuleParams{
-			Command:     `/bin/bash -c 'echo -e "$$0" > $out' $content`,
+			Command:     `/bin/bash -c 'echo -e -n "$$0" > $out' $content`,
 			Description: "writing file $out",
 		},
 		"content")
@@ -133,9 +134,7 @@
 	shellUnescaper = strings.NewReplacer(`'\''`, `'`)
 )
 
-// WriteFileRule creates a ninja rule to write contents to a file.  The contents will be escaped
-// so that the file contains exactly the contents passed to the function, plus a trailing newline.
-func WriteFileRule(ctx BuilderContext, outputFile WritablePath, content string) {
+func buildWriteFileRule(ctx BuilderContext, outputFile WritablePath, content string) {
 	content = echoEscaper.Replace(content)
 	content = proptools.ShellEscape(content)
 	if content == "" {
@@ -151,6 +150,31 @@
 	})
 }
 
+// WriteFileRule creates a ninja rule to write contents to a file.  The contents will be escaped
+// so that the file contains exactly the contents passed to the function, plus a trailing newline.
+func WriteFileRule(ctx BuilderContext, outputFile WritablePath, content string) {
+	// This is MAX_ARG_STRLEN subtracted with some safety to account for shell escapes
+	const SHARD_SIZE = 131072 - 10000
+
+	content += "\n"
+	if len(content) > SHARD_SIZE {
+		var chunks WritablePaths
+		for i, c := range ShardString(content, SHARD_SIZE) {
+			tempPath := outputFile.ReplaceExtension(ctx, fmt.Sprintf("%s.%d", outputFile.Ext(), i))
+			buildWriteFileRule(ctx, tempPath, c)
+			chunks = append(chunks, tempPath)
+		}
+		ctx.Build(pctx, BuildParams{
+			Rule:        Cat,
+			Inputs:      chunks.Paths(),
+			Output:      outputFile,
+			Description: "Merging to " + outputFile.Base(),
+		})
+		return
+	}
+	buildWriteFileRule(ctx, outputFile, content)
+}
+
 // shellUnescape reverses proptools.ShellEscape
 func shellUnescape(s string) string {
 	// Remove leading and trailing quotes if present
diff --git a/android/module.go b/android/module.go
index 0716b5d..b6729c0 100644
--- a/android/module.go
+++ b/android/module.go
@@ -503,8 +503,12 @@
 	// A suffix to add to the artifact file name (before any extension).
 	Suffix *string `android:"arch_variant"`
 
-	// A string tag to select the OutputFiles associated with the tag. Defaults to the
-	// the empty "" string.
+	// A string tag to select the OutputFiles associated with the tag.
+	//
+	// If no tag is specified then it will select the default dist paths provided
+	// by the module type. If a tag of "" is specified then it will return the
+	// default output files provided by the modules, i.e. the result of calling
+	// OutputFiles("").
 	Tag *string `android:"arch_variant"`
 }
 
@@ -733,9 +737,45 @@
 	Dists []Dist `android:"arch_variant"`
 }
 
+// The key to use in TaggedDistFiles when a Dist structure does not specify a
+// tag property. This intentionally does not use "" as the default because that
+// would mean that an empty tag would have a different meaning when used in a dist
+// structure that when used to reference a specific set of output paths using the
+// :module{tag} syntax, which passes tag to the OutputFiles(tag) method.
+const DefaultDistTag = "<default-dist-tag>"
+
 // A map of OutputFile tag keys to Paths, for disting purposes.
 type TaggedDistFiles map[string]Paths
 
+// addPathsForTag adds a mapping from the tag to the paths. If the map is nil
+// then it will create a map, update it and then return it. If a mapping already
+// exists for the tag then the paths are appended to the end of the current list
+// of paths, ignoring any duplicates.
+func (t TaggedDistFiles) addPathsForTag(tag string, paths ...Path) TaggedDistFiles {
+	if t == nil {
+		t = make(TaggedDistFiles)
+	}
+
+	for _, distFile := range paths {
+		if distFile != nil && !t[tag].containsPath(distFile) {
+			t[tag] = append(t[tag], distFile)
+		}
+	}
+
+	return t
+}
+
+// merge merges the entries from the other TaggedDistFiles object into this one.
+// If the TaggedDistFiles is nil then it will create a new instance, merge the
+// other into it, and then return it.
+func (t TaggedDistFiles) merge(other TaggedDistFiles) TaggedDistFiles {
+	for tag, paths := range other {
+		t = t.addPathsForTag(tag, paths...)
+	}
+
+	return t
+}
+
 func MakeDefaultDistFiles(paths ...Path) TaggedDistFiles {
 	for _, path := range paths {
 		if path == nil {
@@ -744,7 +784,7 @@
 	}
 
 	// The default OutputFile tag is the empty "" string.
-	return TaggedDistFiles{"": paths}
+	return TaggedDistFiles{DefaultDistTag: paths}
 }
 
 type hostAndDeviceProperties struct {
@@ -970,6 +1010,9 @@
 	noticeFiles        Paths
 	phonies            map[string]Paths
 
+	// The files to copy to the dist as explicitly specified in the .bp file.
+	distFiles TaggedDistFiles
+
 	// Used by buildTargetSingleton to create checkbuild and per-directory build targets
 	// Only set on the final variant of each module
 	installTarget    WritablePath
@@ -1071,23 +1114,30 @@
 }
 
 func (m *ModuleBase) GenerateTaggedDistFiles(ctx BaseModuleContext) TaggedDistFiles {
-	distFiles := make(TaggedDistFiles)
+	var distFiles TaggedDistFiles
 	for _, dist := range m.Dists() {
-		var tag string
-		var distFilesForTag Paths
-		if dist.Tag == nil {
-			tag = ""
-		} else {
-			tag = *dist.Tag
-		}
-		distFilesForTag, err := m.base().module.(OutputFileProducer).OutputFiles(tag)
-		if err != nil {
-			ctx.PropertyErrorf("dist.tag", "%s", err.Error())
-		}
-		for _, distFile := range distFilesForTag {
-			if distFile != nil && !distFiles[tag].containsPath(distFile) {
-				distFiles[tag] = append(distFiles[tag], distFile)
+		// If no tag is specified then it means to use the default dist paths so use
+		// the special tag name which represents that.
+		tag := proptools.StringDefault(dist.Tag, DefaultDistTag)
+
+		if outputFileProducer, ok := m.module.(OutputFileProducer); ok {
+			// Call the OutputFiles(tag) method to get the paths associated with the tag.
+			distFilesForTag, err := outputFileProducer.OutputFiles(tag)
+
+			// If the tag was not supported and is not DefaultDistTag then it is an error.
+			// Failing to find paths for DefaultDistTag is not an error. It just means
+			// that the module type requires the legacy behavior.
+			if err != nil && tag != DefaultDistTag {
+				ctx.PropertyErrorf("dist.tag", "%s", err.Error())
 			}
+
+			distFiles = distFiles.addPathsForTag(tag, distFilesForTag...)
+		} else if tag != DefaultDistTag {
+			// If the tag was specified then it is an error if the module does not
+			// implement OutputFileProducer because there is no other way of accessing
+			// the paths for the specified tag.
+			ctx.PropertyErrorf("dist.tag",
+				"tag %s not supported because the module does not implement OutputFileProducer", tag)
 		}
 	}
 
@@ -1618,6 +1668,15 @@
 			return
 		}
 
+		// Create the set of tagged dist files after calling GenerateAndroidBuildActions
+		// as GenerateTaggedDistFiles() calls OutputFiles(tag) and so relies on the
+		// output paths being set which must be done before or during
+		// GenerateAndroidBuildActions.
+		m.distFiles = m.GenerateTaggedDistFiles(ctx)
+		if ctx.Failed() {
+			return
+		}
+
 		m.installFiles = append(m.installFiles, ctx.installFiles...)
 		m.checkbuildFiles = append(m.checkbuildFiles, ctx.checkbuildFiles...)
 		m.packagingSpecs = append(m.packagingSpecs, ctx.packagingSpecs...)
@@ -2340,10 +2399,6 @@
 		if m.Config().KatiEnabled() && !m.InstallBypassMake() {
 			return true
 		}
-
-		if m.Config().SkipMegaDeviceInstall(fullInstallPath.String()) {
-			return true
-		}
 	}
 
 	return false
diff --git a/android/packaging.go b/android/packaging.go
index 512e4ba..09432e6 100644
--- a/android/packaging.go
+++ b/android/packaging.go
@@ -21,10 +21,10 @@
 	"github.com/google/blueprint"
 )
 
-// PackagingSpec abstracts a request to place a built artifact at a certain path in a package.
-// A package can be the traditional <partition>.img, but isn't limited to those. Other examples could
-// be a new filesystem image that is a subset of system.img (e.g. for an Android-like mini OS running
-// on a VM), or a zip archive for some of the host tools.
+// PackagingSpec abstracts a request to place a built artifact at a certain path in a package. A
+// package can be the traditional <partition>.img, but isn't limited to those. Other examples could
+// be a new filesystem image that is a subset of system.img (e.g. for an Android-like mini OS
+// running on a VM), or a zip archive for some of the host tools.
 type PackagingSpec struct {
 	// Path relative to the root of the package
 	relPathInPackage string
@@ -40,15 +40,25 @@
 	executable bool
 }
 
+// Get file name of installed package
+func (p *PackagingSpec) FileName() string {
+	if p.relPathInPackage != "" {
+		return filepath.Base(p.relPathInPackage)
+	}
+
+	return ""
+}
+
 type PackageModule interface {
 	Module
 	packagingBase() *PackagingBase
 
 	// AddDeps adds dependencies to the `deps` modules. This should be called in DepsMutator.
-	AddDeps(ctx BottomUpMutatorContext)
+	// When adding the dependencies, depTag is used as the tag.
+	AddDeps(ctx BottomUpMutatorContext, depTag blueprint.DependencyTag)
 
 	// CopyDepsToZip zips the built artifacts of the dependencies into the given zip file and
-	// returns zip entries in it.  This is expected to be called in GenerateAndroidBuildActions,
+	// returns zip entries in it. This is expected to be called in GenerateAndroidBuildActions,
 	// followed by a build rule that unzips it and creates the final output (img, zip, tar.gz,
 	// etc.) from the extracted files
 	CopyDepsToZip(ctx ModuleContext, zipOut OutputPath) []string
@@ -59,9 +69,9 @@
 type PackagingBase struct {
 	properties PackagingProperties
 
-	// Allows this module to skip missing dependencies. In most cases, this
-	// is not required, but for rare cases like when there's a dependency
-	// to a module which exists in certain repo checkouts, this is needed.
+	// Allows this module to skip missing dependencies. In most cases, this is not required, but
+	// for rare cases like when there's a dependency to a module which exists in certain repo
+	// checkouts, this is needed.
 	IgnoreMissingDependencies bool
 }
 
@@ -82,10 +92,6 @@
 	Multilib packagingMultilibProperties `android:"arch_variant"`
 }
 
-type packagingDependencyTag struct{ blueprint.BaseDependencyTag }
-
-var depTag = packagingDependencyTag{}
-
 func InitPackageModule(p PackageModule) {
 	base := p.packagingBase()
 	p.AddProperties(&base.properties)
@@ -95,10 +101,10 @@
 	return p
 }
 
-// From deps and multilib.*.deps, select the dependencies that are for the given arch
-// deps is for the current archicture when this module is not configured for multi target.
-// When configured for multi target, deps is selected for each of the targets and is NOT
-// selected for the current architecture which would be Common.
+// From deps and multilib.*.deps, select the dependencies that are for the given arch deps is for
+// the current archicture when this module is not configured for multi target. When configured for
+// multi target, deps is selected for each of the targets and is NOT selected for the current
+// architecture which would be Common.
 func (p *PackagingBase) getDepsForArch(ctx BaseModuleContext, arch ArchType) []string {
 	var ret []string
 	if arch == ctx.Target().Arch.ArchType && len(ctx.MultiTargets()) == 0 {
@@ -134,7 +140,7 @@
 }
 
 // See PackageModule.AddDeps
-func (p *PackagingBase) AddDeps(ctx BottomUpMutatorContext) {
+func (p *PackagingBase) AddDeps(ctx BottomUpMutatorContext, depTag blueprint.DependencyTag) {
 	for _, t := range p.getSupportedTargets(ctx) {
 		for _, dep := range p.getDepsForArch(ctx, t.Arch.ArchType) {
 			if p.IgnoreMissingDependencies && !ctx.OtherModuleExists(dep) {
@@ -147,15 +153,9 @@
 
 // See PackageModule.CopyDepsToZip
 func (p *PackagingBase) CopyDepsToZip(ctx ModuleContext, zipOut OutputPath) (entries []string) {
-	var supportedArches []string
-	for _, t := range p.getSupportedTargets(ctx) {
-		supportedArches = append(supportedArches, t.Arch.ArchType.String())
-	}
 	m := make(map[string]PackagingSpec)
 	ctx.WalkDeps(func(child Module, parent Module) bool {
-		// Don't track modules with unsupported arch
-		// TODO(jiyong): remove this when aosp/1501613 lands.
-		if !InList(child.Target().Arch.ArchType.String(), supportedArches) {
+		if !IsInstallDepNeeded(ctx.OtherModuleDependencyTag(child)) {
 			return false
 		}
 		for _, ps := range child.PackagingSpecs() {
@@ -166,7 +166,7 @@
 		return true
 	})
 
-	builder := NewRuleBuilder()
+	builder := NewRuleBuilder(pctx, ctx)
 
 	dir := PathForModuleOut(ctx, ".zip").OutputPath
 	builder.Command().Text("rm").Flag("-rf").Text(dir.String())
@@ -193,13 +193,13 @@
 	}
 
 	builder.Command().
-		BuiltTool(ctx, "soong_zip").
+		BuiltTool("soong_zip").
 		FlagWithOutput("-o ", zipOut).
 		FlagWithArg("-C ", dir.String()).
 		Flag("-L 0"). // no compression because this will be unzipped soon
 		FlagWithArg("-D ", dir.String())
 	builder.Command().Text("rm").Flag("-rf").Text(dir.String())
 
-	builder.Build(pctx, ctx, "zip_deps", fmt.Sprintf("Zipping deps for %s", ctx.ModuleName()))
+	builder.Build("zip_deps", fmt.Sprintf("Zipping deps for %s", ctx.ModuleName()))
 	return entries
 }
diff --git a/android/packaging_test.go b/android/packaging_test.go
index 7710c7f..7269bfb 100644
--- a/android/packaging_test.go
+++ b/android/packaging_test.go
@@ -17,6 +17,8 @@
 import (
 	"reflect"
 	"testing"
+
+	"github.com/google/blueprint"
 )
 
 // Module to be packaged
@@ -27,6 +29,12 @@
 	}
 }
 
+// dep tag used in this test. All dependencies are considered as installable.
+type installDepTag struct {
+	blueprint.BaseDependencyTag
+	InstallAlwaysNeededDependencyTag
+}
+
 func componentTestModuleFactory() Module {
 	m := &componentTestModule{}
 	m.AddProperties(&m.props)
@@ -35,7 +43,7 @@
 }
 
 func (m *componentTestModule) DepsMutator(ctx BottomUpMutatorContext) {
-	ctx.AddDependency(ctx.Module(), nil, m.props.Deps...)
+	ctx.AddDependency(ctx.Module(), installDepTag{}, m.props.Deps...)
 }
 
 func (m *componentTestModule) GenerateAndroidBuildActions(ctx ModuleContext) {
@@ -61,7 +69,7 @@
 }
 
 func (m *packageTestModule) DepsMutator(ctx BottomUpMutatorContext) {
-	m.AddDeps(ctx)
+	m.AddDeps(ctx, installDepTag{})
 }
 
 func (m *packageTestModule) GenerateAndroidBuildActions(ctx ModuleContext) {
diff --git a/android/paths.go b/android/paths.go
index a62c9e3..5a41cf1 100644
--- a/android/paths.go
+++ b/android/paths.go
@@ -138,6 +138,8 @@
 	// the writablePath method doesn't directly do anything,
 	// but it allows a struct to distinguish between whether or not it implements the WritablePath interface
 	writablePath()
+
+	ReplaceExtension(ctx PathContext, ext string) OutputPath
 }
 
 type genPathProvider interface {
@@ -665,7 +667,7 @@
 	return Paths(ret)
 }
 
-// WritablePaths is a slice of WritablePaths, used for multiple outputs.
+// WritablePaths is a slice of WritablePath, used for multiple outputs.
 type WritablePaths []WritablePath
 
 // Strings returns the string forms of the writable paths.
@@ -1249,6 +1251,10 @@
 	return p.config.buildDir
 }
 
+func (p InstallPath) ReplaceExtension(ctx PathContext, ext string) OutputPath {
+	panic("Not implemented")
+}
+
 var _ Path = InstallPath{}
 var _ WritablePath = InstallPath{}
 
@@ -1511,6 +1517,10 @@
 	return p.config.buildDir
 }
 
+func (p PhonyPath) ReplaceExtension(ctx PathContext, ext string) OutputPath {
+	panic("Not implemented")
+}
+
 var _ Path = PhonyPath{}
 var _ WritablePath = PhonyPath{}
 
diff --git a/android/proto.go b/android/proto.go
index b712258..0be7893 100644
--- a/android/proto.go
+++ b/android/proto.go
@@ -122,7 +122,7 @@
 	} `android:"arch_variant"`
 }
 
-func ProtoRule(ctx ModuleContext, rule *RuleBuilder, protoFile Path, flags ProtoFlags, deps Paths,
+func ProtoRule(rule *RuleBuilder, protoFile Path, flags ProtoFlags, deps Paths,
 	outDir WritablePath, depFile WritablePath, outputs WritablePaths) {
 
 	var protoBase string
@@ -134,7 +134,7 @@
 	}
 
 	rule.Command().
-		BuiltTool(ctx, "aprotoc").
+		BuiltTool("aprotoc").
 		FlagWithArg(flags.OutTypeFlag+"=", strings.Join(flags.OutParams, ",")+":"+outDir.String()).
 		FlagWithDepFile("--dependency_out=", depFile).
 		FlagWithArg("-I ", protoBase).
@@ -144,5 +144,5 @@
 		ImplicitOutputs(outputs)
 
 	rule.Command().
-		BuiltTool(ctx, "dep_fixer").Flag(depFile.String())
+		BuiltTool("dep_fixer").Flag(depFile.String())
 }
diff --git a/android/rule_builder.go b/android/rule_builder.go
index 3efe9f8..e2d8187 100644
--- a/android/rule_builder.go
+++ b/android/rule_builder.go
@@ -37,6 +37,9 @@
 // RuleBuilder provides an alternative to ModuleContext.Rule and ModuleContext.Build to add a command line to the build
 // graph.
 type RuleBuilder struct {
+	pctx PackageContext
+	ctx  BuilderContext
+
 	commands         []*RuleBuilderCommand
 	installs         RuleBuilderInstalls
 	temporariesSet   map[WritablePath]bool
@@ -44,14 +47,16 @@
 	sbox             bool
 	highmem          bool
 	remoteable       RemoteRuleSupports
-	sboxOutDir       WritablePath
+	outDir           WritablePath
 	sboxManifestPath WritablePath
 	missingDeps      []string
 }
 
 // NewRuleBuilder returns a newly created RuleBuilder.
-func NewRuleBuilder() *RuleBuilder {
+func NewRuleBuilder(pctx PackageContext, ctx BuilderContext) *RuleBuilder {
 	return &RuleBuilder{
+		pctx:           pctx,
+		ctx:            ctx,
 		temporariesSet: make(map[WritablePath]bool),
 	}
 }
@@ -130,7 +135,7 @@
 		panic("Sbox() is not compatible with Restat()")
 	}
 	r.sbox = true
-	r.sboxOutDir = outputDir
+	r.outDir = outputDir
 	r.sboxManifestPath = manifestPath
 	return r
 }
@@ -146,8 +151,7 @@
 // race with any call to Build.
 func (r *RuleBuilder) Command() *RuleBuilderCommand {
 	command := &RuleBuilderCommand{
-		sbox:   r.sbox,
-		outDir: r.sboxOutDir,
+		rule: r,
 	}
 	r.commands = append(r.commands, command)
 	return command
@@ -395,19 +399,19 @@
 var _ BuilderContext = ModuleContext(nil)
 var _ BuilderContext = SingletonContext(nil)
 
-func (r *RuleBuilder) depFileMergerCmd(ctx PathContext, depFiles WritablePaths) *RuleBuilderCommand {
+func (r *RuleBuilder) depFileMergerCmd(depFiles WritablePaths) *RuleBuilderCommand {
 	return r.Command().
-		BuiltTool(ctx, "dep_fixer").
+		BuiltTool("dep_fixer").
 		Inputs(depFiles.Paths())
 }
 
 // Build adds the built command line to the build graph, with dependencies on Inputs and Tools, and output files for
 // Outputs.
-func (r *RuleBuilder) Build(pctx PackageContext, ctx BuilderContext, name string, desc string) {
+func (r *RuleBuilder) Build(name string, desc string) {
 	name = ninjaNameEscape(name)
 
 	if len(r.missingDeps) > 0 {
-		ctx.Build(pctx, BuildParams{
+		r.ctx.Build(pctx, BuildParams{
 			Rule:        ErrorRule,
 			Outputs:     r.Outputs(),
 			OrderOnly:   r.OrderOnlys(),
@@ -426,13 +430,13 @@
 		depFormat = blueprint.DepsGCC
 		if len(depFiles) > 1 {
 			// Add a command locally that merges all depfiles together into the first depfile.
-			r.depFileMergerCmd(ctx, depFiles)
+			r.depFileMergerCmd(depFiles)
 
 			if r.sbox {
 				// Check for Rel() errors, as all depfiles should be in the output dir.  Errors
 				// will be reported to the ctx.
 				for _, path := range depFiles[1:] {
-					Rel(ctx, r.sboxOutDir.String(), path.String())
+					Rel(r.ctx, r.outDir.String(), path.String())
 				}
 			}
 		}
@@ -468,7 +472,7 @@
 		// to the output directory.
 		sboxOutputs := make([]string, len(outputs))
 		for i, output := range outputs {
-			rel := Rel(ctx, r.sboxOutDir.String(), output.String())
+			rel := Rel(r.ctx, r.outDir.String(), output.String())
 			sboxOutputs[i] = filepath.Join(sboxOutDir, rel)
 			command.CopyAfter = append(command.CopyAfter, &sbox_proto.Copy{
 				From: proto.String(filepath.Join(sboxOutSubDir, rel)),
@@ -483,23 +487,27 @@
 
 		// Verify that the manifest textproto is not inside the sbox output directory, otherwise
 		// it will get deleted when the sbox rule clears its output directory.
-		_, manifestInOutDir := MaybeRel(ctx, r.sboxOutDir.String(), r.sboxManifestPath.String())
+		_, manifestInOutDir := MaybeRel(r.ctx, r.outDir.String(), r.sboxManifestPath.String())
 		if manifestInOutDir {
-			ReportPathErrorf(ctx, "sbox rule %q manifestPath %q must not be in outputDir %q",
-				name, r.sboxManifestPath.String(), r.sboxOutDir.String())
+			ReportPathErrorf(r.ctx, "sbox rule %q manifestPath %q must not be in outputDir %q",
+				name, r.sboxManifestPath.String(), r.outDir.String())
 		}
 
 		// Create a rule to write the manifest as a the textproto.
-		WriteFileRule(ctx, r.sboxManifestPath, proto.MarshalTextString(&manifest))
+		WriteFileRule(r.ctx, r.sboxManifestPath, proto.MarshalTextString(&manifest))
 
 		// Generate a new string to use as the command line of the sbox rule.  This uses
 		// a RuleBuilderCommand as a convenience method of building the command line, then
 		// converts it to a string to replace commandString.
-		sboxCmd := &RuleBuilderCommand{}
-		sboxCmd.Text("rm -rf").Output(r.sboxOutDir)
+		sboxCmd := &RuleBuilderCommand{
+			rule: &RuleBuilder{
+				ctx: r.ctx,
+			},
+		}
+		sboxCmd.Text("rm -rf").Output(r.outDir)
 		sboxCmd.Text("&&")
-		sboxCmd.BuiltTool(ctx, "sbox").
-			Flag("--sandbox-path").Text(shared.TempDirForOutDir(PathForOutput(ctx).String())).
+		sboxCmd.BuiltTool("sbox").
+			Flag("--sandbox-path").Text(shared.TempDirForOutDir(PathForOutput(r.ctx).String())).
 			Flag("--manifest").Input(r.sboxManifestPath)
 
 		// Replace the command string, and add the sbox tool and manifest textproto to the
@@ -528,19 +536,19 @@
 	}
 
 	var pool blueprint.Pool
-	if ctx.Config().UseGoma() && r.remoteable.Goma {
+	if r.ctx.Config().UseGoma() && r.remoteable.Goma {
 		// When USE_GOMA=true is set and the rule is supported by goma, allow jobs to run outside the local pool.
-	} else if ctx.Config().UseRBE() && r.remoteable.RBE {
+	} else if r.ctx.Config().UseRBE() && r.remoteable.RBE {
 		// When USE_RBE=true is set and the rule is supported by RBE, use the remotePool.
 		pool = remotePool
 	} else if r.highmem {
 		pool = highmemPool
-	} else if ctx.Config().UseRemoteBuild() {
+	} else if r.ctx.Config().UseRemoteBuild() {
 		pool = localPool
 	}
 
-	ctx.Build(pctx, BuildParams{
-		Rule: ctx.Rule(pctx, name, blueprint.RuleParams{
+	r.ctx.Build(r.pctx, BuildParams{
+		Rule: r.ctx.Rule(pctx, name, blueprint.RuleParams{
 			Command:        commandString,
 			CommandDeps:    tools.Strings(),
 			Restat:         r.restat,
@@ -564,6 +572,8 @@
 // RuleBuilderCommand, so they can be used chained or unchained.  All methods that add text implicitly add a single
 // space as a separator from the previous method.
 type RuleBuilderCommand struct {
+	rule *RuleBuilder
+
 	buf            strings.Builder
 	inputs         Paths
 	implicits      Paths
@@ -576,16 +586,11 @@
 
 	// spans [start,end) of the command that should not be ninja escaped
 	unescapedSpans [][2]int
-
-	sbox bool
-	// outDir is the directory that will contain the output files of the rules.  sbox will copy
-	// the output files from the sandbox directory to this directory when it finishes.
-	outDir WritablePath
 }
 
 func (c *RuleBuilderCommand) addInput(path Path) string {
-	if c.sbox {
-		if rel, isRel, _ := maybeRelErr(c.outDir.String(), path.String()); isRel {
+	if c.rule.sbox {
+		if rel, isRel, _ := maybeRelErr(c.rule.outDir.String(), path.String()); isRel {
 			return filepath.Join(sboxOutDir, rel)
 		}
 	}
@@ -594,8 +599,8 @@
 }
 
 func (c *RuleBuilderCommand) addImplicit(path Path) string {
-	if c.sbox {
-		if rel, isRel, _ := maybeRelErr(c.outDir.String(), path.String()); isRel {
+	if c.rule.sbox {
+		if rel, isRel, _ := maybeRelErr(c.rule.outDir.String(), path.String()); isRel {
 			return filepath.Join(sboxOutDir, rel)
 		}
 	}
@@ -607,22 +612,19 @@
 	c.orderOnlys = append(c.orderOnlys, path)
 }
 
-func (c *RuleBuilderCommand) outputStr(path WritablePath) string {
-	if c.sbox {
-		return SboxPathForOutput(path, c.outDir)
+// PathForOutput takes an output path and returns the appropriate path to use on the command
+// line.  If sbox was enabled via a call to RuleBuilder.Sbox(), it returns a path with the
+// placeholder prefix used for outputs in sbox.  If sbox is not enabled it returns the
+// original path.
+func (c *RuleBuilderCommand) PathForOutput(path WritablePath) string {
+	if c.rule.sbox {
+		// Errors will be handled in RuleBuilder.Build where we have a context to report them
+		rel, _, _ := maybeRelErr(c.rule.outDir.String(), path.String())
+		return filepath.Join(sboxOutDir, rel)
 	}
 	return path.String()
 }
 
-// SboxPathForOutput takes an output path and the out directory passed to RuleBuilder.Sbox(),
-// and returns the corresponding path for the output in the sbox sandbox.  This can be used
-// on the RuleBuilder command line to reference the output.
-func SboxPathForOutput(path WritablePath, outDir WritablePath) string {
-	// Errors will be handled in RuleBuilder.Build where we have a context to report them
-	rel, _, _ := maybeRelErr(outDir.String(), path.String())
-	return filepath.Join(sboxOutDir, rel)
-}
-
 // Text adds the specified raw text to the command line.  The text should not contain input or output paths or the
 // rule will not have them listed in its dependencies or outputs.
 func (c *RuleBuilderCommand) Text(text string) *RuleBuilderCommand {
@@ -699,8 +701,8 @@
 //
 // It is equivalent to:
 //  cmd.Tool(ctx.Config().HostToolPath(ctx, tool))
-func (c *RuleBuilderCommand) BuiltTool(ctx PathContext, tool string) *RuleBuilderCommand {
-	return c.Tool(ctx.Config().HostToolPath(ctx, tool))
+func (c *RuleBuilderCommand) BuiltTool(tool string) *RuleBuilderCommand {
+	return c.Tool(c.rule.ctx.Config().HostToolPath(c.rule.ctx, tool))
 }
 
 // PrebuiltBuildTool adds the specified tool path from prebuils/build-tools.  The path will be also added to the
@@ -768,7 +770,7 @@
 // RuleBuilder.Outputs.
 func (c *RuleBuilderCommand) Output(path WritablePath) *RuleBuilderCommand {
 	c.outputs = append(c.outputs, path)
-	return c.Text(c.outputStr(path))
+	return c.Text(c.PathForOutput(path))
 }
 
 // Outputs adds the specified output paths to the command line, separated by spaces.  The paths will also be added to
@@ -783,7 +785,7 @@
 // OutputDir adds the output directory to the command line. This is only available when used with RuleBuilder.Sbox,
 // and will be the temporary output directory managed by sbox, not the final one.
 func (c *RuleBuilderCommand) OutputDir() *RuleBuilderCommand {
-	if !c.sbox {
+	if !c.rule.sbox {
 		panic("OutputDir only valid with Sbox")
 	}
 	return c.Text(sboxOutDir)
@@ -794,7 +796,7 @@
 // commands in a single RuleBuilder then RuleBuilder.Build will add an extra command to merge the depfiles together.
 func (c *RuleBuilderCommand) DepFile(path WritablePath) *RuleBuilderCommand {
 	c.depFiles = append(c.depFiles, path)
-	return c.Text(c.outputStr(path))
+	return c.Text(c.PathForOutput(path))
 }
 
 // ImplicitOutput adds the specified output path to the dependencies returned by RuleBuilder.Outputs without modifying
@@ -885,14 +887,14 @@
 // will also be added to the outputs returned by RuleBuilder.Outputs.
 func (c *RuleBuilderCommand) FlagWithOutput(flag string, path WritablePath) *RuleBuilderCommand {
 	c.outputs = append(c.outputs, path)
-	return c.Text(flag + c.outputStr(path))
+	return c.Text(flag + c.PathForOutput(path))
 }
 
 // FlagWithDepFile adds the specified flag and depfile path to the command line, with no separator between them.  The path
 // will also be added to the outputs returned by RuleBuilder.Outputs.
 func (c *RuleBuilderCommand) FlagWithDepFile(flag string, path WritablePath) *RuleBuilderCommand {
 	c.depFiles = append(c.depFiles, path)
-	return c.Text(flag + c.outputStr(path))
+	return c.Text(flag + c.PathForOutput(path))
 }
 
 // FlagWithRspFileInputList adds the specified flag and path to an rspfile to the command line, with no separator
@@ -987,3 +989,21 @@
 	h.Write([]byte(srcFileList))
 	return fmt.Sprintf("%x", h.Sum(nil))
 }
+
+// BuilderContextForTesting returns a BuilderContext for the given config that can be used for tests
+// that need to call methods that take a BuilderContext.
+func BuilderContextForTesting(config Config) BuilderContext {
+	pathCtx := PathContextForTesting(config)
+	return builderContextForTests{
+		PathContext: pathCtx,
+	}
+}
+
+type builderContextForTests struct {
+	PathContext
+}
+
+func (builderContextForTests) Rule(PackageContext, string, blueprint.RuleParams, ...string) blueprint.Rule {
+	return nil
+}
+func (builderContextForTests) Build(PackageContext, BuildParams) {}
diff --git a/android/rule_builder_test.go b/android/rule_builder_test.go
index dc360c3..e676e4a 100644
--- a/android/rule_builder_test.go
+++ b/android/rule_builder_test.go
@@ -27,8 +27,8 @@
 	"android/soong/shared"
 )
 
-func pathContext() PathContext {
-	return PathContextForTesting(TestConfig("out", nil, "", map[string][]byte{
+func builderContext() BuilderContext {
+	return BuilderContextForTesting(TestConfig("out", nil, "", map[string][]byte{
 		"ld":      nil,
 		"a.o":     nil,
 		"b.o":     nil,
@@ -44,9 +44,9 @@
 }
 
 func ExampleRuleBuilder() {
-	rule := NewRuleBuilder()
+	ctx := builderContext()
 
-	ctx := pathContext()
+	rule := NewRuleBuilder(pctx, ctx)
 
 	rule.Command().
 		Tool(PathForSource(ctx, "ld")).
@@ -55,7 +55,7 @@
 	rule.Command().Text("echo success")
 
 	// To add the command to the build graph:
-	// rule.Build(pctx, ctx, "link", "link")
+	// rule.Build("link", "link")
 
 	fmt.Printf("commands: %q\n", strings.Join(rule.Commands(), " && "))
 	fmt.Printf("tools: %q\n", rule.Tools())
@@ -70,9 +70,9 @@
 }
 
 func ExampleRuleBuilder_SymlinkOutputs() {
-	rule := NewRuleBuilder()
+	ctx := builderContext()
 
-	ctx := pathContext()
+	rule := NewRuleBuilder(pctx, ctx)
 
 	rule.Command().
 		Tool(PathForSource(ctx, "ln")).
@@ -96,9 +96,9 @@
 }
 
 func ExampleRuleBuilder_Temporary() {
-	rule := NewRuleBuilder()
+	ctx := builderContext()
 
-	ctx := pathContext()
+	rule := NewRuleBuilder(pctx, ctx)
 
 	rule.Command().
 		Tool(PathForSource(ctx, "cp")).
@@ -123,9 +123,9 @@
 }
 
 func ExampleRuleBuilder_DeleteTemporaryFiles() {
-	rule := NewRuleBuilder()
+	ctx := builderContext()
 
-	ctx := pathContext()
+	rule := NewRuleBuilder(pctx, ctx)
 
 	rule.Command().
 		Tool(PathForSource(ctx, "cp")).
@@ -151,9 +151,9 @@
 }
 
 func ExampleRuleBuilder_Installs() {
-	rule := NewRuleBuilder()
+	ctx := builderContext()
 
-	ctx := pathContext()
+	rule := NewRuleBuilder(pctx, ctx)
 
 	out := PathForOutput(ctx, "linked")
 
@@ -171,9 +171,9 @@
 }
 
 func ExampleRuleBuilderCommand() {
-	rule := NewRuleBuilder()
+	ctx := builderContext()
 
-	ctx := pathContext()
+	rule := NewRuleBuilder(pctx, ctx)
 
 	// chained
 	rule.Command().
@@ -194,24 +194,24 @@
 }
 
 func ExampleRuleBuilderCommand_Flag() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "ls")).Flag("-l"))
 	// Output:
 	// ls -l
 }
 
 func ExampleRuleBuilderCommand_Flags() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "ls")).Flags([]string{"-l", "-a"}))
 	// Output:
 	// ls -l -a
 }
 
 func ExampleRuleBuilderCommand_FlagWithArg() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "ls")).
 		FlagWithArg("--sort=", "time"))
 	// Output:
@@ -219,8 +219,8 @@
 }
 
 func ExampleRuleBuilderCommand_FlagForEachArg() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "ls")).
 		FlagForEachArg("--sort=", []string{"time", "size"}))
 	// Output:
@@ -228,8 +228,8 @@
 }
 
 func ExampleRuleBuilderCommand_FlagForEachInput() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "turbine")).
 		FlagForEachInput("--classpath ", PathsForTesting("a.jar", "b.jar")))
 	// Output:
@@ -237,8 +237,8 @@
 }
 
 func ExampleRuleBuilderCommand_FlagWithInputList() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "java")).
 		FlagWithInputList("-classpath=", PathsForTesting("a.jar", "b.jar"), ":"))
 	// Output:
@@ -246,8 +246,8 @@
 }
 
 func ExampleRuleBuilderCommand_FlagWithInput() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "java")).
 		FlagWithInput("-classpath=", PathForSource(ctx, "a")))
 	// Output:
@@ -255,8 +255,8 @@
 }
 
 func ExampleRuleBuilderCommand_FlagWithList() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "ls")).
 		FlagWithList("--sort=", []string{"time", "size"}, ","))
 	// Output:
@@ -264,8 +264,8 @@
 }
 
 func ExampleRuleBuilderCommand_FlagWithRspFileInputList() {
-	ctx := pathContext()
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Tool(PathForSource(ctx, "javac")).
 		FlagWithRspFileInputList("@", PathsForTesting("a.java", "b.java")).
 		NinjaEscapedString())
@@ -274,7 +274,8 @@
 }
 
 func ExampleRuleBuilderCommand_String() {
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Text("FOO=foo").
 		Text("echo $FOO").
 		String())
@@ -283,7 +284,8 @@
 }
 
 func ExampleRuleBuilderCommand_NinjaEscapedString() {
-	fmt.Println(NewRuleBuilder().Command().
+	ctx := builderContext()
+	fmt.Println(NewRuleBuilder(pctx, ctx).Command().
 		Text("FOO=foo").
 		Text("echo $FOO").
 		NinjaEscapedString())
@@ -305,7 +307,10 @@
 		"input3":     nil,
 	}
 
-	ctx := PathContextForTesting(TestConfig("out", nil, "", fs))
+	pathCtx := PathContextForTesting(TestConfig("out", nil, "", fs))
+	ctx := builderContextForTests{
+		PathContext: pathCtx,
+	}
 
 	addCommands := func(rule *RuleBuilder) {
 		cmd := rule.Command().
@@ -355,7 +360,7 @@
 	wantSymlinkOutputs := PathsForOutput(ctx, []string{"ImplicitSymlinkOutput", "SymlinkOutput"})
 
 	t.Run("normal", func(t *testing.T) {
-		rule := NewRuleBuilder()
+		rule := NewRuleBuilder(pctx, ctx)
 		addCommands(rule)
 
 		wantCommands := []string{
@@ -389,13 +394,13 @@
 			t.Errorf("\nwant rule.OrderOnlys() = %#v\n                got %#v", w, g)
 		}
 
-		if g, w := rule.depFileMergerCmd(ctx, rule.DepFiles()).String(), wantDepMergerCommand; g != w {
+		if g, w := rule.depFileMergerCmd(rule.DepFiles()).String(), wantDepMergerCommand; g != w {
 			t.Errorf("\nwant rule.depFileMergerCmd() = %#v\n                   got %#v", w, g)
 		}
 	})
 
 	t.Run("sbox", func(t *testing.T) {
-		rule := NewRuleBuilder().Sbox(PathForOutput(ctx, ""),
+		rule := NewRuleBuilder(pctx, ctx).Sbox(PathForOutput(ctx, ""),
 			PathForOutput(ctx, "sbox.textproto"))
 		addCommands(rule)
 
@@ -427,7 +432,7 @@
 			t.Errorf("\nwant rule.OrderOnlys() = %#v\n                got %#v", w, g)
 		}
 
-		if g, w := rule.depFileMergerCmd(ctx, rule.DepFiles()).String(), wantDepMergerCommand; g != w {
+		if g, w := rule.depFileMergerCmd(rule.DepFiles()).String(), wantDepMergerCommand; g != w {
 			t.Errorf("\nwant rule.depFileMergerCmd() = %#v\n                   got %#v", w, g)
 		}
 	})
@@ -476,7 +481,7 @@
 }
 
 func testRuleBuilder_Build(ctx BuilderContext, in Paths, out, outDep, outDir, manifestPath WritablePath, restat, sbox bool) {
-	rule := NewRuleBuilder()
+	rule := NewRuleBuilder(pctx, ctx)
 
 	if sbox {
 		rule.Sbox(outDir, manifestPath)
@@ -488,7 +493,7 @@
 		rule.Restat()
 	}
 
-	rule.Build(pctx, ctx, "rule", "desc")
+	rule.Build("rule", "desc")
 }
 
 func TestRuleBuilder_Build(t *testing.T) {
diff --git a/android/test_suites.go b/android/test_suites.go
index 19444a8..7ecb8d2 100644
--- a/android/test_suites.go
+++ b/android/test_suites.go
@@ -63,13 +63,13 @@
 	testCasesDir := pathForInstall(ctx, BuildOs, X86, "testcases", false).ToMakePath()
 
 	outputFile := PathForOutput(ctx, "packaging", "robolectric-tests.zip")
-	rule := NewRuleBuilder()
-	rule.Command().BuiltTool(ctx, "soong_zip").
+	rule := NewRuleBuilder(pctx, ctx)
+	rule.Command().BuiltTool("soong_zip").
 		FlagWithOutput("-o ", outputFile).
 		FlagWithArg("-P ", "host/testcases").
 		FlagWithArg("-C ", testCasesDir.String()).
 		FlagWithRspFileInputList("-r ", installedPaths.Paths())
-	rule.Build(pctx, ctx, "robolectric_tests_zip", "robolectric-tests.zip")
+	rule.Build("robolectric_tests_zip", "robolectric-tests.zip")
 
 	return outputFile
 }
diff --git a/android/util.go b/android/util.go
index 65c5f1b..0f940fa 100644
--- a/android/util.go
+++ b/android/util.go
@@ -29,56 +29,44 @@
 	return append([]string(nil), s...)
 }
 
+// JoinWithPrefix prepends the prefix to each string in the list and
+// returns them joined together with " " as separator.
 func JoinWithPrefix(strs []string, prefix string) string {
 	if len(strs) == 0 {
 		return ""
 	}
 
-	if len(strs) == 1 {
-		return prefix + strs[0]
+	var buf strings.Builder
+	buf.WriteString(prefix)
+	buf.WriteString(strs[0])
+	for i := 1; i < len(strs); i++ {
+		buf.WriteString(" ")
+		buf.WriteString(prefix)
+		buf.WriteString(strs[i])
 	}
-
-	n := len(" ") * (len(strs) - 1)
-	for _, s := range strs {
-		n += len(prefix) + len(s)
-	}
-
-	ret := make([]byte, 0, n)
-	for i, s := range strs {
-		if i != 0 {
-			ret = append(ret, ' ')
-		}
-		ret = append(ret, prefix...)
-		ret = append(ret, s...)
-	}
-	return string(ret)
+	return buf.String()
 }
 
+// JoinWithSuffix appends the suffix to each string in the list and
+// returns them joined together with given separator.
 func JoinWithSuffix(strs []string, suffix string, separator string) string {
 	if len(strs) == 0 {
 		return ""
 	}
 
-	if len(strs) == 1 {
-		return strs[0] + suffix
+	var buf strings.Builder
+	buf.WriteString(strs[0])
+	buf.WriteString(suffix)
+	for i := 1; i < len(strs); i++ {
+		buf.WriteString(separator)
+		buf.WriteString(strs[i])
+		buf.WriteString(suffix)
 	}
-
-	n := len(" ") * (len(strs) - 1)
-	for _, s := range strs {
-		n += len(suffix) + len(s)
-	}
-
-	ret := make([]byte, 0, n)
-	for i, s := range strs {
-		if i != 0 {
-			ret = append(ret, separator...)
-		}
-		ret = append(ret, s...)
-		ret = append(ret, suffix...)
-	}
-	return string(ret)
+	return buf.String()
 }
 
+// SortedIntKeys returns the keys of the given integer-keyed map in the ascending order
+// TODO(asmundak): once Go has generics, combine this with SortedStringKeys below.
 func SortedIntKeys(m interface{}) []int {
 	v := reflect.ValueOf(m)
 	if v.Kind() != reflect.Map {
@@ -93,6 +81,7 @@
 	return s
 }
 
+// SorterStringKeys returns the keys of the given string-keyed map in the ascending order
 func SortedStringKeys(m interface{}) []string {
 	v := reflect.ValueOf(m)
 	if v.Kind() != reflect.Map {
@@ -107,6 +96,7 @@
 	return s
 }
 
+// SortedStringMapValues returns the values of the string-values map in the ascending order
 func SortedStringMapValues(m interface{}) []string {
 	v := reflect.ValueOf(m)
 	if v.Kind() != reflect.Map {
@@ -121,6 +111,7 @@
 	return s
 }
 
+// IndexList returns the index of the first occurrence of the given string in the list or -1
 func IndexList(s string, list []string) int {
 	for i, l := range list {
 		if l == s {
@@ -131,6 +122,7 @@
 	return -1
 }
 
+// InList checks if the string belongs to the list
 func InList(s string, list []string) bool {
 	return IndexList(s, list) != -1
 }
@@ -176,7 +168,10 @@
 	return -1
 }
 
+// FilterList divides the string list into two lists: one with the strings belonging
+// to the given filter list, and the other with the remaining ones
 func FilterList(list []string, filter []string) (remainder []string, filtered []string) {
+	// InList is O(n). May be worth using more efficient lookup for longer lists.
 	for _, l := range list {
 		if InList(l, filter) {
 			filtered = append(filtered, l)
@@ -188,6 +183,8 @@
 	return
 }
 
+// RemoveListFromList removes the strings belonging to the filter list from the
+// given list and returns the result
 func RemoveListFromList(list []string, filter_out []string) (result []string) {
 	result = make([]string, 0, len(list))
 	for _, l := range list {
@@ -198,20 +195,18 @@
 	return
 }
 
+// RemoveFromList removes given string from the string list.
 func RemoveFromList(s string, list []string) (bool, []string) {
-	i := IndexList(s, list)
-	if i == -1 {
-		return false, list
-	}
-
-	result := make([]string, 0, len(list)-1)
-	result = append(result, list[:i]...)
-	for _, l := range list[i+1:] {
-		if l != s {
-			result = append(result, l)
+	result := make([]string, 0, len(list))
+	var removed bool
+	for _, item := range list {
+		if item != s {
+			result = append(result, item)
+		} else {
+			removed = true
 		}
 	}
-	return true, result
+	return removed, result
 }
 
 // FirstUniqueStrings returns all unique elements of a slice of strings, keeping the first copy of
@@ -317,11 +312,10 @@
 	return s[1], s[2], true
 }
 
+// GetNumericSdkVersion removes the first occurrence of system_ in a string,
+// which is assumed to be something like "system_1.2.3"
 func GetNumericSdkVersion(v string) string {
-	if strings.Contains(v, "system_") {
-		return strings.Replace(v, "system_", "", 1)
-	}
-	return v
+	return strings.Replace(v, "system_", "", 1)
 }
 
 // copied from build/kati/strutil.go
@@ -334,17 +328,17 @@
 		return str
 	}
 	in := str
-	trimed := str
+	trimmed := str
 	if ps[0] != "" {
-		trimed = strings.TrimPrefix(in, ps[0])
-		if trimed == in {
+		trimmed = strings.TrimPrefix(in, ps[0])
+		if trimmed == in {
 			return str
 		}
 	}
-	in = trimed
+	in = trimmed
 	if ps[1] != "" {
-		trimed = strings.TrimSuffix(in, ps[1])
-		if trimed == in {
+		trimmed = strings.TrimSuffix(in, ps[1])
+		if trimmed == in {
 			return str
 		}
 	}
@@ -353,7 +347,7 @@
 	if len(rs) != 2 {
 		return repl
 	}
-	return rs[0] + trimed + rs[1]
+	return rs[0] + trimmed + rs[1]
 }
 
 // copied from build/kati/strutil.go
@@ -407,6 +401,23 @@
 	return ret
 }
 
+// ShardString takes a string and returns a slice of strings where the length of each one is
+// at most shardSize.
+func ShardString(s string, shardSize int) []string {
+	if len(s) == 0 {
+		return nil
+	}
+	ret := make([]string, 0, (len(s)+shardSize-1)/shardSize)
+	for len(s) > shardSize {
+		ret = append(ret, s[0:shardSize])
+		s = s[shardSize:]
+	}
+	if len(s) > 0 {
+		ret = append(ret, s)
+	}
+	return ret
+}
+
 // ShardStrings takes a slice of strings, and returns a slice of slices of strings where each one has at most shardSize
 // elements.
 func ShardStrings(s []string, shardSize int) [][]string {
@@ -424,13 +435,15 @@
 	return ret
 }
 
+// CheckDuplicate checks if there are duplicates in given string list.
+// If there are, it returns first such duplicate and true.
 func CheckDuplicate(values []string) (duplicate string, found bool) {
 	seen := make(map[string]string)
 	for _, v := range values {
 		if duplicate, found = seen[v]; found {
-			return
+			return duplicate, true
 		}
 		seen[v] = v
 	}
-	return
+	return "", false
 }
diff --git a/android/variable.go b/android/variable.go
index a9a9c87..0df5272 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -347,6 +347,9 @@
 
 	EnforceProductPartitionInterface *bool `json:",omitempty"`
 
+	EnforceInterPartitionJavaSdkLibrary *bool    `json:",omitempty"`
+	InterPartitionJavaLibraryAllowList  []string `json:",omitempty"`
+
 	InstallExtraFlattenedApexes *bool `json:",omitempty"`
 
 	BoardUsesRecoveryAsBoot *bool `json:",omitempty"`
diff --git a/apex/Android.bp b/apex/Android.bp
index 1a5f683..9e8c30d 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -9,6 +9,7 @@
         "soong-cc",
         "soong-java",
         "soong-python",
+        "soong-rust",
         "soong-sh",
     ],
     srcs: [
diff --git a/apex/androidmk.go b/apex/androidmk.go
index fe89b73..da38c2a 100644
--- a/apex/androidmk.go
+++ b/apex/androidmk.go
@@ -334,7 +334,6 @@
 
 func (a *apexBundle) androidMkForType() android.AndroidMkData {
 	return android.AndroidMkData{
-		DistFiles: a.distFiles,
 		Custom: func(w io.Writer, name, prefix, moduleDir string, data android.AndroidMkData) {
 			moduleNames := []string{}
 			apexType := a.properties.ApexType
diff --git a/apex/apex.go b/apex/apex.go
index d0e0156..7ab7454 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -32,6 +32,7 @@
 	prebuilt_etc "android/soong/etc"
 	"android/soong/java"
 	"android/soong/python"
+	"android/soong/rust"
 	"android/soong/sh"
 )
 
@@ -179,6 +180,9 @@
 	// List of JNI libraries that are embedded inside this APEX.
 	Jni_libs []string
 
+	// List of rust dyn libraries
+	Rust_dyn_libs []string
+
 	// List of native executables that are embedded inside this APEX.
 	Binaries []string
 
@@ -350,7 +354,8 @@
 
 	prebuiltFileToDelete string
 
-	distFiles android.TaggedDistFiles
+	// Path of API coverage generate file
+	coverageOutputPath android.ModuleOutPath
 }
 
 // apexFileClass represents a type of file that can be included in APEX.
@@ -513,13 +518,15 @@
 func addDependenciesForNativeModules(ctx android.BottomUpMutatorContext, nativeModules ApexNativeDependencies, target android.Target, imageVariation string) {
 	binVariations := target.Variations()
 	libVariations := append(target.Variations(), blueprint.Variation{Mutator: "link", Variation: "shared"})
+	rustLibVariations := append(target.Variations(), blueprint.Variation{Mutator: "rust_libraries", Variation: "dylib"})
 
 	if ctx.Device() {
 		binVariations = append(binVariations, blueprint.Variation{Mutator: "image", Variation: imageVariation})
 		libVariations = append(libVariations,
 			blueprint.Variation{Mutator: "image", Variation: imageVariation},
-			blueprint.Variation{Mutator: "version", Variation: ""}, // "" is the non-stub variant
-		)
+			blueprint.Variation{Mutator: "version", Variation: ""}) // "" is the non-stub variant
+		rustLibVariations = append(rustLibVariations,
+			blueprint.Variation{Mutator: "image", Variation: imageVariation})
 	}
 
 	// Use *FarVariation* to be able to depend on modules having conflicting variations with
@@ -529,6 +536,7 @@
 	ctx.AddFarVariationDependencies(binVariations, testTag, nativeModules.Tests...)
 	ctx.AddFarVariationDependencies(libVariations, jniLibTag, nativeModules.Jni_libs...)
 	ctx.AddFarVariationDependencies(libVariations, sharedLibTag, nativeModules.Native_shared_libs...)
+	ctx.AddFarVariationDependencies(rustLibVariations, sharedLibTag, nativeModules.Rust_dyn_libs...)
 }
 
 func (a *apexBundle) combineProperties(ctx android.BottomUpMutatorContext) {
@@ -1096,7 +1104,8 @@
 // Implements android.OutputFileProducer
 func (a *apexBundle) OutputFiles(tag string) (android.Paths, error) {
 	switch tag {
-	case "":
+	case "", android.DefaultDistTag:
+		// This is the default dist path.
 		return android.Paths{a.outputFile}, nil
 	default:
 		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
@@ -1264,6 +1273,35 @@
 	return af
 }
 
+func apexFileForRustExecutable(ctx android.BaseModuleContext, rustm *rust.Module) apexFile {
+	dirInApex := "bin"
+	if rustm.Target().NativeBridge == android.NativeBridgeEnabled {
+		dirInApex = filepath.Join(dirInApex, rustm.Target().NativeBridgeRelativePath)
+	}
+	fileToCopy := rustm.OutputFile().Path()
+	androidMkModuleName := rustm.BaseModuleName() + rustm.Properties.SubName
+	af := newApexFile(ctx, fileToCopy, androidMkModuleName, dirInApex, nativeExecutable, rustm)
+	return af
+}
+
+func apexFileForRustLibrary(ctx android.BaseModuleContext, rustm *rust.Module) apexFile {
+	// Decide the APEX-local directory by the multilib of the library
+	// In the future, we may query this to the module.
+	var dirInApex string
+	switch rustm.Arch().ArchType.Multilib {
+	case "lib32":
+		dirInApex = "lib"
+	case "lib64":
+		dirInApex = "lib64"
+	}
+	if rustm.Target().NativeBridge == android.NativeBridgeEnabled {
+		dirInApex = filepath.Join(dirInApex, rustm.Target().NativeBridgeRelativePath)
+	}
+	fileToCopy := rustm.OutputFile().Path()
+	androidMkModuleName := rustm.BaseModuleName() + rustm.Properties.SubName
+	return newApexFile(ctx, fileToCopy, androidMkModuleName, dirInApex, nativeSharedLib, rustm)
+}
+
 func apexFileForPyBinary(ctx android.BaseModuleContext, py *python.Module) apexFile {
 	dirInApex := "bin"
 	fileToCopy := py.HostToolPath().Path()
@@ -1501,8 +1539,11 @@
 					filesInfo = append(filesInfo, apexFileForPyBinary(ctx, py))
 				} else if gb, ok := child.(bootstrap.GoBinaryTool); ok && a.Host() {
 					filesInfo = append(filesInfo, apexFileForGoBinary(ctx, depName, gb))
+				} else if rust, ok := child.(*rust.Module); ok {
+					filesInfo = append(filesInfo, apexFileForRustExecutable(ctx, rust))
+					return true // track transitive dependencies
 				} else {
-					ctx.PropertyErrorf("binaries", "%q is neither cc_binary, (embedded) py_binary, (host) blueprint_go_binary, (host) bootstrap_go_binary, nor sh_binary", depName)
+					ctx.PropertyErrorf("binaries", "%q is neither cc_binary, rust_binary, (embedded) py_binary, (host) blueprint_go_binary, (host) bootstrap_go_binary, nor sh_binary", depName)
 				}
 			case javaLibTag:
 				switch child.(type) {
@@ -1625,7 +1666,7 @@
 							// system libraries.
 							if !am.DirectlyInAnyApex() {
 								// we need a module name for Make
-								name := cc.ImplementationModuleName(ctx)
+								name := cc.ImplementationModuleNameForMake(ctx)
 
 								if !proptools.Bool(a.properties.Use_vendor) {
 									// we don't use subName(.vendor) for a "use_vendor: true" apex
@@ -1663,6 +1704,13 @@
 					if prebuilt, ok := child.(prebuilt_etc.PrebuiltEtcModule); ok {
 						filesInfo = append(filesInfo, apexFileForPrebuiltEtc(ctx, prebuilt, depName))
 					}
+				} else if rust.IsDylibDepTag(depTag) {
+					if rustm, ok := child.(*rust.Module); ok && rustm.IsInstallableToApex() {
+						af := apexFileForRustLibrary(ctx, rustm)
+						af.transitiveDep = true
+						filesInfo = append(filesInfo, af)
+						return true // track transitive dependencies
+					}
 				} else if _, ok := depTag.(android.CopyDirectlyInAnyApexTag); ok {
 					// nothing
 				} else if am.CanHaveApexVariants() && am.IsInstallableToApex() {
@@ -1798,7 +1846,6 @@
 	}
 	a.buildApexDependencyInfo(ctx)
 	a.buildLintReports(ctx)
-	a.distFiles = a.GenerateTaggedDistFiles(ctx)
 
 	// Append meta-files to the filesInfo list so that they are reflected in Android.mk as well.
 	if a.installable() {
@@ -1969,7 +2016,9 @@
 			// The dynamic linker and crash_dump tool in the runtime APEX is the only
 			// exception to this rule. It can't make the static dependencies dynamic
 			// because it can't do the dynamic linking for itself.
-			if apexName == "com.android.runtime" && (fromName == "linker" || fromName == "crash_dump") {
+			// Same rule should be applied to linkerconfig, because it should be executed
+			// only with static linked libraries before linker is available with ld.config.txt
+			if apexName == "com.android.runtime" && (fromName == "linker" || fromName == "crash_dump" || fromName == "linkerconfig") {
 				return false
 			}
 
diff --git a/apex/apex_test.go b/apex/apex_test.go
index 33e5077..0b67ef5 100644
--- a/apex/apex_test.go
+++ b/apex/apex_test.go
@@ -32,6 +32,7 @@
 	"android/soong/dexpreopt"
 	prebuilt_etc "android/soong/etc"
 	"android/soong/java"
+	"android/soong/rust"
 	"android/soong/sh"
 )
 
@@ -136,6 +137,8 @@
 
 	bp = bp + cc.GatherRequiredDepsForTest(android.Android)
 
+	bp = bp + rust.GatherRequiredDepsForTest()
+
 	bp = bp + java.GatherRequiredDepsForTest()
 
 	fs := map[string][]byte{
@@ -185,6 +188,7 @@
 		"bar/baz":                                    nil,
 		"testdata/baz":                               nil,
 		"AppSet.apks":                                nil,
+		"foo.rs":                                     nil,
 	}
 
 	cc.GatherRequiredFilesForTest(fs)
@@ -241,6 +245,7 @@
 	ctx.PostDepsMutators(android.RegisterVisibilityRuleEnforcer)
 
 	cc.RegisterRequiredBuildComponentsForTest(ctx)
+	rust.RegisterRequiredBuildComponentsForTest(ctx)
 
 	ctx.RegisterModuleType("cc_test", cc.TestFactory)
 	ctx.RegisterModuleType("vndk_prebuilt_shared", cc.VndkPrebuiltSharedFactory)
@@ -349,10 +354,12 @@
 			manifest: ":myapex.manifest",
 			androidManifest: ":myapex.androidmanifest",
 			key: "myapex.key",
+			binaries: ["foo.rust"],
 			native_shared_libs: ["mylib"],
+			rust_dyn_libs: ["libfoo.dylib.rust"],
 			multilib: {
 				both: {
-					binaries: ["foo",],
+					binaries: ["foo"],
 				}
 			},
 			java_libs: [
@@ -415,6 +422,28 @@
 			apex_available: [ "myapex", "com.android.gki.*" ],
 		}
 
+		rust_binary {
+		        name: "foo.rust",
+			srcs: ["foo.rs"],
+			rlibs: ["libfoo.rlib.rust"],
+			dylibs: ["libfoo.dylib.rust"],
+			apex_available: ["myapex"],
+		}
+
+		rust_library_rlib {
+		        name: "libfoo.rlib.rust",
+			srcs: ["foo.rs"],
+			crate_name: "foo",
+			apex_available: ["myapex"],
+		}
+
+		rust_library_dylib {
+		        name: "libfoo.dylib.rust",
+			srcs: ["foo.rs"],
+			crate_name: "foo",
+			apex_available: ["myapex"],
+		}
+
 		apex {
 			name: "com.android.gki.fake",
 			binaries: ["foo"],
@@ -529,16 +558,20 @@
 	ensureListContains(t, ctx.ModuleVariantsForTests("mylib"), "android_arm64_armv8-a_shared_apex10000")
 	ensureListContains(t, ctx.ModuleVariantsForTests("myjar"), "android_common_apex10000")
 	ensureListContains(t, ctx.ModuleVariantsForTests("myjar_dex"), "android_common_apex10000")
+	ensureListContains(t, ctx.ModuleVariantsForTests("foo.rust"), "android_arm64_armv8-a_apex10000")
 
 	// Ensure that apex variant is created for the indirect dep
 	ensureListContains(t, ctx.ModuleVariantsForTests("mylib2"), "android_arm64_armv8-a_shared_apex10000")
 	ensureListContains(t, ctx.ModuleVariantsForTests("myotherjar"), "android_common_apex10000")
+	ensureListContains(t, ctx.ModuleVariantsForTests("libfoo.rlib.rust"), "android_arm64_armv8-a_rlib_dylib-std_apex10000")
+	ensureListContains(t, ctx.ModuleVariantsForTests("libfoo.dylib.rust"), "android_arm64_armv8-a_dylib_apex10000")
 
 	// Ensure that both direct and indirect deps are copied into apex
 	ensureContains(t, copyCmds, "image.apex/lib64/mylib.so")
 	ensureContains(t, copyCmds, "image.apex/lib64/mylib2.so")
 	ensureContains(t, copyCmds, "image.apex/javalib/myjar_stem.jar")
 	ensureContains(t, copyCmds, "image.apex/javalib/myjar_dex.jar")
+	ensureContains(t, copyCmds, "image.apex/lib64/libfoo.dylib.rust.dylib.so")
 	// .. but not for java libs
 	ensureNotContains(t, copyCmds, "image.apex/javalib/myotherjar.jar")
 	ensureNotContains(t, copyCmds, "image.apex/javalib/msharedjar.jar")
@@ -2798,18 +2831,18 @@
 	// non-APEX variant does not have __ANDROID_APEX__ defined
 	mylibCFlags := ctx.ModuleForTests("mylib", "android_arm64_armv8-a_static").Rule("cc").Args["cFlags"]
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX__")
-	ensureNotContains(t, mylibCFlags, "-D__ANDROID_SDK_VERSION__")
+	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_MIN_SDK_VERSION__")
 
 	// APEX variant has __ANDROID_APEX__ and __ANDROID_APEX_SDK__ defined
 	mylibCFlags = ctx.ModuleForTests("mylib", "android_arm64_armv8-a_static_apex10000").Rule("cc").Args["cFlags"]
 	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX__")
-	ensureContains(t, mylibCFlags, "-D__ANDROID_SDK_VERSION__=10000")
+	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX_MIN_SDK_VERSION__=10000")
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_MYAPEX__")
 
 	// APEX variant has __ANDROID_APEX__ and __ANDROID_APEX_SDK__ defined
 	mylibCFlags = ctx.ModuleForTests("mylib", "android_arm64_armv8-a_static_apex29").Rule("cc").Args["cFlags"]
 	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX__")
-	ensureContains(t, mylibCFlags, "-D__ANDROID_SDK_VERSION__=29")
+	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX_MIN_SDK_VERSION__=29")
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_OTHERAPEX__")
 
 	// When a cc_library sets use_apex_name_macro: true each apex gets a unique variant and
@@ -2831,10 +2864,10 @@
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_MYAPEX__")
 	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX_OTHERAPEX__")
 
-	// recovery variant does not set __ANDROID_SDK_VERSION__
+	// recovery variant does not set __ANDROID_APEX_MIN_SDK_VERSION__
 	mylibCFlags = ctx.ModuleForTests("mylib3", "android_recovery_arm64_armv8-a_static").Rule("cc").Args["cFlags"]
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX__")
-	ensureNotContains(t, mylibCFlags, "-D__ANDROID_SDK_VERSION__")
+	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_MIN_SDK_VERSION__")
 
 	// When a dependency of a cc_library sets use_apex_name_macro: true each apex gets a unique
 	// variant.
@@ -2855,10 +2888,10 @@
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_MYAPEX__")
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_OTHERAPEX__")
 
-	// recovery variant does not set __ANDROID_SDK_VERSION__
+	// recovery variant does not set __ANDROID_APEX_MIN_SDK_VERSION__
 	mylibCFlags = ctx.ModuleForTests("mylib2", "android_recovery_arm64_armv8-a_static").Rule("cc").Args["cFlags"]
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX__")
-	ensureNotContains(t, mylibCFlags, "-D__ANDROID_SDK_VERSION__")
+	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_MIN_SDK_VERSION__")
 }
 
 func TestHeaderLibsDependency(t *testing.T) {
@@ -6153,6 +6186,57 @@
 	`)
 }
 
+func TestPreferredPrebuiltSharedLibDep(t *testing.T) {
+	ctx, config := testApex(t, `
+		apex {
+			name: "myapex",
+			key: "myapex.key",
+			native_shared_libs: ["mylib"],
+		}
+
+		apex_key {
+			name: "myapex.key",
+			public_key: "testkey.avbpubkey",
+			private_key: "testkey.pem",
+		}
+
+		cc_library {
+			name: "mylib",
+			srcs: ["mylib.cpp"],
+			apex_available: ["myapex"],
+			shared_libs: ["otherlib"],
+			system_shared_libs: [],
+		}
+
+		cc_library {
+			name: "otherlib",
+			srcs: ["mylib.cpp"],
+			stubs: {
+				versions: ["current"],
+			},
+		}
+
+		cc_prebuilt_library_shared {
+			name: "otherlib",
+			prefer: true,
+			srcs: ["prebuilt.so"],
+			stubs: {
+				versions: ["current"],
+			},
+		}
+	`)
+
+	ab := ctx.ModuleForTests("myapex", "android_common_myapex_image").Module().(*apexBundle)
+	data := android.AndroidMkDataForTest(t, config, "", ab)
+	var builder strings.Builder
+	data.Custom(&builder, ab.BaseModuleName(), "TARGET_", "", data)
+	androidMk := builder.String()
+
+	// The make level dependency needs to be on otherlib - prebuilt_otherlib isn't
+	// a thing there.
+	ensureContains(t, androidMk, "LOCAL_REQUIRED_MODULES += otherlib\n")
+}
+
 func TestMain(m *testing.M) {
 	run := func() int {
 		setUp()
diff --git a/apex/builder.go b/apex/builder.go
index b858135..66eaff1 100644
--- a/apex/builder.go
+++ b/apex/builder.go
@@ -37,6 +37,7 @@
 
 func init() {
 	pctx.Import("android/soong/android")
+	pctx.Import("android/soong/cc/config")
 	pctx.Import("android/soong/java")
 	pctx.HostBinToolVariable("apexer", "apexer")
 	// ART minimal builds (using the master-art manifest) do not have the "frameworks/base"
@@ -65,6 +66,7 @@
 	pctx.HostBinToolVariable("extract_apks", "extract_apks")
 	pctx.HostBinToolVariable("make_f2fs", "make_f2fs")
 	pctx.HostBinToolVariable("sload_f2fs", "sload_f2fs")
+	pctx.SourcePathVariable("genNdkUsedbyApexPath", "build/soong/scripts/gen_ndk_usedby_apex.sh")
 }
 
 var (
@@ -176,6 +178,12 @@
 		Description: "Diff ${image_content_file} and ${allowed_files_file}",
 	}, "image_content_file", "allowed_files_file", "apex_module_name")
 
+	generateAPIsUsedbyApexRule = pctx.StaticRule("generateAPIsUsedbyApexRule", blueprint.RuleParams{
+		Command:     "$genNdkUsedbyApexPath ${image_dir} ${readelf} ${out}",
+		CommandDeps: []string{"${genNdkUsedbyApexPath}"},
+		Description: "Generate symbol list used by Apex",
+	}, "image_dir", "readelf")
+
 	// Don't add more rules here. Consider using android.NewRuleBuilder instead.
 )
 
@@ -262,7 +270,7 @@
 	}
 
 	output := android.PathForModuleOut(ctx, "file_contexts")
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	switch a.properties.ApexType {
 	case imageApex:
@@ -294,7 +302,7 @@
 		panic(fmt.Errorf("unsupported type %v", a.properties.ApexType))
 	}
 
-	rule.Build(pctx, ctx, "file_contexts."+a.Name(), "Generate file_contexts")
+	rule.Build("file_contexts."+a.Name(), "Generate file_contexts")
 	return output.OutputPath
 }
 
@@ -329,14 +337,14 @@
 // included in the APEX without actually downloading and extracting it.
 func (a *apexBundle) buildInstalledFilesFile(ctx android.ModuleContext, builtApex android.Path, imageDir android.Path) android.OutputPath {
 	output := android.PathForModuleOut(ctx, "installed-files.txt")
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.Command().
 		Implicit(builtApex).
 		Text("(cd " + imageDir.String() + " ; ").
 		Text("find . \\( -type f -o -type l \\) -printf \"%s %p\\n\") ").
 		Text(" | sort -nr > ").
 		Output(output)
-	rule.Build(pctx, ctx, "installed-files."+a.Name(), "Installed files")
+	rule.Build("installed-files."+a.Name(), "Installed files")
 	return output.OutputPath
 }
 
@@ -675,6 +683,22 @@
 			Description: "apex proto convert",
 		})
 
+		implicitInputs = append(implicitInputs, unsignedOutputFile)
+
+		// Run coverage analysis
+		apisUsedbyOutputFile := android.PathForModuleOut(ctx, a.Name()+".txt")
+		ctx.Build(pctx, android.BuildParams{
+			Rule:        generateAPIsUsedbyApexRule,
+			Implicits:   implicitInputs,
+			Description: "coverage",
+			Output:      apisUsedbyOutputFile,
+			Args: map[string]string{
+				"image_dir": imageDir.String(),
+				"readelf":   "${config.ClangBin}/llvm-readelf",
+			},
+		})
+		a.coverageOutputPath = apisUsedbyOutputFile
+
 		bundleConfig := a.buildBundleConfig(ctx)
 
 		var abis []string
diff --git a/cc/Android.bp b/cc/Android.bp
index ff2cdf3..88104e2 100644
--- a/cc/Android.bp
+++ b/cc/Android.bp
@@ -72,6 +72,8 @@
         "vendor_public_library.go",
 
         "testing.go",
+
+        "stub_library.go",
     ],
     testSrcs: [
         "cc_test.go",
diff --git a/cc/androidmk.go b/cc/androidmk.go
index d32e4de..320e69b 100644
--- a/cc/androidmk.go
+++ b/cc/androidmk.go
@@ -334,8 +334,7 @@
 	entries.Class = "NATIVE_TESTS"
 	entries.ExtraEntries = append(entries.ExtraEntries, func(entries *android.AndroidMkEntries) {
 		if len(benchmark.Properties.Test_suites) > 0 {
-			entries.SetString("LOCAL_COMPATIBILITY_SUITE",
-				strings.Join(benchmark.Properties.Test_suites, " "))
+			entries.AddCompatibilityTestSuites(benchmark.Properties.Test_suites...)
 		}
 		if benchmark.testConfig != nil {
 			entries.SetString("LOCAL_FULL_TEST_CONFIG", benchmark.testConfig.String())
@@ -360,8 +359,7 @@
 	}
 	entries.ExtraEntries = append(entries.ExtraEntries, func(entries *android.AndroidMkEntries) {
 		if len(test.Properties.Test_suites) > 0 {
-			entries.SetString("LOCAL_COMPATIBILITY_SUITE",
-				strings.Join(test.Properties.Test_suites, " "))
+			entries.AddCompatibilityTestSuites(test.Properties.Test_suites...)
 		}
 		if test.testConfig != nil {
 			entries.SetString("LOCAL_FULL_TEST_CONFIG", test.testConfig.String())
diff --git a/cc/binary.go b/cc/binary.go
index fbd293e..fa3966f 100644
--- a/cc/binary.go
+++ b/cc/binary.go
@@ -373,7 +373,7 @@
 	if String(binary.Properties.Prefix_symbols) != "" {
 		afterPrefixSymbols := outputFile
 		outputFile = android.PathForModuleOut(ctx, "unprefixed", fileName)
-		TransformBinaryPrefixSymbols(ctx, String(binary.Properties.Prefix_symbols), outputFile,
+		transformBinaryPrefixSymbols(ctx, String(binary.Properties.Prefix_symbols), outputFile,
 			builderFlags, afterPrefixSymbols)
 	}
 
@@ -428,13 +428,13 @@
 	linkerDeps = append(linkerDeps, flags.LdFlagsDeps...)
 
 	// Register link action.
-	TransformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs, deps.StaticLibs,
+	transformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs, deps.StaticLibs,
 		deps.LateStaticLibs, deps.WholeStaticLibs, linkerDeps, deps.CrtBegin, deps.CrtEnd, true,
 		builderFlags, outputFile, nil)
 
 	objs.coverageFiles = append(objs.coverageFiles, deps.StaticLibObjs.coverageFiles...)
 	objs.coverageFiles = append(objs.coverageFiles, deps.WholeStaticLibObjs.coverageFiles...)
-	binary.coverageOutputFile = TransformCoverageFilesToZip(ctx, objs, binary.getStem(ctx))
+	binary.coverageOutputFile = transformCoverageFilesToZip(ctx, objs, binary.getStem(ctx))
 
 	// Need to determine symlinks early since some targets (ie APEX) need this
 	// information but will not call 'install'
diff --git a/cc/builder.go b/cc/builder.go
index 81c09b1..5545a5b 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -19,7 +19,6 @@
 // functions.
 
 import (
-	"fmt"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -40,6 +39,7 @@
 var (
 	pctx = android.NewPackageContext("android/soong/cc")
 
+	// Rule to invoke gcc with given command, flags, and dependencies. Outputs a .d depfile.
 	cc = pctx.AndroidRemoteStaticRule("cc", android.RemoteRuleSupports{Goma: true, RBE: true},
 		blueprint.RuleParams{
 			Depfile:     "${out}.d",
@@ -49,6 +49,7 @@
 		},
 		"ccCmd", "cFlags")
 
+	// Rule to invoke gcc with given command and flags, but no dependencies.
 	ccNoDeps = pctx.AndroidStaticRule("ccNoDeps",
 		blueprint.RuleParams{
 			Command:     "$relPwd $ccCmd -c $cFlags -o $out $in",
@@ -56,6 +57,8 @@
 		},
 		"ccCmd", "cFlags")
 
+	// Rules to invoke ld to link binaries. Uses a .rsp file to list dependencies, as there may
+	// be many.
 	ld, ldRE = remoteexec.StaticRules(pctx, "ld",
 		blueprint.RuleParams{
 			Command: "$reTemplate$ldCmd ${crtBegin} @${out}.rsp " +
@@ -76,6 +79,7 @@
 			Platform:        map[string]string{remoteexec.PoolKey: "${config.RECXXLinksPool}"},
 		}, []string{"ldCmd", "crtBegin", "libFlags", "crtEnd", "ldFlags", "extraLibFlags"}, []string{"implicitInputs", "implicitOutputs"})
 
+	// Rules for .o files to combine to other .o files, using ld partial linking.
 	partialLd, partialLdRE = remoteexec.StaticRules(pctx, "partialLd",
 		blueprint.RuleParams{
 			// Without -no-pie, clang 7.0 adds -pie to link Android files,
@@ -91,6 +95,7 @@
 			Platform:        map[string]string{remoteexec.PoolKey: "${config.RECXXLinksPool}"},
 		}, []string{"ldCmd", "ldFlags"}, []string{"implicitInputs", "inCommaList", "implicitOutputs"})
 
+	// Rule to invoke `ar` with given cmd and flags, but no static library depenencies.
 	ar = pctx.AndroidStaticRule("ar",
 		blueprint.RuleParams{
 			Command:        "rm -f ${out} && $arCmd $arFlags $out @${out}.rsp",
@@ -100,6 +105,8 @@
 		},
 		"arCmd", "arFlags")
 
+	// Rule to invoke `ar` with given cmd, flags, and library dependencies. Generates a .a
+	// (archive) file from .o files.
 	arWithLibs = pctx.AndroidStaticRule("arWithLibs",
 		blueprint.RuleParams{
 			Command:        "rm -f ${out} && $arCmd $arObjFlags $out @${out}.rsp && $arCmd $arLibFlags $out $arLibs",
@@ -109,12 +116,7 @@
 		},
 		"arCmd", "arObjFlags", "arObjs", "arLibFlags", "arLibs")
 
-	darwinStrip = pctx.AndroidStaticRule("darwinStrip",
-		blueprint.RuleParams{
-			Command:     "${config.MacStripPath} -u -r -o $out $in",
-			CommandDeps: []string{"${config.MacStripPath}"},
-		})
-
+	// Rule to run objcopy --prefix-symbols (to prefix all symbols in a file with a given string).
 	prefixSymbols = pctx.AndroidStaticRule("prefixSymbols",
 		blueprint.RuleParams{
 			Command:     "$objcopyCmd --prefix-symbols=${prefix} ${in} ${out}",
@@ -125,6 +127,24 @@
 	_ = pctx.SourcePathVariable("stripPath", "build/soong/scripts/strip.sh")
 	_ = pctx.SourcePathVariable("xzCmd", "prebuilts/build-tools/${config.HostPrebuiltTag}/bin/xz")
 
+	// Rule to invoke `strip` (to discard symbols and data from object files).
+	strip = pctx.AndroidStaticRule("strip",
+		blueprint.RuleParams{
+			Depfile:     "${out}.d",
+			Deps:        blueprint.DepsGCC,
+			Command:     "CROSS_COMPILE=$crossCompile XZ=$xzCmd CLANG_BIN=${config.ClangBin} $stripPath ${args} -i ${in} -o ${out} -d ${out}.d",
+			CommandDeps: []string{"$stripPath", "$xzCmd"},
+			Pool:        darwinStripPool,
+		},
+		"args", "crossCompile")
+
+	// Rule to invoke `strip` (to discard symbols and data from object files) on darwin architecture.
+	darwinStrip = pctx.AndroidStaticRule("darwinStrip",
+		blueprint.RuleParams{
+			Command:     "${config.MacStripPath} -u -r -o $out $in",
+			CommandDeps: []string{"${config.MacStripPath}"},
+		})
+
 	// b/132822437: objcopy uses a file descriptor per .o file when called on .a files, which runs the system out of
 	// file descriptors on darwin.  Limit concurrent calls to 5 on darwin.
 	darwinStripPool = func() blueprint.Pool {
@@ -137,18 +157,9 @@
 		}
 	}()
 
-	strip = pctx.AndroidStaticRule("strip",
-		blueprint.RuleParams{
-			Depfile:     "${out}.d",
-			Deps:        blueprint.DepsGCC,
-			Command:     "CROSS_COMPILE=$crossCompile XZ=$xzCmd CLANG_BIN=${config.ClangBin} $stripPath ${args} -i ${in} -o ${out} -d ${out}.d",
-			CommandDeps: []string{"$stripPath", "$xzCmd"},
-			Pool:        darwinStripPool,
-		},
-		"args", "crossCompile")
-
 	_ = pctx.SourcePathVariable("archiveRepackPath", "build/soong/scripts/archive_repack.sh")
 
+	// Rule to repack an archive (.a) file with a subset of object files.
 	archiveRepack = pctx.AndroidStaticRule("archiveRepack",
 		blueprint.RuleParams{
 			Depfile:     "${out}.d",
@@ -158,6 +169,7 @@
 		},
 		"objects")
 
+	// Rule to create an empty file at a given path.
 	emptyFile = pctx.AndroidStaticRule("emptyFile",
 		blueprint.RuleParams{
 			Command: "rm -f $out && touch $out",
@@ -165,6 +177,7 @@
 
 	_ = pctx.SourcePathVariable("tocPath", "build/soong/scripts/toc.sh")
 
+	// A rule for extracting a table of contents from a shared library (.so).
 	toc = pctx.AndroidStaticRule("toc",
 		blueprint.RuleParams{
 			Depfile:     "${out}.d",
@@ -175,6 +188,7 @@
 		},
 		"crossCompile", "format")
 
+	// Rule for invoking clang-tidy (a clang-based linter).
 	clangTidy, clangTidyRE = remoteexec.StaticRules(pctx, "clangTidy",
 		blueprint.RuleParams{
 			Command:     "rm -f $out && $reTemplate${config.ClangBin}/clang-tidy $tidyFlags $in -- $cFlags && touch $out",
@@ -193,6 +207,7 @@
 
 	_ = pctx.SourcePathVariable("yasmCmd", "prebuilts/misc/${config.HostPrebuiltTag}/yasm/yasm")
 
+	// Rule for invoking yasm to compile .asm assembly files.
 	yasm = pctx.AndroidStaticRule("yasm",
 		blueprint.RuleParams{
 			Command:     "$yasmCmd $asFlags -o $out $in && $yasmCmd $asFlags -M $in >$out.d",
@@ -202,6 +217,7 @@
 		},
 		"asFlags")
 
+	// Rule to invoke windres, for interaction with Windows resources.
 	windres = pctx.AndroidStaticRule("windres",
 		blueprint.RuleParams{
 			Command:     "$windresCmd $flags -I$$(dirname $in) -i $in -o $out --preprocessor \"${config.ClangBin}/clang -E -xc-header -DRC_INVOKED\"",
@@ -220,13 +236,15 @@
 			Labels:       map[string]string{"type": "abi-dump", "tool": "header-abi-dumper"},
 			ExecStrategy: "${config.REAbiDumperExecStrategy}",
 			Platform: map[string]string{
-				remoteexec.PoolKey:      "${config.RECXXPool}",
+				remoteexec.PoolKey: "${config.RECXXPool}",
 			},
 		}, []string{"cFlags", "exportDirs"}, nil)
 
 	_ = pctx.SourcePathVariable("sAbiLinker", "prebuilts/clang-tools/${config.HostPrebuiltTag}/bin/header-abi-linker")
 	_ = pctx.SourcePathVariable("sAbiLinkerLibs", "prebuilts/clang-tools/${config.HostPrebuiltTag}/lib64")
 
+	// Rule to combine .dump sAbi dump files from multiple source files into a single .ldump
+	// sAbi dump file.
 	sAbiLink, sAbiLinkRE = remoteexec.StaticRules(pctx, "sAbiLink",
 		blueprint.RuleParams{
 			Command:        "$reTemplate$sAbiLinker -o ${out} $symbolFilter -arch $arch  $exportedHeaderFlags @${out}.rsp ",
@@ -245,6 +263,7 @@
 
 	_ = pctx.SourcePathVariable("sAbiDiffer", "prebuilts/clang-tools/${config.HostPrebuiltTag}/bin/header-abi-diff")
 
+	// Rule to compare linked sAbi dump files (.ldump).
 	sAbiDiff = pctx.RuleFunc("sAbiDiff",
 		func(ctx android.PackageRuleContext) blueprint.RuleParams {
 			commandStr := "($sAbiDiffer ${extraFlags} -lib ${libName} -arch ${arch} -o ${out} -new ${in} -old ${referenceDump})"
@@ -258,11 +277,13 @@
 		},
 		"extraFlags", "referenceDump", "libName", "arch", "createReferenceDumpFlags")
 
+	// Rule to unzip a reference abi dump.
 	unzipRefSAbiDump = pctx.AndroidStaticRule("unzipRefSAbiDump",
 		blueprint.RuleParams{
 			Command: "gunzip -c $in > $out",
 		})
 
+	// Rule to zip files.
 	zip = pctx.AndroidStaticRule("zip",
 		blueprint.RuleParams{
 			Command:        "${SoongZipCmd} -o ${out} -C $$OUT_DIR -r ${out}.rsp",
@@ -278,6 +299,8 @@
 		func(ctx android.PackageVarContext) string { return ctx.Config().XrefCorpusName() })
 	_ = pctx.VariableFunc("kytheCuEncoding",
 		func(ctx android.PackageVarContext) string { return ctx.Config().XrefCuEncoding() })
+
+	// Rule to use kythe extractors to generate .kzip files, used to build code cross references.
 	kytheExtract = pctx.StaticRule("kythe",
 		blueprint.RuleParams{
 			Command: `rm -f $out && ` +
@@ -310,7 +333,11 @@
 	pctx.Import("android/soong/remoteexec")
 }
 
+// builderFlags contains various types of command line flags (and settings) for use in building
+// build statements related to C++.
 type builderFlags struct {
+	// Global flags (which build system or toolchain is responsible for). These are separate from
+	// local flags because they should appear first (so that they may be overridden by local flags).
 	globalCommonFlags     string
 	globalAsFlags         string
 	globalYasmFlags       string
@@ -321,6 +348,7 @@
 	globalCppFlags        string
 	globalLdFlags         string
 
+	// Local flags (which individual modules are responsible for). These may override global flags.
 	localCommonFlags     string
 	localAsFlags         string
 	localYasmFlags       string
@@ -331,32 +359,37 @@
 	localCppFlags        string
 	localLdFlags         string
 
-	libFlags      string
-	extraLibFlags string
-	tidyFlags     string
-	sAbiFlags     string
-	aidlFlags     string
-	rsFlags       string
+	libFlags      string // Flags to add to the linker directly after specifying libraries to link.
+	extraLibFlags string // Flags to add to the linker last.
+	tidyFlags     string // Flags that apply to clang-tidy
+	sAbiFlags     string // Flags that apply to header-abi-dumps
+	aidlFlags     string // Flags that apply to aidl source files
+	rsFlags       string // Flags that apply to renderscript source files
 	toolchain     config.Toolchain
-	tidy          bool
-	gcovCoverage  bool
-	sAbiDump      bool
-	emitXrefs     bool
 
-	assemblerWithCpp bool
+	// True if these extra features are enabled.
+	tidy         bool
+	gcovCoverage bool
+	sAbiDump     bool
+	emitXrefs    bool
+
+	assemblerWithCpp bool // True if .s files should be processed with the c preprocessor.
 
 	systemIncludeFlags string
 
+	// True if static libraries should be grouped (using `-Wl,--start-group` and `-Wl,--end-group`).
 	groupStaticLibs bool
 
 	proto            android.ProtoFlags
-	protoC           bool
-	protoOptionsFile bool
+	protoC           bool // If true, compile protos as `.c` files. Otherwise, output as `.cc`.
+	protoOptionsFile bool // If true, output a proto options file.
 
 	yacc *YaccProperties
 	lex  *LexProperties
 }
 
+// StripFlags represents flags related to stripping. This is separate from builderFlags, as these
+// flags are useful outside of this package (such as for Rust).
 type StripFlags struct {
 	Toolchain                     config.Toolchain
 	StripKeepSymbols              bool
@@ -367,6 +400,7 @@
 	StripUseGnuStrip              bool
 }
 
+// Objects is a collection of file paths corresponding to outputs for C++ related build statements.
 type Objects struct {
 	objFiles      android.Paths
 	tidyFiles     android.Paths
@@ -396,9 +430,10 @@
 }
 
 // Generate rules for compiling multiple .c, .cpp, or .S files to individual .o files
-func TransformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles android.Paths,
+func transformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles android.Paths,
 	flags builderFlags, pathDeps android.Paths, cFlagsDeps android.Paths) Objects {
 
+	// Source files are one-to-one with tidy, coverage, or kythe files, if enabled.
 	objFiles := make(android.Paths, len(srcFiles))
 	var tidyFiles android.Paths
 	if flags.tidy {
@@ -468,6 +503,7 @@
 
 		objFiles[i] = objFile
 
+		// Register compilation build statements. The actual rule used depends on the source file type.
 		switch srcFile.Ext() {
 		case ".asm":
 			ctx.Build(pctx, android.BuildParams{
@@ -532,8 +568,11 @@
 			ccCmd = "clang++"
 			moduleFlags = cppflags
 			moduleToolingFlags = toolingCppflags
+		case ".h", ".hpp":
+			ctx.PropertyErrorf("srcs", "Header file %s is not supported, instead use export_include_dirs or local_include_dirs.", srcFile)
+			continue
 		default:
-			ctx.ModuleErrorf("File %s has unknown extension", srcFile)
+			ctx.PropertyErrorf("srcs", "File %s has unknown extension. Supported extensions: .s, .S, .c, .cpp, .cc, .cxx, .mm", srcFile)
 			continue
 		}
 
@@ -562,6 +601,7 @@
 			},
 		})
 
+		// Register post-process build statements (such as for tidy or kythe).
 		if emitXref {
 			kytheFile := android.ObjPathWithExt(ctx, subdir, srcFile, "kzip")
 			ctx.Build(pctx, android.BuildParams{
@@ -639,7 +679,7 @@
 }
 
 // Generate a rule for compiling multiple .o files to a static library (.a)
-func TransformObjToStaticLib(ctx android.ModuleContext,
+func transformObjToStaticLib(ctx android.ModuleContext,
 	objFiles android.Paths, wholeStaticLibs android.Paths,
 	flags builderFlags, outputFile android.ModuleOutPath, deps android.Paths) {
 
@@ -682,7 +722,7 @@
 
 // Generate a rule for compiling multiple .o files, plus static libraries, whole static libraries,
 // and shared libraries, to a shared library (.so) or dynamic executable
-func TransformObjToDynamicBinary(ctx android.ModuleContext,
+func transformObjToDynamicBinary(ctx android.ModuleContext,
 	objFiles, sharedLibs, staticLibs, lateStaticLibs, wholeStaticLibs, deps android.Paths,
 	crtBegin, crtEnd android.OptionalPath, groupLate bool, flags builderFlags, outputFile android.WritablePath, implicitOutputs android.WritablePaths) {
 
@@ -763,7 +803,7 @@
 
 // Generate a rule to combine .dump sAbi dump files from multiple source files
 // into a single .ldump sAbi dump file
-func TransformDumpToLinkedDump(ctx android.ModuleContext, sAbiDumps android.Paths, soFile android.Path,
+func transformDumpToLinkedDump(ctx android.ModuleContext, sAbiDumps android.Paths, soFile android.Path,
 	baseName, exportedHeaderFlags string, symbolFile android.OptionalPath,
 	excludedSymbolVersions, excludedSymbolTags []string) android.OptionalPath {
 
@@ -810,7 +850,8 @@
 	return android.OptionalPathForPath(outputFile)
 }
 
-func UnzipRefDump(ctx android.ModuleContext, zippedRefDump android.Path, baseName string) android.Path {
+// unzipRefDump registers a build statement to unzip a reference abi dump.
+func unzipRefDump(ctx android.ModuleContext, zippedRefDump android.Path, baseName string) android.Path {
 	outputFile := android.PathForModuleOut(ctx, baseName+"_ref.lsdump")
 	ctx.Build(pctx, android.BuildParams{
 		Rule:        unzipRefSAbiDump,
@@ -821,7 +862,8 @@
 	return outputFile
 }
 
-func SourceAbiDiff(ctx android.ModuleContext, inputDump android.Path, referenceDump android.Path,
+// sourceAbiDiff registers a build statement to compare linked sAbi dump files (.ldump).
+func sourceAbiDiff(ctx android.ModuleContext, inputDump android.Path, referenceDump android.Path,
 	baseName, exportedHeaderFlags string, checkAllApis, isLlndk, isNdk, isVndkExt bool) android.OptionalPath {
 
 	outputFile := android.PathForModuleOut(ctx, baseName+".abidiff")
@@ -872,7 +914,7 @@
 }
 
 // Generate a rule for extracting a table of contents from a shared library (.so)
-func TransformSharedObjectToToc(ctx android.ModuleContext, inputFile android.Path,
+func transformSharedObjectToToc(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath, flags builderFlags) {
 
 	var format string
@@ -901,7 +943,7 @@
 }
 
 // Generate a rule for compiling multiple .o files to a .o using ld partial linking
-func TransformObjsToObj(ctx android.ModuleContext, objFiles android.Paths,
+func transformObjsToObj(ctx android.ModuleContext, objFiles android.Paths,
 	flags builderFlags, outputFile android.WritablePath, deps android.Paths) {
 
 	ldCmd := "${config.ClangBin}/clang++"
@@ -926,8 +968,8 @@
 	})
 }
 
-// Generate a rule for runing objcopy --prefix-symbols on a binary
-func TransformBinaryPrefixSymbols(ctx android.ModuleContext, prefix string, inputFile android.Path,
+// Generate a rule for running objcopy --prefix-symbols on a binary
+func transformBinaryPrefixSymbols(ctx android.ModuleContext, prefix string, inputFile android.Path,
 	flags builderFlags, outputFile android.WritablePath) {
 
 	objcopyCmd := gccCmd(flags.toolchain, "objcopy")
@@ -944,7 +986,8 @@
 	})
 }
 
-func TransformStrip(ctx android.ModuleContext, inputFile android.Path,
+// Registers a build statement to invoke `strip` (to discard symbols and data from object files).
+func transformStrip(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath, flags StripFlags) {
 
 	crossCompile := gccCmd(flags.Toolchain, "")
@@ -980,7 +1023,8 @@
 	})
 }
 
-func TransformDarwinStrip(ctx android.ModuleContext, inputFile android.Path,
+// Registers build statement to invoke `strip` on darwin architecture.
+func transformDarwinStrip(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath) {
 
 	ctx.Build(pctx, android.BuildParams{
@@ -991,7 +1035,8 @@
 	})
 }
 
-func TransformCoverageFilesToZip(ctx android.ModuleContext,
+// Registers build statement to zip one or more coverage files.
+func transformCoverageFilesToZip(ctx android.ModuleContext,
 	inputs Objects, baseName string) android.OptionalPath {
 
 	if len(inputs.coverageFiles) > 0 {
@@ -1010,7 +1055,8 @@
 	return android.OptionalPath{}
 }
 
-func TransformArchiveRepack(ctx android.ModuleContext, inputFile android.Path,
+// Rule to repack an archive (.a) file with a subset of object files.
+func transformArchiveRepack(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath, objects []string) {
 
 	ctx.Build(pctx, android.BuildParams{
@@ -1027,33 +1073,3 @@
 func gccCmd(toolchain config.Toolchain, cmd string) string {
 	return filepath.Join(toolchain.GccRoot(), "bin", toolchain.GccTriple()+"-"+cmd)
 }
-
-func splitListForSize(list android.Paths, limit int) (lists []android.Paths, err error) {
-	var i int
-
-	start := 0
-	bytes := 0
-	for i = range list {
-		l := len(list[i].String())
-		if l > limit {
-			return nil, fmt.Errorf("list element greater than size limit (%d)", limit)
-		}
-		if bytes+l > limit {
-			lists = append(lists, list[start:i])
-			start = i
-			bytes = 0
-		}
-		bytes += l + 1 // count a space between each list element
-	}
-
-	lists = append(lists, list[start:])
-
-	totalLen := 0
-	for _, l := range lists {
-		totalLen += len(l)
-	}
-	if totalLen != len(list) {
-		panic(fmt.Errorf("Failed breaking up list, %d != %d", len(list), totalLen))
-	}
-	return lists, nil
-}
diff --git a/cc/cc.go b/cc/cc.go
index 6deb1b4..b1c1264 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -91,6 +91,14 @@
 	ctx.RegisterSingletonType("kythe_extract_all", kytheExtractAllFactory)
 }
 
+// Deps is a struct containing module names of dependencies, separated by the kind of dependency.
+// Mutators should use `AddVariationDependencies` or its sibling methods to add actual dependency
+// edges to these modules.
+// This object is constructed in DepsMutator, by calling to various module delegates to set
+// relevant fields. For example, `module.compiler.compilerDeps()` may append type-specific
+// dependencies.
+// This is then consumed by the same DepsMutator, which will call `ctx.AddVariationDependencies()`
+// (or its sibling methods) to set real dependencies on the given modules.
 type Deps struct {
 	SharedLibs, LateSharedLibs                  []string
 	StaticLibs, LateStaticLibs, WholeStaticLibs []string
@@ -103,6 +111,7 @@
 	// Used by DepsMutator to pass system_shared_libs information to check_elf_file.py.
 	SystemSharedLibs []string
 
+	// If true, statically link the unwinder into native libraries/binaries.
 	StaticUnwinderIfLegacy bool
 
 	ReexportSharedLibHeaders, ReexportStaticLibHeaders, ReexportHeaderLibHeaders []string
@@ -122,6 +131,11 @@
 	DynamicLinker   string
 }
 
+// PathDeps is a struct containing file paths to dependencies of a module.
+// It's constructed in depsToPath() by traversing the direct dependencies of the current module.
+// It's used to construct flags for various build statements (such as for compiling and linking).
+// It is then passed to module decorator functions responsible for registering build statements
+// (such as `module.compiler.compile()`).`
 type PathDeps struct {
 	// Paths to .so files
 	SharedLibs, EarlySharedLibs, LateSharedLibs android.Paths
@@ -182,8 +196,12 @@
 	LdFlags         []string // Flags that apply to linker command lines
 }
 
+// Flags contains various types of command line flags (and settings) for use in building build
+// statements related to C++.
 type Flags struct {
-	Local  LocalOrGlobalFlags
+	// Local flags (which individual modules are responsible for). These may override global flags.
+	Local LocalOrGlobalFlags
+	// Global flags (which build system or toolchain is responsible for).
 	Global LocalOrGlobalFlags
 
 	aidlFlags     []string // Flags that apply to aidl source files
@@ -198,19 +216,23 @@
 	SystemIncludeFlags []string
 
 	Toolchain    config.Toolchain
-	Tidy         bool
-	GcovCoverage bool
-	SAbiDump     bool
+	Tidy         bool // True if clang-tidy is enabled.
+	GcovCoverage bool // True if coverage files should be generated.
+	SAbiDump     bool // True if header abi dumps should be generated.
 	EmitXrefs    bool // If true, generate Ninja rules to generate emitXrefs input files for Kythe
 
+	// The instruction set required for clang ("arm" or "thumb").
 	RequiredInstructionSet string
-	DynamicLinker          string
+	// The target-device system path to the dynamic linker.
+	DynamicLinker string
 
 	CFlagsDeps  android.Paths // Files depended on by compiler flags
 	LdFlagsDeps android.Paths // Files depended on by linker flags
 
+	// True if .s files should be processed with the c preprocessor.
 	AssemblerWithCpp bool
-	GroupStaticLibs  bool
+	// True if static libraries should be grouped (using `-Wl,--start-group` and `-Wl,--end-group`).
+	GroupStaticLibs bool
 
 	proto            android.ProtoFlags
 	protoC           bool // Whether to use C instead of C++
@@ -358,6 +380,10 @@
 	Double_loadable *bool
 }
 
+// ModuleContextIntf is an interface (on a module context helper) consisting of functions related
+// to understanding  details about the type of the current module.
+// For example, one might call these functions to determine whether the current module is a static
+// library and/or is installed in vendor directories.
 type ModuleContextIntf interface {
 	static() bool
 	staticBinary() bool
@@ -412,6 +438,8 @@
 	ModuleContextIntf
 }
 
+// feature represents additional (optional) steps to building cc-related modules, such as invocation
+// of clang-tidy.
 type feature interface {
 	begin(ctx BaseModuleContext)
 	deps(ctx DepsContext, deps Deps) Deps
@@ -419,6 +447,9 @@
 	props() []interface{}
 }
 
+// compiler is the interface for a compiler helper object. Different module decorators may implement
+// this helper differently. For example, compiling a `cc_library` may use a different build
+// statement than building a `toolchain_library`.
 type compiler interface {
 	compilerInit(ctx BaseModuleContext)
 	compilerDeps(ctx DepsContext, deps Deps) Deps
@@ -430,6 +461,9 @@
 	compile(ctx ModuleContext, flags Flags, deps PathDeps) Objects
 }
 
+// linker is the interface for a linker decorator object. Individual module types can provide
+// their own implementation for this decorator, and thus specify custom logic regarding build
+// statements pertaining to linking.
 type linker interface {
 	linkerInit(ctx BaseModuleContext)
 	linkerDeps(ctx DepsContext, deps Deps) Deps
@@ -445,15 +479,19 @@
 	coverageOutputFilePath() android.OptionalPath
 
 	// Get the deps that have been explicitly specified in the properties.
-	// Only updates the
 	linkerSpecifiedDeps(specifiedDeps specifiedDeps) specifiedDeps
 }
 
+// specifiedDeps is a tuple struct representing dependencies of a linked binary owned by the linker.
 type specifiedDeps struct {
-	sharedLibs       []string
-	systemSharedLibs []string // Note nil and [] are semantically distinct.
+	sharedLibs []string
+	// Note nil and [] are semantically distinct. [] prevents linking against the defaults (usually
+	// libc, libm, etc.)
+	systemSharedLibs []string
 }
 
+// installer is the interface for an installer helper object. This helper is responsible for
+// copying build outputs to the appropriate locations so that they may be installed on device.
 type installer interface {
 	installerProps() []interface{}
 	install(ctx ModuleContext, path android.Path)
@@ -584,7 +622,7 @@
 	genHeaderExportDepTag = dependencyTag{name: "gen header export"}
 	objDepTag             = dependencyTag{name: "obj"}
 	linkerFlagsDepTag     = dependencyTag{name: "linker flags file"}
-	dynamicLinkerDepTag   = dependencyTag{name: "dynamic linker"}
+	dynamicLinkerDepTag   = installDependencyTag{name: "dynamic linker"}
 	reuseObjTag           = dependencyTag{name: "reuse objects"}
 	staticVariantTag      = dependencyTag{name: "static variant"}
 	vndkExtDepTag         = dependencyTag{name: "vndk extends"}
@@ -626,7 +664,18 @@
 
 // Module contains the properties and members used by all C/C++ module types, and implements
 // the blueprint.Module interface.  It delegates to compiler, linker, and installer interfaces
-// to construct the output file.  Behavior can be customized with a Customizer interface
+// to construct the output file.  Behavior can be customized with a Customizer, or "decorator",
+// interface.
+//
+// To define a C/C++ related module, construct a new Module object and point its delegates to
+// type-specific structs. These delegates will be invoked to register module-specific build
+// statements which may be unique to the module type. For example, module.compiler.compile() should
+// be defined so as to register build statements which are responsible for compiling the module.
+//
+// Another example: to construct a cc_binary module, one can create a `cc.binaryDecorator` struct
+// which implements the `linker` and `installer` interfaces, and points the `linker` and `installer`
+// members of the cc.Module to this decorator. Thus, a cc_binary module has custom linker and
+// installer logic.
 type Module struct {
 	android.ModuleBase
 	android.DefaultableModuleBase
@@ -643,18 +692,23 @@
 	// Allowable SdkMemberTypes of this module type.
 	sdkMemberTypes []android.SdkMemberType
 
-	// delegates, initialize before calling Init
-	features  []feature
+	// decorator delegates, initialize before calling Init
+	// these may contain module-specific implementations, and effectively allow for custom
+	// type-specific logic. These members may reference different objects or the same object.
+	// Functions of these decorators will be invoked to initialize and register type-specific
+	// build statements.
 	compiler  compiler
 	linker    linker
 	installer installer
-	stl       *stl
-	sanitize  *sanitize
-	coverage  *coverage
-	sabi      *sabi
-	vndkdep   *vndkdep
-	lto       *lto
-	pgo       *pgo
+
+	features []feature
+	stl      *stl
+	sanitize *sanitize
+	coverage *coverage
+	sabi     *sabi
+	vndkdep  *vndkdep
+	lto      *lto
+	pgo      *pgo
 
 	library libraryInterface
 
@@ -1045,6 +1099,19 @@
 	return name
 }
 
+// Similar to ImplementationModuleName, but uses the Make variant of the module
+// name as base name, for use in AndroidMk output. E.g. for a prebuilt module
+// where the Soong name is prebuilt_foo, this returns foo (which works in Make
+// under the premise that the prebuilt module overrides its source counterpart
+// if it is exposed to Make).
+func (c *Module) ImplementationModuleNameForMake(ctx android.BaseModuleContext) string {
+	name := c.BaseModuleName()
+	if versioned, ok := c.linker.(versionedInterface); ok {
+		name = versioned.implementationModuleName(name)
+	}
+	return name
+}
+
 func (c *Module) bootstrap() bool {
 	return Bool(c.Properties.Bootstrap)
 }
@@ -1074,7 +1141,7 @@
 
 func isBionic(name string) bool {
 	switch name {
-	case "libc", "libm", "libdl", "libdl_android", "linker":
+	case "libc", "libm", "libdl", "libdl_android", "linker", "linkerconfig":
 		return true
 	}
 	return false
diff --git a/cc/cc_test.go b/cc/cc_test.go
index 7c98585..af9b943 100644
--- a/cc/cc_test.go
+++ b/cc/cc_test.go
@@ -2913,114 +2913,6 @@
 	}
 }
 
-var (
-	str11 = "01234567891"
-	str10 = str11[:10]
-	str9  = str11[:9]
-	str5  = str11[:5]
-	str4  = str11[:4]
-)
-
-var splitListForSizeTestCases = []struct {
-	in   []string
-	out  [][]string
-	size int
-}{
-	{
-		in:   []string{str10},
-		out:  [][]string{{str10}},
-		size: 10,
-	},
-	{
-		in:   []string{str9},
-		out:  [][]string{{str9}},
-		size: 10,
-	},
-	{
-		in:   []string{str5},
-		out:  [][]string{{str5}},
-		size: 10,
-	},
-	{
-		in:   []string{str11},
-		out:  nil,
-		size: 10,
-	},
-	{
-		in:   []string{str10, str10},
-		out:  [][]string{{str10}, {str10}},
-		size: 10,
-	},
-	{
-		in:   []string{str9, str10},
-		out:  [][]string{{str9}, {str10}},
-		size: 10,
-	},
-	{
-		in:   []string{str10, str9},
-		out:  [][]string{{str10}, {str9}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str4},
-		out:  [][]string{{str5, str4}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str4, str5},
-		out:  [][]string{{str5, str4}, {str5}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str4, str5, str4},
-		out:  [][]string{{str5, str4}, {str5, str4}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str4, str5, str5},
-		out:  [][]string{{str5, str4}, {str5}, {str5}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str5, str5, str4},
-		out:  [][]string{{str5}, {str5}, {str5, str4}},
-		size: 10,
-	},
-	{
-		in:   []string{str9, str11},
-		out:  nil,
-		size: 10,
-	},
-	{
-		in:   []string{str11, str9},
-		out:  nil,
-		size: 10,
-	},
-}
-
-func TestSplitListForSize(t *testing.T) {
-	for _, testCase := range splitListForSizeTestCases {
-		out, _ := splitListForSize(android.PathsForTesting(testCase.in...), testCase.size)
-
-		var outStrings [][]string
-
-		if len(out) > 0 {
-			outStrings = make([][]string, len(out))
-			for i, o := range out {
-				outStrings[i] = o.Strings()
-			}
-		}
-
-		if !reflect.DeepEqual(outStrings, testCase.out) {
-			t.Errorf("incorrect output:")
-			t.Errorf("     input: %#v", testCase.in)
-			t.Errorf("      size: %d", testCase.size)
-			t.Errorf("  expected: %#v", testCase.out)
-			t.Errorf("       got: %#v", outStrings)
-		}
-	}
-}
-
 var staticLinkDepOrderTestCases = []struct {
 	// This is a string representation of a map[moduleName][]moduleDependency .
 	// It models the dependencies declared in an Android.bp file.
diff --git a/cc/cflag_artifacts.go b/cc/cflag_artifacts.go
index 855ff25..be46fc0 100644
--- a/cc/cflag_artifacts.go
+++ b/cc/cflag_artifacts.go
@@ -68,7 +68,7 @@
 
 	cleanedName := strings.Replace(flag, "=", "_", -1)
 	filename, filepath := s.incrementFile(ctx, cleanedName, part)
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.Command().Textf("rm -f %s", filepath.String())
 
 	if using {
@@ -84,7 +84,7 @@
 	length := len(modules)
 
 	if length == 0 {
-		rule.Build(pctx, ctx, filename, "gen "+filename)
+		rule.Build(filename, "gen "+filename)
 		part++
 	}
 
@@ -98,11 +98,11 @@
 				strings.Join(proptools.ShellEscapeList(shard), " ")).
 			FlagWithOutput(">> ", filepath).
 			Text("; done")
-		rule.Build(pctx, ctx, filename, "gen "+filename)
+		rule.Build(filename, "gen "+filename)
 
 		if index+1 != len(moduleShards) {
 			filename, filepath = s.incrementFile(ctx, cleanedName, part+index+1)
-			rule = android.NewRuleBuilder()
+			rule = android.NewRuleBuilder(pctx, ctx)
 			rule.Command().Textf("rm -f %s", filepath.String())
 		}
 	}
@@ -121,14 +121,14 @@
 	for _, flag := range TrackedCFlags {
 		// Generate build rule to combine related intermediary files into a
 		// C Flag artifact
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 		filename := s.genFlagFilename(flag)
 		outputpath := android.PathForOutput(ctx, "cflags", filename)
 		rule.Command().
 			Text("cat").
 			Inputs(s.interOutputs[flag].Paths()).
 			FlagWithOutput("> ", outputpath)
-		rule.Build(pctx, ctx, filename, "gen "+filename)
+		rule.Build(filename, "gen "+filename)
 		s.outputs = append(s.outputs, outputpath)
 	}
 }
diff --git a/cc/compiler.go b/cc/compiler.go
index 04ed80d..b78bb6c 100644
--- a/cc/compiler.go
+++ b/cc/compiler.go
@@ -366,7 +366,7 @@
 		}
 		if ctx.Device() {
 			flags.Global.CommonFlags = append(flags.Global.CommonFlags,
-				fmt.Sprintf("-D__ANDROID_SDK_VERSION__=%d",
+				fmt.Sprintf("-D__ANDROID_APEX_MIN_SDK_VERSION__=%d",
 					ctx.apexSdkVersion().FinalOrFutureInt()))
 		}
 	}
@@ -649,7 +649,7 @@
 func compileObjs(ctx android.ModuleContext, flags builderFlags,
 	subdir string, srcFiles, pathDeps android.Paths, cFlagsDeps android.Paths) Objects {
 
-	return TransformSourceToObj(ctx, subdir, srcFiles, flags, pathDeps, cFlagsDeps)
+	return transformSourceToObj(ctx, subdir, srcFiles, flags, pathDeps, cFlagsDeps)
 }
 
 var thirdPartyDirPrefixExceptions = []*regexp.Regexp{
diff --git a/cc/config/vndk.go b/cc/config/vndk.go
index 563ce76..a548452 100644
--- a/cc/config/vndk.go
+++ b/cc/config/vndk.go
@@ -21,7 +21,6 @@
 	"android.hardware.automotive.occupant_awareness-ndk_platform",
 	"android.hardware.light-ndk_platform",
 	"android.hardware.identity-ndk_platform",
-	"android.hardware.keymint-ndk_platform",
 	"android.hardware.keymint-unstable-ndk_platform",
 	"android.hardware.nfc@1.2",
 	"android.hardware.power-ndk_platform",
diff --git a/cc/fuzz.go b/cc/fuzz.go
index dddfe94..6b17c48 100644
--- a/cc/fuzz.go
+++ b/cc/fuzz.go
@@ -246,25 +246,25 @@
 	fuzz.binaryDecorator.baseInstaller.install(ctx, file)
 
 	fuzz.corpus = android.PathsForModuleSrc(ctx, fuzz.Properties.Corpus)
-	builder := android.NewRuleBuilder()
+	builder := android.NewRuleBuilder(pctx, ctx)
 	intermediateDir := android.PathForModuleOut(ctx, "corpus")
 	for _, entry := range fuzz.corpus {
 		builder.Command().Text("cp").
 			Input(entry).
 			Output(intermediateDir.Join(ctx, entry.Base()))
 	}
-	builder.Build(pctx, ctx, "copy_corpus", "copy corpus")
+	builder.Build("copy_corpus", "copy corpus")
 	fuzz.corpusIntermediateDir = intermediateDir
 
 	fuzz.data = android.PathsForModuleSrc(ctx, fuzz.Properties.Data)
-	builder = android.NewRuleBuilder()
+	builder = android.NewRuleBuilder(pctx, ctx)
 	intermediateDir = android.PathForModuleOut(ctx, "data")
 	for _, entry := range fuzz.data {
 		builder.Command().Text("cp").
 			Input(entry).
 			Output(intermediateDir.Join(ctx, entry.Rel()))
 	}
-	builder.Build(pctx, ctx, "copy_data", "copy data")
+	builder.Build("copy_data", "copy data")
 	fuzz.dataIntermediateDir = intermediateDir
 
 	if fuzz.Properties.Dictionary != nil {
@@ -419,12 +419,12 @@
 		sharedLibraries := collectAllSharedDependencies(ctx, module)
 
 		var files []fileToZip
-		builder := android.NewRuleBuilder()
+		builder := android.NewRuleBuilder(pctx, ctx)
 
 		// Package the corpora into a zipfile.
 		if fuzzModule.corpus != nil {
 			corpusZip := archDir.Join(ctx, module.Name()+"_seed_corpus.zip")
-			command := builder.Command().BuiltTool(ctx, "soong_zip").
+			command := builder.Command().BuiltTool("soong_zip").
 				Flag("-j").
 				FlagWithOutput("-o ", corpusZip)
 			command.FlagWithRspFileInputList("-r ", fuzzModule.corpus)
@@ -434,7 +434,7 @@
 		// Package the data into a zipfile.
 		if fuzzModule.data != nil {
 			dataZip := archDir.Join(ctx, module.Name()+"_data.zip")
-			command := builder.Command().BuiltTool(ctx, "soong_zip").
+			command := builder.Command().BuiltTool("soong_zip").
 				FlagWithOutput("-o ", dataZip)
 			for _, f := range fuzzModule.data {
 				intermediateDir := strings.TrimSuffix(f.String(), f.Rel())
@@ -492,7 +492,7 @@
 		}
 
 		fuzzZip := archDir.Join(ctx, module.Name()+".zip")
-		command := builder.Command().BuiltTool(ctx, "soong_zip").
+		command := builder.Command().BuiltTool("soong_zip").
 			Flag("-j").
 			FlagWithOutput("-o ", fuzzZip)
 		for _, file := range files {
@@ -504,7 +504,7 @@
 			command.FlagWithInput("-f ", file.SourceFilePath)
 		}
 
-		builder.Build(pctx, ctx, "create-"+fuzzZip.String(),
+		builder.Build("create-"+fuzzZip.String(),
 			"Package "+module.Name()+" for "+archString+"-"+hostOrTargetString)
 
 		// Don't add modules to 'make haiku' that are set to not be exported to the
@@ -531,11 +531,11 @@
 		filesToZip := archDirs[archOs]
 		arch := archOs.arch
 		hostOrTarget := archOs.hostOrTarget
-		builder := android.NewRuleBuilder()
+		builder := android.NewRuleBuilder(pctx, ctx)
 		outputFile := android.PathForOutput(ctx, "fuzz-"+hostOrTarget+"-"+arch+".zip")
 		s.packages = append(s.packages, outputFile)
 
-		command := builder.Command().BuiltTool(ctx, "soong_zip").
+		command := builder.Command().BuiltTool("soong_zip").
 			Flag("-j").
 			FlagWithOutput("-o ", outputFile).
 			Flag("-L 0") // No need to try and re-compress the zipfiles.
@@ -549,7 +549,7 @@
 			command.FlagWithInput("-f ", fileToZip.SourceFilePath)
 		}
 
-		builder.Build(pctx, ctx, "create-fuzz-package-"+arch+"-"+hostOrTarget,
+		builder.Build("create-fuzz-package-"+arch+"-"+hostOrTarget,
 			"Create fuzz target packages for "+arch+"-"+hostOrTarget)
 	}
 }
diff --git a/cc/gen.go b/cc/gen.go
index 5895b31..75b9e49 100644
--- a/cc/gen.go
+++ b/cc/gen.go
@@ -75,10 +75,9 @@
 	cmd := rule.Command()
 
 	// Fix up #line markers to not use the sbox temporary directory
-	// android.SboxPathForOutput(outDir, outDir) returns the sbox placeholder for the out
+	// android.sboxPathForOutput(outDir, outDir) returns the sbox placeholder for the out
 	// directory itself, without any filename appended.
-	// TODO(ccross): make this cmd.PathForOutput(outDir) instead.
-	sboxOutDir := android.SboxPathForOutput(outDir, outDir)
+	sboxOutDir := cmd.PathForOutput(outDir)
 	sedCmd := "sed -i.bak 's#" + sboxOutDir + "#" + outDir.String() + "#'"
 	rule.Command().Text(sedCmd).Input(outFile)
 	rule.Command().Text(sedCmd).Input(headerFile)
@@ -137,7 +136,7 @@
 	}
 
 	cmd := rule.Command()
-	cmd.BuiltTool(ctx, "aidl-cpp").
+	cmd.BuiltTool("aidl-cpp").
 		FlagWithDepFile("-d", depFile).
 		Flag("--ninja").
 		Flag(aidlFlags).
@@ -232,7 +231,7 @@
 	var yaccRule_ *android.RuleBuilder
 	yaccRule := func() *android.RuleBuilder {
 		if yaccRule_ == nil {
-			yaccRule_ = android.NewRuleBuilder().Sbox(android.PathForModuleGen(ctx, "yacc"),
+			yaccRule_ = android.NewRuleBuilder(pctx, ctx).Sbox(android.PathForModuleGen(ctx, "yacc"),
 				android.PathForModuleGen(ctx, "yacc.sbox.textproto"))
 		}
 		return yaccRule_
@@ -262,7 +261,7 @@
 			deps = append(deps, headerFile)
 		case ".aidl":
 			if aidlRule == nil {
-				aidlRule = android.NewRuleBuilder().Sbox(android.PathForModuleGen(ctx, "aidl"),
+				aidlRule = android.NewRuleBuilder(pctx, ctx).Sbox(android.PathForModuleGen(ctx, "aidl"),
 					android.PathForModuleGen(ctx, "aidl.sbox.textproto"))
 			}
 			cppFile := android.GenPathWithExt(ctx, "aidl", srcFile, "cpp")
@@ -285,11 +284,11 @@
 	}
 
 	if aidlRule != nil {
-		aidlRule.Build(pctx, ctx, "aidl", "gen aidl")
+		aidlRule.Build("aidl", "gen aidl")
 	}
 
 	if yaccRule_ != nil {
-		yaccRule_.Build(pctx, ctx, "yacc", "gen yacc")
+		yaccRule_.Build("yacc", "gen yacc")
 	}
 
 	if len(rsFiles) > 0 {
diff --git a/cc/library.go b/cc/library.go
index 7ae75f2..c626b03 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -897,9 +897,9 @@
 		}
 	}
 
-	TransformObjToStaticLib(ctx, library.objects.objFiles, deps.WholeStaticLibsFromPrebuilts, builderFlags, outputFile, objs.tidyFiles)
+	transformObjToStaticLib(ctx, library.objects.objFiles, deps.WholeStaticLibsFromPrebuilts, builderFlags, outputFile, objs.tidyFiles)
 
-	library.coverageOutputFile = TransformCoverageFilesToZip(ctx, library.objects, ctx.ModuleName())
+	library.coverageOutputFile = transformCoverageFilesToZip(ctx, library.objects, ctx.ModuleName())
 
 	ctx.CheckbuildFile(outputFile)
 
@@ -974,7 +974,7 @@
 	// depending on a table of contents file instead of the library itself.
 	tocFile := outputFile.ReplaceExtension(ctx, flags.Toolchain.ShlibSuffix()[1:]+".toc")
 	library.tocFile = android.OptionalPathForPath(tocFile)
-	TransformSharedObjectToToc(ctx, outputFile, tocFile, builderFlags)
+	transformSharedObjectToToc(ctx, outputFile, tocFile, builderFlags)
 
 	stripFlags := flagsToStripFlags(flags)
 	if library.stripper.NeedsStrip(ctx) {
@@ -1019,7 +1019,7 @@
 
 	if Bool(library.Properties.Sort_bss_symbols_by_size) {
 		unsortedOutputFile := android.PathForModuleOut(ctx, "unsorted", fileName)
-		TransformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
+		transformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
 			deps.StaticLibs, deps.LateStaticLibs, deps.WholeStaticLibs,
 			linkerDeps, deps.CrtBegin, deps.CrtEnd, false, builderFlags, unsortedOutputFile, implicitOutputs)
 
@@ -1029,7 +1029,7 @@
 		linkerDeps = append(linkerDeps, symbolOrderingFile)
 	}
 
-	TransformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
+	transformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
 		deps.StaticLibs, deps.LateStaticLibs, deps.WholeStaticLibs,
 		linkerDeps, deps.CrtBegin, deps.CrtEnd, false, builderFlags, outputFile, implicitOutputs)
 
@@ -1039,7 +1039,7 @@
 	objs.sAbiDumpFiles = append(objs.sAbiDumpFiles, deps.StaticLibObjs.sAbiDumpFiles...)
 	objs.sAbiDumpFiles = append(objs.sAbiDumpFiles, deps.WholeStaticLibObjs.sAbiDumpFiles...)
 
-	library.coverageOutputFile = TransformCoverageFilesToZip(ctx, objs, library.getLibName(ctx))
+	library.coverageOutputFile = transformCoverageFilesToZip(ctx, objs, library.getLibName(ctx))
 	library.linkSAbiDumpFiles(ctx, objs, fileName, unstrippedOutputFile)
 
 	var staticAnalogue *StaticLibraryInfo
@@ -1115,7 +1115,7 @@
 		return refAbiDumpTextFile.Path()
 	}
 	if refAbiDumpGzipFile.Valid() {
-		return UnzipRefDump(ctx, refAbiDumpGzipFile.Path(), fileName)
+		return unzipRefDump(ctx, refAbiDumpGzipFile.Path(), fileName)
 	}
 	return nil
 }
@@ -1141,7 +1141,7 @@
 			SourceAbiFlags = append(SourceAbiFlags, "-I"+reexportedInclude)
 		}
 		exportedHeaderFlags := strings.Join(SourceAbiFlags, " ")
-		library.sAbiOutputFile = TransformDumpToLinkedDump(ctx, objs.sAbiDumpFiles, soFile, fileName, exportedHeaderFlags,
+		library.sAbiOutputFile = transformDumpToLinkedDump(ctx, objs.sAbiDumpFiles, soFile, fileName, exportedHeaderFlags,
 			android.OptionalPathForModuleSrc(ctx, library.symbolFileForAbiCheck(ctx)),
 			library.Properties.Header_abi_checker.Exclude_symbol_versions,
 			library.Properties.Header_abi_checker.Exclude_symbol_tags)
@@ -1150,7 +1150,7 @@
 
 		refAbiDumpFile := getRefAbiDumpFile(ctx, vndkVersion, fileName)
 		if refAbiDumpFile != nil {
-			library.sAbiDiff = SourceAbiDiff(ctx, library.sAbiOutputFile.Path(),
+			library.sAbiDiff = sourceAbiDiff(ctx, library.sAbiOutputFile.Path(),
 				refAbiDumpFile, fileName, exportedHeaderFlags,
 				Bool(library.Properties.Header_abi_checker.Check_all_apis),
 				ctx.isLlndk(ctx.Config()), ctx.isNdk(ctx.Config()), ctx.isVndkExt())
@@ -1754,13 +1754,13 @@
 		hashedOutputfile := outputFile
 		outputFile = android.PathForModuleOut(ctx, "unhashed", fileName)
 
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 		rule.Command().
-			BuiltTool(ctx, "bssl_inject_hash").
+			BuiltTool("bssl_inject_hash").
 			Flag("-sha256").
 			FlagWithInput("-in-object ", outputFile).
 			FlagWithOutput("-o ", hashedOutputfile)
-		rule.Build(pctx, ctx, "injectCryptoHash", "inject crypto hash")
+		rule.Build("injectCryptoHash", "inject crypto hash")
 	}
 
 	return outputFile
diff --git a/cc/object.go b/cc/object.go
index ab2672b..3ce7676 100644
--- a/cc/object.go
+++ b/cc/object.go
@@ -124,7 +124,7 @@
 
 		if String(object.Properties.Prefix_symbols) != "" {
 			output := android.PathForModuleOut(ctx, ctx.ModuleName()+objectExtension)
-			TransformBinaryPrefixSymbols(ctx, String(object.Properties.Prefix_symbols), outputFile,
+			transformBinaryPrefixSymbols(ctx, String(object.Properties.Prefix_symbols), outputFile,
 				builderFlags, output)
 			outputFile = output
 		}
@@ -134,12 +134,12 @@
 
 		if String(object.Properties.Prefix_symbols) != "" {
 			input := android.PathForModuleOut(ctx, "unprefixed", ctx.ModuleName()+objectExtension)
-			TransformBinaryPrefixSymbols(ctx, String(object.Properties.Prefix_symbols), input,
+			transformBinaryPrefixSymbols(ctx, String(object.Properties.Prefix_symbols), input,
 				builderFlags, output)
 			output = input
 		}
 
-		TransformObjsToObj(ctx, objs.objFiles, builderFlags, output, flags.LdFlagsDeps)
+		transformObjsToObj(ctx, objs.objFiles, builderFlags, output, flags.LdFlagsDeps)
 	}
 
 	ctx.CheckbuildFile(outputFile)
diff --git a/cc/prebuilt.go b/cc/prebuilt.go
index 8873883..37df4ba 100644
--- a/cc/prebuilt.go
+++ b/cc/prebuilt.go
@@ -146,7 +146,7 @@
 			// depending on a table of contents file instead of the library itself.
 			tocFile := android.PathForModuleOut(ctx, libName+".toc")
 			p.tocFile = android.OptionalPathForPath(tocFile)
-			TransformSharedObjectToToc(ctx, outputFile, tocFile, builderFlags)
+			transformSharedObjectToToc(ctx, outputFile, tocFile, builderFlags)
 
 			if ctx.Windows() && p.properties.Windows_import_lib != nil {
 				// Consumers of this library actually links to the import library in build
diff --git a/cc/proto.go b/cc/proto.go
index 9c102a2..4466144 100644
--- a/cc/proto.go
+++ b/cc/proto.go
@@ -50,11 +50,11 @@
 	depFile := ccFile.ReplaceExtension(ctx, "d")
 	outputs := android.WritablePaths{ccFile, headerFile}
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
-	android.ProtoRule(ctx, rule, protoFile, flags.proto, protoDeps, outDir, depFile, outputs)
+	android.ProtoRule(rule, protoFile, flags.proto, protoDeps, outDir, depFile, outputs)
 
-	rule.Build(pctx, ctx, "protoc_"+protoFile.Rel(), "protoc "+protoFile.Rel())
+	rule.Build("protoc_"+protoFile.Rel(), "protoc "+protoFile.Rel())
 
 	return ccFile, headerFile
 }
diff --git a/cc/sanitize.go b/cc/sanitize.go
index dbc52a5..22ee25f 100644
--- a/cc/sanitize.go
+++ b/cc/sanitize.go
@@ -169,14 +169,14 @@
 		Cfi              *bool    `android:"arch_variant"`
 		Integer_overflow *bool    `android:"arch_variant"`
 		Misc_undefined   []string `android:"arch_variant"`
-		No_recover       []string
-	}
+		No_recover       []string `android:"arch_variant"`
+	} `android:"arch_variant"`
 
 	// Sanitizers to run with flag configuration specified
 	Config struct {
 		// Enables CFI support flags for assembly-heavy libraries
 		Cfi_assembly_support *bool `android:"arch_variant"`
-	}
+	} `android:"arch_variant"`
 
 	// value to pass to -fsanitize-recover=
 	Recover []string
diff --git a/cc/strip.go b/cc/strip.go
index e9aec91..b1f34bb 100644
--- a/cc/strip.go
+++ b/cc/strip.go
@@ -23,19 +23,23 @@
 // StripProperties defines the type of stripping applied to the module.
 type StripProperties struct {
 	Strip struct {
-		// whether to disable all stripping.
+		// none forces all stripping to be disabled.
+		// Device modules default to stripping enabled leaving mini debuginfo.
+		// Host modules default to stripping disabled, but can be enabled by setting any other
+		// strip boolean property.
 		None *bool `android:"arch_variant"`
 
-		// whether to strip everything, including the mini debug info.
+		// all forces stripping everything, including the mini debug info.
 		All *bool `android:"arch_variant"`
 
-		// whether to keep the symbols.
+		// keep_symbols enables stripping but keeps all symbols.
 		Keep_symbols *bool `android:"arch_variant"`
 
-		// keeps only the symbols defined here.
+		// keep_symbols_list specifies a list of symbols to keep if keep_symbols is enabled.
+		// If it is unset then all symbols are kept.
 		Keep_symbols_list []string `android:"arch_variant"`
 
-		// whether to keep the symbols and the debug frames.
+		// keep_symbols_and_debug_frame enables stripping but keeps all symbols and debug frames.
 		Keep_symbols_and_debug_frame *bool `android:"arch_variant"`
 	} `android:"arch_variant"`
 }
@@ -47,14 +51,18 @@
 
 // NeedsStrip determines if stripping is required for a module.
 func (stripper *Stripper) NeedsStrip(actx android.ModuleContext) bool {
-	// TODO(ccross): enable host stripping when Kati is enabled? Make never had support for stripping host binaries.
-	return (!actx.Config().KatiEnabled() || actx.Device()) && !Bool(stripper.StripProperties.Strip.None)
+	forceDisable := Bool(stripper.StripProperties.Strip.None)
+	defaultEnable := (!actx.Config().KatiEnabled() || actx.Device())
+	forceEnable := Bool(stripper.StripProperties.Strip.All) ||
+		Bool(stripper.StripProperties.Strip.Keep_symbols) ||
+		Bool(stripper.StripProperties.Strip.Keep_symbols_and_debug_frame)
+	return !forceDisable && (forceEnable || defaultEnable)
 }
 
 func (stripper *Stripper) strip(actx android.ModuleContext, in android.Path, out android.ModuleOutPath,
 	flags StripFlags, isStaticLib bool) {
 	if actx.Darwin() {
-		TransformDarwinStrip(actx, in, out)
+		transformDarwinStrip(actx, in, out)
 	} else {
 		if Bool(stripper.StripProperties.Strip.Keep_symbols) {
 			flags.StripKeepSymbols = true
@@ -68,7 +76,7 @@
 		if actx.Config().Debuggable() && !flags.StripKeepMiniDebugInfo && !isStaticLib {
 			flags.StripAddGnuDebuglink = true
 		}
-		TransformStrip(actx, in, out, flags)
+		transformStrip(actx, in, out, flags)
 	}
 }
 
diff --git a/cc/stub_library.go b/cc/stub_library.go
new file mode 100644
index 0000000..76d236c
--- /dev/null
+++ b/cc/stub_library.go
@@ -0,0 +1,82 @@
+// Copyright 2020 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cc
+
+import (
+	"strings"
+
+	"android/soong/android"
+)
+
+func init() {
+	// Use singleton type to gather all generated soong modules.
+	android.RegisterSingletonType("stublibraries", stubLibrariesSingleton)
+}
+
+type stubLibraries struct {
+	stubLibraryMap map[string]bool
+}
+
+// Check if the module defines stub, or itself is stub
+func isStubTarget(m *Module) bool {
+	if m.IsStubs() || m.HasStubsVariants() {
+		return true
+	}
+
+	// Library which defines LLNDK Stub is also Stub target.
+	// Pure LLNDK Stub target would not contain any packaging
+	// with target file path.
+	if library, ok := m.linker.(*libraryDecorator); ok {
+		if library.Properties.Llndk_stubs != nil {
+			return true
+		}
+	}
+
+	return false
+}
+
+// Get target file name to be installed from this module
+func getInstalledFileName(m *Module) string {
+	for _, ps := range m.PackagingSpecs() {
+		if name := ps.FileName(); name != "" {
+			return name
+		}
+	}
+	return ""
+}
+
+func (s *stubLibraries) GenerateBuildActions(ctx android.SingletonContext) {
+	// Visit all generated soong modules and store stub library file names.
+	ctx.VisitAllModules(func(module android.Module) {
+		if m, ok := module.(*Module); ok {
+			if isStubTarget(m) {
+				if name := getInstalledFileName(m); name != "" {
+					s.stubLibraryMap[name] = true
+				}
+			}
+		}
+	})
+}
+
+func stubLibrariesSingleton() android.Singleton {
+	return &stubLibraries{
+		stubLibraryMap: make(map[string]bool),
+	}
+}
+
+func (s *stubLibraries) MakeVars(ctx android.MakeVarsContext) {
+	// Convert stub library file names into Makefile variable.
+	ctx.Strict("STUB_LIBRARIES", strings.Join(android.SortedStringKeys(s.stubLibraryMap), " "))
+}
diff --git a/cc/testing.go b/cc/testing.go
index 198764b..95a93a0 100644
--- a/cc/testing.go
+++ b/cc/testing.go
@@ -166,6 +166,10 @@
 			product_available: true,
 			recovery_available: true,
 			src: "",
+			apex_available: [
+				"//apex_available:platform",
+				"//apex_available:anyapex",
+			],
 		}
 
 		toolchain_library {
diff --git a/cc/toolchain_library.go b/cc/toolchain_library.go
index 0c934ad..bda73ea 100644
--- a/cc/toolchain_library.go
+++ b/cc/toolchain_library.go
@@ -90,7 +90,7 @@
 	if library.Properties.Repack_objects_to_keep != nil {
 		fileName := ctx.ModuleName() + staticLibraryExtension
 		repackedPath := android.PathForModuleOut(ctx, fileName)
-		TransformArchiveRepack(ctx, outputFile, repackedPath, library.Properties.Repack_objects_to_keep)
+		transformArchiveRepack(ctx, outputFile, repackedPath, library.Properties.Repack_objects_to_keep)
 		outputFile = repackedPath
 	}
 
diff --git a/cc/vendor_snapshot.go b/cc/vendor_snapshot.go
index 6563f6e..3ef0b62 100644
--- a/cc/vendor_snapshot.go
+++ b/cc/vendor_snapshot.go
@@ -339,7 +339,7 @@
 		// depending on a table of contents file instead of the library itself.
 		tocFile := android.PathForModuleOut(ctx, libName+".toc")
 		p.tocFile = android.OptionalPathForPath(tocFile)
-		TransformSharedObjectToToc(ctx, in, tocFile, builderFlags)
+		transformSharedObjectToToc(ctx, in, tocFile, builderFlags)
 
 		ctx.SetProvider(SharedLibraryInfoProvider, SharedLibraryInfo{
 			SharedLibrary:           in,
@@ -1124,7 +1124,7 @@
 		ctx,
 		snapshotDir,
 		c.name+"-"+ctx.Config().DeviceName()+".zip")
-	zipRule := android.NewRuleBuilder()
+	zipRule := android.NewRuleBuilder(pctx, ctx)
 
 	// filenames in rspfile from FlagWithRspFileInputList might be single-quoted. Remove it with tr
 	snapshotOutputList := android.PathForOutput(
@@ -1140,12 +1140,12 @@
 	zipRule.Temporary(snapshotOutputList)
 
 	zipRule.Command().
-		BuiltTool(ctx, "soong_zip").
+		BuiltTool("soong_zip").
 		FlagWithOutput("-o ", zipPath).
 		FlagWithArg("-C ", android.PathForOutput(ctx, snapshotDir).String()).
 		FlagWithInput("-l ", snapshotOutputList)
 
-	zipRule.Build(pctx, ctx, zipPath.String(), c.name+" snapshot "+zipPath.String())
+	zipRule.Build(zipPath.String(), c.name+" snapshot "+zipPath.String())
 	zipRule.DeleteTemporaryFiles()
 	c.snapshotZipFile = android.OptionalPathForPath(zipPath)
 }
diff --git a/cc/vndk.go b/cc/vndk.go
index 4a005f3..d57cdf7 100644
--- a/cc/vndk.go
+++ b/cc/vndk.go
@@ -727,7 +727,7 @@
 		var txtBuilder strings.Builder
 		for idx, k := range android.SortedStringKeys(m) {
 			if idx > 0 {
-				txtBuilder.WriteString("\\n")
+				txtBuilder.WriteString("\n")
 			}
 			txtBuilder.WriteString(k)
 			txtBuilder.WriteString(" ")
@@ -762,7 +762,7 @@
 	})
 
 	zipPath := android.PathForOutput(ctx, snapshotDir, "android-vndk-"+ctx.DeviceConfig().DeviceArch()+".zip")
-	zipRule := android.NewRuleBuilder()
+	zipRule := android.NewRuleBuilder(pctx, ctx)
 
 	// filenames in rspfile from FlagWithRspFileInputList might be single-quoted. Remove it with xargs
 	snapshotOutputList := android.PathForOutput(ctx, snapshotDir, "android-vndk-"+ctx.DeviceConfig().DeviceArch()+"_list")
@@ -775,12 +775,12 @@
 	zipRule.Temporary(snapshotOutputList)
 
 	zipRule.Command().
-		BuiltTool(ctx, "soong_zip").
+		BuiltTool("soong_zip").
 		FlagWithOutput("-o ", zipPath).
 		FlagWithArg("-C ", android.PathForOutput(ctx, snapshotDir).String()).
 		FlagWithInput("-l ", snapshotOutputList)
 
-	zipRule.Build(pctx, ctx, zipPath.String(), "vndk snapshot "+zipPath.String())
+	zipRule.Build(zipPath.String(), "vndk snapshot "+zipPath.String())
 	zipRule.DeleteTemporaryFiles()
 	c.vndkSnapshotZipFile = android.OptionalPathForPath(zipPath)
 }
diff --git a/cc/vndk_prebuilt.go b/cc/vndk_prebuilt.go
index c0320eb..e6e2ad8 100644
--- a/cc/vndk_prebuilt.go
+++ b/cc/vndk_prebuilt.go
@@ -154,7 +154,7 @@
 		// depending on a table of contents file instead of the library itself.
 		tocFile := android.PathForModuleOut(ctx, libName+".toc")
 		p.tocFile = android.OptionalPathForPath(tocFile)
-		TransformSharedObjectToToc(ctx, in, tocFile, builderFlags)
+		transformSharedObjectToToc(ctx, in, tocFile, builderFlags)
 
 		p.androidMkSuffix = p.NameSuffix()
 
diff --git a/cmd/sbox/sbox.go b/cmd/sbox/sbox.go
index 633c6b2..a4f57ea 100644
--- a/cmd/sbox/sbox.go
+++ b/cmd/sbox/sbox.go
@@ -16,6 +16,8 @@
 
 import (
 	"bytes"
+	"crypto/sha1"
+	"encoding/hex"
 	"errors"
 	"flag"
 	"fmt"
@@ -121,7 +123,22 @@
 		return fmt.Errorf("failed to create %q: %w", sandboxesRoot, err)
 	}
 
-	tempDir, err := ioutil.TempDir(sandboxesRoot, "sbox")
+	// This tool assumes that there are no two concurrent runs with the same
+	// manifestFile. It should therefore be safe to use the hash of the
+	// manifestFile as the temporary directory name. We do this because it
+	// makes the temporary directory name deterministic. There are some
+	// tools that embed the name of the temporary output in the output, and
+	// they otherwise cause non-determinism, which then poisons actions
+	// depending on this one.
+	hash := sha1.New()
+	hash.Write([]byte(manifestFile))
+	tempDir := filepath.Join(sandboxesRoot, "sbox", hex.EncodeToString(hash.Sum(nil)))
+
+	err = os.RemoveAll(tempDir)
+	if err != nil {
+		return err
+	}
+	err = os.MkdirAll(tempDir, 0777)
 	if err != nil {
 		return fmt.Errorf("failed to create temporary dir in %q: %w", sandboxesRoot, err)
 	}
diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index eeee3a8..907bed3 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -91,7 +91,7 @@
 	srcDir := filepath.Dir(flag.Arg(0))
 	var ctx *android.Context
 	configuration := newConfig(srcDir)
-	extraNinjaDeps := []string{configuration.ConfigFileName, configuration.ProductVariablesFileName}
+	extraNinjaDeps := []string{configuration.ProductVariablesFileName}
 
 	// Read the SOONG_DELVE again through configuration so that there is a dependency on the environment variable
 	// and soong_build will rerun when it is set for the first time.
diff --git a/cmd/soong_build/queryview_test.go b/cmd/soong_build/queryview_test.go
index 525802a..9471a91 100644
--- a/cmd/soong_build/queryview_test.go
+++ b/cmd/soong_build/queryview_test.go
@@ -53,6 +53,12 @@
 	android.ModuleBase
 }
 
+// OutputFiles is needed because some instances of this module use dist with a
+// tag property which requires the module implements OutputFileProducer.
+func (m *customModule) OutputFiles(tag string) (android.Paths, error) {
+	return android.PathsForTesting("path" + tag), nil
+}
+
 func (m *customModule) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 	// nothing for now.
 }
diff --git a/dexpreopt/class_loader_context.go b/dexpreopt/class_loader_context.go
index 22f712c..3759217 100644
--- a/dexpreopt/class_loader_context.go
+++ b/dexpreopt/class_loader_context.go
@@ -22,17 +22,214 @@
 	"android/soong/android"
 )
 
-// These libs are added as <uses-library> dependencies for apps if the targetSdkVersion in the
-// app manifest is less than the specified version. This is needed because these libraries haven't
-// existed prior to certain SDK version, but classes in them were in bootclasspath jars, etc.
-// Some of the compatibility libraries are optional (their <uses-library> tag has "required=false"),
-// so that if this library is missing this in not a build or run-time error.
+// This comment describes the following:
+//   1. the concept of class loader context (CLC) and its relation to classpath
+//   2. how PackageManager constructs CLC from shared libraries and their dependencies
+//   3. build-time vs. run-time CLC and why this matters for dexpreopt
+//   4. manifest fixer: a tool that adds missing <uses-library> tags to the manifests
+//   5. build system support for CLC
+//
+// 1. Class loader context
+// -----------------------
+//
+// Java libraries and apps that have run-time dependency on other libraries should list the used
+// libraries in their manifest (AndroidManifest.xml file). Each used library should be specified in
+// a <uses-library> tag that has the library name and an optional attribute specifying if the
+// library is optional or required. Required libraries are necessary for the library/app to run (it
+// will fail at runtime if the library cannot be loaded), and optional libraries are used only if
+// they are present (if not, the library/app can run without them).
+//
+// The libraries listed in <uses-library> tags are in the classpath of a library/app.
+//
+// Besides libraries, an app may also use another APK (for example in the case of split APKs), or
+// anything that gets added by the app dynamically. In general, it is impossible to know at build
+// time what the app may use at runtime. In the build system we focus on the known part: libraries.
+//
+// Class loader context (CLC) is a tree-like structure that describes class loader hierarchy. The
+// build system uses CLC in a more narrow sense: it is a tree of libraries that represents
+// transitive closure of all <uses-library> dependencies of a library/app. The top-level elements of
+// a CLC are the direct <uses-library> dependencies specified in the manifest (aka. classpath). Each
+// node of a CLC tree is a <uses-library> which may have its own <uses-library> sub-nodes.
+//
+// Because <uses-library> dependencies are, in general, a graph and not necessarily a tree, CLC may
+// contain subtrees for the same library multiple times. In other words, CLC is the dependency graph
+// "unfolded" to a tree. The duplication is only on a logical level, and the actual underlying class
+// loaders are not duplicated (at runtime there is a single class loader instance for each library).
+//
+// Example: A has <uses-library> tags B, C and D; C has <uses-library tags> B and D;
+//          D has <uses-library> E; B and E have no <uses-library> dependencies. The CLC is:
+//    A
+//    ├── B
+//    ├── C
+//    │   ├── B
+//    │   └── D
+//    │       └── E
+//    └── D
+//        └── E
+//
+// CLC defines the lookup order of libraries when resolving Java classes used by the library/app.
+// The lookup order is important because libraries may contain duplicate classes, and the class is
+// resolved to the first match.
+//
+// 2. PackageManager and "shared" libraries
+// ----------------------------------------
+//
+// In order to load an APK at runtime, PackageManager (in frameworks/base) creates a CLC. It adds
+// the libraries listed in the <uses-library> tags in the app's manifest as top-level CLC elements.
+// For each of the used libraries PackageManager gets all its <uses-library> dependencies (specified
+// as tags in the manifest of that library) and adds a nested CLC for each dependency. This process
+// continues recursively until all leaf nodes of the constructed CLC tree are libraries that have no
+// <uses-library> dependencies.
+//
+// PackageManager is aware only of "shared" libraries. The definition of "shared" here differs from
+// its usual meaning (as in shared vs. static). In Android, Java "shared" libraries are those listed
+// in /system/etc/permissions/platform.xml file. This file is installed on device. Each entry in it
+// contains the name of a "shared" library, a path to its DEX jar file and a list of dependencies
+// (other "shared" libraries that this one uses at runtime and specifies them in <uses-library> tags
+// in its manifest).
+//
+// In other words, there are two sources of information that allow PackageManager to construct CLC
+// at runtime: <uses-library> tags in the manifests and "shared" library dependencies in
+// /system/etc/permissions/platform.xml.
+//
+// 3. Build-time and run-time CLC and dexpreopt
+// --------------------------------------------
+//
+// CLC is needed not only when loading a library/app, but also when compiling it. Compilation may
+// happen either on device (known as "dexopt") or during the build (known as "dexpreopt"). Since
+// dexopt takes place on device, it has the same information as PackageManager (manifests and
+// shared library dependencies). Dexpreopt, on the other hand, takes place on host and in a totally
+// different environment, and it has to get the same information from the build system (see the
+// section about build system support below).
+//
+// Thus, the build-time CLC used by dexpreopt and the run-time CLC used by PackageManager are
+// the same thing, but computed in two different ways.
+//
+// It is important that build-time and run-time CLCs coincide, otherwise the AOT-compiled code
+// created by dexpreopt will be rejected. In order to check the equality of build-time and
+// run-time CLCs, the dex2oat compiler records build-time CLC in the *.odex files (in the
+// "classpath" field of the OAT file header). To find the stored CLC, use the following command:
+// `oatdump --oat-file=<FILE> | grep '^classpath = '`.
+//
+// Mismatch between build-time and run-time CLC is reported in logcat during boot (search with
+// `logcat | grep -E 'ClassLoaderContext [a-z ]+ mismatch'`. Mismatch is bad for performance, as it
+// forces the library/app to either be dexopted, or to run without any optimizations (e.g. the app's
+// code may need to be extracted in memory from the APK, a very expensive operation).
+//
+// A <uses-library> can be either optional or required. From dexpreopt standpoint, required library
+// must be present at build time (its absence is a build error). An optional library may be either
+// present or absent at build time: if present, it will be added to the CLC, passed to dex2oat and
+// recorded in the *.odex file; otherwise, if the library is absent, it will be skipped and not
+// added to CLC. If there is a mismatch between built-time and run-time status (optional library is
+// present in one case, but not the other), then the build-time and run-time CLCs won't match and
+// the compiled code will be rejected. It is unknown at build time if the library will be present at
+// runtime, therefore either including or excluding it may cause CLC mismatch.
+//
+// 4. Manifest fixer
+// -----------------
+//
+// Sometimes <uses-library> tags are missing from the source manifest of a library/app. This may
+// happen for example if one of the transitive dependencies of the library/app starts using another
+// <uses-library>, and the library/app's manifest isn't updated to include it.
+//
+// Soong can compute some of the missing <uses-library> tags for a given library/app automatically
+// as SDK libraries in the transitive dependency closure of the library/app. The closure is needed
+// because a library/app may depend on a static library that may in turn depend on an SDK library,
+// (possibly transitively via another library).
+//
+// Not all <uses-library> tags can be computed in this way, because some of the <uses-library>
+// dependencies are not SDK libraries, or they are not reachable via transitive dependency closure.
+// But when possible, allowing Soong to calculate the manifest entries is less prone to errors and
+// simplifies maintenance. For example, consider a situation when many apps use some static library
+// that adds a new <uses-library> dependency -- all the apps will have to be updated. That is
+// difficult to maintain.
+//
+// Soong computes the libraries that need to be in the manifest as the top-level libraries in CLC.
+// These libraries are passed to the manifest_fixer.
+//
+// All libraries added to the manifest should be "shared" libraries, so that PackageManager can look
+// up their dependencies and reconstruct the nested subcontexts at runtime. There is no build check
+// to ensure this, it is an assumption.
+//
+// 5. Build system support
+// -----------------------
+//
+// In order to construct CLC for dexpreopt and manifest_fixer, the build system needs to know all
+// <uses-library> dependencies of the dexpreopted library/app (including transitive dependencies).
+// For each <uses-librarry> dependency it needs to know the following information:
+//
+//   - the real name of the <uses-library> (it may be different from the module name)
+//   - build-time (on host) and run-time (on device) paths to the DEX jar file of the library
+//   - whether this library is optional or required
+//   - all <uses-library> dependencies
+//
+// Since the build system doesn't have access to the manifest contents (it cannot read manifests at
+// the time of build rule generation), it is necessary to copy this information to the Android.bp
+// and Android.mk files. For blueprints, the relevant properties are `uses_libs` and
+// `optional_uses_libs`. For makefiles, relevant variables are `LOCAL_USES_LIBRARIES` and
+// `LOCAL_OPTIONAL_USES_LIBRARIES`. It is preferable to avoid specifying these properties explicilty
+// when they can be computed automatically by Soong (as the transitive closure of SDK library
+// dependencies).
+//
+// Some of the Java libraries that are used as <uses-library> are not SDK libraries (they are
+// defined as `java_library` rather than `java_sdk_library` in the Android.bp files). In order for
+// the build system to handle them automatically like SDK libraries, it is possible to set a
+// property `provides_uses_lib` or variable `LOCAL_PROVIDES_USES_LIBRARY` on the blueprint/makefile
+// module of such library. This property can also be used to specify real library name in cases
+// when it differs from the module name.
+//
+// Because the information from the manifests has to be duplicated in the Android.bp/Android.mk
+// files, there is a danger that it may get out of sync. To guard against that, the build system
+// generates a rule that checks the metadata in the build files against the contents of a manifest
+// (verify_uses_libraries). The manifest can be available as a source file, or as part of a prebuilt
+// APK. Note that reading the manifests at the Ninja stage of the build is fine, unlike the build
+// rule generation phase.
+//
+// ClassLoaderContext is a structure that represents CLC.
+//
+type ClassLoaderContext struct {
+	// The name of the library.
+	Name string
+
+	// On-host build path to the library dex file (used in dex2oat argument --class-loader-context).
+	Host android.Path
+
+	// On-device install path (used in dex2oat argument --stored-class-loader-context).
+	Device string
+
+	// Nested sub-CLC for dependencies.
+	Subcontexts []*ClassLoaderContext
+}
+
+// ClassLoaderContextMap is a map from SDK version to CLC. There is a special entry with key
+// AnySdkVersion that stores unconditional CLC that is added regardless of the target SDK version.
+//
+// Conditional CLC is for compatibility libraries which didn't exist prior to a certain SDK version
+// (say, N), but classes in them were in the bootclasspath jars, etc., and in version N they have
+// been separated into a standalone <uses-library>. Compatibility libraries should only be in the
+// CLC if the library/app that uses them has `targetSdkVersion` less than N in the manifest.
+//
+// Currently only apps (but not libraries) use conditional CLC.
+//
+// Target SDK version information is unavailable to the build system at rule generation time, so
+// the build system doesn't know whether conditional CLC is needed for a given app or not. So it
+// generates a build rule that includes conditional CLC for all versions, extracts the target SDK
+// version from the manifest, and filters the CLCs based on that version. Exact final CLC that is
+// passed to dex2oat is unknown to the build system, and gets known only at Ninja stage.
+//
+type ClassLoaderContextMap map[int][]*ClassLoaderContext
+
+// Compatibility libraries. Some are optional, and some are required: this is the default that
+// affects how they are handled by the Soong logic that automatically adds implicit SDK libraries
+// to the manifest_fixer, but an explicit `uses_libs`/`optional_uses_libs` can override this.
 var OrgApacheHttpLegacy = "org.apache.http.legacy"
 var AndroidTestBase = "android.test.base"
 var AndroidTestMock = "android.test.mock"
 var AndroidHidlBase = "android.hidl.base-V1.0-java"
 var AndroidHidlManager = "android.hidl.manager-V1.0-java"
 
+// Compatibility libraries grouped by version/optionality (for convenience, to avoid repeating the
+// same lists in multiple places).
 var OptionalCompatUsesLibs28 = []string{
 	OrgApacheHttpLegacy,
 }
@@ -55,30 +252,6 @@
 // last). We use the converntional "current" SDK level (10000), but any big number would do as well.
 const AnySdkVersion int = android.FutureApiLevelInt
 
-// ClassLoaderContext is a tree of libraries used by the dexpreopted module with their dependencies.
-// The context is used by dex2oat to compile the module and recorded in the AOT-compiled files, so
-// that it can be checked agains the run-time class loader context on device. If there is a mismatch
-// at runtime, AOT-compiled code is rejected.
-type ClassLoaderContext struct {
-	// The name of the library (same as the name of the module that contains it).
-	Name string
-
-	// On-host build path to the library dex file (used in dex2oat argument --class-loader-context).
-	Host android.Path
-
-	// On-device install path (used in dex2oat argument --stored-class-loader-context).
-	Device string
-
-	// Nested class loader subcontexts for dependencies.
-	Subcontexts []*ClassLoaderContext
-}
-
-// ClassLoaderContextMap is a map from SDK version to a class loader context.
-// There is a special entry with key AnySdkVersion that stores unconditional class loader context.
-// Other entries store conditional contexts that should be added for some apps that have
-// targetSdkVersion in the manifest lower than the key SDK version.
-type ClassLoaderContextMap map[int][]*ClassLoaderContext
-
 // Add class loader context for the given library to the map entry for the given SDK version.
 func (clcMap ClassLoaderContextMap) addContext(ctx android.ModuleInstallPathContext, sdkVer int, lib string,
 	hostPath, installPath android.Path, strict bool, nestedClcMap ClassLoaderContextMap) error {
@@ -257,6 +430,7 @@
 	return true, nil
 }
 
+// Helper function for validateClassLoaderContext() that handles recursion.
 func validateClassLoaderContextRec(sdkVer int, clcs []*ClassLoaderContext) (bool, error) {
 	for _, clc := range clcs {
 		if clc.Host == nil || clc.Device == UnknownInstallLibraryPath {
@@ -296,6 +470,7 @@
 	return clcStr, android.FirstUniquePaths(paths)
 }
 
+// Helper function for ComputeClassLoaderContext() that handles recursion.
 func computeClassLoaderContextRec(clcs []*ClassLoaderContext) (string, string, android.Paths) {
 	var paths android.Paths
 	var clcsHost, clcsTarget []string
@@ -320,7 +495,7 @@
 	return clcHost, clcTarget, paths
 }
 
-// Paths to a <uses-library> on host and on device.
+// JSON representation of <uses-library> paths on host and on device.
 type jsonLibraryPath struct {
 	Host   string
 	Device string
diff --git a/dexpreopt/dexpreopt.go b/dexpreopt/dexpreopt.go
index 65380fe..b0a684e 100644
--- a/dexpreopt/dexpreopt.go
+++ b/dexpreopt/dexpreopt.go
@@ -51,7 +51,7 @@
 
 // GenerateDexpreoptRule generates a set of commands that will preopt a module based on a GlobalConfig and a
 // ModuleConfig.  The produced files and their install locations will be available through rule.Installs().
-func GenerateDexpreoptRule(ctx android.PathContext, globalSoong *GlobalSoongConfig,
+func GenerateDexpreoptRule(ctx android.BuilderContext, globalSoong *GlobalSoongConfig,
 	global *GlobalConfig, module *ModuleConfig) (rule *android.RuleBuilder, err error) {
 
 	defer func() {
@@ -67,7 +67,7 @@
 		}
 	}()
 
-	rule = android.NewRuleBuilder()
+	rule = android.NewRuleBuilder(pctx, ctx)
 
 	generateProfile := module.ProfileClassListing.Valid() && !global.DisableGenerateProfile
 	generateBootProfile := module.ProfileBootListing.Valid() && !global.DisableGenerateProfile
diff --git a/dexpreopt/dexpreopt_gen/dexpreopt_gen.go b/dexpreopt/dexpreopt_gen/dexpreopt_gen.go
index e89f045..32c4f84 100644
--- a/dexpreopt/dexpreopt_gen/dexpreopt_gen.go
+++ b/dexpreopt/dexpreopt_gen/dexpreopt_gen.go
@@ -27,6 +27,7 @@
 	"android/soong/android"
 	"android/soong/dexpreopt"
 
+	"github.com/google/blueprint"
 	"github.com/google/blueprint/pathtools"
 )
 
@@ -38,12 +39,16 @@
 	outDir                = flag.String("out_dir", "", "path to output directory")
 )
 
-type pathContext struct {
+type builderContext struct {
 	config android.Config
 }
 
-func (x *pathContext) Config() android.Config     { return x.config }
-func (x *pathContext) AddNinjaFileDeps(...string) {}
+func (x *builderContext) Config() android.Config                            { return x.config }
+func (x *builderContext) AddNinjaFileDeps(...string)                        {}
+func (x *builderContext) Build(android.PackageContext, android.BuildParams) {}
+func (x *builderContext) Rule(android.PackageContext, string, blueprint.RuleParams, ...string) blueprint.Rule {
+	return nil
+}
 
 func main() {
 	flag.Parse()
@@ -76,7 +81,7 @@
 		usage("--module configuration file is required")
 	}
 
-	ctx := &pathContext{android.NullConfig(*outDir)}
+	ctx := &builderContext{android.NullConfig(*outDir)}
 
 	globalSoongConfigData, err := ioutil.ReadFile(*globalSoongConfigPath)
 	if err != nil {
@@ -133,7 +138,7 @@
 	writeScripts(ctx, globalSoongConfig, globalConfig, moduleConfig, *dexpreoptScriptPath)
 }
 
-func writeScripts(ctx android.PathContext, globalSoong *dexpreopt.GlobalSoongConfig,
+func writeScripts(ctx android.BuilderContext, globalSoong *dexpreopt.GlobalSoongConfig,
 	global *dexpreopt.GlobalConfig, module *dexpreopt.ModuleConfig, dexpreoptScriptPath string) {
 	dexpreoptRule, err := dexpreopt.GenerateDexpreoptRule(ctx, globalSoong, global, module)
 	if err != nil {
diff --git a/dexpreopt/dexpreopt_test.go b/dexpreopt/dexpreopt_test.go
index feabd70..59278fd 100644
--- a/dexpreopt/dexpreopt_test.go
+++ b/dexpreopt/dexpreopt_test.go
@@ -60,7 +60,7 @@
 
 func TestDexPreopt(t *testing.T) {
 	config := android.TestConfig("out", nil, "", nil)
-	ctx := android.PathContextForTesting(config)
+	ctx := android.BuilderContextForTesting(config)
 	globalSoong := GlobalSoongConfigForTests(config)
 	global := GlobalConfigForTests(ctx)
 	module := testSystemModuleConfig(ctx, "test")
@@ -82,7 +82,7 @@
 
 func TestDexPreoptSystemOther(t *testing.T) {
 	config := android.TestConfig("out", nil, "", nil)
-	ctx := android.PathContextForTesting(config)
+	ctx := android.BuilderContextForTesting(config)
 	globalSoong := GlobalSoongConfigForTests(config)
 	global := GlobalConfigForTests(ctx)
 	systemModule := testSystemModuleConfig(ctx, "Stest")
@@ -142,7 +142,7 @@
 
 func TestDexPreoptProfile(t *testing.T) {
 	config := android.TestConfig("out", nil, "", nil)
-	ctx := android.PathContextForTesting(config)
+	ctx := android.BuilderContextForTesting(config)
 	globalSoong := GlobalSoongConfigForTests(config)
 	global := GlobalConfigForTests(ctx)
 	module := testSystemModuleConfig(ctx, "test")
diff --git a/filesystem/filesystem.go b/filesystem/filesystem.go
index a1605b4..c6181bc 100644
--- a/filesystem/filesystem.go
+++ b/filesystem/filesystem.go
@@ -18,6 +18,8 @@
 	"fmt"
 
 	"android/soong/android"
+
+	"github.com/google/blueprint"
 )
 
 func init() {
@@ -27,8 +29,16 @@
 type filesystem struct {
 	android.ModuleBase
 	android.PackagingBase
+
+	output     android.OutputPath
+	installDir android.InstallPath
 }
 
+// android_filesystem packages a set of modules and their transitive dependencies into a filesystem
+// image. The filesystem images are expected to be mounted in the target device, which means the
+// modules in the filesystem image are built for the target device (i.e. Android, not Linux host).
+// The modules are placed in the filesystem image just like they are installed to the ordinary
+// partitions like system.img. For example, cc_library modules are placed under ./lib[64] directory.
 func filesystemFactory() android.Module {
 	module := &filesystem{}
 	android.InitPackageModule(module)
@@ -36,8 +46,14 @@
 	return module
 }
 
+var dependencyTag = struct{ blueprint.BaseDependencyTag }{}
+
 func (f *filesystem) DepsMutator(ctx android.BottomUpMutatorContext) {
-	f.AddDeps(ctx)
+	f.AddDeps(ctx, dependencyTag)
+}
+
+func (f *filesystem) installFileName() string {
+	return f.BaseModuleName() + ".img"
 }
 
 var pctx = android.NewPackageContext("android/soong/filesystem")
@@ -47,9 +63,9 @@
 	f.CopyDepsToZip(ctx, zipFile)
 
 	rootDir := android.PathForModuleOut(ctx, "root").OutputPath
-	builder := android.NewRuleBuilder()
+	builder := android.NewRuleBuilder(pctx, ctx)
 	builder.Command().
-		BuiltTool(ctx, "zipsync").
+		BuiltTool("zipsync").
 		FlagWithArg("-d ", rootDir.String()). // zipsync wipes this. No need to clear.
 		Input(zipFile)
 
@@ -64,13 +80,32 @@
 		Text(">").Output(propFile).
 		Implicit(mkuserimg)
 
-	image := android.PathForModuleOut(ctx, "filesystem.img").OutputPath
-	builder.Command().BuiltTool(ctx, "build_image").
+	f.output = android.PathForModuleOut(ctx, "filesystem.img").OutputPath
+	builder.Command().BuiltTool("build_image").
 		Text(rootDir.String()). // input directory
 		Input(propFile).
-		Output(image).
+		Output(f.output).
 		Text(rootDir.String()) // directory where to find fs_config_files|dirs
 
 	// rootDir is not deleted. Might be useful for quick inspection.
-	builder.Build(pctx, ctx, "build_filesystem_image", fmt.Sprintf("Creating filesystem %s", f.BaseModuleName()))
+	builder.Build("build_filesystem_image", fmt.Sprintf("Creating filesystem %s", f.BaseModuleName()))
+
+	f.installDir = android.PathForModuleInstall(ctx, "etc")
+	ctx.InstallFile(f.installDir, f.installFileName(), f.output)
+}
+
+var _ android.AndroidMkEntriesProvider = (*filesystem)(nil)
+
+// Implements android.AndroidMkEntriesProvider
+func (f *filesystem) AndroidMkEntries() []android.AndroidMkEntries {
+	return []android.AndroidMkEntries{android.AndroidMkEntries{
+		Class:      "ETC",
+		OutputFile: android.OptionalPathForPath(f.output),
+		ExtraEntries: []android.AndroidMkExtraEntriesFunc{
+			func(entries *android.AndroidMkEntries) {
+				entries.SetString("LOCAL_MODULE_PATH", f.installDir.ToMakePath().String())
+				entries.SetString("LOCAL_INSTALLED_MODULE_STEM", f.installFileName())
+			},
+		},
+	}}
 }
diff --git a/genrule/genrule.go b/genrule/genrule.go
index d667e94..93938c9 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -12,6 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// A genrule module takes a list of source files ("srcs" property), an optional
+// list of tools ("tools" property), and a command line ("cmd" property), to
+// generate output files ("out" property).
+
 package genrule
 
 import (
@@ -47,6 +51,8 @@
 var (
 	pctx = android.NewPackageContext("android/soong/genrule")
 
+	// Used by gensrcs when there is more than 1 shard to merge the outputs
+	// of each shard into a zip file.
 	gensrcsMerge = pctx.AndroidStaticRule("gensrcsMerge", blueprint.RuleParams{
 		Command:        "${soongZip} -o ${tmpZip} @${tmpZip}.rsp && ${zipSync} -d ${genDir} ${tmpZip}",
 		CommandDeps:    []string{"${soongZip}", "${zipSync}"},
@@ -115,6 +121,7 @@
 	// Properties for Bazel migration purposes.
 	bazel.Properties
 }
+
 type Module struct {
 	android.ModuleBase
 	android.DefaultableModuleBase
@@ -127,6 +134,9 @@
 
 	properties generatorProperties
 
+	// For the different tasks that genrule and gensrc generate. genrule will
+	// generate 1 task, and gensrc will generate 1 or more tasks based on the
+	// number of shards the input files are sharded into.
 	taskGenerator taskFunc
 
 	deps        android.Paths
@@ -151,11 +161,12 @@
 	in         android.Paths
 	out        android.WritablePaths
 	depFile    android.WritablePath
-	copyTo     android.WritablePaths
+	copyTo     android.WritablePaths // For gensrcs to set on gensrcsMerge rule.
 	genDir     android.WritablePath
 	extraTools android.Paths // dependencies on tools used by the generator
 
-	cmd    string
+	cmd string
+	// For gensrsc sharding.
 	shard  int
 	shards int
 }
@@ -324,14 +335,34 @@
 	var outputFiles android.WritablePaths
 	var zipArgs strings.Builder
 
+	// Generate tasks, either from genrule or gensrcs.
 	for _, task := range g.taskGenerator(ctx, String(g.properties.Cmd), srcFiles) {
 		if len(task.out) == 0 {
 			ctx.ModuleErrorf("must have at least one output file")
 			return
 		}
 
+		// Pick a unique path outside the task.genDir for the sbox manifest textproto,
+		// a unique rule name, and the user-visible description.
+		manifestName := "genrule.sbox.textproto"
+		desc := "generate"
+		name := "generator"
+		if task.shards > 0 {
+			manifestName = "genrule_" + strconv.Itoa(task.shard) + ".sbox.textproto"
+			desc += " " + strconv.Itoa(task.shard)
+			name += strconv.Itoa(task.shard)
+		} else if len(task.out) == 1 {
+			desc += " " + task.out[0].Base()
+		}
+
+		manifestPath := android.PathForModuleOut(ctx, manifestName)
+
+		// Use a RuleBuilder to create a rule that runs the command inside an sbox sandbox.
+		rule := android.NewRuleBuilder(pctx, ctx).Sbox(task.genDir, manifestPath)
+		cmd := rule.Command()
+
 		for _, out := range task.out {
-			addLocationLabel(out.Rel(), []string{android.SboxPathForOutput(out, task.genDir)})
+			addLocationLabel(out.Rel(), []string{cmd.PathForOutput(out)})
 		}
 
 		referencedDepfile := false
@@ -362,7 +393,7 @@
 			case "out":
 				var sandboxOuts []string
 				for _, out := range task.out {
-					sandboxOuts = append(sandboxOuts, android.SboxPathForOutput(out, task.genDir))
+					sandboxOuts = append(sandboxOuts, cmd.PathForOutput(out))
 				}
 				return strings.Join(sandboxOuts, " "), nil
 			case "depfile":
@@ -372,7 +403,7 @@
 				}
 				return "__SBOX_DEPFILE__", nil
 			case "genDir":
-				return android.SboxPathForOutput(task.genDir, task.genDir), nil
+				return cmd.PathForOutput(task.genDir), nil
 			default:
 				if strings.HasPrefix(name, "location ") {
 					label := strings.TrimSpace(strings.TrimPrefix(name, "location "))
@@ -414,24 +445,6 @@
 		}
 		g.rawCommands = append(g.rawCommands, rawCommand)
 
-		// Pick a unique path outside the task.genDir for the sbox manifest textproto,
-		// a unique rule name, and the user-visible description.
-		manifestName := "genrule.sbox.textproto"
-		desc := "generate"
-		name := "generator"
-		if task.shards > 0 {
-			manifestName = "genrule_" + strconv.Itoa(task.shard) + ".sbox.textproto"
-			desc += " " + strconv.Itoa(task.shard)
-			name += strconv.Itoa(task.shard)
-		} else if len(task.out) == 1 {
-			desc += " " + task.out[0].Base()
-		}
-
-		manifestPath := android.PathForModuleOut(ctx, manifestName)
-
-		// Use a RuleBuilder to create a rule that runs the command inside an sbox sandbox.
-		rule := android.NewRuleBuilder().Sbox(task.genDir, manifestPath)
-		cmd := rule.Command()
 		cmd.Text(rawCommand)
 		cmd.ImplicitOutputs(task.out)
 		cmd.Implicits(task.in)
@@ -442,7 +455,7 @@
 		}
 
 		// Create the rule to run the genrule command inside sbox.
-		rule.Build(pctx, ctx, name, desc)
+		rule.Build(name, desc)
 
 		if len(task.copyTo) > 0 {
 			// If copyTo is set, multiple shards need to be copied into a single directory.
@@ -600,6 +613,10 @@
 			}
 
 			genDir := android.PathForModuleGen(ctx, genSubDir)
+			// TODO(ccross): this RuleBuilder is a hack to be able to call
+			// rule.Command().PathForOutput.  Replace this with passing the rule into the
+			// generator.
+			rule := android.NewRuleBuilder(pctx, ctx).Sbox(genDir, nil)
 
 			for _, in := range shard {
 				outFile := android.GenPathWithExt(ctx, finalSubDir, in, String(properties.Output_extension))
@@ -622,11 +639,11 @@
 					case "in":
 						return in.String(), nil
 					case "out":
-						return android.SboxPathForOutput(outFile, genDir), nil
+						return rule.Command().PathForOutput(outFile), nil
 					case "depfile":
 						// Generate a depfile for each output file.  Store the list for
 						// later in order to combine them all into a single depfile.
-						depFile := android.SboxPathForOutput(outFile.ReplaceExtension(ctx, "d"), genDir)
+						depFile := rule.Command().PathForOutput(outFile.ReplaceExtension(ctx, "d"))
 						commandDepFiles = append(commandDepFiles, depFile)
 						return depFile, nil
 					default:
@@ -691,7 +708,7 @@
 	Shard_size *int64
 }
 
-const defaultShardSize = 100
+const defaultShardSize = 50
 
 func NewGenRule() *Module {
 	properties := &genRuleProperties{}
diff --git a/java/Android.bp b/java/Android.bp
index 9e8dc78..39502b3 100644
--- a/java/Android.bp
+++ b/java/Android.bp
@@ -48,6 +48,7 @@
         "robolectric.go",
         "sdk.go",
         "sdk_library.go",
+        "sdk_library_external.go",
         "support_libraries.go",
         "sysprop.go",
         "system_modules.go",
diff --git a/java/aapt2.go b/java/aapt2.go
index 04e4de5..5346ddf 100644
--- a/java/aapt2.go
+++ b/java/aapt2.go
@@ -25,12 +25,9 @@
 	"android/soong/android"
 )
 
-const AAPT2_SHARD_SIZE = 100
-
 // Convert input resource file path to output file path.
 // values-[config]/<file>.xml -> values-[config]_<file>.arsc.flat;
-// For other resource file, just replace the last "/" with "_" and
-// add .flat extension.
+// For other resource file, just replace the last "/" with "_" and add .flat extension.
 func pathToAapt2Path(ctx android.ModuleContext, res android.Path) android.WritablePath {
 
 	name := res.Base()
@@ -43,6 +40,7 @@
 	return android.PathForModuleOut(ctx, "aapt2", subDir, name)
 }
 
+// pathsToAapt2Paths Calls pathToAapt2Path on each entry of the given Paths, i.e. []Path.
 func pathsToAapt2Paths(ctx android.ModuleContext, resPaths android.Paths) android.WritablePaths {
 	outPaths := make(android.WritablePaths, len(resPaths))
 
@@ -53,6 +51,9 @@
 	return outPaths
 }
 
+// Shard resource files for efficiency. See aapt2Compile for details.
+const AAPT2_SHARD_SIZE = 100
+
 var aapt2CompileRule = pctx.AndroidStaticRule("aapt2Compile",
 	blueprint.RuleParams{
 		Command:     `${config.Aapt2Cmd} compile -o $outDir $cFlags $in`,
@@ -60,14 +61,26 @@
 	},
 	"outDir", "cFlags")
 
+// aapt2Compile compiles resources and puts the results in the requested directory.
 func aapt2Compile(ctx android.ModuleContext, dir android.Path, paths android.Paths,
 	flags []string) android.WritablePaths {
 
+	// Shard the input paths so that they can be processed in parallel. If we shard them into too
+	// small chunks, the additional cost of spinning up aapt2 outweighs the performance gain. The
+	// current shard size, 100, seems to be a good balance between the added cost and the gain.
+	// The aapt2 compile actions are trivially short, but each action in ninja takes on the order of
+	// ~10 ms to run. frameworks/base/core/res/res has >10k resource files, so compiling each one
+	// with an individual action could take 100 CPU seconds. Sharding them reduces the overhead of
+	// starting actions by a factor of 100, at the expense of recompiling more files when one
+	// changes.  Since the individual compiles are trivial it's a good tradeoff.
 	shards := android.ShardPaths(paths, AAPT2_SHARD_SIZE)
 
 	ret := make(android.WritablePaths, 0, len(paths))
 
 	for i, shard := range shards {
+		// This should be kept in sync with pathToAapt2Path. The aapt2 compile command takes an
+		// output directory path, but not output file paths. So, outPaths is just where we expect
+		// the output files will be located.
 		outPaths := pathsToAapt2Paths(ctx, shard)
 		ret = append(ret, outPaths...)
 
@@ -82,6 +95,12 @@
 			Inputs:      shard,
 			Outputs:     outPaths,
 			Args: map[string]string{
+				// The aapt2 compile command takes an output directory path, but not output file paths.
+				// outPaths specified above is only used for dependency management purposes. In order for
+				// the outPaths values to match the actual outputs from aapt2, the dir parameter value
+				// must be a common prefix path of the paths values, and the top-level path segment used
+				// below, "aapt2", must always be kept in sync with the one in pathToAapt2Path.
+				// TODO(b/174505750): Make this easier and robust to use.
 				"outDir": android.PathForModuleOut(ctx, "aapt2", dir.String()).String(),
 				"cFlags": strings.Join(flags, " "),
 			},
@@ -104,6 +123,8 @@
 		},
 	}, "cFlags", "resZipDir", "zipSyncFlags")
 
+// Unzips the given compressed file and compiles the resource source files in it. The zipPrefix
+// parameter points to the subdirectory in the zip file where the resource files are located.
 func aapt2CompileZip(ctx android.ModuleContext, flata android.WritablePath, zip android.Path, zipPrefix string,
 	flags []string) {
 
@@ -163,6 +184,7 @@
 	var inFlags []string
 
 	if len(compiledRes) > 0 {
+		// Create a file that contains the list of all compiled resource file paths.
 		resFileList := android.PathForModuleOut(ctx, "aapt2", "res.list")
 		// Write out file lists to files
 		ctx.Build(pctx, android.BuildParams{
@@ -174,10 +196,12 @@
 
 		deps = append(deps, compiledRes...)
 		deps = append(deps, resFileList)
+		// aapt2 filepath arguments that start with "@" mean file-list files.
 		inFlags = append(inFlags, "@"+resFileList.String())
 	}
 
 	if len(compiledOverlay) > 0 {
+		// Compiled overlay files are processed the same way as compiled resources.
 		overlayFileList := android.PathForModuleOut(ctx, "aapt2", "overlay.list")
 		ctx.Build(pctx, android.BuildParams{
 			Rule:        fileListToFileRule,
@@ -188,9 +212,11 @@
 
 		deps = append(deps, compiledOverlay...)
 		deps = append(deps, overlayFileList)
+		// Compiled overlay files are passed over to aapt2 using -R option.
 		inFlags = append(inFlags, "-R", "@"+overlayFileList.String())
 	}
 
+	// Set auxiliary outputs as implicit outputs to establish correct dependency chains.
 	implicitOutputs := append(splitPackages, proguardOptions, genJar, rTxt, extraPackages)
 	linkOutput := packageRes
 
@@ -212,6 +238,10 @@
 		Implicits:       deps,
 		Output:          linkOutput,
 		ImplicitOutputs: implicitOutputs,
+		// Note the absence of splitPackages. The caller is supposed to compose and provide --split flag
+		// values via the flags parameter when it wants to split outputs.
+		// TODO(b/174509108): Perhaps we can process it in this func while keeping the code reasonably
+		// tidy.
 		Args: map[string]string{
 			"flags":           strings.Join(flags, " "),
 			"inFlags":         strings.Join(inFlags, " "),
@@ -230,6 +260,8 @@
 		CommandDeps: []string{"${config.Aapt2Cmd}"},
 	})
 
+// Converts xml files and resource tables (resources.arsc) in the given jar/apk file to a proto
+// format. The proto definition is available at frameworks/base/tools/aapt2/Resources.proto.
 func aapt2Convert(ctx android.ModuleContext, out android.WritablePath, in android.Path) {
 	ctx.Build(pctx, android.BuildParams{
 		Rule:        aapt2ConvertRule,
diff --git a/java/androidmk.go b/java/androidmk.go
index 386a97f..fc573c8 100644
--- a/java/androidmk.go
+++ b/java/androidmk.go
@@ -85,7 +85,6 @@
 	} else {
 		entriesList = append(entriesList, android.AndroidMkEntries{
 			Class:      "JAVA_LIBRARIES",
-			DistFiles:  library.distFiles,
 			OutputFile: android.OptionalPathForPath(library.outputFile),
 			Include:    "$(BUILD_SYSTEM)/soong_java_prebuilt.mk",
 			ExtraEntries: []android.AndroidMkExtraEntriesFunc{
@@ -140,9 +139,9 @@
 func testSuiteComponent(entries *android.AndroidMkEntries, test_suites []string) {
 	entries.SetString("LOCAL_MODULE_TAGS", "tests")
 	if len(test_suites) > 0 {
-		entries.AddStrings("LOCAL_COMPATIBILITY_SUITE", test_suites...)
+		entries.AddCompatibilityTestSuites(test_suites...)
 	} else {
-		entries.SetString("LOCAL_COMPATIBILITY_SUITE", "null-suite")
+		entries.AddCompatibilityTestSuites("null-suite")
 	}
 }
 
@@ -524,17 +523,12 @@
 	// Note that dstubs.apiFile can be also be nil if WITHOUT_CHECKS_API is true.
 	// TODO(b/146727827): Revert when we do not need to generate stubs and API separately.
 
-	var distFiles android.TaggedDistFiles
-	if dstubs.apiFile != nil {
-		distFiles = android.MakeDefaultDistFiles(dstubs.apiFile)
-	}
 	outputFile := android.OptionalPathForPath(dstubs.stubsSrcJar)
 	if !outputFile.Valid() {
 		outputFile = android.OptionalPathForPath(dstubs.apiFile)
 	}
 	return []android.AndroidMkEntries{android.AndroidMkEntries{
 		Class:      "JAVA_LIBRARIES",
-		DistFiles:  distFiles,
 		OutputFile: outputFile,
 		Include:    "$(BUILD_SYSTEM)/soong_droiddoc_prebuilt.mk",
 		ExtraEntries: []android.AndroidMkExtraEntriesFunc{
diff --git a/java/androidmk_test.go b/java/androidmk_test.go
index 075b7aa..233e9d5 100644
--- a/java/androidmk_test.go
+++ b/java/androidmk_test.go
@@ -16,7 +16,6 @@
 
 import (
 	"reflect"
-	"strings"
 	"testing"
 
 	"android/soong/android"
@@ -135,182 +134,6 @@
 	}
 }
 
-func TestDistWithTag(t *testing.T) {
-	ctx, config := testJava(t, `
-		java_library {
-			name: "foo_without_tag",
-			srcs: ["a.java"],
-			compile_dex: true,
-			dist: {
-				targets: ["hi"],
-			},
-		}
-		java_library {
-			name: "foo_with_tag",
-			srcs: ["a.java"],
-			compile_dex: true,
-			dist: {
-				targets: ["hi"],
-				tag: ".jar",
-			},
-		}
-	`)
-
-	withoutTagEntries := android.AndroidMkEntriesForTest(t, config, "", ctx.ModuleForTests("foo_without_tag", "android_common").Module())
-	withTagEntries := android.AndroidMkEntriesForTest(t, config, "", ctx.ModuleForTests("foo_with_tag", "android_common").Module())
-
-	if len(withoutTagEntries) != 2 || len(withTagEntries) != 2 {
-		t.Errorf("two mk entries per module expected, got %d and %d", len(withoutTagEntries), len(withTagEntries))
-	}
-	if len(withTagEntries[0].DistFiles[".jar"]) != 1 ||
-		!strings.Contains(withTagEntries[0].DistFiles[".jar"][0].String(), "/javac/foo_with_tag.jar") {
-		t.Errorf("expected DistFiles to contain classes.jar, got %v", withTagEntries[0].DistFiles)
-	}
-	if len(withoutTagEntries[0].DistFiles[".jar"]) > 0 {
-		t.Errorf("did not expect explicit DistFile for .jar tag, got %v", withoutTagEntries[0].DistFiles[".jar"])
-	}
-}
-
-func TestDistWithDest(t *testing.T) {
-	ctx, config := testJava(t, `
-		java_library {
-			name: "foo",
-			srcs: ["a.java"],
-			compile_dex: true,
-			dist: {
-				targets: ["my_goal"],
-				dest: "my/custom/dest/dir",
-			},
-		}
-	`)
-
-	module := ctx.ModuleForTests("foo", "android_common").Module()
-	entries := android.AndroidMkEntriesForTest(t, config, "", module)
-	if len(entries) != 2 {
-		t.Errorf("Expected 2 AndroidMk entries, got %d", len(entries))
-	}
-
-	distStrings := entries[0].GetDistForGoals(module)
-
-	if len(distStrings) != 2 {
-		t.Errorf("Expected 2 entries for dist: PHONY and dist-for-goals, but got %q", distStrings)
-	}
-
-	if distStrings[0] != ".PHONY: my_goal\n" {
-		t.Errorf("Expected .PHONY entry to declare my_goal, but got: %s", distStrings[0])
-	}
-
-	if !strings.Contains(distStrings[1], "$(call dist-for-goals,my_goal") ||
-		!strings.Contains(distStrings[1], ".intermediates/foo/android_common/dex/foo.jar:my/custom/dest/dir") {
-		t.Errorf(
-			"Expected dist-for-goals entry to contain my_goal and new dest dir, but got: %s", distStrings[1])
-	}
-}
-
-func TestDistsWithAllProperties(t *testing.T) {
-	ctx, config := testJava(t, `
-		java_library {
-			name: "foo",
-			srcs: ["a.java"],
-			compile_dex: true,
-			dist: {
-				targets: ["baz"],
-			},
-			dists: [
-				{
-					targets: ["bar"],
-					tag: ".jar",
-					dest: "bar.jar",
-					dir: "bar/dir",
-					suffix: ".qux",
-				},
-			]
-		}
-	`)
-
-	module := ctx.ModuleForTests("foo", "android_common").Module()
-	entries := android.AndroidMkEntriesForTest(t, config, "", module)
-	if len(entries) != 2 {
-		t.Errorf("Expected 2 AndroidMk entries, got %d", len(entries))
-	}
-
-	distStrings := entries[0].GetDistForGoals(module)
-
-	if len(distStrings) != 4 {
-		t.Errorf("Expected 4 entries for dist: PHONY and dist-for-goals, but got %d", len(distStrings))
-	}
-
-	if distStrings[0] != ".PHONY: bar\n" {
-		t.Errorf("Expected .PHONY entry to declare bar, but got: %s", distStrings[0])
-	}
-
-	if !strings.Contains(distStrings[1], "$(call dist-for-goals,bar") ||
-		!strings.Contains(
-			distStrings[1],
-			".intermediates/foo/android_common/javac/foo.jar:bar/dir/bar.qux.jar") {
-		t.Errorf(
-			"Expected dist-for-goals entry to contain bar and new dest dir, but got: %s", distStrings[1])
-	}
-
-	if distStrings[2] != ".PHONY: baz\n" {
-		t.Errorf("Expected .PHONY entry to declare baz, but got: %s", distStrings[2])
-	}
-
-	if !strings.Contains(distStrings[3], "$(call dist-for-goals,baz") ||
-		!strings.Contains(distStrings[3], ".intermediates/foo/android_common/dex/foo.jar:foo.jar") {
-		t.Errorf(
-			"Expected dist-for-goals entry to contain my_other_goal and new dest dir, but got: %s",
-			distStrings[3])
-	}
-}
-
-func TestDistsWithTag(t *testing.T) {
-	ctx, config := testJava(t, `
-		java_library {
-			name: "foo_without_tag",
-			srcs: ["a.java"],
-			compile_dex: true,
-			dists: [
-				{
-					targets: ["hi"],
-				},
-			],
-		}
-		java_library {
-			name: "foo_with_tag",
-			srcs: ["a.java"],
-			compile_dex: true,
-			dists: [
-				{
-					targets: ["hi"],
-					tag: ".jar",
-				},
-			],
-		}
-	`)
-
-	moduleWithoutTag := ctx.ModuleForTests("foo_without_tag", "android_common").Module()
-	moduleWithTag := ctx.ModuleForTests("foo_with_tag", "android_common").Module()
-
-	withoutTagEntries := android.AndroidMkEntriesForTest(t, config, "", moduleWithoutTag)
-	withTagEntries := android.AndroidMkEntriesForTest(t, config, "", moduleWithTag)
-
-	if len(withoutTagEntries) != 2 || len(withTagEntries) != 2 {
-		t.Errorf("two mk entries per module expected, got %d and %d", len(withoutTagEntries), len(withTagEntries))
-	}
-
-	distFilesWithoutTag := withoutTagEntries[0].DistFiles
-	distFilesWithTag := withTagEntries[0].DistFiles
-
-	if len(distFilesWithTag[".jar"]) != 1 ||
-		!strings.Contains(distFilesWithTag[".jar"][0].String(), "/javac/foo_with_tag.jar") {
-		t.Errorf("expected foo_with_tag's .jar-tagged DistFiles to contain classes.jar, got %v", distFilesWithTag[".jar"])
-	}
-	if len(distFilesWithoutTag[".jar"]) > 0 {
-		t.Errorf("did not expect foo_without_tag's .jar-tagged DistFiles to contain files, but got %v", distFilesWithoutTag[".jar"])
-	}
-}
-
 func TestJavaSdkLibrary_RequireXmlPermissionFile(t *testing.T) {
 	ctx, config := testJava(t, `
 		java_sdk_library {
diff --git a/java/app.go b/java/app.go
index 3384bbd..4bf9d33 100755
--- a/java/app.go
+++ b/java/app.go
@@ -1115,8 +1115,8 @@
 	}
 
 	fixedConfig := android.PathForModuleOut(ctx, "test_config_fixer", "AndroidTest.xml")
-	rule := android.NewRuleBuilder()
-	command := rule.Command().BuiltTool(ctx, "test_config_fixer").Input(testConfig).Output(fixedConfig)
+	rule := android.NewRuleBuilder(pctx, ctx)
+	command := rule.Command().BuiltTool("test_config_fixer").Input(testConfig).Output(fixedConfig)
 	fixNeeded := false
 
 	if ctx.ModuleName() != a.installApkName {
@@ -1131,7 +1131,7 @@
 	}
 
 	if fixNeeded {
-		rule.Build(pctx, ctx, "fix_test_config", "fix test config")
+		rule.Build("fix_test_config", "fix test config")
 		return fixedConfig
 	}
 	return testConfig
@@ -1440,15 +1440,15 @@
 		})
 		return
 	}
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.Command().
 		Textf(`if (zipinfo %s 'lib/*.so' 2>/dev/null | grep -v ' stor ' >/dev/null) ; then`, inputPath).
-		BuiltTool(ctx, "zip2zip").
+		BuiltTool("zip2zip").
 		FlagWithInput("-i ", inputPath).
 		FlagWithOutput("-o ", outputPath).
 		FlagWithArg("-0 ", "'lib/**/*.so'").
 		Textf(`; else cp -f %s %s; fi`, inputPath, outputPath)
-	rule.Build(pctx, ctx, "uncompress-embedded-jni-libs", "Uncompress embedded JIN libs")
+	rule.Build("uncompress-embedded-jni-libs", "Uncompress embedded JIN libs")
 }
 
 // Returns whether this module should have the dex file stored uncompressed in the APK.
@@ -1467,15 +1467,15 @@
 
 func (a *AndroidAppImport) uncompressDex(
 	ctx android.ModuleContext, inputPath android.Path, outputPath android.OutputPath) {
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.Command().
 		Textf(`if (zipinfo %s '*.dex' 2>/dev/null | grep -v ' stor ' >/dev/null) ; then`, inputPath).
-		BuiltTool(ctx, "zip2zip").
+		BuiltTool("zip2zip").
 		FlagWithInput("-i ", inputPath).
 		FlagWithOutput("-o ", outputPath).
 		FlagWithArg("-0 ", "'classes*.dex'").
 		Textf(`; else cp -f %s %s; fi`, inputPath, outputPath)
-	rule.Build(pctx, ctx, "uncompress-dex", "Uncompress dex files")
+	rule.Build("uncompress-dex", "Uncompress dex files")
 }
 
 func (a *AndroidAppImport) GenerateAndroidBuildActions(ctx android.ModuleContext) {
@@ -2015,8 +2015,8 @@
 func (u *usesLibrary) verifyUsesLibrariesManifest(ctx android.ModuleContext, manifest android.Path) android.Path {
 	outputFile := android.PathForModuleOut(ctx, "manifest_check", "AndroidManifest.xml")
 
-	rule := android.NewRuleBuilder()
-	cmd := rule.Command().BuiltTool(ctx, "manifest_check").
+	rule := android.NewRuleBuilder(pctx, ctx)
+	cmd := rule.Command().BuiltTool("manifest_check").
 		Flag("--enforce-uses-libraries").
 		Input(manifest).
 		FlagWithOutput("-o ", outputFile)
@@ -2029,7 +2029,7 @@
 		cmd.FlagWithArg("--optional-uses-library ", lib)
 	}
 
-	rule.Build(pctx, ctx, "verify_uses_libraries", "verify <uses-library>")
+	rule.Build("verify_uses_libraries", "verify <uses-library>")
 
 	return outputFile
 }
@@ -2039,7 +2039,7 @@
 func (u *usesLibrary) verifyUsesLibrariesAPK(ctx android.ModuleContext, apk android.Path) android.Path {
 	outputFile := android.PathForModuleOut(ctx, "verify_uses_libraries", apk.Base())
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	aapt := ctx.Config().HostToolPath(ctx, "aapt")
 	rule.Command().
 		Textf("aapt_binary=%s", aapt.String()).Implicit(aapt).
@@ -2048,7 +2048,7 @@
 		Tool(android.PathForSource(ctx, "build/make/core/verify_uses_libraries.sh")).Input(apk)
 	rule.Command().Text("cp -f").Input(apk).Output(outputFile)
 
-	rule.Build(pctx, ctx, "verify_uses_libraries", "verify <uses-library>")
+	rule.Build("verify_uses_libraries", "verify <uses-library>")
 
 	return outputFile
 }
diff --git a/java/boot_jars.go b/java/boot_jars.go
index e706547..823275b 100644
--- a/java/boot_jars.go
+++ b/java/boot_jars.go
@@ -85,8 +85,8 @@
 
 	timestamp := android.PathForOutput(ctx, "boot-jars-package-check/stamp")
 
-	rule := android.NewRuleBuilder()
-	checkBootJars := rule.Command().BuiltTool(ctx, "check_boot_jars").
+	rule := android.NewRuleBuilder(pctx, ctx)
+	checkBootJars := rule.Command().BuiltTool("check_boot_jars").
 		Input(ctx.Config().HostToolPath(ctx, "dexdump")).
 		Input(android.PathForSource(ctx, "build/soong/scripts/check_boot_jars/package_allowed_list.txt"))
 
@@ -109,7 +109,7 @@
 	}
 
 	checkBootJars.Text("&& touch").Output(timestamp)
-	rule.Build(pctx, ctx, "boot_jars_package_check", "check boot jar packages")
+	rule.Build("boot_jars_package_check", "check boot jar packages")
 
 	// The check-boot-jars phony target depends on the timestamp created if the check succeeds.
 	ctx.Phony("check-boot-jars", timestamp)
diff --git a/java/dexpreopt.go b/java/dexpreopt.go
index a21fb76..67738d4 100644
--- a/java/dexpreopt.go
+++ b/java/dexpreopt.go
@@ -216,7 +216,7 @@
 		return dexJarFile
 	}
 
-	dexpreoptRule.Build(pctx, ctx, "dexpreopt", "dexpreopt")
+	dexpreoptRule.Build("dexpreopt", "dexpreopt")
 
 	d.builtInstalled = dexpreoptRule.Installs().String()
 
diff --git a/java/dexpreopt_bootjars.go b/java/dexpreopt_bootjars.go
index f9975ba..f16ddf1 100644
--- a/java/dexpreopt_bootjars.go
+++ b/java/dexpreopt_bootjars.go
@@ -25,11 +25,177 @@
 	"github.com/google/blueprint/proptools"
 )
 
+// This comment describes:
+//   1. ART boot images in general (their types, structure, file layout, etc.)
+//   2. build system support for boot images
+//
+// 1. ART boot images
+// ------------------
+//
+// A boot image in ART is a set of files that contain AOT-compiled native code and a heap snapshot
+// of AOT-initialized classes for the bootclasspath Java libraries. A boot image is compiled from a
+// set of DEX jars by the dex2oat compiler. A boot image is used for two purposes: 1) it is
+// installed on device and loaded at runtime, and 2) other Java libraries and apps are compiled
+// against it (compilation may take place either on host, known as "dexpreopt", or on device, known
+// as "dexopt").
+//
+// A boot image is not a single file, but a collection of interrelated files. Each boot image has a
+// number of components that correspond to the Java libraries that constitute it. For each component
+// there are multiple files:
+//   - *.oat or *.odex file with native code (architecture-specific, one per instruction set)
+//   - *.art file with pre-initialized Java classes (architecture-specific, one per instruction set)
+//   - *.vdex file with verification metadata for the DEX bytecode (architecture independent)
+//
+// *.vdex files for the boot images do not contain the DEX bytecode itself, because the
+// bootclasspath DEX files are stored on disk in uncompressed and aligned form. Consequently a boot
+// image is not self-contained and cannot be used without its DEX files. To simplify the management
+// of boot image files, ART uses a certain naming scheme and associates the following metadata with
+// each boot image:
+//   - A stem, which is a symbolic name that is prepended to boot image file names.
+//   - A location (on-device path to the boot image files).
+//   - A list of boot image locations (on-device paths to dependency boot images).
+//   - A set of DEX locations (on-device paths to the DEX files, one location for one DEX file used
+//     to compile the boot image).
+//
+// There are two kinds of boot images:
+//   - primary boot images
+//   - boot image extensions
+//
+// 1.1. Primary boot images
+// ------------------------
+//
+// A primary boot image is compiled for a core subset of bootclasspath Java libraries. It does not
+// depend on any other images, and other boot images may depend on it.
+//
+// For example, assuming that the stem is "boot", the location is /apex/com.android.art/javalib/,
+// the set of core bootclasspath libraries is A B C, and the boot image is compiled for ARM targets
+// (32 and 64 bits), it will have three components with the following files:
+//   - /apex/com.android.art/javalib/{arm,arm64}/boot.{art,oat,vdex}
+//   - /apex/com.android.art/javalib/{arm,arm64}/boot-B.{art,oat,vdex}
+//   - /apex/com.android.art/javalib/{arm,arm64}/boot-C.{art,oat,vdex}
+//
+// The files of the first component are special: they do not have the component name appended after
+// the stem. This naming convention dates back to the times when the boot image was not split into
+// components, and there were just boot.oat and boot.art. The decision to split was motivated by
+// licensing reasons for one of the bootclasspath libraries.
+//
+// As of November 2020 the only primary boot image in Android is the image in the ART APEX
+// com.android.art. The primary ART boot image contains the Core libraries that are part of the ART
+// module. When the ART module gets updated, the primary boot image will be updated with it, and all
+// dependent images will get invalidated (the checksum of the primary image stored in dependent
+// images will not match), unless they are updated in sync with the ART module.
+//
+// 1.2. Boot image extensions
+// --------------------------
+//
+// A boot image extension is compiled for a subset of bootclasspath Java libraries (in particular,
+// this subset does not include the Core bootclasspath libraries that go into the primary boot
+// image). A boot image extension depends on the primary boot image and optionally some other boot
+// image extensions. Other images may depend on it. In other words, boot image extensions can form
+// acyclic dependency graphs.
+//
+// The motivation for boot image extensions comes from the Mainline project. Consider a situation
+// when the list of bootclasspath libraries is A B C, and both A and B are parts of the Android
+// platform, but C is part of an updatable APEX com.android.C. When the APEX is updated, the Java
+// code for C might have changed compared to the code that was used to compile the boot image.
+// Consequently, the whole boot image is obsolete and invalidated (even though the code for A and B
+// that does not depend on C is up to date). To avoid this, the original monolithic boot image is
+// split in two parts: the primary boot image that contains A B, and the boot image extension that
+// contains C and depends on the primary boot image (extends it).
+//
+// For example, assuming that the stem is "boot", the location is /system/framework, the set of
+// bootclasspath libraries is D E (where D is part of the platform and is located in
+// /system/framework, and E is part of a non-updatable APEX com.android.E and is located in
+// /apex/com.android.E/javalib), and the boot image is compiled for ARM targets (32 and 64 bits),
+// it will have two components with the following files:
+//   - /system/framework/{arm,arm64}/boot-D.{art,oat,vdex}
+//   - /system/framework/{arm,arm64}/boot-E.{art,oat,vdex}
+//
+// As of November 2020 the only boot image extension in Android is the Framework boot image
+// extension. It extends the primary ART boot image and contains Framework libraries and other
+// bootclasspath libraries from the platform and non-updatable APEXes that are not included in the
+// ART image. The Framework boot image extension is updated together with the platform. In the
+// future other boot image extensions may be added for some updatable modules.
+//
+//
+// 2. Build system support for boot images
+// ---------------------------------------
+//
+// The primary ART boot image needs to be compiled with one dex2oat invocation that depends on DEX
+// jars for the core libraries. Framework boot image extension needs to be compiled with one dex2oat
+// invocation that depends on the primary ART boot image and all bootclasspath DEX jars except the
+// Core libraries.
+//
+// 2.1. Libraries that go in the boot images
+// -----------------------------------------
+//
+// The contents of each boot image are determined by the PRODUCT variables. The primary ART APEX
+// boot image contains libraries listed in the ART_APEX_JARS variable in the AOSP makefiles. The
+// Framework boot image extension contains libraries specified in the PRODUCT_BOOT_JARS and
+// PRODUCT_BOOT_JARS_EXTRA variables. The AOSP makefiles specify some common Framework libraries,
+// but more product-specific libraries can be added in the product makefiles.
+//
+// Each component of the PRODUCT_BOOT_JARS and PRODUCT_BOOT_JARS_EXTRA variables is either a simple
+// name (if the library is a part of the Platform), or a colon-separated pair <apex, name> (if the
+// library is a part of a non-updatable APEX).
+//
+// A related variable PRODUCT_UPDATABLE_BOOT_JARS contains bootclasspath libraries that are in
+// updatable APEXes. They are not included in the boot image.
+//
+// One exception to the above rules are "coverage" builds (a special build flavor which requires
+// setting environment variable EMMA_INSTRUMENT_FRAMEWORK=true). In coverage builds the Java code in
+// boot image libraries is instrumented, which means that the instrumentation library (jacocoagent)
+// needs to be added to the list of bootclasspath DEX jars.
+//
+// In general, there is a requirement that the source code for a boot image library must be
+// available at build time (e.g. it cannot be a stub that has a separate implementation library).
+//
+// 2.2. Static configs
+// -------------------
+//
+// Because boot images are used to dexpreopt other Java modules, the paths to boot image files must
+// be known by the time dexpreopt build rules for the dependent modules are generated. Boot image
+// configs are constructed very early during the build, before build rule generation. The configs
+// provide predefined paths to boot image files (these paths depend only on static build
+// configuration, such as PRODUCT variables, and use hard-coded directory names).
+//
+// 2.3. Singleton
+// --------------
+//
+// Build rules for the boot images are generated with a Soong singleton. Because a singleton has no
+// dependencies on other modules, it has to find the modules for the DEX jars using VisitAllModules.
+// Soong loops through all modules and compares each module against a list of bootclasspath library
+// names. Then it generates build rules that copy DEX jars from their intermediate module-specific
+// locations to the hard-coded locations predefined in the boot image configs.
+//
+// It would be possible to use a module with proper dependencies instead, but that would require
+// changes in the way Soong generates variables for Make: a singleton can use one MakeVars() method
+// that writes variables to out/soong/make_vars-*.mk, which is included early by the main makefile,
+// but module(s) would have to use out/soong/Android-*.mk which has a group of LOCAL_* variables
+// for each module, and is included later.
+//
+// 2.4. Install rules
+// ------------------
+//
+// The primary boot image and the Framework extension are installed in different ways. The primary
+// boot image is part of the ART APEX: it is copied into the APEX intermediate files, packaged
+// together with other APEX contents, extracted and mounted on device. The Framework boot image
+// extension is installed by the rules defined in makefiles (make/core/dex_preopt_libart.mk). Soong
+// writes out a few DEXPREOPT_IMAGE_* variables for Make; these variables contain boot image names,
+// paths and so on.
+//
+// 2.5. JIT-Zygote configuration
+// -----------------------------
+//
+// One special configuration is JIT-Zygote build, when the primary ART image is used for compiling
+// apps instead of the Framework boot image extension (see DEXPREOPT_USE_ART_IMAGE and UseArtImage).
+//
+
 func init() {
 	RegisterDexpreoptBootJarsComponents(android.InitRegistrationContext)
 }
 
-// Target-independent description of pre-compiled boot image.
+// Target-independent description of a boot image.
 type bootImageConfig struct {
 	// If this image is an extension, the image that it extends.
 	extends *bootImageConfig
@@ -66,7 +232,7 @@
 	variants []*bootImageVariant
 }
 
-// Target-dependent description of pre-compiled boot image.
+// Target-dependent description of a boot image.
 type bootImageVariant struct {
 	*bootImageConfig
 
@@ -90,6 +256,7 @@
 	unstrippedInstalls android.RuleBuilderInstalls
 }
 
+// Get target-specific boot image variant for the given boot image config and target.
 func (image bootImageConfig) getVariant(target android.Target) *bootImageVariant {
 	for _, variant := range image.variants {
 		if variant.target.Os == target.Os && variant.target.Arch.ArchType == target.Arch.ArchType {
@@ -99,7 +266,7 @@
 	return nil
 }
 
-// Return any (the first) variant which is for the device (as opposed to for the host)
+// Return any (the first) variant which is for the device (as opposed to for the host).
 func (image bootImageConfig) getAnyAndroidVariant() *bootImageVariant {
 	for _, variant := range image.variants {
 		if variant.target.Os == android.Android {
@@ -109,10 +276,12 @@
 	return nil
 }
 
+// Return the name of a boot image module given a boot image config and a component (module) index.
+// A module name is a combination of the Java library name, and the boot image stem (that is stored
+// in the config).
 func (image bootImageConfig) moduleName(ctx android.PathContext, idx int) string {
-	// Dexpreopt on the boot class path produces multiple files. The first dex file
-	// is converted into 'name'.art (to match the legacy assumption that 'name'.art
-	// exists), and the rest are converted to 'name'-<jar>.art.
+	// The first module of the primary boot image is special: its module name has only the stem, but
+	// not the library name. All other module names are of the form <stem>-<library name>
 	m := image.modules.Jar(idx)
 	name := image.stem
 	if idx != 0 || image.extends != nil {
@@ -121,6 +290,7 @@
 	return name
 }
 
+// Return the name of the first boot image module, or stem if the list of modules is empty.
 func (image bootImageConfig) firstModuleNameOrStem(ctx android.PathContext) string {
 	if image.modules.Len() > 0 {
 		return image.moduleName(ctx, 0)
@@ -129,6 +299,8 @@
 	}
 }
 
+// Return filenames for the given boot image component, given the output directory and a list of
+// extensions.
 func (image bootImageConfig) moduleFiles(ctx android.PathContext, dir android.OutputPath, exts ...string) android.OutputPaths {
 	ret := make(android.OutputPaths, 0, image.modules.Len()*len(exts))
 	for i := 0; i < image.modules.Len(); i++ {
@@ -140,17 +312,26 @@
 	return ret
 }
 
+// Return boot image locations (as a list of symbolic paths).
+//
 // The image "location" is a symbolic path that, with multiarchitecture support, doesn't really
 // exist on the device. Typically it is /apex/com.android.art/javalib/boot.art and should be the
 // same for all supported architectures on the device. The concrete architecture specific files
 // actually end up in architecture-specific sub-directory such as arm, arm64, x86, or x86_64.
 //
-// For example a physical file
-// "/apex/com.android.art/javalib/x86/boot.art" has "image location"
-// "/apex/com.android.art/javalib/boot.art" (which is not an actual file).
+// For example a physical file /apex/com.android.art/javalib/x86/boot.art has "image location"
+// /apex/com.android.art/javalib/boot.art (which is not an actual file).
+//
+// For a primary boot image the list of locations has a single element.
+//
+// For a boot image extension the list of locations contains a location for all dependency images
+// (including the primary image) and the location of the extension itself. For example, for the
+// Framework boot image extension that depends on the primary ART boot image the list contains two
+// elements.
 //
 // The location is passed as an argument to the ART tools like dex2oat instead of the real path.
 // ART tools will then reconstruct the architecture-specific real path.
+//
 func (image *bootImageVariant) imageLocations() (imageLocations []string) {
 	if image.extends != nil {
 		imageLocations = image.extends.getVariant(image.target).imageLocations()
@@ -158,18 +339,6 @@
 	return append(imageLocations, dexpreopt.PathToLocation(image.images, image.target.Arch.ArchType))
 }
 
-func concat(lists ...[]string) []string {
-	var size int
-	for _, l := range lists {
-		size += len(l)
-	}
-	ret := make([]string, 0, size)
-	for _, l := range lists {
-		ret = append(ret, l...)
-	}
-	return ret
-}
-
 func dexpreoptBootJarsFactory() android.Singleton {
 	return &dexpreoptBootJars{}
 }
@@ -182,10 +351,21 @@
 	return dexpreopt.GetGlobalConfig(ctx).DisablePreopt
 }
 
+// Singleton for generating boot image build rules.
 type dexpreoptBootJars struct {
+	// Default boot image config (currently always the Framework boot image extension). It should be
+	// noted that JIT-Zygote builds use ART APEX image instead of the Framework boot image extension,
+	// but the switch is handled not here, but in the makefiles (triggered with
+	// DEXPREOPT_USE_ART_IMAGE=true).
 	defaultBootImage *bootImageConfig
-	otherImages      []*bootImageConfig
 
+	// Other boot image configs (currently the list contains only the primary ART APEX image. It
+	// used to contain an experimental JIT-Zygote image (now replaced with the ART APEX image). In
+	// the future other boot image extensions may be added.
+	otherImages []*bootImageConfig
+
+	// Build path to a config file that Soong writes for Make (to be used in makefiles that install
+	// the default boot image).
 	dexpreoptConfigForMake android.WritablePath
 }
 
@@ -205,7 +385,7 @@
 	return files
 }
 
-// dexpreoptBoot singleton rules
+// Generate build rules for boot images.
 func (d *dexpreoptBootJars) GenerateBuildActions(ctx android.SingletonContext) {
 	if skipDexpreoptBootJars(ctx) {
 		return
@@ -334,9 +514,10 @@
 		}
 	}
 
-	// The path to bootclasspath dex files needs to be known at module GenerateAndroidBuildAction time, before
-	// the bootclasspath modules have been compiled.  Copy the dex jars there so the module rules that have
-	// already been set up can find them.
+	// The paths to bootclasspath DEX files need to be known at module GenerateAndroidBuildAction
+	// time, before the boot images are built (these paths are used in dexpreopt rule generation for
+	// Java libraries and apps). Generate rules that copy bootclasspath DEX jars to the predefined
+	// paths.
 	for i := range bootDexJars {
 		ctx.Build(pctx, android.BuildParams{
 			Rule:   android.Cp,
@@ -358,19 +539,20 @@
 	}
 
 	if image.zip != nil {
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 		rule.Command().
-			BuiltTool(ctx, "soong_zip").
+			BuiltTool("soong_zip").
 			FlagWithOutput("-o ", image.zip).
 			FlagWithArg("-C ", image.dir.Join(ctx, android.Android.String()).String()).
 			FlagWithInputList("-f ", zipFiles, " -f ")
 
-		rule.Build(pctx, ctx, "zip_"+image.name, "zip "+image.name+" image")
+		rule.Build("zip_"+image.name, "zip "+image.name+" image")
 	}
 
 	return image
 }
 
+// Generate boot image build rules for a specific target.
 func buildBootImageVariant(ctx android.SingletonContext, image *bootImageVariant,
 	profile android.Path, missingDeps []string) android.WritablePaths {
 
@@ -386,7 +568,7 @@
 	oatLocation := dexpreopt.PathToLocation(outputPath, arch)
 	imagePath := outputPath.ReplaceExtension(ctx, "art")
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.MissingDeps(missingDeps)
 
 	rule.Command().Text("mkdir").Flag("-p").Flag(symbolsDir.String())
@@ -428,12 +610,15 @@
 	}
 
 	if image.extends != nil {
+		// It is a boot image extension, so it needs the boot image it depends on (in this case the
+		// primary ART APEX image).
 		artImage := image.primaryImages
 		cmd.
 			Flag("--runtime-arg").FlagWithInputList("-Xbootclasspath:", image.dexPathsDeps.Paths(), ":").
 			Flag("--runtime-arg").FlagWithList("-Xbootclasspath-locations:", image.dexLocationsDeps, ":").
 			FlagWithArg("--boot-image=", dexpreopt.PathToLocation(artImage, arch)).Implicit(artImage)
 	} else {
+		// It is a primary image, so it needs a base address.
 		cmd.FlagWithArg("--base=", ctx.Config().LibartImgDeviceBaseAddress())
 	}
 
@@ -504,7 +689,7 @@
 			android.RuleBuilderInstall{unstrippedOat, filepath.Join(installDir, unstrippedOat.Base())})
 	}
 
-	rule.Build(pctx, ctx, image.name+"JarsDexpreopt_"+image.target.String(), "dexpreopt "+image.name+" jars "+arch.String())
+	rule.Build(image.name+"JarsDexpreopt_"+image.target.String(), "dexpreopt "+image.name+" jars "+arch.String())
 
 	// save output and installed files for makevars
 	image.installs = rule.Installs()
@@ -528,7 +713,7 @@
 	profile := ctx.Config().Once(bootImageProfileRuleKey, func() interface{} {
 		defaultProfile := "frameworks/base/config/boot-image-profile.txt"
 
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 		rule.MissingDeps(missingDeps)
 
 		var bootImageProfile android.Path
@@ -559,7 +744,7 @@
 
 		rule.Install(profile, "/system/etc/boot-image.prof")
 
-		rule.Build(pctx, ctx, "bootJarsProfile", "profile boot jars")
+		rule.Build("bootJarsProfile", "profile boot jars")
 
 		image.profileInstalls = rule.Installs()
 
@@ -581,7 +766,7 @@
 		return nil
 	}
 	return ctx.Config().Once(bootFrameworkProfileRuleKey, func() interface{} {
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 		rule.MissingDeps(missingDeps)
 
 		// Some branches like master-art-host don't have frameworks/base, so manually
@@ -609,7 +794,7 @@
 			FlagWithOutput("--reference-profile-file=", profile)
 
 		rule.Install(profile, "/system/etc/boot-image.bprof")
-		rule.Build(pctx, ctx, "bootFrameworkProfile", "profile boot framework jars")
+		rule.Build("bootFrameworkProfile", "profile boot framework jars")
 		image.profileInstalls = append(image.profileInstalls, rule.Installs()...)
 
 		return profile
@@ -654,7 +839,7 @@
 		// WriteFileRule automatically adds the last end-of-line.
 		android.WriteFileRule(ctx, updatableBcpPackages, strings.Join(updatablePackages, "\n"))
 
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 		rule.MissingDeps(missingDeps)
 		rule.Install(updatableBcpPackages, "/system/etc/"+updatableBcpPackagesName)
 		// TODO: Rename `profileInstalls` to `extraInstalls`?
@@ -678,25 +863,25 @@
 		}
 		// Create a rule to call oatdump.
 		output := android.PathForOutput(ctx, "boot."+suffix+".oatdump.txt")
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 		rule.Command().
 			// TODO: for now, use the debug version for better error reporting
-			BuiltTool(ctx, "oatdumpd").
+			BuiltTool("oatdumpd").
 			FlagWithInputList("--runtime-arg -Xbootclasspath:", image.dexPathsDeps.Paths(), ":").
 			FlagWithList("--runtime-arg -Xbootclasspath-locations:", image.dexLocationsDeps, ":").
 			FlagWithArg("--image=", strings.Join(image.imageLocations(), ":")).Implicits(image.imagesDeps.Paths()).
 			FlagWithOutput("--output=", output).
 			FlagWithArg("--instruction-set=", arch.String())
-		rule.Build(pctx, ctx, "dump-oat-boot-"+suffix, "dump oat boot "+arch.String())
+		rule.Build("dump-oat-boot-"+suffix, "dump oat boot "+arch.String())
 
 		// Create a phony rule that depends on the output file and prints the path.
 		phony := android.PathForPhony(ctx, "dump-oat-boot-"+suffix)
-		rule = android.NewRuleBuilder()
+		rule = android.NewRuleBuilder(pctx, ctx)
 		rule.Command().
 			Implicit(output).
 			ImplicitOutput(phony).
 			Text("echo").FlagWithArg("Output in ", output.String())
-		rule.Build(pctx, ctx, "phony-dump-oat-boot-"+suffix, "dump oat boot "+arch.String())
+		rule.Build("phony-dump-oat-boot-"+suffix, "dump oat boot "+arch.String())
 
 		allPhonies = append(allPhonies, phony)
 	}
@@ -717,7 +902,9 @@
 	android.WriteFileRule(ctx, path, string(data))
 }
 
-// Export paths for default boot image to Make
+// Define Make variables for boot image names, paths, etc. These variables are used in makefiles
+// (make/core/dex_preopt_libart.mk) to generate install rules that copy boot image files to the
+// correct output directories.
 func (d *dexpreoptBootJars) MakeVars(ctx android.MakeVarsContext) {
 	if d.dexpreoptConfigForMake != nil {
 		ctx.Strict("DEX_PREOPT_CONFIG_FOR_MAKE", d.dexpreoptConfigForMake.String())
@@ -731,6 +918,11 @@
 		ctx.Strict("DEXPREOPT_BOOTCLASSPATH_DEX_LOCATIONS", strings.Join(image.getAnyAndroidVariant().dexLocationsDeps, " "))
 
 		var imageNames []string
+		// TODO: the primary ART boot image should not be exposed to Make, as it is installed in a
+		// different way as a part of the ART APEX. However, there is a special JIT-Zygote build
+		// configuration which uses the primary ART image instead of the Framework boot image
+		// extension, and it relies on the ART image being exposed to Make. To fix this, it is
+		// necessary to rework the logic in makefiles.
 		for _, current := range append(d.otherImages, image) {
 			imageNames = append(imageNames, current.name)
 			for _, variant := range current.variants {
diff --git a/java/droiddoc.go b/java/droiddoc.go
index cf7f4fb..9c88a3c 100644
--- a/java/droiddoc.go
+++ b/java/droiddoc.go
@@ -671,7 +671,7 @@
 
 	j.stubsSrcJar = nil
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	rule.Command().Text("rm -rf").Text(outDir.String())
 	rule.Command().Text("mkdir -p").Text(outDir.String())
@@ -689,7 +689,7 @@
 		Flag("-Xdoclint:none")
 
 	rule.Command().
-		BuiltTool(ctx, "soong_zip").
+		BuiltTool("soong_zip").
 		Flag("-write_if_changed").
 		Flag("-d").
 		FlagWithOutput("-o ", j.docZip).
@@ -700,7 +700,7 @@
 
 	zipSyncCleanupCmd(rule, srcJarDir)
 
-	rule.Build(pctx, ctx, "javadoc", "javadoc")
+	rule.Build("javadoc", "javadoc")
 }
 
 //
@@ -845,7 +845,7 @@
 	outDir, srcJarDir, srcJarList android.Path, sourcepaths android.Paths) *android.RuleBuilderCommand {
 
 	cmd := rule.Command().
-		BuiltTool(ctx, "soong_javac_wrapper").Tool(config.JavadocCmd(ctx)).
+		BuiltTool("soong_javac_wrapper").Tool(config.JavadocCmd(ctx)).
 		Flag(config.JavacVmFlags).
 		FlagWithArg("-encoding ", "UTF-8").
 		FlagWithRspFileInputList("@", srcs).
@@ -914,7 +914,7 @@
 	dokkaClasspath := append(bootclasspath.Paths(), classpath.Paths()...)
 
 	return rule.Command().
-		BuiltTool(ctx, "dokka").
+		BuiltTool("dokka").
 		Flag(config.JavacVmFlags).
 		Flag(srcJarDir.String()).
 		FlagWithInputList("-classpath ", dokkaClasspath, ":").
@@ -934,7 +934,7 @@
 	outDir := android.PathForModuleOut(ctx, "out")
 	srcJarDir := android.PathForModuleOut(ctx, "srcjars")
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	srcJarList := zipSyncCmd(ctx, rule, srcJarDir, d.Javadoc.srcJars)
 
@@ -968,7 +968,7 @@
 	}
 
 	rule.Command().
-		BuiltTool(ctx, "soong_zip").
+		BuiltTool("soong_zip").
 		Flag("-write_if_changed").
 		Flag("-d").
 		FlagWithOutput("-o ", d.docZip).
@@ -979,7 +979,7 @@
 
 	zipSyncCleanupCmd(rule, srcJarDir)
 
-	rule.Build(pctx, ctx, "javadoc", desc)
+	rule.Build("javadoc", desc)
 }
 
 //
@@ -1050,7 +1050,8 @@
 		return android.Paths{d.stubsSrcJar}, nil
 	case ".docs.zip":
 		return android.Paths{d.docZip}, nil
-	case ".api.txt":
+	case ".api.txt", android.DefaultDistTag:
+		// This is the default dist path for dist properties that have no tag property.
 		return android.Paths{d.apiFilePath}, nil
 	case ".removed-api.txt":
 		return android.Paths{d.removedApiFilePath}, nil
@@ -1277,7 +1278,7 @@
 		}).NoVarTemplate(ctx.Config()))
 	}
 
-	cmd.BuiltTool(ctx, "metalava").
+	cmd.BuiltTool("metalava").
 		Flag(config.JavacVmFlags).
 		Flag("-J--add-opens=java.base/java.util=ALL-UNNAMED").
 		FlagWithArg("-encoding ", "UTF-8").
@@ -1332,7 +1333,7 @@
 
 	srcJarDir := android.PathForModuleOut(ctx, "srcjars")
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	if BoolDefault(d.properties.High_mem, false) {
 		// This metalava run uses lots of memory, restrict the number of metalava jobs that can run in parallel.
@@ -1479,19 +1480,19 @@
 		cmd.FlagWithArg("--error-message:compatibility:released ", msg)
 	}
 
-	impRule := android.NewRuleBuilder()
+	impRule := android.NewRuleBuilder(pctx, ctx)
 	impCmd := impRule.Command()
 	// An action that copies the ninja generated rsp file to a new location. This allows us to
 	// add a large number of inputs to a file without exceeding bash command length limits (which
 	// would happen if we use the WriteFile rule). The cp is needed because RuleBuilder sets the
 	// rsp file to be ${output}.rsp.
 	impCmd.Text("cp").FlagWithRspFileInputList("", cmd.GetImplicits()).Output(implicitsRsp)
-	impRule.Build(pctx, ctx, "implicitsGen", "implicits generation")
+	impRule.Build("implicitsGen", "implicits generation")
 	cmd.Implicit(implicitsRsp)
 
 	if generateStubs {
 		rule.Command().
-			BuiltTool(ctx, "soong_zip").
+			BuiltTool("soong_zip").
 			Flag("-write_if_changed").
 			Flag("-jar").
 			FlagWithOutput("-o ", d.Javadoc.stubsSrcJar).
@@ -1502,7 +1503,7 @@
 	if Bool(d.properties.Write_sdk_values) {
 		d.metadataZip = android.PathForModuleOut(ctx, ctx.ModuleName()+"-metadata.zip")
 		rule.Command().
-			BuiltTool(ctx, "soong_zip").
+			BuiltTool("soong_zip").
 			Flag("-write_if_changed").
 			Flag("-d").
 			FlagWithOutput("-o ", d.metadataZip).
@@ -1523,7 +1524,7 @@
 
 	zipSyncCleanupCmd(rule, srcJarDir)
 
-	rule.Build(pctx, ctx, "metalava", "metalava merged")
+	rule.Build("metalava", "metalava merged")
 
 	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") {
 
@@ -1541,7 +1542,7 @@
 
 		d.checkCurrentApiTimestamp = android.PathForModuleOut(ctx, "check_current_api.timestamp")
 
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 
 		// Diff command line.
 		// -F matches the closest "opening" line, such as "package android {"
@@ -1563,7 +1564,7 @@
 			`   1. You can add '@hide' javadoc comments (and remove @SystemApi/@TestApi/etc)\n`+
 			`      to the new methods, etc. shown in the above diff.\n\n`+
 			`   2. You can update current.txt and/or removed.txt by executing the following command:\n`+
-			`         make %s-update-current-api\n\n`+
+			`         m %s-update-current-api\n\n`+
 			`      To submit the revised current.txt to the main Android repository,\n`+
 			`      you will need approval.\n`+
 			`******************************\n`, ctx.ModuleName())
@@ -1575,12 +1576,12 @@
 			Text("; exit 38").
 			Text(")")
 
-		rule.Build(pctx, ctx, "metalavaCurrentApiCheck", "check current API")
+		rule.Build("metalavaCurrentApiCheck", "check current API")
 
 		d.updateCurrentApiTimestamp = android.PathForModuleOut(ctx, "update_current_api.timestamp")
 
 		// update API rule
-		rule = android.NewRuleBuilder()
+		rule = android.NewRuleBuilder(pctx, ctx)
 
 		rule.Command().Text("( true")
 
@@ -1601,7 +1602,7 @@
 			Text("; exit 38").
 			Text(")")
 
-		rule.Build(pctx, ctx, "metalavaCurrentApiUpdate", "update current API")
+		rule.Build("metalavaCurrentApiUpdate", "update current API")
 	}
 
 	if String(d.properties.Check_nullability_warnings) != "" {
@@ -1624,7 +1625,7 @@
 			`       and submitting the updated file as part of your change.`,
 			d.nullabilityWarningsFile, checkNullabilityWarnings)
 
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 
 		rule.Command().
 			Text("(").
@@ -1636,7 +1637,7 @@
 			Text("; exit 38").
 			Text(")")
 
-		rule.Build(pctx, ctx, "nullabilityWarningsCheck", "nullability warnings check")
+		rule.Build("nullabilityWarningsCheck", "nullability warnings check")
 	}
 }
 
@@ -1721,7 +1722,7 @@
 
 	rule.Temporary(srcJarList)
 
-	rule.Command().BuiltTool(ctx, "zipsync").
+	rule.Command().BuiltTool("zipsync").
 		FlagWithArg("-d ", srcJarDir.String()).
 		FlagWithOutput("-l ", srcJarList).
 		FlagWithArg("-f ", `"*.java"`).
@@ -1782,9 +1783,9 @@
 	srcGlob := localSrcDir + "/**/*"
 	srcPaths := android.PathsForModuleSrc(ctx, []string{srcGlob})
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.Command().
-		BuiltTool(ctx, "soong_zip").
+		BuiltTool("soong_zip").
 		Flag("-write_if_changed").
 		Flag("-jar").
 		FlagWithOutput("-o ", p.stubsSrcJar).
@@ -1793,7 +1794,7 @@
 
 	rule.Restat()
 
-	rule.Build(pctx, ctx, "zip src", "Create srcjar from prebuilt source")
+	rule.Build("zip src", "Create srcjar from prebuilt source")
 }
 
 func (p *PrebuiltStubsSources) Prebuilt() *android.Prebuilt {
diff --git a/java/gen.go b/java/gen.go
index d50a665..5766a94 100644
--- a/java/gen.go
+++ b/java/gen.go
@@ -57,7 +57,7 @@
 
 		outDir := srcJarFile.ReplaceExtension(ctx, "tmp")
 
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 
 		rule.Command().Text("rm -rf").Flag(outDir.String())
 		rule.Command().Text("mkdir -p").Flag(outDir.String())
@@ -98,7 +98,7 @@
 			ruleDesc += " " + strconv.Itoa(i)
 		}
 
-		rule.Build(pctx, ctx, ruleName, ruleDesc)
+		rule.Build(ruleName, ruleDesc)
 	}
 
 	return srcJarFiles
diff --git a/java/hiddenapi.go b/java/hiddenapi.go
index 63b801a..71f1e57 100644
--- a/java/hiddenapi.go
+++ b/java/hiddenapi.go
@@ -135,12 +135,12 @@
 	})
 	h.metadataCSVPath = metadataCSV
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.Command().
-		BuiltTool(ctx, "merge_csv").
+		BuiltTool("merge_csv").
 		FlagWithInput("--zip_input=", classesJar).
 		FlagWithOutput("--output=", indexCSV)
-	rule.Build(pctx, ctx, "merged-hiddenapi-index", "Merged Hidden API index")
+	rule.Build("merged-hiddenapi-index", "Merged Hidden API index")
 	h.indexCSVPath = indexCSV
 }
 
diff --git a/java/hiddenapi_singleton.go b/java/hiddenapi_singleton.go
index e57f323..ce8410e 100644
--- a/java/hiddenapi_singleton.go
+++ b/java/hiddenapi_singleton.go
@@ -189,7 +189,7 @@
 	}
 
 	// Singleton rule which applies hiddenapi on all boot class path dex files.
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	outputPath := hiddenAPISingletonPaths(ctx).stubFlags
 	tempPath := android.PathForOutput(ctx, outputPath.Rel()+".tmp")
@@ -208,7 +208,7 @@
 
 	commitChangeForRestat(rule, tempPath, outputPath)
 
-	rule.Build(pctx, ctx, "hiddenAPIStubFlagsFile", "hiddenapi stub flags")
+	rule.Build("hiddenAPIStubFlagsFile", "hiddenapi stub flags")
 }
 
 // flagsRule creates a rule to build hiddenapi-flags.csv out of flags.csv files generated for boot image modules and
@@ -236,7 +236,7 @@
 		ctx.Errorf("Failed to find combined-removed-dex.")
 	}
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	outputPath := hiddenAPISingletonPaths(ctx).flags
 	tempPath := android.PathForOutput(ctx, outputPath.Rel()+".tmp")
@@ -259,14 +259,14 @@
 		FlagWithInput("--blocked ",
 			android.PathForSource(ctx, "frameworks/base/config/hiddenapi-force-blocked.txt")).
 		FlagWithInput("--blocked ",
-			android.PathForSource(ctx, "frameworks/base/config/hiddenapi-temp-blocklist.txt")).
+			android.PathForSource(ctx, "frameworks/base/config/hiddenapi-temp-blocklist.txt")).FlagWithArg("--tag ", "lo-prio").
 		FlagWithInput("--unsupported ", android.PathForSource(
 			ctx, "frameworks/base/config/hiddenapi-unsupported-packages.txt")).Flag("--packages ").
 		FlagWithOutput("--output ", tempPath)
 
 	commitChangeForRestat(rule, tempPath, outputPath)
 
-	rule.Build(pctx, ctx, "hiddenAPIFlagsFile", "hiddenapi flags")
+	rule.Build("hiddenAPIFlagsFile", "hiddenapi flags")
 
 	return outputPath
 }
@@ -274,14 +274,14 @@
 // emptyFlagsRule creates a rule to build an empty hiddenapi-flags.csv, which is needed by master-art-host builds that
 // have a partial manifest without frameworks/base but still need to build a boot image.
 func emptyFlagsRule(ctx android.SingletonContext) android.Path {
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	outputPath := hiddenAPISingletonPaths(ctx).flags
 
 	rule.Command().Text("rm").Flag("-f").Output(outputPath)
 	rule.Command().Text("touch").Output(outputPath)
 
-	rule.Build(pctx, ctx, "emptyHiddenAPIFlagsFile", "empty hiddenapi flags")
+	rule.Build("emptyHiddenAPIFlagsFile", "empty hiddenapi flags")
 
 	return outputPath
 }
@@ -299,16 +299,16 @@
 		}
 	})
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	outputPath := hiddenAPISingletonPaths(ctx).metadata
 
 	rule.Command().
-		BuiltTool(ctx, "merge_csv").
+		BuiltTool("merge_csv").
 		FlagWithOutput("--output=", outputPath).
 		Inputs(metadataCSV)
 
-	rule.Build(pctx, ctx, "hiddenAPIGreylistMetadataFile", "hiddenapi greylist metadata")
+	rule.Build("hiddenAPIGreylistMetadataFile", "hiddenapi greylist metadata")
 
 	return outputPath
 }
@@ -399,13 +399,13 @@
 		}
 	})
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.Command().
-		BuiltTool(ctx, "merge_csv").
+		BuiltTool("merge_csv").
 		FlagWithArg("--header=", "signature,file,startline,startcol,endline,endcol,properties").
 		FlagWithOutput("--output=", hiddenAPISingletonPaths(ctx).index).
 		Inputs(indexes)
-	rule.Build(pctx, ctx, "singleton-merged-hiddenapi-index", "Singleton merged Hidden API index")
+	rule.Build("singleton-merged-hiddenapi-index", "Singleton merged Hidden API index")
 
 	h.index = hiddenAPISingletonPaths(ctx).index
 }
diff --git a/java/java.go b/java/java.go
index bf139a8..3d121cc 100644
--- a/java/java.go
+++ b/java/java.go
@@ -456,8 +456,6 @@
 	// list of the xref extraction files
 	kytheFiles android.Paths
 
-	distFiles android.TaggedDistFiles
-
 	// Collect the module directory for IDE info in java/jdeps.go.
 	modulePaths []string
 
@@ -486,6 +484,8 @@
 	switch tag {
 	case "":
 		return append(android.Paths{j.outputFile}, j.extraOutputFiles...), nil
+	case android.DefaultDistTag:
+		return android.Paths{j.outputFile}, nil
 	case ".jar":
 		return android.Paths{j.implementationAndResourcesJar}, nil
 	case ".proguard_map":
@@ -772,6 +772,37 @@
 	libDeps := ctx.AddVariationDependencies(nil, libTag, rewriteSyspropLibs(j.properties.Libs, "libs")...)
 	ctx.AddVariationDependencies(nil, staticLibTag, rewriteSyspropLibs(j.properties.Static_libs, "static_libs")...)
 
+	if ctx.DeviceConfig().VndkVersion() != "" && ctx.Config().EnforceInterPartitionJavaSdkLibrary() {
+		// Require java_sdk_library at inter-partition java dependency to ensure stable
+		// interface between partitions. If inter-partition java_library dependency is detected,
+		// raise build error because java_library doesn't have a stable interface.
+		//
+		// Inputs:
+		//    PRODUCT_ENFORCE_INTER_PARTITION_JAVA_SDK_LIBRARY
+		//      if true, enable enforcement
+		//    PRODUCT_INTER_PARTITION_JAVA_LIBRARY_ALLOWLIST
+		//      exception list of java_library names to allow inter-partition dependency
+		for idx, lib := range j.properties.Libs {
+			if libDeps[idx] == nil {
+				continue
+			}
+
+			if _, ok := syspropPublicStubs[lib]; ok {
+				continue
+			}
+
+			if javaDep, ok := libDeps[idx].(javaSdkLibraryEnforceContext); ok {
+				// java_sdk_library is always allowed at inter-partition dependency.
+				// So, skip check.
+				if _, ok := javaDep.(*SdkLibrary); ok {
+					continue
+				}
+
+				j.checkPartitionsForJavaDependency(ctx, "libs", javaDep)
+			}
+		}
+	}
+
 	// For library dependencies that are component libraries (like stubs), add the implementation
 	// as a dependency (dexpreopt needs to be against the implementation library, not stubs).
 	for _, dep := range libDeps {
@@ -1415,6 +1446,9 @@
 		kotlincFlags := j.properties.Kotlincflags
 		CheckKotlincFlags(ctx, kotlincFlags)
 
+		// Dogfood the JVM_IR backend.
+		kotlincFlags = append(kotlincFlags, "-Xuse-ir")
+
 		// If there are kotlin files, compile them first but pass all the kotlin and java files
 		// kotlinc will use the java files to resolve types referenced by the kotlin files, but
 		// won't emit any classes for them.
@@ -2112,8 +2146,6 @@
 	if lib := proptools.String(j.usesLibraryProperties.Provides_uses_lib); lib != "" {
 		j.classLoaderContexts.AddContext(ctx, lib, j.DexJarBuildPath(), j.DexJarInstallPath())
 	}
-
-	j.distFiles = j.GenerateTaggedDistFiles(ctx)
 }
 
 func (j *Library) DepsMutator(ctx android.BottomUpMutatorContext) {
@@ -3051,21 +3083,21 @@
 	dexOutputFile := android.PathForModuleOut(ctx, ctx.ModuleName()+".jar")
 
 	if j.dexpreopter.uncompressedDex {
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 
 		temporary := android.PathForModuleOut(ctx, ctx.ModuleName()+".jar.unaligned")
 		rule.Temporary(temporary)
 
 		// use zip2zip to uncompress classes*.dex files
 		rule.Command().
-			BuiltTool(ctx, "zip2zip").
+			BuiltTool("zip2zip").
 			FlagWithInput("-i ", inputJar).
 			FlagWithOutput("-o ", temporary).
 			FlagWithArg("-0 ", "'classes*.dex'")
 
 		// use zipalign to align uncompressed classes*.dex files
 		rule.Command().
-			BuiltTool(ctx, "zipalign").
+			BuiltTool("zipalign").
 			Flag("-f").
 			Text("4").
 			Input(temporary).
@@ -3073,7 +3105,7 @@
 
 		rule.DeleteTemporaryFiles()
 
-		rule.Build(pctx, ctx, "uncompress_dex", "uncompress dex")
+		rule.Build("uncompress_dex", "uncompress dex")
 	} else {
 		ctx.Build(pctx, android.BuildParams{
 			Rule:   android.Cp,
diff --git a/java/java_test.go b/java/java_test.go
index 83db443..f7cf03f 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -805,6 +805,165 @@
 	})
 }
 
+func TestJavaSdkLibraryEnforce(t *testing.T) {
+	partitionToBpOption := func(partition string) string {
+		switch partition {
+		case "system":
+			return ""
+		case "vendor":
+			return "soc_specific: true,"
+		case "product":
+			return "product_specific: true,"
+		default:
+			panic("Invalid partition group name: " + partition)
+		}
+	}
+
+	type testConfigInfo struct {
+		libraryType                string
+		fromPartition              string
+		toPartition                string
+		enforceVendorInterface     bool
+		enforceProductInterface    bool
+		enforceJavaSdkLibraryCheck bool
+		allowList                  []string
+	}
+
+	createTestConfig := func(info testConfigInfo) android.Config {
+		bpFileTemplate := `
+			java_library {
+				name: "foo",
+				srcs: ["foo.java"],
+				libs: ["bar"],
+				sdk_version: "current",
+				%s
+			}
+
+			%s {
+				name: "bar",
+				srcs: ["bar.java"],
+				sdk_version: "current",
+				%s
+			}
+		`
+
+		bpFile := fmt.Sprintf(bpFileTemplate,
+			partitionToBpOption(info.fromPartition),
+			info.libraryType,
+			partitionToBpOption(info.toPartition))
+
+		config := testConfig(nil, bpFile, nil)
+		configVariables := config.TestProductVariables
+
+		configVariables.EnforceProductPartitionInterface = proptools.BoolPtr(info.enforceProductInterface)
+		if info.enforceVendorInterface {
+			configVariables.DeviceVndkVersion = proptools.StringPtr("current")
+		}
+		configVariables.EnforceInterPartitionJavaSdkLibrary = proptools.BoolPtr(info.enforceJavaSdkLibraryCheck)
+		configVariables.InterPartitionJavaLibraryAllowList = info.allowList
+
+		return config
+	}
+
+	isValidDependency := func(configInfo testConfigInfo) bool {
+		if configInfo.enforceVendorInterface == false {
+			return true
+		}
+
+		if configInfo.enforceJavaSdkLibraryCheck == false {
+			return true
+		}
+
+		if inList("bar", configInfo.allowList) {
+			return true
+		}
+
+		if configInfo.libraryType == "java_library" {
+			if configInfo.fromPartition != configInfo.toPartition {
+				if !configInfo.enforceProductInterface &&
+					((configInfo.fromPartition == "system" && configInfo.toPartition == "product") ||
+						(configInfo.fromPartition == "product" && configInfo.toPartition == "system")) {
+					return true
+				}
+				return false
+			}
+		}
+
+		return true
+	}
+
+	errorMessage := "is not allowed across the partitions"
+
+	allPartitionCombinations := func() [][2]string {
+		var result [][2]string
+		partitions := []string{"system", "vendor", "product"}
+
+		for _, fromPartition := range partitions {
+			for _, toPartition := range partitions {
+				result = append(result, [2]string{fromPartition, toPartition})
+			}
+		}
+
+		return result
+	}
+
+	allFlagCombinations := func() [][3]bool {
+		var result [][3]bool
+		flagValues := [2]bool{false, true}
+
+		for _, vendorInterface := range flagValues {
+			for _, productInterface := range flagValues {
+				for _, enableEnforce := range flagValues {
+					result = append(result, [3]bool{vendorInterface, productInterface, enableEnforce})
+				}
+			}
+		}
+
+		return result
+	}
+
+	for _, libraryType := range []string{"java_library", "java_sdk_library"} {
+		for _, partitionValues := range allPartitionCombinations() {
+			for _, flagValues := range allFlagCombinations() {
+				testInfo := testConfigInfo{
+					libraryType:                libraryType,
+					fromPartition:              partitionValues[0],
+					toPartition:                partitionValues[1],
+					enforceVendorInterface:     flagValues[0],
+					enforceProductInterface:    flagValues[1],
+					enforceJavaSdkLibraryCheck: flagValues[2],
+				}
+
+				if isValidDependency(testInfo) {
+					testJavaWithConfig(t, createTestConfig(testInfo))
+				} else {
+					testJavaErrorWithConfig(t, errorMessage, createTestConfig(testInfo))
+				}
+			}
+		}
+	}
+
+	testJavaWithConfig(t, createTestConfig(testConfigInfo{
+		libraryType:                "java_library",
+		fromPartition:              "vendor",
+		toPartition:                "system",
+		enforceVendorInterface:     true,
+		enforceProductInterface:    true,
+		enforceJavaSdkLibraryCheck: true,
+		allowList:                  []string{"bar"},
+	}))
+
+	testJavaErrorWithConfig(t, errorMessage, createTestConfig(testConfigInfo{
+		libraryType:                "java_library",
+		fromPartition:              "vendor",
+		toPartition:                "system",
+		enforceVendorInterface:     true,
+		enforceProductInterface:    true,
+		enforceJavaSdkLibraryCheck: true,
+		allowList:                  []string{"foo"},
+	}))
+}
+
 func TestDefaults(t *testing.T) {
 	ctx, _ := testJava(t, `
 		java_defaults {
diff --git a/java/kotlin.go b/java/kotlin.go
index e8c030a..8067ad5 100644
--- a/java/kotlin.go
+++ b/java/kotlin.go
@@ -63,9 +63,9 @@
 		// we can't use the rsp file because it is already being used for srcs.
 		// Insert a second rule to write out the list of resources to a file.
 		commonSrcsList := android.PathForModuleOut(ctx, "kotlinc_common_srcs.list")
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 		rule.Command().Text("cp").FlagWithRspFileInputList("", commonSrcFiles).Output(commonSrcsList)
-		rule.Build(pctx, ctx, "kotlin_common_srcs_list", "kotlin common_srcs list")
+		rule.Build("kotlin_common_srcs_list", "kotlin common_srcs list")
 		return android.OptionalPathForPath(commonSrcsList)
 	}
 	return android.OptionalPath{}
diff --git a/java/lint.go b/java/lint.go
index 11f92e5..cd2a904 100644
--- a/java/lint.go
+++ b/java/lint.go
@@ -176,9 +176,9 @@
 		// we can't use the rsp file because it is already being used for srcs.
 		// Insert a second rule to write out the list of resources to a file.
 		resourcesList = android.PathForModuleOut(ctx, "lint", "resources.list")
-		resListRule := android.NewRuleBuilder()
+		resListRule := android.NewRuleBuilder(pctx, ctx)
 		resListRule.Command().Text("cp").FlagWithRspFileInputList("", l.resources).Output(resourcesList)
-		resListRule.Build(pctx, ctx, "lint_resources_list", "lint resources list")
+		resListRule.Build("lint_resources_list", "lint resources list")
 		deps = append(deps, l.resources...)
 	}
 
@@ -192,7 +192,7 @@
 	srcJarList := zipSyncCmd(ctx, rule, srcJarDir, l.srcJars)
 
 	cmd := rule.Command().
-		BuiltTool(ctx, "lint-project-xml").
+		BuiltTool("lint-project-xml").
 		FlagWithOutput("--project_out ", projectXMLPath).
 		FlagWithOutput("--config_out ", configXMLPath).
 		FlagWithArg("--name ", ctx.ModuleName())
@@ -284,7 +284,7 @@
 		}
 	}
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	if l.manifest == nil {
 		manifest := l.generateManifest(ctx, rule)
@@ -347,7 +347,7 @@
 
 	rule.Command().Text("rm -rf").Flag(cacheDir.String()).Flag(homeDir.String())
 
-	rule.Build(pctx, ctx, "lint", "lint")
+	rule.Build("lint", "lint")
 
 	l.outputs = lintOutputs{
 		html: html,
@@ -511,12 +511,12 @@
 		return paths[i].String() < paths[j].String()
 	})
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
-	rule.Command().BuiltTool(ctx, "soong_zip").
+	rule.Command().BuiltTool("soong_zip").
 		FlagWithOutput("-o ", outputPath).
 		FlagWithArg("-C ", android.PathForIntermediates(ctx).String()).
 		FlagWithRspFileInputList("-r ", paths)
 
-	rule.Build(pctx, ctx, outputPath.Base(), outputPath.Base())
+	rule.Build(outputPath.Base(), outputPath.Base())
 }
diff --git a/java/platform_compat_config.go b/java/platform_compat_config.go
index cb8e684..9bc821d 100644
--- a/java/platform_compat_config.go
+++ b/java/platform_compat_config.go
@@ -86,15 +86,15 @@
 		return
 	}
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	outputPath := platformCompatConfigPath(ctx)
 
 	rule.Command().
-		BuiltTool(ctx, "process-compat-config").
+		BuiltTool("process-compat-config").
 		FlagForEachInput("--xml ", compatConfigMetadata).
 		FlagWithOutput("--merged-config ", outputPath)
 
-	rule.Build(pctx, ctx, "merged-compat-config", "Merge compat config")
+	rule.Build("merged-compat-config", "Merge compat config")
 
 	p.metadata = outputPath
 }
@@ -106,7 +106,7 @@
 }
 
 func (p *platformCompatConfig) GenerateAndroidBuildActions(ctx android.ModuleContext) {
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	configFileName := p.Name() + ".xml"
 	metadataFileName := p.Name() + "_meta.xml"
@@ -115,13 +115,13 @@
 	path := android.PathForModuleSrc(ctx, String(p.properties.Src))
 
 	rule.Command().
-		BuiltTool(ctx, "process-compat-config").
+		BuiltTool("process-compat-config").
 		FlagWithInput("--jar ", path).
 		FlagWithOutput("--device-config ", p.configFile).
 		FlagWithOutput("--merged-config ", p.metadataFile)
 
 	p.installDirPath = android.PathForModuleInstall(ctx, "etc", "compatconfig")
-	rule.Build(pctx, ctx, configFileName, "Extract compat/compat_config.xml and install it")
+	rule.Build(configFileName, "Extract compat/compat_config.xml and install it")
 
 }
 
diff --git a/java/proto.go b/java/proto.go
index 4d735eb..cc9abbe 100644
--- a/java/proto.go
+++ b/java/proto.go
@@ -34,7 +34,7 @@
 
 		outDir := srcJarFile.ReplaceExtension(ctx, "tmp")
 
-		rule := android.NewRuleBuilder()
+		rule := android.NewRuleBuilder(pctx, ctx)
 
 		rule.Command().Text("rm -rf").Flag(outDir.String())
 		rule.Command().Text("mkdir -p").Flag(outDir.String())
@@ -42,13 +42,13 @@
 		for _, protoFile := range shard {
 			depFile := srcJarFile.InSameDir(ctx, protoFile.String()+".d")
 			rule.Command().Text("mkdir -p").Flag(filepath.Dir(depFile.String()))
-			android.ProtoRule(ctx, rule, protoFile, flags, flags.Deps, outDir, depFile, nil)
+			android.ProtoRule(rule, protoFile, flags, flags.Deps, outDir, depFile, nil)
 		}
 
 		// Proto generated java files have an unknown package name in the path, so package the entire output directory
 		// into a srcjar.
 		rule.Command().
-			BuiltTool(ctx, "soong_zip").
+			BuiltTool("soong_zip").
 			Flag("-jar").
 			Flag("-write_if_changed").
 			FlagWithOutput("-o ", srcJarFile).
@@ -66,7 +66,7 @@
 			ruleDesc += " " + strconv.Itoa(i)
 		}
 
-		rule.Build(pctx, ctx, ruleName, ruleDesc)
+		rule.Build(ruleName, ruleDesc)
 	}
 
 	return srcJarFiles
diff --git a/java/robolectric.go b/java/robolectric.go
index 62d1d99..419efda 100644
--- a/java/robolectric.go
+++ b/java/robolectric.go
@@ -199,7 +199,7 @@
 
 func generateRoboTestConfig(ctx android.ModuleContext, outputFile android.WritablePath,
 	instrumentedApp *AndroidApp) {
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	manifest := instrumentedApp.mergedManifestFile
 	resourceApk := instrumentedApp.outputFile
@@ -213,11 +213,11 @@
 		Implicit(manifest).
 		Implicit(resourceApk)
 
-	rule.Build(pctx, ctx, "generate_test_config", "generate test_config.properties")
+	rule.Build("generate_test_config", "generate test_config.properties")
 }
 
 func generateSameDirRoboTestConfigJar(ctx android.ModuleContext, outputFile android.ModuleOutPath) {
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	outputDir := outputFile.InSameDir(ctx)
 	configFile := outputDir.Join(ctx, "com/android/tools/test_config.properties")
@@ -230,12 +230,12 @@
 		Textf(`echo "android_resource_apk=%s.apk"`, ctx.ModuleName()).
 		Text(") >>").Output(configFile)
 	rule.Command().
-		BuiltTool(ctx, "soong_zip").
+		BuiltTool("soong_zip").
 		FlagWithArg("-C ", outputDir.String()).
 		FlagWithInput("-f ", configFile).
 		FlagWithOutput("-o ", outputFile)
 
-	rule.Build(pctx, ctx, "generate_test_config_samedir", "generate test_config.properties")
+	rule.Build("generate_test_config_samedir", "generate test_config.properties")
 }
 
 func (r *robolectricTest) generateRoboSrcJar(ctx android.ModuleContext, outputFile android.WritablePath,
diff --git a/java/sdk.go b/java/sdk.go
index 971791f..32a4b5a 100644
--- a/java/sdk.go
+++ b/java/sdk.go
@@ -544,7 +544,7 @@
 
 	commitChangeForRestat(rule, tempPath, combinedAidl)
 
-	rule.Build(pctx, ctx, "framework_aidl", "generate framework.aidl")
+	rule.Build("framework_aidl", "generate framework.aidl")
 }
 
 // Creates a version of framework.aidl for the non-updatable part of the platform.
@@ -558,7 +558,7 @@
 
 	commitChangeForRestat(rule, tempPath, combinedAidl)
 
-	rule.Build(pctx, ctx, "framework_non_updatable_aidl", "generate framework_non_updatable.aidl")
+	rule.Build("framework_non_updatable_aidl", "generate framework_non_updatable.aidl")
 }
 
 func createFrameworkAidl(stubsModules []string, path android.OutputPath, ctx android.SingletonContext) *android.RuleBuilder {
@@ -586,7 +586,7 @@
 		}
 	}
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.MissingDeps(missingDeps)
 
 	var aidls android.Paths
@@ -597,7 +597,7 @@
 			rule.Command().
 				Text("rm -f").Output(aidl)
 			rule.Command().
-				BuiltTool(ctx, "sdkparcelables").
+				BuiltTool("sdkparcelables").
 				Input(jar).
 				Output(aidl)
 
@@ -632,7 +632,7 @@
 func createAPIFingerprint(ctx android.SingletonContext) {
 	out := ApiFingerprintPath(ctx)
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	rule.Command().
 		Text("rm -f").Output(out)
@@ -659,7 +659,7 @@
 			Output(out)
 	}
 
-	rule.Build(pctx, ctx, "api_fingerprint", "generate api_fingerprint.txt")
+	rule.Build("api_fingerprint", "generate api_fingerprint.txt")
 }
 
 func ApiFingerprintPath(ctx android.PathContext) android.OutputPath {
diff --git a/java/sdk_library.go b/java/sdk_library.go
index b832678..4e33d74 100644
--- a/java/sdk_library.go
+++ b/java/sdk_library.go
@@ -1281,11 +1281,7 @@
 			Include_dirs       []string
 			Local_include_dirs []string
 		}
-		Dist struct {
-			Targets []string
-			Dest    *string
-			Dir     *string
-		}
+		Dists []android.Dist
 	}{}
 
 	// The stubs source processing uses the same compile time classpath when extracting the
@@ -1385,11 +1381,23 @@
 		}
 	}
 
-	// Dist the api txt artifact for sdk builds.
 	if !Bool(module.sdkLibraryProperties.No_dist) {
-		props.Dist.Targets = []string{"sdk", "win_sdk"}
-		props.Dist.Dest = proptools.StringPtr(fmt.Sprintf("%v.txt", module.distStem()))
-		props.Dist.Dir = proptools.StringPtr(path.Join(module.apiDistPath(apiScope), "api"))
+		// Dist the api txt and removed api txt artifacts for sdk builds.
+		distDir := proptools.StringPtr(path.Join(module.apiDistPath(apiScope), "api"))
+		for _, p := range []struct {
+			tag     string
+			pattern string
+		}{
+			{tag: ".api.txt", pattern: "%s.txt"},
+			{tag: ".removed-api.txt", pattern: "%s-removed.txt"},
+		} {
+			props.Dists = append(props.Dists, android.Dist{
+				Targets: []string{"sdk", "win_sdk"},
+				Dir:     distDir,
+				Dest:    proptools.StringPtr(fmt.Sprintf(p.pattern, module.distStem())),
+				Tag:     proptools.StringPtr(p.tag),
+			})
+		}
 	}
 
 	mctx.CreateModule(DroidstubsFactory, &props)
@@ -2168,12 +2176,12 @@
 	xmlContent := fmt.Sprintf(permissionsTemplate, libName, module.implPath(ctx))
 
 	module.outputFilePath = android.PathForModuleOut(ctx, libName+".xml").OutputPath
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	rule.Command().
 		Text("/bin/bash -c \"echo -e '" + xmlContent + "'\" > ").
 		Output(module.outputFilePath)
 
-	rule.Build(pctx, ctx, "java_sdk_xml", "Permission XML")
+	rule.Build("java_sdk_xml", "Permission XML")
 
 	module.installDirPath = android.PathForModuleInstall(ctx, "etc", module.SubDir())
 }
diff --git a/java/sdk_library_external.go b/java/sdk_library_external.go
new file mode 100644
index 0000000..2934936
--- /dev/null
+++ b/java/sdk_library_external.go
@@ -0,0 +1,109 @@
+// Copyright 2020 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package java
+
+import (
+	"android/soong/android"
+)
+
+type partitionGroup int
+
+// Representation of partition group for checking inter-partition library dependencies.
+// Between system and system_ext, there are no restrictions of dependencies,
+// so we can treat these partitions as the same in terms of inter-partition dependency.
+// Same policy is applied between vendor and odm partiton.
+const (
+	partitionGroupNone partitionGroup = iota
+	// group for system, and system_ext partition
+	partitionGroupSystem
+	// group for vendor and odm partition
+	partitionGroupVendor
+	// product partition
+	partitionGroupProduct
+)
+
+func (g partitionGroup) String() string {
+	switch g {
+	case partitionGroupSystem:
+		return "system"
+	case partitionGroupVendor:
+		return "vendor"
+	case partitionGroupProduct:
+		return "product"
+	}
+
+	return ""
+}
+
+// Get partition group of java module that can be used at inter-partition dependency check.
+// We currently have three groups
+//   (system, system_ext) => system partition group
+//   (vendor, odm) => vendor partition group
+//   (product) => product partition group
+func (j *Module) partitionGroup(ctx android.EarlyModuleContext) partitionGroup {
+	// system and system_ext partition can be treated as the same in terms of inter-partition dependency.
+	if j.Platform() || j.SystemExtSpecific() {
+		return partitionGroupSystem
+	}
+
+	// vendor and odm partition can be treated as the same in terms of inter-partition dependency.
+	if j.SocSpecific() || j.DeviceSpecific() {
+		return partitionGroupVendor
+	}
+
+	// product partition is independent.
+	if j.ProductSpecific() {
+		return partitionGroupProduct
+	}
+
+	panic("Cannot determine partition type")
+}
+
+func (j *Module) allowListedInterPartitionJavaLibrary(ctx android.EarlyModuleContext) bool {
+	return inList(j.Name(), ctx.Config().InterPartitionJavaLibraryAllowList())
+}
+
+type javaSdkLibraryEnforceContext interface {
+	Name() string
+	allowListedInterPartitionJavaLibrary(ctx android.EarlyModuleContext) bool
+	partitionGroup(ctx android.EarlyModuleContext) partitionGroup
+}
+
+var _ javaSdkLibraryEnforceContext = (*Module)(nil)
+
+func (j *Module) checkPartitionsForJavaDependency(ctx android.EarlyModuleContext, propName string, dep javaSdkLibraryEnforceContext) {
+	if dep.allowListedInterPartitionJavaLibrary(ctx) {
+		return
+	}
+
+	// If product interface is not enforced, skip check between system and product partition.
+	// But still need to check between product and vendor partition because product interface flag
+	// just represents enforcement between product and system, and vendor interface enforcement
+	// that is enforced here by precondition is representing enforcement between vendor and other partitions.
+	if !ctx.Config().EnforceProductPartitionInterface() {
+		productToSystem := j.partitionGroup(ctx) == partitionGroupProduct && dep.partitionGroup(ctx) == partitionGroupSystem
+		systemToProduct := j.partitionGroup(ctx) == partitionGroupSystem && dep.partitionGroup(ctx) == partitionGroupProduct
+
+		if productToSystem || systemToProduct {
+			return
+		}
+	}
+
+	// If module and dependency library is inter-partition
+	if j.partitionGroup(ctx) != dep.partitionGroup(ctx) {
+		errorFormat := "dependency on java_library (%q) is not allowed across the partitions (%s -> %s), use java_sdk_library instead"
+		ctx.PropertyErrorf(propName, errorFormat, dep.Name(), j.partitionGroup(ctx), dep.partitionGroup(ctx))
+	}
+}
diff --git a/linkerconfig/linkerconfig.go b/linkerconfig/linkerconfig.go
index 1c44c74..d538ce4 100644
--- a/linkerconfig/linkerconfig.go
+++ b/linkerconfig/linkerconfig.go
@@ -68,13 +68,13 @@
 	inputFile := android.PathForModuleSrc(ctx, android.String(l.properties.Src))
 	l.outputFilePath = android.PathForModuleOut(ctx, "linker.config.pb").OutputPath
 	l.installDirPath = android.PathForModuleInstall(ctx, "etc")
-	linkerConfigRule := android.NewRuleBuilder()
+	linkerConfigRule := android.NewRuleBuilder(pctx, ctx)
 	linkerConfigRule.Command().
-		BuiltTool(ctx, "conv_linker_config").
+		BuiltTool("conv_linker_config").
 		Flag("proto").
 		FlagWithInput("-s ", inputFile).
 		FlagWithOutput("-o ", l.outputFilePath)
-	linkerConfigRule.Build(pctx, ctx, "conv_linker_config",
+	linkerConfigRule.Build("conv_linker_config",
 		"Generate linker config protobuf "+l.outputFilePath.String())
 
 	if proptools.BoolDefault(l.properties.Installable, true) {
@@ -102,6 +102,7 @@
 				entries.SetString("LOCAL_MODULE_PATH", l.installDirPath.ToMakePath().String())
 				entries.SetString("LOCAL_INSTALLED_MODULE_STEM", l.outputFilePath.Base())
 				entries.SetBoolIfTrue("LOCAL_UNINSTALLABLE_MODULE", !installable)
+				entries.SetString("LINKER_CONFIG_PATH_"+l.Name(), l.OutputFile().String())
 			},
 		},
 	}}
diff --git a/linkerconfig/proto/Android.bp b/linkerconfig/proto/Android.bp
index c04887e..4d97128 100644
--- a/linkerconfig/proto/Android.bp
+++ b/linkerconfig/proto/Android.bp
@@ -7,6 +7,10 @@
         type: "lite",
     },
     srcs: ["linker_config.proto"],
+    apex_available: [
+        "//apex_available:platform",
+        "//apex_available:anyapex",
+    ],
 }
 
 python_library_host {
diff --git a/python/androidmk.go b/python/androidmk.go
index e60c538..60637d3 100644
--- a/python/androidmk.go
+++ b/python/androidmk.go
@@ -49,7 +49,7 @@
 	entries.Class = "EXECUTABLES"
 
 	entries.ExtraEntries = append(entries.ExtraEntries, func(entries *android.AndroidMkEntries) {
-		entries.AddStrings("LOCAL_COMPATIBILITY_SUITE", p.binaryProperties.Test_suites...)
+		entries.AddCompatibilityTestSuites(p.binaryProperties.Test_suites...)
 	})
 	base.subAndroidMk(entries, p.pythonInstaller)
 }
@@ -58,7 +58,7 @@
 	entries.Class = "NATIVE_TESTS"
 
 	entries.ExtraEntries = append(entries.ExtraEntries, func(entries *android.AndroidMkEntries) {
-		entries.AddStrings("LOCAL_COMPATIBILITY_SUITE", p.binaryDecorator.binaryProperties.Test_suites...)
+		entries.AddCompatibilityTestSuites(p.binaryDecorator.binaryProperties.Test_suites...)
 		if p.testConfig != nil {
 			entries.SetString("LOCAL_FULL_TEST_CONFIG", p.testConfig.String())
 		}
diff --git a/python/binary.go b/python/binary.go
index 1d2400e..416a7ee 100644
--- a/python/binary.go
+++ b/python/binary.go
@@ -81,7 +81,7 @@
 func PythonBinaryHostFactory() android.Module {
 	module, _ := NewBinary(android.HostSupported)
 
-	return module.Init()
+	return module.init()
 }
 
 func (binary *binaryDecorator) autorun() bool {
diff --git a/python/library.go b/python/library.go
index 0c8d613..b724d2b 100644
--- a/python/library.go
+++ b/python/library.go
@@ -28,11 +28,11 @@
 func PythonLibraryHostFactory() android.Module {
 	module := newModule(android.HostSupported, android.MultilibFirst)
 
-	return module.Init()
+	return module.init()
 }
 
 func PythonLibraryFactory() android.Module {
 	module := newModule(android.HostAndDeviceSupported, android.MultilibBoth)
 
-	return module.Init()
+	return module.init()
 }
diff --git a/python/proto.go b/python/proto.go
index b71e047..53ebb58 100644
--- a/python/proto.go
+++ b/python/proto.go
@@ -24,17 +24,17 @@
 	outDir := srcsZipFile.ReplaceExtension(ctx, "tmp")
 	depFile := srcsZipFile.ReplaceExtension(ctx, "srcszip.d")
 
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 
 	rule.Command().Text("rm -rf").Flag(outDir.String())
 	rule.Command().Text("mkdir -p").Flag(outDir.String())
 
-	android.ProtoRule(ctx, rule, protoFile, flags, flags.Deps, outDir, depFile, nil)
+	android.ProtoRule(rule, protoFile, flags, flags.Deps, outDir, depFile, nil)
 
 	// Proto generated python files have an unknown package name in the path, so package the entire output directory
 	// into a srcszip.
 	zipCmd := rule.Command().
-		BuiltTool(ctx, "soong_zip").
+		BuiltTool("soong_zip").
 		FlagWithOutput("-o ", srcsZipFile)
 	if pkgPath != "" {
 		zipCmd.FlagWithArg("-P ", pkgPath)
@@ -44,7 +44,7 @@
 
 	rule.Command().Text("rm -rf").Flag(outDir.String())
 
-	rule.Build(pctx, ctx, "protoc_"+protoFile.Rel(), "protoc "+protoFile.Rel())
+	rule.Build("protoc_"+protoFile.Rel(), "protoc "+protoFile.Rel())
 
 	return srcsZipFile
 }
diff --git a/python/python.go b/python/python.go
index 7e376c6..b3e3d13 100644
--- a/python/python.go
+++ b/python/python.go
@@ -20,7 +20,6 @@
 	"fmt"
 	"path/filepath"
 	"regexp"
-	"sort"
 	"strings"
 
 	"github.com/google/blueprint"
@@ -33,33 +32,34 @@
 	android.PreDepsMutators(RegisterPythonPreDepsMutators)
 }
 
+// Exported to support other packages using Python modules in tests.
 func RegisterPythonPreDepsMutators(ctx android.RegisterMutatorsContext) {
 	ctx.BottomUp("python_version", versionSplitMutator()).Parallel()
 }
 
-// the version properties that apply to python libraries and binaries.
+// the version-specific properties that apply to python modules.
 type VersionProperties struct {
-	// true, if the module is required to be built with this version.
+	// whether the module is required to be built with this version.
+	// Defaults to true for Python 3, and false otherwise.
 	Enabled *bool `android:"arch_variant"`
 
-	// non-empty list of .py files under this strict Python version.
-	// srcs may reference the outputs of other modules that produce source files like genrule
-	// or filegroup using the syntax ":module".
+	// list of source files specific to this Python version.
+	// Using the syntax ":module", srcs may reference the outputs of other modules that produce source files,
+	// e.g. genrule or filegroup.
 	Srcs []string `android:"path,arch_variant"`
 
-	// list of source files that should not be used to build the Python module.
-	// This is most useful in the arch/multilib variants to remove non-common files
+	// list of source files that should not be used to build the Python module for this version.
+	// This is most useful to remove files that are not common to all Python versions.
 	Exclude_srcs []string `android:"path,arch_variant"`
 
-	// list of the Python libraries under this Python version.
+	// list of the Python libraries used only for this Python version.
 	Libs []string `android:"arch_variant"`
 
-	// true, if the binary is required to be built with embedded launcher.
-	// TODO(nanzhang): Remove this flag when embedded Python3 is supported later.
-	Embedded_launcher *bool `android:"arch_variant"`
+	// whether the binary is required to be built with embedded launcher for this version, defaults to false.
+	Embedded_launcher *bool `android:"arch_variant"` // TODO(b/174041232): Remove this property
 }
 
-// properties that apply to python libraries and binaries.
+// properties that apply to all python modules
 type BaseProperties struct {
 	// the package path prefix within the output artifact at which to place the source/data
 	// files of the current module.
@@ -93,10 +93,12 @@
 	Libs []string `android:"arch_variant"`
 
 	Version struct {
-		// all the "srcs" or Python dependencies that are to be used only for Python2.
+		// Python2-specific properties, including whether Python2 is supported for this module
+		// and version-specific sources, exclusions and dependencies.
 		Py2 VersionProperties `android:"arch_variant"`
 
-		// all the "srcs" or Python dependencies that are to be used only for Python3.
+		// Python3-specific properties, including whether Python3 is supported for this module
+		// and version-specific sources, exclusions and dependencies.
 		Py3 VersionProperties `android:"arch_variant"`
 	} `android:"arch_variant"`
 
@@ -105,14 +107,16 @@
 	// runtime.
 	Actual_version string `blueprint:"mutated"`
 
-	// true, if the module is required to be built with actual_version.
+	// whether the module is required to be built with actual_version.
+	// this is set by the python version mutator based on version-specific properties
 	Enabled *bool `blueprint:"mutated"`
 
-	// true, if the binary is required to be built with embedded launcher.
-	// TODO(nanzhang): Remove this flag when embedded Python3 is supported later.
+	// whether the binary is required to be built with embedded launcher for this actual_version.
+	// this is set by the python version mutator based on version-specific properties
 	Embedded_launcher *bool `blueprint:"mutated"`
 }
 
+// Used to store files of current module after expanding dependencies
 type pathMapping struct {
 	dest string
 	src  android.Path
@@ -129,11 +133,14 @@
 	hod      android.HostOrDeviceSupported
 	multilib android.Multilib
 
-	// the bootstrapper is used to bootstrap .par executable.
-	// bootstrapper might be nil (Python library module).
+	// interface used to bootstrap .par executable when embedded_launcher is true
+	// this should be set by Python modules which are runnable, e.g. binaries and tests
+	// bootstrapper might be nil (e.g. Python library module).
 	bootstrapper bootstrapper
 
-	// the installer might be nil.
+	// interface that implements functions required for installation
+	// this should be set by Python modules which are runnable, e.g. binaries and tests
+	// installer might be nil (e.g. Python library module).
 	installer installer
 
 	// the Python files of current module after expanding source dependencies.
@@ -153,9 +160,11 @@
 	// (.intermediate) module output path as installation source.
 	installSource android.OptionalPath
 
+	// Map to ensure sub-part of the AndroidMk for this module is only added once
 	subAndroidMkOnce map[subAndroidMkProvider]bool
 }
 
+// newModule generates new Python base module
 func newModule(hod android.HostOrDeviceSupported, multilib android.Multilib) *Module {
 	return &Module{
 		hod:      hod,
@@ -163,6 +172,7 @@
 	}
 }
 
+// bootstrapper interface should be implemented for runnable modules, e.g. binary and test
 type bootstrapper interface {
 	bootstrapperProps() []interface{}
 	bootstrap(ctx android.ModuleContext, ActualVersion string, embeddedLauncher bool,
@@ -172,36 +182,45 @@
 	autorun() bool
 }
 
+// installer interface should be implemented for installable modules, e.g. binary and test
 type installer interface {
 	install(ctx android.ModuleContext, path android.Path)
 	setAndroidMkSharedLibs(sharedLibs []string)
 }
 
-type PythonDependency interface {
-	GetSrcsPathMappings() []pathMapping
-	GetDataPathMappings() []pathMapping
-	GetSrcsZip() android.Path
+// interface implemented by Python modules to provide source and data mappings and zip to python
+// modules that depend on it
+type pythonDependency interface {
+	getSrcsPathMappings() []pathMapping
+	getDataPathMappings() []pathMapping
+	getSrcsZip() android.Path
 }
 
-func (p *Module) GetSrcsPathMappings() []pathMapping {
+// getSrcsPathMappings gets this module's path mapping of src source path : runfiles destination
+func (p *Module) getSrcsPathMappings() []pathMapping {
 	return p.srcsPathMappings
 }
 
-func (p *Module) GetDataPathMappings() []pathMapping {
+// getSrcsPathMappings gets this module's path mapping of data source path : runfiles destination
+func (p *Module) getDataPathMappings() []pathMapping {
 	return p.dataPathMappings
 }
 
-func (p *Module) GetSrcsZip() android.Path {
+// getSrcsZip returns the filepath where the current module's source/data files are zipped.
+func (p *Module) getSrcsZip() android.Path {
 	return p.srcsZip
 }
 
-var _ PythonDependency = (*Module)(nil)
+var _ pythonDependency = (*Module)(nil)
 
 var _ android.AndroidMkEntriesProvider = (*Module)(nil)
 
-func (p *Module) Init() android.Module {
-
+func (p *Module) init(additionalProps ...interface{}) android.Module {
 	p.AddProperties(&p.properties, &p.protoProperties)
+
+	// Add additional properties for bootstrapping/installation
+	// This is currently tied to the bootstrapper interface;
+	// however, these are a combination of properties for the installation and bootstrapping of a module
 	if p.bootstrapper != nil {
 		p.AddProperties(p.bootstrapper.bootstrapperProps()...)
 	}
@@ -212,13 +231,19 @@
 	return p
 }
 
+// Python-specific tag to transfer information on the purpose of a dependency.
+// This is used when adding a dependency on a module, which can later be accessed when visiting
+// dependencies.
 type dependencyTag struct {
 	blueprint.BaseDependencyTag
 	name string
 }
 
+// Python-specific tag that indicates that installed files of this module should depend on installed
+// files of the dependency
 type installDependencyTag struct {
 	blueprint.BaseDependencyTag
+	// embedding this struct provides the installation dependency requirement
 	android.InstallAlwaysNeededDependencyTag
 	name string
 }
@@ -228,7 +253,7 @@
 	javaDataTag          = dependencyTag{name: "javaData"}
 	launcherTag          = dependencyTag{name: "launcher"}
 	launcherSharedLibTag = installDependencyTag{name: "launcherSharedLib"}
-	pyIdentifierRegexp   = regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_-]*$`)
+	pathComponentRegexp  = regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_-]*$`)
 	pyExt                = ".py"
 	protoExt             = ".proto"
 	pyVersion2           = "PY2"
@@ -237,35 +262,37 @@
 	mainFileName         = "__main__.py"
 	entryPointFile       = "entry_point.txt"
 	parFileExt           = ".zip"
-	internal             = "internal"
+	internalPath         = "internal"
 )
 
-// create version variants for modules.
+// versionSplitMutator creates version variants for modules and appends the version-specific
+// properties for a given variant to the properties in the variant module
 func versionSplitMutator() func(android.BottomUpMutatorContext) {
 	return func(mctx android.BottomUpMutatorContext) {
 		if base, ok := mctx.Module().(*Module); ok {
 			versionNames := []string{}
+			// collect version specific properties, so that we can merge version-specific properties
+			// into the module's overall properties
 			versionProps := []VersionProperties{}
 			// PY3 is first so that we alias the PY3 variant rather than PY2 if both
 			// are available
-			if !(base.properties.Version.Py3.Enabled != nil &&
-				*(base.properties.Version.Py3.Enabled) == false) {
+			if proptools.BoolDefault(base.properties.Version.Py3.Enabled, true) {
 				versionNames = append(versionNames, pyVersion3)
 				versionProps = append(versionProps, base.properties.Version.Py3)
 			}
-			if base.properties.Version.Py2.Enabled != nil &&
-				*(base.properties.Version.Py2.Enabled) == true {
+			if proptools.BoolDefault(base.properties.Version.Py2.Enabled, false) {
 				versionNames = append(versionNames, pyVersion2)
 				versionProps = append(versionProps, base.properties.Version.Py2)
 			}
 			modules := mctx.CreateLocalVariations(versionNames...)
+			// Alias module to the first variant
 			if len(versionNames) > 0 {
 				mctx.AliasVariation(versionNames[0])
 			}
 			for i, v := range versionNames {
 				// set the actual version for Python module.
 				modules[i].(*Module).properties.Actual_version = v
-				// append versioned properties for the Python module
+				// append versioned properties for the Python module to the overall properties
 				err := proptools.AppendMatchingProperties([]interface{}{&modules[i].(*Module).properties}, &versionProps[i], nil)
 				if err != nil {
 					panic(err)
@@ -275,14 +302,19 @@
 	}
 }
 
+// HostToolPath returns a path if appropriate such that this module can be used as a host tool,
+// fulfilling HostToolProvider interface.
 func (p *Module) HostToolPath() android.OptionalPath {
 	if p.installer == nil {
 		// python_library is just meta module, and doesn't have any installer.
 		return android.OptionalPath{}
 	}
+	// TODO: This should only be set when building host binaries -- tests built for device would be
+	// setting this incorrectly.
 	return android.OptionalPathForPath(p.installer.(*binaryDecorator).path)
 }
 
+// OutputFiles returns output files based on given tag, returns an error if tag is unsupported.
 func (p *Module) OutputFiles(tag string) (android.Paths, error) {
 	switch tag {
 	case "":
@@ -296,12 +328,12 @@
 }
 
 func (p *Module) isEmbeddedLauncherEnabled() bool {
-	return Bool(p.properties.Embedded_launcher)
+	return p.installer != nil && Bool(p.properties.Embedded_launcher)
 }
 
-func hasSrcExt(srcs []string, ext string) bool {
-	for _, src := range srcs {
-		if filepath.Ext(src) == ext {
+func anyHasExt(paths []string, ext string) bool {
+	for _, p := range paths {
+		if filepath.Ext(p) == ext {
 			return true
 		}
 	}
@@ -309,10 +341,14 @@
 	return false
 }
 
-func (p *Module) hasSrcExt(ctx android.BottomUpMutatorContext, ext string) bool {
-	return hasSrcExt(p.properties.Srcs, ext)
+func (p *Module) anySrcHasExt(ctx android.BottomUpMutatorContext, ext string) bool {
+	return anyHasExt(p.properties.Srcs, ext)
 }
 
+// DepsMutator mutates dependencies for this module:
+//  * handles proto dependencies,
+//  * if required, specifies launcher and adds launcher dependencies,
+//  * applies python version mutations to Python dependencies
 func (p *Module) DepsMutator(ctx android.BottomUpMutatorContext) {
 	android.ProtoDeps(ctx, &p.protoProperties)
 
@@ -320,66 +356,61 @@
 		{"python_version", p.properties.Actual_version},
 	}
 
-	if p.hasSrcExt(ctx, protoExt) && p.Name() != "libprotobuf-python" {
+	// If sources contain a proto file, add dependency on libprotobuf-python
+	if p.anySrcHasExt(ctx, protoExt) && p.Name() != "libprotobuf-python" {
 		ctx.AddVariationDependencies(versionVariation, pythonLibTag, "libprotobuf-python")
 	}
+
+	// Add python library dependencies for this python version variation
 	ctx.AddVariationDependencies(versionVariation, pythonLibTag, android.LastUniqueStrings(p.properties.Libs)...)
 
-	switch p.properties.Actual_version {
-	case pyVersion2:
+	// If this module will be installed and has an embedded launcher, we need to add dependencies for:
+	//   * standard library
+	//   * launcher
+	//   * shared dependencies of the launcher
+	if p.installer != nil && p.isEmbeddedLauncherEnabled() {
+		var stdLib string
+		var launcherModule string
+		// Add launcher shared lib dependencies. Ideally, these should be
+		// derived from the `shared_libs` property of the launcher. However, we
+		// cannot read the property at this stage and it will be too late to add
+		// dependencies later.
+		launcherSharedLibDeps := []string{
+			"libsqlite",
+		}
+		// Add launcher-specific dependencies for bionic
+		if ctx.Target().Os.Bionic() {
+			launcherSharedLibDeps = append(launcherSharedLibDeps, "libc", "libdl", "libm")
+		}
 
-		if p.bootstrapper != nil && p.isEmbeddedLauncherEnabled() {
-			ctx.AddVariationDependencies(versionVariation, pythonLibTag, "py2-stdlib")
+		switch p.properties.Actual_version {
+		case pyVersion2:
+			stdLib = "py2-stdlib"
 
-			launcherModule := "py2-launcher"
+			launcherModule = "py2-launcher"
 			if p.bootstrapper.autorun() {
 				launcherModule = "py2-launcher-autorun"
 			}
-			ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherTag, launcherModule)
+			launcherSharedLibDeps = append(launcherSharedLibDeps, "libc++")
 
-			// Add py2-launcher shared lib dependencies. Ideally, these should be
-			// derived from the `shared_libs` property of "py2-launcher". However, we
-			// cannot read the property at this stage and it will be too late to add
-			// dependencies later.
-			ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherSharedLibTag, "libsqlite")
-			ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherSharedLibTag, "libc++")
+		case pyVersion3:
+			stdLib = "py3-stdlib"
 
-			if ctx.Target().Os.Bionic() {
-				ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherSharedLibTag,
-					"libc", "libdl", "libm")
-			}
-		}
-
-	case pyVersion3:
-
-		if p.bootstrapper != nil && p.isEmbeddedLauncherEnabled() {
-			ctx.AddVariationDependencies(versionVariation, pythonLibTag, "py3-stdlib")
-
-			launcherModule := "py3-launcher"
+			launcherModule = "py3-launcher"
 			if p.bootstrapper.autorun() {
 				launcherModule = "py3-launcher-autorun"
 			}
-			ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherTag, launcherModule)
-
-			// Add py3-launcher shared lib dependencies. Ideally, these should be
-			// derived from the `shared_libs` property of "py3-launcher". However, we
-			// cannot read the property at this stage and it will be too late to add
-			// dependencies later.
-			ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherSharedLibTag, "libsqlite")
 
 			if ctx.Device() {
-				ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherSharedLibTag,
-					"liblog")
+				launcherSharedLibDeps = append(launcherSharedLibDeps, "liblog")
 			}
-
-			if ctx.Target().Os.Bionic() {
-				ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherSharedLibTag,
-					"libc", "libdl", "libm")
-			}
+		default:
+			panic(fmt.Errorf("unknown Python Actual_version: %q for module: %q.",
+				p.properties.Actual_version, ctx.ModuleName()))
 		}
-	default:
-		panic(fmt.Errorf("unknown Python Actual_version: %q for module: %q.",
-			p.properties.Actual_version, ctx.ModuleName()))
+		ctx.AddVariationDependencies(versionVariation, pythonLibTag, stdLib)
+		ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherTag, launcherModule)
+		ctx.AddFarVariationDependencies(ctx.Target().Variations(), launcherSharedLibTag, launcherSharedLibDeps...)
 	}
 
 	// Emulate the data property for java_data but with the arch variation overridden to "common"
@@ -389,19 +420,25 @@
 }
 
 func (p *Module) GenerateAndroidBuildActions(ctx android.ModuleContext) {
-	p.GeneratePythonBuildActions(ctx)
+	p.generatePythonBuildActions(ctx)
 
-	// Only Python binaries and test has non-empty bootstrapper.
+	// Only Python binary and test modules have non-empty bootstrapper.
 	if p.bootstrapper != nil {
-		p.walkTransitiveDeps(ctx)
-		embeddedLauncher := false
-		embeddedLauncher = p.isEmbeddedLauncherEnabled()
+		// if the module is being installed, we need to collect all transitive dependencies to embed in
+		// the final par
+		p.collectPathsFromTransitiveDeps(ctx)
+		// bootstrap the module, including resolving main file, getting launcher path, and
+		// registering actions to build the par file
+		// bootstrap returns the binary output path
 		p.installSource = p.bootstrapper.bootstrap(ctx, p.properties.Actual_version,
-			embeddedLauncher, p.srcsPathMappings, p.srcsZip, p.depsSrcsZips)
+			p.isEmbeddedLauncherEnabled(), p.srcsPathMappings, p.srcsZip, p.depsSrcsZips)
 	}
 
+	// Only Python binary and test modules have non-empty installer.
 	if p.installer != nil {
 		var sharedLibs []string
+		// if embedded launcher is enabled, we need to collect the shared library depenendencies of the
+		// launcher
 		ctx.VisitDirectDeps(func(dep android.Module) {
 			if ctx.OtherModuleDependencyTag(dep) == launcherSharedLibTag {
 				sharedLibs = append(sharedLibs, ctx.OtherModuleName(dep))
@@ -409,18 +446,16 @@
 		})
 		p.installer.setAndroidMkSharedLibs(sharedLibs)
 
+		// Install the par file from installSource
 		if p.installSource.Valid() {
 			p.installer.install(ctx, p.installSource.Path())
 		}
 	}
-
 }
 
-func (p *Module) GeneratePythonBuildActions(ctx android.ModuleContext) {
-	// expand python files from "srcs" property.
-	srcs := p.properties.Srcs
-	exclude_srcs := p.properties.Exclude_srcs
-	expandedSrcs := android.PathsForModuleSrcExcludes(ctx, srcs, exclude_srcs)
+// generatePythonBuildActions performs build actions common to all Python modules
+func (p *Module) generatePythonBuildActions(ctx android.ModuleContext) {
+	expandedSrcs := android.PathsForModuleSrcExcludes(ctx, p.properties.Srcs, p.properties.Exclude_srcs)
 	requiresSrcs := true
 	if p.bootstrapper != nil && !p.bootstrapper.autorun() {
 		requiresSrcs = false
@@ -437,9 +472,10 @@
 		expandedData = append(expandedData, android.OutputFilesForModule(ctx, javaData, "")...)
 	}
 
-	// sanitize pkg_path.
+	// Validate pkg_path property
 	pkgPath := String(p.properties.Pkg_path)
 	if pkgPath != "" {
+		// TODO: export validation from android/paths.go handling to replace this duplicated functionality
 		pkgPath = filepath.Clean(String(p.properties.Pkg_path))
 		if pkgPath == ".." || strings.HasPrefix(pkgPath, "../") ||
 			strings.HasPrefix(pkgPath, "/") {
@@ -448,22 +484,35 @@
 				String(p.properties.Pkg_path))
 			return
 		}
-		if p.properties.Is_internal != nil && *p.properties.Is_internal {
-			pkgPath = filepath.Join(internal, pkgPath)
-		}
-	} else {
-		if p.properties.Is_internal != nil && *p.properties.Is_internal {
-			pkgPath = internal
-		}
+	}
+	// If property Is_internal is set, prepend pkgPath with internalPath
+	if proptools.BoolDefault(p.properties.Is_internal, false) {
+		pkgPath = filepath.Join(internalPath, pkgPath)
 	}
 
+	// generate src:destination path mappings for this module
 	p.genModulePathMappings(ctx, pkgPath, expandedSrcs, expandedData)
 
+	// generate the zipfile of all source and data files
 	p.srcsZip = p.createSrcsZip(ctx, pkgPath)
 }
 
-// generate current module unique pathMappings: <dest: runfiles_path, src: source_path>
-// for python/data files.
+func isValidPythonPath(path string) error {
+	identifiers := strings.Split(strings.TrimSuffix(path, filepath.Ext(path)), "/")
+	for _, token := range identifiers {
+		if !pathComponentRegexp.MatchString(token) {
+			return fmt.Errorf("the path %q contains invalid subpath %q. "+
+				"Subpaths must be at least one character long. "+
+				"The first character must an underscore or letter. "+
+				"Following characters may be any of: letter, digit, underscore, hyphen.",
+				path, token)
+		}
+	}
+	return nil
+}
+
+// For this module, generate unique pathMappings: <dest: runfiles_path, src: source_path>
+// for python/data files expanded from properties.
 func (p *Module) genModulePathMappings(ctx android.ModuleContext, pkgPath string,
 	expandedSrcs, expandedData android.Paths) {
 	// fetch <runfiles_path, source_path> pairs from "src" and "data" properties to
@@ -477,17 +526,11 @@
 			continue
 		}
 		runfilesPath := filepath.Join(pkgPath, s.Rel())
-		identifiers := strings.Split(strings.TrimSuffix(runfilesPath,
-			filepath.Ext(runfilesPath)), "/")
-		for _, token := range identifiers {
-			if !pyIdentifierRegexp.MatchString(token) {
-				ctx.PropertyErrorf("srcs", "the path %q contains invalid token %q.",
-					runfilesPath, token)
-			}
+		if err := isValidPythonPath(runfilesPath); err != nil {
+			ctx.PropertyErrorf("srcs", err.Error())
 		}
-		if fillInMap(ctx, destToPySrcs, runfilesPath, s.String(), p.Name(), p.Name()) {
-			p.srcsPathMappings = append(p.srcsPathMappings,
-				pathMapping{dest: runfilesPath, src: s})
+		if !checkForDuplicateOutputPath(ctx, destToPySrcs, runfilesPath, s.String(), p.Name(), p.Name()) {
+			p.srcsPathMappings = append(p.srcsPathMappings, pathMapping{dest: runfilesPath, src: s})
 		}
 	}
 
@@ -497,22 +540,23 @@
 			continue
 		}
 		runfilesPath := filepath.Join(pkgPath, d.Rel())
-		if fillInMap(ctx, destToPyData, runfilesPath, d.String(), p.Name(), p.Name()) {
+		if !checkForDuplicateOutputPath(ctx, destToPyData, runfilesPath, d.String(), p.Name(), p.Name()) {
 			p.dataPathMappings = append(p.dataPathMappings,
 				pathMapping{dest: runfilesPath, src: d})
 		}
 	}
 }
 
-// register build actions to zip current module's sources.
+// createSrcsZip registers build actions to zip current module's sources and data.
 func (p *Module) createSrcsZip(ctx android.ModuleContext, pkgPath string) android.Path {
 	relativeRootMap := make(map[string]android.Paths)
 	pathMappings := append(p.srcsPathMappings, p.dataPathMappings...)
 
 	var protoSrcs android.Paths
-	// "srcs" or "data" properties may have filegroup so it might happen that
-	// the relative root for each source path is different.
+	// "srcs" or "data" properties may contain filegroup so it might happen that
+	// the root directory for each source path is different.
 	for _, path := range pathMappings {
+		// handle proto sources separately
 		if path.src.Ext() == protoExt {
 			protoSrcs = append(protoSrcs, path.src)
 		} else {
@@ -537,24 +581,21 @@
 	}
 
 	if len(relativeRootMap) > 0 {
-		var keys []string
-
 		// in order to keep stable order of soong_zip params, we sort the keys here.
-		for k := range relativeRootMap {
-			keys = append(keys, k)
-		}
-		sort.Strings(keys)
+		roots := android.SortedStringKeys(relativeRootMap)
 
 		parArgs := []string{}
 		if pkgPath != "" {
+			// use package path as path prefix
 			parArgs = append(parArgs, `-P `+pkgPath)
 		}
-		implicits := android.Paths{}
-		for _, k := range keys {
-			parArgs = append(parArgs, `-C `+k)
-			for _, path := range relativeRootMap[k] {
+		paths := android.Paths{}
+		for _, root := range roots {
+			// specify relative root of file in following -f arguments
+			parArgs = append(parArgs, `-C `+root)
+			for _, path := range relativeRootMap[root] {
 				parArgs = append(parArgs, `-f `+path.String())
-				implicits = append(implicits, path)
+				paths = append(paths, path)
 			}
 		}
 
@@ -563,13 +604,15 @@
 			Rule:        zip,
 			Description: "python library archive",
 			Output:      origSrcsZip,
-			Implicits:   implicits,
+			// as zip rule does not use $in, there is no real need to distinguish between Inputs and Implicits
+			Implicits: paths,
 			Args: map[string]string{
 				"args": strings.Join(parArgs, " "),
 			},
 		})
 		zips = append(zips, origSrcsZip)
 	}
+	// we may have multiple zips due to separate handling of proto source files
 	if len(zips) == 1 {
 		return zips[0]
 	} else {
@@ -584,25 +627,27 @@
 	}
 }
 
+// isPythonLibModule returns whether the given module is a Python library Module or not
+// This is distinguished by the fact that Python libraries are not installable, while other Python
+// modules are.
 func isPythonLibModule(module blueprint.Module) bool {
 	if m, ok := module.(*Module); ok {
-		// Python library has no bootstrapper or installer.
-		if m.bootstrapper != nil || m.installer != nil {
-			return false
+		// Python library has no bootstrapper or installer
+		if m.bootstrapper == nil && m.installer == nil {
+			return true
 		}
-		return true
 	}
 	return false
 }
 
-// check Python source/data files duplicates for whole runfiles tree since Python binary/test
-// need collect and zip all srcs of whole transitive dependencies to a final par file.
-func (p *Module) walkTransitiveDeps(ctx android.ModuleContext) {
+// collectPathsFromTransitiveDeps checks for source/data files for duplicate paths
+// for module and its transitive dependencies and collects list of data/source file
+// zips for transitive dependencies.
+func (p *Module) collectPathsFromTransitiveDeps(ctx android.ModuleContext) {
 	// fetch <runfiles_path, source_path> pairs from "src" and "data" properties to
 	// check duplicates.
 	destToPySrcs := make(map[string]string)
 	destToPyData := make(map[string]string)
-
 	for _, path := range p.srcsPathMappings {
 		destToPySrcs[path.dest] = path.src.String()
 	}
@@ -614,6 +659,7 @@
 
 	// visit all its dependencies in depth first.
 	ctx.WalkDeps(func(child, parent android.Module) bool {
+		// we only collect dependencies tagged as python library deps
 		if ctx.OtherModuleDependencyTag(child) != pythonLibTag {
 			return false
 		}
@@ -623,44 +669,46 @@
 		seen[child] = true
 		// Python modules only can depend on Python libraries.
 		if !isPythonLibModule(child) {
-			panic(fmt.Errorf(
+			ctx.PropertyErrorf("libs",
 				"the dependency %q of module %q is not Python library!",
-				ctx.ModuleName(), ctx.OtherModuleName(child)))
+				ctx.ModuleName(), ctx.OtherModuleName(child))
 		}
-		if dep, ok := child.(PythonDependency); ok {
-			srcs := dep.GetSrcsPathMappings()
+		// collect source and data paths, checking that there are no duplicate output file conflicts
+		if dep, ok := child.(pythonDependency); ok {
+			srcs := dep.getSrcsPathMappings()
 			for _, path := range srcs {
-				if !fillInMap(ctx, destToPySrcs,
-					path.dest, path.src.String(), ctx.ModuleName(), ctx.OtherModuleName(child)) {
-					continue
-				}
-			}
-			data := dep.GetDataPathMappings()
-			for _, path := range data {
-				fillInMap(ctx, destToPyData,
+				checkForDuplicateOutputPath(ctx, destToPySrcs,
 					path.dest, path.src.String(), ctx.ModuleName(), ctx.OtherModuleName(child))
 			}
-			p.depsSrcsZips = append(p.depsSrcsZips, dep.GetSrcsZip())
+			data := dep.getDataPathMappings()
+			for _, path := range data {
+				checkForDuplicateOutputPath(ctx, destToPyData,
+					path.dest, path.src.String(), ctx.ModuleName(), ctx.OtherModuleName(child))
+			}
+			p.depsSrcsZips = append(p.depsSrcsZips, dep.getSrcsZip())
 		}
 		return true
 	})
 }
 
-func fillInMap(ctx android.ModuleContext, m map[string]string,
-	key, value, curModule, otherModule string) bool {
-	if oldValue, found := m[key]; found {
+// chckForDuplicateOutputPath checks whether outputPath has already been included in map m, which
+// would result in two files being placed in the same location.
+// If there is a duplicate path, an error is thrown and true is returned
+// Otherwise, outputPath: srcPath is added to m and returns false
+func checkForDuplicateOutputPath(ctx android.ModuleContext, m map[string]string, outputPath, srcPath, curModule, otherModule string) bool {
+	if oldSrcPath, found := m[outputPath]; found {
 		ctx.ModuleErrorf("found two files to be placed at the same location within zip %q."+
 			" First file: in module %s at path %q."+
 			" Second file: in module %s at path %q.",
-			key, curModule, oldValue, otherModule, value)
-		return false
-	} else {
-		m[key] = value
+			outputPath, curModule, oldSrcPath, otherModule, srcPath)
+		return true
 	}
+	m[outputPath] = srcPath
 
-	return true
+	return false
 }
 
+// InstallInData returns true as Python is not supported in the system partition
 func (p *Module) InstallInData() bool {
 	return true
 }
diff --git a/python/python_test.go b/python/python_test.go
index 64bc4f6..5c4efa7 100644
--- a/python/python_test.go
+++ b/python/python_test.go
@@ -44,7 +44,7 @@
 	pkgPathErrTemplate       = moduleVariantErrTemplate +
 		"pkg_path: %q must be a relative path contained in par file."
 	badIdentifierErrTemplate = moduleVariantErrTemplate +
-		"srcs: the path %q contains invalid token %q."
+		"srcs: the path %q contains invalid subpath %q."
 	dupRunfileErrTemplate = moduleVariantErrTemplate +
 		"found two files to be placed at the same location within zip %q." +
 		" First file: in module %s at path %q." +
@@ -370,7 +370,7 @@
 	} else {
 		sort.Strings(expErrs)
 		for i, v := range actErrStrs {
-			if v != expErrs[i] {
+			if !strings.Contains(v, expErrs[i]) {
 				testErrs = append(testErrs, errors.New(v))
 			}
 		}
diff --git a/python/test.go b/python/test.go
index 4df71c1..b7cd475 100644
--- a/python/test.go
+++ b/python/test.go
@@ -108,12 +108,12 @@
 func PythonTestHostFactory() android.Module {
 	module := NewTest(android.HostSupportedNoCross)
 
-	return module.Init()
+	return module.init()
 }
 
 func PythonTestFactory() android.Module {
 	module := NewTest(android.HostAndDeviceSupported)
 	module.multilib = android.MultilibBoth
 
-	return module.Init()
+	return module.init()
 }
diff --git a/rust/androidmk.go b/rust/androidmk.go
index 74cd9bf..c181d67 100644
--- a/rust/androidmk.go
+++ b/rust/androidmk.go
@@ -43,7 +43,7 @@
 }
 
 func (mod *Module) AndroidMkEntries() []android.AndroidMkEntries {
-	if mod.Properties.HideFromMake {
+	if mod.Properties.HideFromMake || mod.hideApexVariantFromMake {
 
 		return []android.AndroidMkEntries{android.AndroidMkEntries{Disabled: true}}
 	}
@@ -90,7 +90,7 @@
 	test.binaryDecorator.AndroidMk(ctx, ret)
 	ret.Class = "NATIVE_TESTS"
 	ret.ExtraEntries = append(ret.ExtraEntries, func(entries *android.AndroidMkEntries) {
-		entries.AddStrings("LOCAL_COMPATIBILITY_SUITE", test.Properties.Test_suites...)
+		entries.AddCompatibilityTestSuites(test.Properties.Test_suites...)
 		if test.testConfig != nil {
 			entries.SetString("LOCAL_FULL_TEST_CONFIG", test.testConfig.String())
 		}
diff --git a/rust/clippy_test.go b/rust/clippy_test.go
index 132b7b8..e24f666 100644
--- a/rust/clippy_test.go
+++ b/rust/clippy_test.go
@@ -18,6 +18,7 @@
 	"testing"
 
 	"android/soong/android"
+	"android/soong/cc"
 )
 
 func TestClippy(t *testing.T) {
@@ -45,6 +46,7 @@
 		}`
 
 	bp = bp + GatherRequiredDepsForTest()
+	bp = bp + cc.GatherRequiredDepsForTest(android.NoOsType)
 
 	fs := map[string][]byte{
 		// Reuse the same blueprint file for subdirectories.
diff --git a/rust/compiler_test.go b/rust/compiler_test.go
index a6dba9e..2b40727 100644
--- a/rust/compiler_test.go
+++ b/rust/compiler_test.go
@@ -19,6 +19,7 @@
 	"testing"
 
 	"android/soong/android"
+	"android/soong/cc"
 )
 
 // Test that feature flags are being correctly generated.
@@ -132,6 +133,7 @@
 		}`
 
 	bp = bp + GatherRequiredDepsForTest()
+	bp = bp + cc.GatherRequiredDepsForTest(android.NoOsType)
 
 	fs := map[string][]byte{
 		// Reuse the same blueprint file for subdirectories.
diff --git a/rust/config/allowed_list.go b/rust/config/allowed_list.go
index 3ad32fa..df31d60 100644
--- a/rust/config/allowed_list.go
+++ b/rust/config/allowed_list.go
@@ -6,12 +6,14 @@
 	// for an example.
 	// TODO(b/160223496): enable rustfmt globally.
 	RustAllowedPaths = []string{
+		"device/google/cuttlefish",
 		"external/adhd",
 		"external/crosvm",
 		"external/minijail",
 		"external/rust",
 		"external/vm_tools/p9",
 		"frameworks/native/libs/binder/rust",
+		"packages/modules/DnsResolver",
 		"packages/modules/Virtualization",
 		"prebuilts/rust",
 		"system/bt",
diff --git a/rust/config/global.go b/rust/config/global.go
index 6e268a0..22d9567 100644
--- a/rust/config/global.go
+++ b/rust/config/global.go
@@ -24,7 +24,7 @@
 var pctx = android.NewPackageContext("android/soong/rust/config")
 
 var (
-	RustDefaultVersion = "1.47.0"
+	RustDefaultVersion = "1.48.0"
 	RustDefaultBase    = "prebuilts/rust/"
 	DefaultEdition     = "2018"
 	Stdlibs            = []string{
diff --git a/rust/library.go b/rust/library.go
index ae33f0f..971588d 100644
--- a/rust/library.go
+++ b/rust/library.go
@@ -428,6 +428,7 @@
 	var srcPath android.Path
 
 	if library.sourceProvider != nil {
+		// Assume the first source from the source provider is the library entry point.
 		srcPath = library.sourceProvider.Srcs()[0]
 	} else {
 		srcPath, _ = srcPathFromModuleSrcs(ctx, library.baseCompiler.Properties.Srcs)
diff --git a/rust/project_json.go b/rust/project_json.go
index 8d9e50c..c4d60ad 100644
--- a/rust/project_json.go
+++ b/rust/project_json.go
@@ -75,12 +75,16 @@
 	android.RegisterSingletonType("rust_project_generator", rustProjectGeneratorSingleton)
 }
 
-// librarySource finds the main source file (.rs) for a crate.
-func librarySource(ctx android.SingletonContext, rModule *Module, rustLib *libraryDecorator) (string, bool) {
-	srcs := rustLib.baseCompiler.Properties.Srcs
+// crateSource finds the main source file (.rs) for a crate.
+func crateSource(ctx android.SingletonContext, rModule *Module, comp *baseCompiler) (string, bool) {
+	srcs := comp.Properties.Srcs
 	if len(srcs) != 0 {
 		return path.Join(ctx.ModuleDir(rModule), srcs[0]), true
 	}
+	rustLib, ok := rModule.compiler.(*libraryDecorator)
+	if !ok {
+		return "", false
+	}
 	if !rustLib.source() {
 		return "", false
 	}
@@ -132,8 +136,15 @@
 	if rModule.compiler == nil {
 		return 0, "", false
 	}
-	rustLib, ok := rModule.compiler.(*libraryDecorator)
-	if !ok {
+	var comp *baseCompiler
+	switch c := rModule.compiler.(type) {
+	case *libraryDecorator:
+		comp = c.baseCompiler
+	case *binaryDecorator:
+		comp = c.baseCompiler
+	case *testDecorator:
+		comp = c.binaryDecorator.baseCompiler
+	default:
 		return 0, "", false
 	}
 	moduleName := ctx.ModuleName(module)
@@ -146,12 +157,12 @@
 		return cInfo.ID, crateName, true
 	}
 	crate := rustProjectCrate{Deps: make([]rustProjectDep, 0), Cfgs: make([]string, 0)}
-	rootModule, ok := librarySource(ctx, rModule, rustLib)
+	rootModule, ok := crateSource(ctx, rModule, comp)
 	if !ok {
 		return 0, "", false
 	}
 	crate.RootModule = rootModule
-	crate.Edition = rustLib.baseCompiler.edition()
+	crate.Edition = comp.edition()
 
 	deps := make(map[string]int)
 	singleton.mergeDependencies(ctx, module, &crate, deps)
diff --git a/rust/project_json_test.go b/rust/project_json_test.go
index 16699c1..aff1697 100644
--- a/rust/project_json_test.go
+++ b/rust/project_json_test.go
@@ -67,6 +67,37 @@
 	return crates
 }
 
+// validateCrate ensures that a crate can be parsed as a map.
+func validateCrate(t *testing.T, crate interface{}) map[string]interface{} {
+	c, ok := crate.(map[string]interface{})
+	if !ok {
+		t.Fatalf("Unexpected type for crate: %v", c)
+	}
+	return c
+}
+
+// validateDependencies parses the dependencies for a crate. It returns a list
+// of the dependencies name.
+func validateDependencies(t *testing.T, crate map[string]interface{}) []string {
+	var dependencies []string
+	deps, ok := crate["deps"].([]interface{})
+	if !ok {
+		t.Errorf("Unexpected format for deps: %v", crate["deps"])
+	}
+	for _, dep := range deps {
+		d, ok := dep.(map[string]interface{})
+		if !ok {
+			t.Errorf("Unexpected format for dependency: %v", dep)
+		}
+		name, ok := d["name"].(string)
+		if !ok {
+			t.Errorf("Dependency is missing the name key: %v", d)
+		}
+		dependencies = append(dependencies, name)
+	}
+	return dependencies
+}
+
 func TestProjectJsonDep(t *testing.T) {
 	bp := `
 	rust_library {
@@ -85,6 +116,29 @@
 	validateJsonCrates(t, jsonContent)
 }
 
+func TestProjectJsonBinary(t *testing.T) {
+	bp := `
+	rust_binary {
+		name: "liba",
+		srcs: ["a/src/lib.rs"],
+		crate_name: "a"
+	}
+	`
+	jsonContent := testProjectJson(t, bp)
+	crates := validateJsonCrates(t, jsonContent)
+	for _, c := range crates {
+		crate := validateCrate(t, c)
+		rootModule, ok := crate["root_module"].(string)
+		if !ok {
+			t.Fatalf("Unexpected type for root_module: %v", crate["root_module"])
+		}
+		if rootModule == "a/src/lib.rs" {
+			return
+		}
+	}
+	t.Errorf("Entry for binary %q not found: %s", "a", jsonContent)
+}
+
 func TestProjectJsonBindGen(t *testing.T) {
 	bp := `
 	rust_library {
@@ -116,10 +170,7 @@
 	jsonContent := testProjectJson(t, bp)
 	crates := validateJsonCrates(t, jsonContent)
 	for _, c := range crates {
-		crate, ok := c.(map[string]interface{})
-		if !ok {
-			t.Fatalf("Unexpected type for crate: %v", c)
-		}
+		crate := validateCrate(t, c)
 		rootModule, ok := crate["root_module"].(string)
 		if !ok {
 			t.Fatalf("Unexpected type for root_module: %v", crate["root_module"])
@@ -133,16 +184,8 @@
 		}
 		// Check that libbindings1 does not depend on itself.
 		if strings.Contains(rootModule, "libbindings1") {
-			deps, ok := crate["deps"].([]interface{})
-			if !ok {
-				t.Errorf("Unexpected format for deps: %v", crate["deps"])
-			}
-			for _, dep := range deps {
-				d, ok := dep.(map[string]interface{})
-				if !ok {
-					t.Errorf("Unexpected format for dep: %v", dep)
-				}
-				if d["name"] == "bindings1" {
+			for _, depName := range validateDependencies(t, crate) {
+				if depName == "bindings1" {
 					t.Errorf("libbindings1 depends on itself")
 				}
 			}
@@ -171,20 +214,18 @@
 	`
 	jsonContent := testProjectJson(t, bp)
 	crates := validateJsonCrates(t, jsonContent)
-	for _, crate := range crates {
-		c := crate.(map[string]interface{})
-		if c["root_module"] == "b/src/lib.rs" {
-			deps, ok := c["deps"].([]interface{})
-			if !ok {
-				t.Errorf("Unexpected format for deps: %v", c["deps"])
-			}
+	for _, c := range crates {
+		crate := validateCrate(t, c)
+		rootModule, ok := crate["root_module"].(string)
+		if !ok {
+			t.Fatalf("Unexpected type for root_module: %v", crate["root_module"])
+		}
+		// Make sure that b has 2 different dependencies.
+		if rootModule == "b/src/lib.rs" {
 			aCount := 0
-			for _, dep := range deps {
-				d, ok := dep.(map[string]interface{})
-				if !ok {
-					t.Errorf("Unexpected format for dep: %v", dep)
-				}
-				if d["name"] == "a" {
+			deps := validateDependencies(t, crate)
+			for _, depName := range deps {
+				if depName == "a" {
 					aCount++
 				}
 			}
diff --git a/rust/protobuf.go b/rust/protobuf.go
index 7d6e1fd..0e79089 100644
--- a/rust/protobuf.go
+++ b/rust/protobuf.go
@@ -46,8 +46,8 @@
 var _ SourceProvider = (*protobufDecorator)(nil)
 
 type ProtobufProperties struct {
-	// Path to the proto file that will be used to generate the source
-	Proto *string `android:"path,arch_variant"`
+	// List of realtive paths to proto files that will be used to generate the source
+	Protos []string `android:"path,arch_variant"`
 
 	// List of additional flags to pass to aprotoc
 	Proto_flags []string `android:"arch_variant"`
@@ -66,6 +66,7 @@
 func (proto *protobufDecorator) GenerateSource(ctx ModuleContext, deps PathDeps) android.Path {
 	var protoFlags android.ProtoFlags
 	var pluginPaths android.Paths
+	var protoNames []string
 
 	protoFlags.OutTypeFlag = "--rust_out"
 	outDir := android.PathForModuleOut(ctx)
@@ -77,10 +78,7 @@
 
 	protoFlags.Deps = append(protoFlags.Deps, pluginPaths...)
 
-	protoFile := android.OptionalPathForModuleSrc(ctx, proto.Properties.Proto)
-	if !protoFile.Valid() {
-		ctx.PropertyErrorf("proto", "invalid path to proto file")
-	}
+	protoFiles := android.PathsForModuleSrc(ctx, proto.Properties.Protos)
 
 	// Add exported dependency include paths
 	for _, include := range deps.depIncludePaths {
@@ -88,35 +86,58 @@
 	}
 
 	stem := proto.BaseSourceProvider.getStem(ctx)
-	// rust protobuf-codegen output <stem>.rs
-	stemFile := android.PathForModuleOut(ctx, stem+".rs")
-	// add mod_<stem>.rs to import <stem>.rs
-	modFile := android.PathForModuleOut(ctx, "mod_"+stem+".rs")
-	// mod_<stem>.rs is the main/first output file to be included/compiled
-	outputs := android.WritablePaths{modFile, stemFile}
-	if proto.plugin == Grpc {
-		outputs = append(outputs, android.PathForModuleOut(ctx, stem+grpcSuffix+".rs"))
+
+	// The mod_stem.rs file is used to avoid collisions if this is not included as a crate.
+	stemFile := android.PathForModuleOut(ctx, "mod_"+stem+".rs")
+
+	// stemFile must be first here as the first path in BaseSourceProvider.OutputFiles is the library entry-point.
+	outputs := android.WritablePaths{stemFile}
+
+	rule := android.NewRuleBuilder(pctx, ctx)
+	for _, protoFile := range protoFiles {
+		protoName := strings.TrimSuffix(protoFile.Base(), ".proto")
+		protoNames = append(protoNames, protoName)
+
+		protoOut := android.PathForModuleOut(ctx, protoName+".rs")
+		ruleOutputs := android.WritablePaths{android.WritablePath(protoOut)}
+
+		if proto.plugin == Grpc {
+			grpcOut := android.PathForModuleOut(ctx, protoName+grpcSuffix+".rs")
+			ruleOutputs = append(ruleOutputs, android.WritablePath(grpcOut))
+		}
+
+		depFile := android.PathForModuleOut(ctx, protoName+".d")
+
+		android.ProtoRule(rule, protoFile, protoFlags, protoFlags.Deps, outDir, depFile, ruleOutputs)
+		outputs = append(outputs, ruleOutputs...)
 	}
-	depFile := android.PathForModuleOut(ctx, "mod_"+stem+".d")
 
-	rule := android.NewRuleBuilder()
-	android.ProtoRule(ctx, rule, protoFile.Path(), protoFlags, protoFlags.Deps, outDir, depFile, outputs)
-	rule.Command().Text("printf '" + proto.getModFileContents(ctx) + "' >").Output(modFile)
-	rule.Build(pctx, ctx, "protoc_"+protoFile.Path().Rel(), "protoc "+protoFile.Path().Rel())
+	rule.Command().
+		Implicits(outputs.Paths()).
+		Text("printf '" + proto.genModFileContents(ctx, protoNames) + "' >").
+		Output(stemFile)
 
-	proto.BaseSourceProvider.OutputFiles = android.Paths{modFile, stemFile}
-	return modFile
+	rule.Build("protoc_"+ctx.ModuleName(), "protoc "+ctx.ModuleName())
+
+	proto.BaseSourceProvider.OutputFiles = outputs.Paths()
+
+	// mod_stem.rs is the entry-point for our library modules, so this is what we return.
+	return stemFile
 }
 
-func (proto *protobufDecorator) getModFileContents(ctx ModuleContext) string {
-	stem := proto.BaseSourceProvider.getStem(ctx)
+func (proto *protobufDecorator) genModFileContents(ctx ModuleContext, protoNames []string) string {
 	lines := []string{
-		"// @generated",
-		fmt.Sprintf("pub mod %s;", stem),
+		"// @Soong generated Source",
+	}
+	for _, protoName := range protoNames {
+		lines = append(lines, fmt.Sprintf("pub mod %s;", protoName))
+
+		if proto.plugin == Grpc {
+			lines = append(lines, fmt.Sprintf("pub mod %s%s;", protoName, grpcSuffix))
+		}
 	}
 
 	if proto.plugin == Grpc {
-		lines = append(lines, fmt.Sprintf("pub mod %s%s;", stem, grpcSuffix))
 		lines = append(
 			lines,
 			"pub mod empty {",
diff --git a/rust/protobuf_test.go b/rust/protobuf_test.go
index 845911f..608a4e8 100644
--- a/rust/protobuf_test.go
+++ b/rust/protobuf_test.go
@@ -25,7 +25,7 @@
 	ctx := testRust(t, `
 		rust_protobuf {
 			name: "librust_proto",
-			proto: "buf.proto",
+			protos: ["buf.proto", "proto.proto"],
 			crate_name: "rust_proto",
 			source_stem: "buf",
 			shared_libs: ["libfoo_shared"],
@@ -60,13 +60,20 @@
 	if w := "-Istatic_include"; !strings.Contains(cmd, w) {
 		t.Errorf("expected %q in %q", w, cmd)
 	}
+
+	// Check proto.rs, the second protobuf, is listed as an output
+	librust_proto_outputs := ctx.ModuleForTests("librust_proto", "android_arm64_armv8-a_source").AllOutputs()
+	if android.InList("proto.rs", librust_proto_outputs) {
+		t.Errorf("rust_protobuf is not producing multiple outputs; expected 'proto.rs' in list, got: %#v ",
+			librust_proto_outputs)
+	}
 }
 
 func TestRustGrpcio(t *testing.T) {
 	ctx := testRust(t, `
 		rust_grpcio {
 			name: "librust_grpcio",
-			proto: "buf.proto",
+			protos: ["buf.proto", "proto.proto"],
 			crate_name: "rust_grpcio",
 			source_stem: "buf",
 			shared_libs: ["libfoo_shared"],
@@ -117,4 +124,11 @@
 	if w := "-Ilibprotobuf-cpp-full-includes"; !strings.Contains(cmd, w) {
 		t.Errorf("expected %q in %q", w, cmd)
 	}
+
+	// Check proto.rs, the second protobuf, is listed as an output
+	librust_grpcio_outputs := ctx.ModuleForTests("librust_grpcio", "android_arm64_armv8-a_source").AllOutputs()
+	if android.InList("proto_grpc.rs", librust_grpcio_outputs) {
+		t.Errorf("rust_protobuf is not producing multiple outputs; expected 'proto_grpc.rs' in list, got: %#v ",
+			librust_grpcio_outputs)
+	}
 }
diff --git a/rust/rust.go b/rust/rust.go
index 5b94045..38caad3 100644
--- a/rust/rust.go
+++ b/rust/rust.go
@@ -74,6 +74,7 @@
 type Module struct {
 	android.ModuleBase
 	android.DefaultableModuleBase
+	android.ApexModuleBase
 
 	Properties BaseProperties
 
@@ -88,6 +89,8 @@
 	subAndroidMkOnce map[SubAndroidMkProvider]bool
 
 	outputFile android.OptionalPath
+
+	hideApexVariantFromMake bool
 }
 
 func (mod *Module) OutputFiles(tag string) (android.Paths, error) {
@@ -508,6 +511,7 @@
 	}
 
 	android.InitAndroidArchModule(mod, mod.hod, mod.multilib)
+	android.InitApexModule(mod)
 
 	android.InitDefaultableModule(mod)
 	return mod
@@ -605,6 +609,11 @@
 		ModuleContext: actx,
 	}
 
+	apexInfo := actx.Provider(android.ApexInfoProvider).(android.ApexInfo)
+	if !apexInfo.IsForPlatform() {
+		mod.hideApexVariantFromMake = true
+	}
+
 	toolchain := mod.toolchain(ctx)
 
 	if !toolchain.Supported() {
@@ -685,6 +694,14 @@
 	proc_macro bool
 }
 
+// InstallDepNeeded returns true for rlibs, dylibs, and proc macros so that they or their transitive
+// dependencies (especially C/C++ shared libs) are installed as dependencies of a rust binary.
+func (d dependencyTag) InstallDepNeeded() bool {
+	return d.library || d.proc_macro
+}
+
+var _ android.InstallNeededDependencyTag = dependencyTag{}
+
 var (
 	customBindgenDepTag = dependencyTag{name: "customBindgenTag"}
 	rlibDepTag          = dependencyTag{name: "rlibTag", library: true}
@@ -694,6 +711,11 @@
 	sourceDepTag        = dependencyTag{name: "source"}
 )
 
+func IsDylibDepTag(depTag blueprint.DependencyTag) bool {
+	tag, ok := depTag.(dependencyTag)
+	return ok && tag == dylibDepTag
+}
+
 type autoDep struct {
 	variation string
 	depTag    dependencyTag
@@ -1052,6 +1074,58 @@
 	return android.OptionalPath{}
 }
 
+var _ android.ApexModule = (*Module)(nil)
+
+func (mod *Module) ShouldSupportSdkVersion(ctx android.BaseModuleContext, sdkVersion android.ApiLevel) error {
+	return nil
+}
+
+func (mod *Module) DepIsInSameApex(ctx android.BaseModuleContext, dep android.Module) bool {
+	depTag := ctx.OtherModuleDependencyTag(dep)
+
+	if ccm, ok := dep.(*cc.Module); ok {
+		if ccm.HasStubsVariants() {
+			if cc.IsSharedDepTag(depTag) {
+				// dynamic dep to a stubs lib crosses APEX boundary
+				return false
+			}
+			if cc.IsRuntimeDepTag(depTag) {
+				// runtime dep to a stubs lib also crosses APEX boundary
+				return false
+			}
+
+			if cc.IsHeaderDepTag(depTag) {
+				return false
+			}
+		}
+		if mod.Static() && cc.IsSharedDepTag(depTag) {
+			// shared_lib dependency from a static lib is considered as crossing
+			// the APEX boundary because the dependency doesn't actually is
+			// linked; the dependency is used only during the compilation phase.
+			return false
+		}
+	}
+
+	if depTag == procMacroDepTag {
+		return false
+	}
+
+	return true
+}
+
+// Overrides ApexModule.IsInstallabeToApex()
+func (mod *Module) IsInstallableToApex() bool {
+	if mod.compiler != nil {
+		if lib, ok := mod.compiler.(*libraryDecorator); ok && (lib.shared() || lib.dylib()) {
+			return true
+		}
+		if _, ok := mod.compiler.(*binaryDecorator); ok {
+			return true
+		}
+	}
+	return false
+}
+
 var Bool = proptools.Bool
 var BoolDefault = proptools.BoolDefault
 var String = proptools.String
diff --git a/rust/rust_test.go b/rust/rust_test.go
index 187f0b6..4edc6cd 100644
--- a/rust/rust_test.go
+++ b/rust/rust_test.go
@@ -106,13 +106,14 @@
 // useMockedFs setup a default mocked filesystem for the test environment.
 func (tctx *testRustCtx) useMockedFs() {
 	tctx.fs = map[string][]byte{
-		"foo.rs":     nil,
-		"foo.c":      nil,
-		"src/bar.rs": nil,
-		"src/any.h":  nil,
-		"buf.proto":  nil,
-		"liby.so":    nil,
-		"libz.so":    nil,
+		"foo.rs":      nil,
+		"foo.c":       nil,
+		"src/bar.rs":  nil,
+		"src/any.h":   nil,
+		"proto.proto": nil,
+		"buf.proto":   nil,
+		"liby.so":     nil,
+		"libz.so":     nil,
 	}
 }
 
@@ -120,6 +121,7 @@
 // attributes of the testRustCtx.
 func (tctx *testRustCtx) generateConfig() {
 	tctx.bp = tctx.bp + GatherRequiredDepsForTest()
+	tctx.bp = tctx.bp + cc.GatherRequiredDepsForTest(android.NoOsType)
 	cc.GatherRequiredFilesForTest(tctx.fs)
 	config := android.TestArchConfig(buildDir, tctx.env, tctx.bp, tctx.fs)
 	tctx.config = &config
diff --git a/rust/source_provider.go b/rust/source_provider.go
index 436518c..7719611 100644
--- a/rust/source_provider.go
+++ b/rust/source_provider.go
@@ -30,6 +30,7 @@
 type BaseSourceProvider struct {
 	Properties SourceProviderProperties
 
+	// The first file in OutputFiles must be the library entry point.
 	OutputFiles      android.Paths
 	subAndroidMkOnce map[SubAndroidMkProvider]bool
 	subName          string
diff --git a/rust/testing.go b/rust/testing.go
index 001f322..a8496d9 100644
--- a/rust/testing.go
+++ b/rust/testing.go
@@ -77,6 +77,7 @@
 			no_libcrt: true,
 			nocrt: true,
 			system_shared_libs: [],
+			apex_available: ["//apex_available:platform", "//apex_available:anyapex"],
 		}
 		cc_library {
 			name: "libprotobuf-cpp-full",
@@ -93,6 +94,7 @@
 			host_supported: true,
                         native_coverage: false,
 			sysroot: true,
+			apex_available: ["//apex_available:platform", "//apex_available:anyapex"],
 		}
 		rust_library {
 			name: "libtest",
@@ -102,6 +104,7 @@
 			host_supported: true,
                         native_coverage: false,
 			sysroot: true,
+			apex_available: ["//apex_available:platform", "//apex_available:anyapex"],
 		}
 		rust_library {
 			name: "libprotobuf",
@@ -122,15 +125,11 @@
 			host_supported: true,
 		}
 
-` + cc.GatherRequiredDepsForTest(android.NoOsType)
+`
 	return bp
 }
 
-func CreateTestContext(config android.Config) *android.TestContext {
-	ctx := android.NewTestArchContext(config)
-	android.RegisterPrebuiltMutators(ctx)
-	ctx.PreArchMutators(android.RegisterDefaultsPreArchMutators)
-	cc.RegisterRequiredBuildComponentsForTest(ctx)
+func RegisterRequiredBuildComponentsForTest(ctx android.RegistrationContext) {
 	ctx.RegisterModuleType("rust_binary", RustBinaryFactory)
 	ctx.RegisterModuleType("rust_binary_host", RustBinaryHostFactory)
 	ctx.RegisterModuleType("rust_bindgen", RustBindgenFactory)
@@ -164,6 +163,14 @@
 		ctx.BottomUp("rust_begin", BeginMutator).Parallel()
 	})
 	ctx.RegisterSingletonType("rust_project_generator", rustProjectGeneratorSingleton)
+}
+
+func CreateTestContext(config android.Config) *android.TestContext {
+	ctx := android.NewTestArchContext(config)
+	android.RegisterPrebuiltMutators(ctx)
+	ctx.PreArchMutators(android.RegisterDefaultsPreArchMutators)
+	cc.RegisterRequiredBuildComponentsForTest(ctx)
+	RegisterRequiredBuildComponentsForTest(ctx)
 
 	return ctx
 }
diff --git a/scripts/conv_linker_config.py b/scripts/conv_linker_config.py
index 81425fb..22fe9f6 100644
--- a/scripts/conv_linker_config.py
+++ b/scripts/conv_linker_config.py
@@ -18,8 +18,10 @@
 import argparse
 import collections
 import json
+import os
 
 import linker_config_pb2
+from google.protobuf.descriptor import FieldDescriptor
 from google.protobuf.json_format import ParseDict
 from google.protobuf.text_format import MessageToString
 
@@ -43,6 +45,40 @@
   print(MessageToString(pb))
 
 
+def SystemProvide(args):
+  pb = linker_config_pb2.LinkerConfig()
+  with open(args.source, 'rb') as f:
+    pb.ParseFromString(f.read())
+  libraries = args.value.split()
+
+  def IsInLibPath(lib_name):
+    lib_path = os.path.join(args.system, 'lib', lib_name)
+    lib64_path = os.path.join(args.system, 'lib64', lib_name)
+    return os.path.exists(lib_path) or os.path.islink(lib_path) or os.path.exists(lib64_path) or os.path.islink(lib64_path)
+
+  installed_libraries = list(filter(IsInLibPath, libraries))
+  for item in installed_libraries:
+    if item not in getattr(pb, 'provideLibs'):
+      getattr(pb, 'provideLibs').append(item)
+  with open(args.output, 'wb') as f:
+    f.write(pb.SerializeToString())
+
+
+def Append(args):
+  pb = linker_config_pb2.LinkerConfig()
+  with open(args.source, 'rb') as f:
+    pb.ParseFromString(f.read())
+
+  if getattr(type(pb), args.key).DESCRIPTOR.label == FieldDescriptor.LABEL_REPEATED:
+    for value in args.value.split():
+      getattr(pb, args.key).append(value)
+  else:
+    setattr(pb, args.key, args.value)
+
+  with open(args.output, 'wb') as f:
+    f.write(pb.SerializeToString())
+
+
 def GetArgParser():
   parser = argparse.ArgumentParser()
   subparsers = parser.add_subparsers()
@@ -73,6 +109,58 @@
       help='Source linker configuration file in protobuf.')
   print_proto.set_defaults(func=Print)
 
+  system_provide_libs = subparsers.add_parser(
+      'systemprovide', help='Append system provide libraries into the configuration.')
+  system_provide_libs.add_argument(
+      '-s',
+      '--source',
+      required=True,
+      type=str,
+      help='Source linker configuration file in protobuf.')
+  system_provide_libs.add_argument(
+      '-o',
+      '--output',
+      required=True,
+      type=str,
+      help='Target linker configuration file to write in protobuf.')
+  system_provide_libs.add_argument(
+      '--value',
+      required=True,
+      type=str,
+      help='Values of the libraries to append. If there are more than one it should be separated by empty space')
+  system_provide_libs.add_argument(
+      '--system',
+      required=True,
+      type=str,
+      help='Path of the system image.')
+  system_provide_libs.set_defaults(func=SystemProvide)
+
+  append = subparsers.add_parser(
+      'append', help='Append value(s) to given key.')
+  append.add_argument(
+      '-s',
+      '--source',
+      required=True,
+      type=str,
+      help='Source linker configuration file in protobuf.')
+  append.add_argument(
+      '-o',
+      '--output',
+      required=True,
+      type=str,
+      help='Target linker configuration file to write in protobuf.')
+  append.add_argument(
+      '--key',
+      required=True,
+      type=str,
+      help='.')
+  append.add_argument(
+      '--value',
+      required=True,
+      type=str,
+      help='Values of the libraries to append. If there are more than one it should be separated by empty space')
+  append.set_defaults(func=Append)
+
   return parser
 
 
diff --git a/scripts/gen_ndk_usedby_apex.sh b/scripts/gen_ndk_usedby_apex.sh
new file mode 100755
index 0000000..f143161
--- /dev/null
+++ b/scripts/gen_ndk_usedby_apex.sh
@@ -0,0 +1,72 @@
+#!/bin/bash -e
+
+# Copyright 2020 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Generates NDK API txt file used by Mainline modules. NDK APIs would have value
+# "UND" in Ndx column and have suffix "@LIB_NAME" in Name column.
+# For example, current line llvm-readelf output is:
+# 1: 00000000     0     FUNC      GLOBAL  DEFAULT   UND   dlopen@LIBC
+# After the parse function below "dlopen" would be write to the output file.
+printHelp() {
+    echo "**************************** Usage Instructions ****************************"
+    echo "This script is used to generate the Mainline modules used-by NDK symbols."
+    echo ""
+    echo "To run this script use: ./ndk_usedby_module.sh \$BINARY_IMAGE_DIRECTORY \$BINARY_LLVM_PATH \$OUTPUT_FILE_PATH"
+    echo "For example: If all the module image files that you would like to run is under directory '/myModule' and output write to /myModule.txt then the command would be:"
+    echo "./ndk_usedby_module.sh /myModule \$BINARY_LLVM_PATH /myModule.txt"
+}
+
+parseReadelfOutput() {
+  while IFS= read -r line
+  do
+      if [[ $line = *FUNC*GLOBAL*UND*@* ]] ;
+      then
+          echo "$line" | sed -r 's/.*UND (.*)@.*/\1/g' >> "$2"
+      fi
+  done < "$1"
+  echo "" >> "$2"
+}
+
+unzipJarAndApk() {
+  tmpUnzippedDir="$1"/tmpUnzipped
+  [[ -e "$tmpUnzippedDir" ]] && rm -rf "$tmpUnzippedDir"
+  mkdir -p "$tmpUnzippedDir"
+  find "$1" -name "*.jar" -exec unzip -o {} -d "$tmpUnzippedDir" \;
+  find "$1" -name "*.apk" -exec unzip -o {} -d "$tmpUnzippedDir" \;
+  find "$tmpUnzippedDir" -name "*.MF" -exec rm {} \;
+}
+
+lookForExecFile() {
+  dir="$1"
+  readelf="$2"
+  find "$dir" -type f -name "*.so"  -exec "$2" --dyn-symbols {} >> "$dir"/../tmpReadelf.txt \;
+  find "$dir" -type f -perm /111 ! -name "*.so"  -exec "$2" --dyn-symbols {} >> "$dir"/../tmpReadelf.txt \;
+}
+
+if [[ "$1" == "help" ]]
+then
+  printHelp
+elif [[ "$#" -ne 3 ]]
+then
+  echo "Wrong argument length. Expecting 3 argument representing image file directory, llvm-readelf tool path, output path."
+else
+  unzipJarAndApk "$1"
+  lookForExecFile "$1" "$2"
+  tmpReadelfOutput="$1/../tmpReadelf.txt"
+  [[ -e "$3" ]] && rm "$3"
+  parseReadelfOutput "$tmpReadelfOutput" "$3"
+  [[ -e "$tmpReadelfOutput" ]] && rm "$tmpReadelfOutput"
+  rm -rf "$1/tmpUnzipped"
+fi
\ No newline at end of file
diff --git a/sdk/update.go b/sdk/update.go
index ba63542..377aaae 100644
--- a/sdk/update.go
+++ b/sdk/update.go
@@ -92,7 +92,7 @@
 }
 
 func (gf *generatedFile) build(pctx android.PackageContext, ctx android.BuilderContext, implicits android.Paths) {
-	rb := android.NewRuleBuilder()
+	rb := android.NewRuleBuilder(pctx, ctx)
 
 	content := gf.content.String()
 
@@ -108,7 +108,7 @@
 		Text("| sed 's/\\\\n/\\n/g' >").Output(gf.path)
 	rb.Command().
 		Text("chmod a+x").Output(gf.path)
-	rb.Build(pctx, ctx, gf.path.Base(), "Build "+gf.path.Base())
+	rb.Build(gf.path.Base(), "Build "+gf.path.Base())
 }
 
 // Collect all the members.
diff --git a/sh/sh_binary.go b/sh/sh_binary.go
index 7e5c344..f86e1fd 100644
--- a/sh/sh_binary.go
+++ b/sh/sh_binary.go
@@ -398,7 +398,7 @@
 			func(entries *android.AndroidMkEntries) {
 				s.customAndroidMkEntries(entries)
 				entries.SetPath("LOCAL_MODULE_PATH", s.installDir.ToMakePath())
-				entries.AddStrings("LOCAL_COMPATIBILITY_SUITE", s.testProperties.Test_suites...)
+				entries.AddCompatibilityTestSuites(s.testProperties.Test_suites...)
 				if s.testConfig != nil {
 					entries.SetPath("LOCAL_FULL_TEST_CONFIG", s.testConfig)
 				}
diff --git a/sysprop/sysprop_library.go b/sysprop/sysprop_library.go
index 828d1cf..6a53414 100644
--- a/sysprop/sysprop_library.go
+++ b/sysprop/sysprop_library.go
@@ -247,16 +247,16 @@
 	m.latestApiFile = android.PathForSource(ctx, ctx.ModuleDir(), "api", baseModuleName+"-latest.txt")
 
 	// dump API rule
-	rule := android.NewRuleBuilder()
+	rule := android.NewRuleBuilder(pctx, ctx)
 	m.dumpedApiFile = android.PathForModuleOut(ctx, "api-dump.txt")
 	rule.Command().
-		BuiltTool(ctx, "sysprop_api_dump").
+		BuiltTool("sysprop_api_dump").
 		Output(m.dumpedApiFile).
 		Inputs(android.PathsForModuleSrc(ctx, m.properties.Srcs))
-	rule.Build(pctx, ctx, baseModuleName+"_api_dump", baseModuleName+" api dump")
+	rule.Build(baseModuleName+"_api_dump", baseModuleName+" api dump")
 
 	// check API rule
-	rule = android.NewRuleBuilder()
+	rule = android.NewRuleBuilder(pctx, ctx)
 
 	// 1. compares current.txt to api-dump.txt
 	// current.txt should be identical to api-dump.txt.
@@ -284,7 +284,7 @@
 
 	rule.Command().
 		Text("( ").
-		BuiltTool(ctx, "sysprop_api_checker").
+		BuiltTool("sysprop_api_checker").
 		Input(m.latestApiFile).
 		Input(m.currentApiFile).
 		Text(" || ( echo").Flag("-e").
@@ -297,7 +297,7 @@
 		Text("touch").
 		Output(m.checkApiFileTimeStamp)
 
-	rule.Build(pctx, ctx, baseModuleName+"_check_api", baseModuleName+" check api")
+	rule.Build(baseModuleName+"_check_api", baseModuleName+" check api")
 }
 
 func (m *syspropLibrary) AndroidMk() android.AndroidMkData {
diff --git a/ui/build/bazel.go b/ui/build/bazel.go
index 2d36f67..910131a 100644
--- a/ui/build/bazel.go
+++ b/ui/build/bazel.go
@@ -15,6 +15,8 @@
 package build
 
 import (
+	"bytes"
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -24,6 +26,29 @@
 	"android/soong/ui/metrics"
 )
 
+func getBazelInfo(ctx Context, config Config, bazelExecutable string, bazelEnv map[string]string, query string) string {
+	infoCmd := Command(ctx, config, "bazel", bazelExecutable)
+
+	if extraStartupArgs, ok := infoCmd.Environment.Get("BAZEL_STARTUP_ARGS"); ok {
+		infoCmd.Args = append(infoCmd.Args, strings.Fields(extraStartupArgs)...)
+	}
+
+	// Obtain the output directory path in the execution root.
+	infoCmd.Args = append(infoCmd.Args,
+		"info",
+		query,
+	)
+
+	for k, v := range bazelEnv {
+		infoCmd.Environment.Set(k, v)
+	}
+
+	infoCmd.Dir = filepath.Join(config.OutDir(), "..")
+
+	queryResult := strings.TrimSpace(string(infoCmd.OutputOrFatal()))
+	return queryResult
+}
+
 // Main entry point to construct the Bazel build command line, environment
 // variables and post-processing steps (e.g. converge output directories)
 func runBazel(ctx Context, config Config) {
@@ -43,14 +68,18 @@
 
 	// Environment variables are the primary mechanism to pass information from
 	// soong_ui configuration or context to Bazel.
-	//
+	bazelEnv := make(map[string]string)
+
 	// Use *_NINJA variables to pass the root-relative path of the combined,
 	// kati-generated, soong-generated, and packaging Ninja files to Bazel.
 	// Bazel reads these from the lunch() repository rule.
-	config.environ.Set("COMBINED_NINJA", config.CombinedNinjaFile())
-	config.environ.Set("KATI_NINJA", config.KatiBuildNinjaFile())
-	config.environ.Set("PACKAGE_NINJA", config.KatiPackageNinjaFile())
-	config.environ.Set("SOONG_NINJA", config.SoongNinjaFile())
+	bazelEnv["COMBINED_NINJA"] = config.CombinedNinjaFile()
+	bazelEnv["KATI_NINJA"] = config.KatiBuildNinjaFile()
+	bazelEnv["PACKAGE_NINJA"] = config.KatiPackageNinjaFile()
+	bazelEnv["SOONG_NINJA"] = config.SoongNinjaFile()
+
+	bazelEnv["DIST_DIR"] = config.DistDir()
+	bazelEnv["SHELL"] = "/bin/bash"
 
 	// `tools/bazel` is the default entry point for executing Bazel in the AOSP
 	// source tree.
@@ -76,16 +105,36 @@
 		"--slim_profile=true",
 	)
 
-	// Append custom build flags to the Bazel command. Changes to these flags
-	// may invalidate Bazel's analysis cache.
-	if extraBuildArgs, ok := cmd.Environment.Get("BAZEL_BUILD_ARGS"); ok {
-		cmd.Args = append(cmd.Args, strings.Fields(extraBuildArgs)...)
-	}
+	if config.UseRBE() {
+		for _, envVar := range []string{
+			// RBE client
+			"RBE_compare",
+			"RBE_exec_strategy",
+			"RBE_invocation_id",
+			"RBE_log_dir",
+			"RBE_platform",
+			"RBE_remote_accept_cache",
+			"RBE_remote_update_cache",
+			"RBE_server_address",
+			// TODO: remove old FLAG_ variables.
+			"FLAG_compare",
+			"FLAG_exec_root",
+			"FLAG_exec_strategy",
+			"FLAG_invocation_id",
+			"FLAG_log_dir",
+			"FLAG_platform",
+			"FLAG_remote_accept_cache",
+			"FLAG_remote_update_cache",
+			"FLAG_server_address",
+		} {
+			cmd.Args = append(cmd.Args,
+				"--action_env="+envVar)
+		}
 
-	// Append the label of the default ninja_build target.
-	cmd.Args = append(cmd.Args,
-		"//:"+config.TargetProduct()+"-"+config.TargetBuildVariant(),
-	)
+		// We need to calculate --RBE_exec_root ourselves
+		ctx.Println("Getting Bazel execution_root...")
+		cmd.Args = append(cmd.Args, "--action_env=RBE_exec_root="+getBazelInfo(ctx, config, bazelExecutable, bazelEnv, "execution_root"))
+	}
 
 	// Ensure that the PATH environment variable value used in the action
 	// environment is the restricted set computed from soong_ui, and not a
@@ -95,15 +144,36 @@
 		cmd.Args = append(cmd.Args, "--action_env=PATH="+pathEnvValue)
 	}
 
-	cmd.Environment.Set("DIST_DIR", config.DistDir())
-	cmd.Environment.Set("SHELL", "/bin/bash")
+	// Append custom build flags to the Bazel command. Changes to these flags
+	// may invalidate Bazel's analysis cache.
+	// These should be appended as the final args, so that they take precedence.
+	if extraBuildArgs, ok := cmd.Environment.Get("BAZEL_BUILD_ARGS"); ok {
+		cmd.Args = append(cmd.Args, strings.Fields(extraBuildArgs)...)
+	}
+
+	// Append the label of the default ninja_build target.
+	cmd.Args = append(cmd.Args,
+		"//:"+config.TargetProduct()+"-"+config.TargetBuildVariant(),
+	)
 
 	// Print the full command line for debugging purposes.
 	ctx.Println(cmd.Cmd)
 
 	// Execute the command at the root of the directory.
 	cmd.Dir = filepath.Join(config.OutDir(), "..")
-	ctx.Status.Status("Starting Bazel..")
+
+	for k, v := range bazelEnv {
+		cmd.Environment.Set(k, v)
+	}
+
+	// Make a human-readable version of the bazelEnv map
+	bazelEnvStringBuffer := new(bytes.Buffer)
+	for k, v := range bazelEnv {
+		fmt.Fprintf(bazelEnvStringBuffer, "%s=%s ", k, v)
+	}
+
+	// Print the full command line (including environment variables) for debugging purposes.
+	ctx.Println("Bazel command line: " + bazelEnvStringBuffer.String() + cmd.Cmd.String() + "\n")
 
 	// Execute the build command.
 	cmd.RunAndStreamOrFatal()
@@ -113,24 +183,8 @@
 	// Ensure that the $OUT_DIR contains the expected set of files by symlinking
 	// the files from the execution root's output direction into $OUT_DIR.
 
-	// Obtain the Bazel output directory for ninja_build.
-	infoCmd := Command(ctx, config, "bazel", bazelExecutable)
-
-	if extraStartupArgs, ok := infoCmd.Environment.Get("BAZEL_STARTUP_ARGS"); ok {
-		infoCmd.Args = append(infoCmd.Args, strings.Fields(extraStartupArgs)...)
-	}
-
-	// Obtain the output directory path in the execution root.
-	infoCmd.Args = append(infoCmd.Args,
-		"info",
-		"output_path",
-	)
-
-	infoCmd.Environment.Set("DIST_DIR", config.DistDir())
-	infoCmd.Environment.Set("SHELL", "/bin/bash")
-	infoCmd.Dir = filepath.Join(config.OutDir(), "..")
-	ctx.Status.Status("Getting Bazel Info..")
-	outputBasePath := string(infoCmd.OutputOrFatal())
+	ctx.Println("Getting Bazel output_path...")
+	outputBasePath := getBazelInfo(ctx, config, bazelExecutable, bazelEnv, "output_path")
 	// TODO: Don't hardcode out/ as the bazel output directory. This is
 	// currently hardcoded as ninja_build.output_root.
 	bazelNinjaBuildOutputRoot := filepath.Join(outputBasePath, "..", "out")
diff --git a/ui/build/build.go b/ui/build/build.go
index cfd0b83..e8f0fc4 100644
--- a/ui/build/build.go
+++ b/ui/build/build.go
@@ -28,7 +28,7 @@
 func SetupOutDir(ctx Context, config Config) {
 	ensureEmptyFileExists(ctx, filepath.Join(config.OutDir(), "Android.mk"))
 	ensureEmptyFileExists(ctx, filepath.Join(config.OutDir(), "CleanSpec.mk"))
-	if !config.SkipMake() {
+	if !config.SkipKati() {
 		// Run soong_build with Kati for a hybrid build, e.g. running the
 		// AndroidMk singleton and postinstall commands. Communicate this to
 		// soong_build by writing an empty .soong.kati_enabled marker file in the
@@ -44,7 +44,7 @@
 	ensureEmptyFileExists(ctx, filepath.Join(config.OutDir(), ".out-dir"))
 
 	if buildDateTimeFile, ok := config.environ.Get("BUILD_DATETIME_FILE"); ok {
-		err := ioutil.WriteFile(buildDateTimeFile, []byte(config.buildDateTime), 0777)
+		err := ioutil.WriteFile(buildDateTimeFile, []byte(config.buildDateTime), 0666) // a+rw
 		if err != nil {
 			ctx.Fatalln("Failed to write BUILD_DATETIME to file:", err)
 		}
@@ -67,8 +67,8 @@
 `))
 
 func createCombinedBuildNinjaFile(ctx Context, config Config) {
-	// If we're in SkipMake mode, skip creating this file if it already exists
-	if config.SkipMake() {
+	// If we're in SkipKati mode, skip creating this file if it already exists
+	if config.SkipKati() {
 		if _, err := os.Stat(config.CombinedNinjaFile()); err == nil || !os.IsNotExist(err) {
 			return
 		}
@@ -85,6 +85,7 @@
 	}
 }
 
+// These are bitmasks which can be used to check whether various flags are set e.g. whether to use Bazel.
 const (
 	BuildNone          = iota
 	BuildProductConfig = 1 << iota
@@ -97,6 +98,7 @@
 	BuildAllWithBazel  = BuildProductConfig | BuildSoong | BuildKati | BuildBazel
 )
 
+// checkProblematicFiles fails the build if existing Android.mk or CleanSpec.mk files are found at the root of the tree.
 func checkProblematicFiles(ctx Context) {
 	files := []string{"Android.mk", "CleanSpec.mk"}
 	for _, file := range files {
@@ -108,6 +110,7 @@
 	}
 }
 
+// checkCaseSensitivity issues a warning if a case-insensitive file system is being used.
 func checkCaseSensitivity(ctx Context, config Config) {
 	outDir := config.OutDir()
 	lowerCase := filepath.Join(outDir, "casecheck.txt")
@@ -115,13 +118,11 @@
 	lowerData := "a"
 	upperData := "B"
 
-	err := ioutil.WriteFile(lowerCase, []byte(lowerData), 0777)
-	if err != nil {
+	if err := ioutil.WriteFile(lowerCase, []byte(lowerData), 0666); err != nil { // a+rw
 		ctx.Fatalln("Failed to check case sensitivity:", err)
 	}
 
-	err = ioutil.WriteFile(upperCase, []byte(upperData), 0777)
-	if err != nil {
+	if err := ioutil.WriteFile(upperCase, []byte(upperData), 0666); err != nil { // a+rw
 		ctx.Fatalln("Failed to check case sensitivity:", err)
 	}
 
@@ -139,18 +140,15 @@
 	}
 }
 
-func help(ctx Context, config Config, what int) {
+// help prints a help/usage message, via the build/make/help.sh script.
+func help(ctx Context, config Config) {
 	cmd := Command(ctx, config, "help.sh", "build/make/help.sh")
 	cmd.Sandbox = dumpvarsSandbox
 	cmd.RunAndPrintOrFatal()
 }
 
-// Build the tree. The 'what' argument can be used to chose which components of
-// the build to run.
-func Build(ctx Context, config Config, what int) {
-	ctx.Verboseln("Starting build with args:", config.Arguments())
-	ctx.Verboseln("Environment:", config.Environment().Environ())
-
+// checkRAM warns if there probably isn't enough RAM to complete a build.
+func checkRAM(ctx Context, config Config) {
 	if totalRAM := config.TotalRAM(); totalRAM != 0 {
 		ram := float32(totalRAM) / (1024 * 1024 * 1024)
 		ctx.Verbosef("Total RAM: %.3vGB", ram)
@@ -166,24 +164,24 @@
 			ctx.Println("-j value.")
 			ctx.Println("************************************************************")
 		} else if ram <= float32(config.Parallel()) {
+			// Want at least 1GB of RAM per job.
 			ctx.Printf("Warning: high -j%d count compared to %.3vGB of RAM", config.Parallel(), ram)
 			ctx.Println("If you run into segfaults or other errors, try a lower -j value")
 		}
 	}
+}
+
+// Build the tree. The 'what' argument can be used to chose which components of
+// the build to run, via checking various bitmasks.
+func Build(ctx Context, config Config, what int) {
+	ctx.Verboseln("Starting build with args:", config.Arguments())
+	ctx.Verboseln("Environment:", config.Environment().Environ())
 
 	ctx.BeginTrace(metrics.Total, "total")
 	defer ctx.EndTrace()
 
-	if config.SkipMake() {
-		ctx.Verboseln("Skipping Make/Kati as requested")
-		what = what & (BuildSoong | BuildNinja)
-	}
-
 	if inList("help", config.Arguments()) {
-		help(ctx, config, what)
-		return
-	} else if inList("clean", config.Arguments()) || inList("clobber", config.Arguments()) {
-		clean(ctx, config)
+		help(ctx, config)
 		return
 	}
 
@@ -191,16 +189,35 @@
 	buildLock := BecomeSingletonOrFail(ctx, config)
 	defer buildLock.Unlock()
 
+	if inList("clean", config.Arguments()) || inList("clobber", config.Arguments()) {
+		clean(ctx, config)
+		return
+	}
+
+	// checkProblematicFiles aborts the build if Android.mk or CleanSpec.mk are found at the root of the tree.
 	checkProblematicFiles(ctx)
 
+	checkRAM(ctx, config)
+
 	SetupOutDir(ctx, config)
 
+	// checkCaseSensitivity issues a warning if a case-insensitive file system is being used.
 	checkCaseSensitivity(ctx, config)
 
 	ensureEmptyDirectoriesExist(ctx, config.TempDir())
 
 	SetupPath(ctx, config)
 
+	if config.SkipConfig() {
+		ctx.Verboseln("Skipping Config as requested")
+		what = what &^ BuildProductConfig
+	}
+
+	if config.SkipKati() {
+		ctx.Verboseln("Skipping Kati as requested")
+		what = what &^ BuildKati
+	}
+
 	if config.StartGoma() {
 		// Ensure start Goma compiler_proxy
 		startGoma(ctx, config)
@@ -216,12 +233,16 @@
 		runMakeProductConfig(ctx, config)
 	}
 
+	// Everything below here depends on product config.
+
 	if inList("installclean", config.Arguments()) ||
 		inList("install-clean", config.Arguments()) {
 		installClean(ctx, config)
 		ctx.Println("Deleted images and staging directories.")
 		return
-	} else if inList("dataclean", config.Arguments()) ||
+	}
+
+	if inList("dataclean", config.Arguments()) ||
 		inList("data-clean", config.Arguments()) {
 		dataClean(ctx, config)
 		ctx.Println("Deleted data files.")
@@ -240,7 +261,7 @@
 		runKatiBuild(ctx, config)
 		runKatiPackage(ctx, config)
 
-		ioutil.WriteFile(config.LastKatiSuffixFile(), []byte(config.KatiSuffix()), 0777)
+		ioutil.WriteFile(config.LastKatiSuffixFile(), []byte(config.KatiSuffix()), 0666) // a+rw
 	} else {
 		// Load last Kati Suffix if it exists
 		if katiSuffix, err := ioutil.ReadFile(config.LastKatiSuffixFile()); err == nil {
@@ -259,7 +280,7 @@
 	}
 
 	if what&BuildNinja != 0 {
-		if !config.SkipMake() {
+		if what&BuildKati != 0 {
 			installCleanIfNecessary(ctx, config)
 		}
 
@@ -267,6 +288,7 @@
 		runNinja(ctx, config)
 	}
 
+	// Currently, using Bazel requires Kati and Soong to run first, so check whether to run Bazel last.
 	if what&BuildBazel != 0 {
 		runBazel(ctx, config)
 	}
@@ -282,14 +304,11 @@
 	subDir := filepath.Join(subDirs...)
 	destDir := filepath.Join(config.DistDir(), "soong_ui", subDir)
 
-	err := os.MkdirAll(destDir, 0777)
-	if err != nil {
+	if err := os.MkdirAll(destDir, 0777); err != nil { // a+rwx
 		ctx.Printf("failed to mkdir %s: %s", destDir, err.Error())
-
 	}
 
-	err = gzipFileToDir(src, destDir)
-	if err != nil {
+	if err := gzipFileToDir(src, destDir); err != nil {
 		ctx.Printf("failed to dist %s: %s", filepath.Base(src), err.Error())
 	}
 }
@@ -304,14 +323,11 @@
 	subDir := filepath.Join(subDirs...)
 	destDir := filepath.Join(config.DistDir(), "soong_ui", subDir)
 
-	err := os.MkdirAll(destDir, 0777)
-	if err != nil {
+	if err := os.MkdirAll(destDir, 0777); err != nil { // a+rwx
 		ctx.Printf("failed to mkdir %s: %s", destDir, err.Error())
-
 	}
 
-	_, err = copyFile(src, filepath.Join(destDir, filepath.Base(src)))
-	if err != nil {
+	if _, err := copyFile(src, filepath.Join(destDir, filepath.Base(src))); err != nil {
 		ctx.Printf("failed to dist %s: %s", filepath.Base(src), err.Error())
 	}
 }
diff --git a/ui/build/config.go b/ui/build/config.go
index 229bd5c..c9911f3 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -46,7 +46,8 @@
 	verbose        bool
 	checkbuild     bool
 	dist           bool
-	skipMake       bool
+	skipConfig     bool
+	skipKati       bool
 	skipSoongTests bool
 
 	// From the product config
@@ -536,7 +537,10 @@
 		} else if arg == "showcommands" {
 			c.verbose = true
 		} else if arg == "--skip-make" {
-			c.skipMake = true
+			c.skipConfig = true
+			c.skipKati = true
+		} else if arg == "--skip-kati" {
+			c.skipKati = true
 		} else if arg == "--skip-soong-tests" {
 			c.skipSoongTests = true
 		} else if len(arg) > 0 && arg[0] == '-' {
@@ -697,7 +701,7 @@
 }
 
 func (c *configImpl) NinjaArgs() []string {
-	if c.skipMake {
+	if c.skipKati {
 		return c.arguments
 	}
 	return c.ninjaArgs
@@ -740,8 +744,12 @@
 	return c.verbose
 }
 
-func (c *configImpl) SkipMake() bool {
-	return c.skipMake
+func (c *configImpl) SkipKati() bool {
+	return c.skipKati
+}
+
+func (c *configImpl) SkipConfig() bool {
+	return c.skipConfig
 }
 
 func (c *configImpl) TargetProduct() string {
diff --git a/ui/build/ninja.go b/ui/build/ninja.go
index ffd1ab9..7799766 100644
--- a/ui/build/ninja.go
+++ b/ui/build/ninja.go
@@ -139,15 +139,6 @@
 			// b/147197813 - used by art-check-debug-apex-gen
 			"EMMA_INSTRUMENT_FRAMEWORK",
 
-			// Goma -- gomacc may not need all of these
-			"GOMA_DIR",
-			"GOMA_DISABLED",
-			"GOMA_FAIL_FAST",
-			"GOMA_FALLBACK",
-			"GOMA_GCE_SERVICE_ACCOUNT",
-			"GOMA_TMP_DIR",
-			"GOMA_USE_LOCAL",
-
 			// RBE client
 			"RBE_compare",
 			"RBE_exec_root",
diff --git a/ui/build/soong.go b/ui/build/soong.go
index bb5cbf0..08c2ee1 100644
--- a/ui/build/soong.go
+++ b/ui/build/soong.go
@@ -30,16 +30,33 @@
 	"android/soong/ui/status"
 )
 
+// This uses Android.bp files and various tools to generate <builddir>/build.ninja.
+//
+// However, the execution of <builddir>/build.ninja happens later in build/soong/ui/build/build.go#Build()
+//
+// We want to rely on as few prebuilts as possible, so there is some bootstrapping here.
+//
+// "Microfactory" is a tool for compiling Go code. We use it to build two other tools:
+// - minibp, used to generate build.ninja files. This is really build/blueprint/bootstrap/command.go#Main()
+// - bpglob, used during incremental builds to identify files in a glob that have changed
+//
+// In reality, several build.ninja files are generated and/or used during the bootstrapping and build process.
+// See build/blueprint/bootstrap/doc.go for more information.
+//
 func runSoong(ctx Context, config Config) {
 	ctx.BeginTrace(metrics.RunSoong, "soong")
 	defer ctx.EndTrace()
 
+	// Use an anonymous inline function for tracing purposes (this pattern is used several times below).
 	func() {
 		ctx.BeginTrace(metrics.RunSoong, "blueprint bootstrap")
 		defer ctx.EndTrace()
 
+		// Use validations to depend on tests.
 		args := []string{"-n"}
+
 		if !config.skipSoongTests {
+			// Run tests.
 			args = append(args, "-t")
 		}
 
@@ -145,7 +162,10 @@
 		cmd.RunAndStreamOrFatal()
 	}
 
+	// This build generates .bootstrap/build.ninja, which is used in the next step.
 	ninja("minibootstrap", ".minibootstrap/build.ninja")
+
+	// This build generates <builddir>/build.ninja, which is used later by build/soong/ui/build/build.go#Build().
 	ninja("bootstrap", ".bootstrap/build.ninja")
 
 	soongBuildMetrics := loadSoongBuildMetrics(ctx, config)
@@ -153,7 +173,7 @@
 
 	distGzipFile(ctx, config, config.SoongNinjaFile(), "soong")
 
-	if !config.SkipMake() {
+	if !config.SkipKati() {
 		distGzipFile(ctx, config, config.SoongAndroidMk(), "soong")
 		distGzipFile(ctx, config, config.SoongMakeVarsMk(), "soong")
 	}
diff --git a/ui/build/upload.go b/ui/build/upload.go
index a9346e0..4f30136 100644
--- a/ui/build/upload.go
+++ b/ui/build/upload.go
@@ -30,32 +30,34 @@
 )
 
 const (
+	// Used to generate a raw protobuf file that contains information
+	// of the list of metrics files from host to destination storage.
 	uploadPbFilename = ".uploader.pb"
 )
 
 var (
-	// For testing purpose
-	getTmpDir = ioutil.TempDir
+	// For testing purpose.
+	tmpDir = ioutil.TempDir
 )
 
 // UploadMetrics uploads a set of metrics files to a server for analysis. An
-// uploader full path is required to be specified in order to upload the set
-// of metrics files. This is accomplished by defining the ANDROID_ENABLE_METRICS_UPLOAD
-// environment variable. The metrics files are copied to a temporary directory
-// and the uploader is then executed in the background to allow the user to continue
-// working.
+// uploader full path is specified in ANDROID_ENABLE_METRICS_UPLOAD environment
+// variable in order to upload the set of metrics files. The metrics files are
+// first copied to a temporary directory and the uploader is then executed in
+// the background to allow the user/system to continue working. Soong communicates
+// to the uploader through the upload_proto raw protobuf file.
 func UploadMetrics(ctx Context, config Config, simpleOutput bool, buildStarted time.Time, files ...string) {
 	ctx.BeginTrace(metrics.RunSetupTool, "upload_metrics")
 	defer ctx.EndTrace()
 
 	uploader := config.MetricsUploaderApp()
-	// No metrics to upload if the path to the uploader was not specified.
 	if uploader == "" {
+		// If the uploader path was not specified, no metrics shall be uploaded.
 		return
 	}
 
-	// Some files may not exist. For example, build errors protobuf file
-	// may not exist since the build was successful.
+	// Some files passed in to this function may not exist. For example,
+	// build errors protobuf file may not exist since the build was successful.
 	var metricsFiles []string
 	for _, f := range files {
 		if _, err := os.Stat(f); err == nil {
@@ -70,7 +72,7 @@
 	// The temporary directory cannot be deleted as the metrics uploader is started
 	// in the background and requires to exist until the operation is done. The
 	// uploader can delete the directory as it is specified in the upload proto.
-	tmpDir, err := getTmpDir("", "upload_metrics")
+	tmpDir, err := tmpDir("", "upload_metrics")
 	if err != nil {
 		ctx.Fatalf("failed to create a temporary directory to store the list of metrics files: %v\n", err)
 	}
@@ -103,7 +105,7 @@
 	}
 
 	// Start the uploader in the background as it takes several milliseconds to start the uploader
-	// and prepare the metrics for upload. This affects small commands like "lunch".
+	// and prepare the metrics for upload. This affects small shell commands like "lunch".
 	cmd := Command(ctx, config, "upload metrics", uploader, "--upload-metrics", pbFile)
 	if simpleOutput {
 		cmd.RunOrFatal()
diff --git a/ui/build/upload_test.go b/ui/build/upload_test.go
index dccf156..768b031 100644
--- a/ui/build/upload_test.go
+++ b/ui/build/upload_test.go
@@ -62,16 +62,16 @@
 			}
 			defer os.RemoveAll(outDir)
 
-			// Supply our own getTmpDir to delete the temp dir once the test is done.
-			orgGetTmpDir := getTmpDir
-			getTmpDir = func(string, string) (string, error) {
+			// Supply our own tmpDir to delete the temp dir once the test is done.
+			orgTmpDir := tmpDir
+			tmpDir = func(string, string) (string, error) {
 				retDir := filepath.Join(outDir, "tmp_upload_dir")
 				if err := os.Mkdir(retDir, 0755); err != nil {
 					t.Fatalf("failed to create temporary directory %q: %v", retDir, err)
 				}
 				return retDir, nil
 			}
-			defer func() { getTmpDir = orgGetTmpDir }()
+			defer func() { tmpDir = orgTmpDir }()
 
 			metricsUploadDir := filepath.Join(outDir, ".metrics_uploader")
 			if err := os.Mkdir(metricsUploadDir, 0755); err != nil {
@@ -134,11 +134,11 @@
 			}
 			defer os.RemoveAll(outDir)
 
-			orgGetTmpDir := getTmpDir
-			getTmpDir = func(string, string) (string, error) {
+			orgTmpDir := tmpDir
+			tmpDir = func(string, string) (string, error) {
 				return tt.tmpDir, tt.tmpDirErr
 			}
-			defer func() { getTmpDir = orgGetTmpDir }()
+			defer func() { tmpDir = orgTmpDir }()
 
 			metricsFile := filepath.Join(outDir, "metrics_file_1")
 			if err := ioutil.WriteFile(metricsFile, []byte("test file"), 0644); err != nil {