Merge "LTO Bp2build"
diff --git a/android/util_test.go b/android/util_test.go
index 1034d9e..5584b38 100644
--- a/android/util_test.go
+++ b/android/util_test.go
@@ -646,7 +646,7 @@
 	t.Run(name, func(t *testing.T) {
 		actual := SortedKeys(input)
 		if !reflect.DeepEqual(actual, expected) {
-			t.Errorf("expected %q, got %q", expected, actual)
+			t.Errorf("expected %v, got %v", expected, actual)
 		}
 	})
 }
diff --git a/apex/Android.bp b/apex/Android.bp
index 018d030..7ffca0e 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -29,6 +29,7 @@
         "bp2build.go",
         "deapexer.go",
         "key.go",
+        "metadata.go",
         "prebuilt.go",
         "testing.go",
         "vndk.go",
@@ -37,6 +38,7 @@
         "apex_test.go",
         "bootclasspath_fragment_test.go",
         "classpath_element_test.go",
+        "metadata_test.go",
         "platform_bootclasspath_test.go",
         "systemserver_classpath_fragment_test.go",
         "vndk_test.go",
diff --git a/apex/metadata.go b/apex/metadata.go
new file mode 100644
index 0000000..b1dff3e
--- /dev/null
+++ b/apex/metadata.go
@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * 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 apex
+
+import (
+	"encoding/json"
+
+	"github.com/google/blueprint"
+
+	"android/soong/android"
+)
+
+var (
+	mtctx = android.NewPackageContext("android/soong/multitree_apex")
+)
+
+func init() {
+	RegisterModulesSingleton(android.InitRegistrationContext)
+}
+
+func RegisterModulesSingleton(ctx android.RegistrationContext) {
+	ctx.RegisterSingletonType("apex_multitree_singleton", multitreeAnalysisSingletonFactory)
+}
+
+var PrepareForTestWithApexMultitreeSingleton = android.FixtureRegisterWithContext(RegisterModulesSingleton)
+
+func multitreeAnalysisSingletonFactory() android.Singleton {
+	return &multitreeAnalysisSingleton{}
+}
+
+type multitreeAnalysisSingleton struct {
+	multitreeApexMetadataPath android.OutputPath
+}
+
+type ApexMultitreeMetadataEntry struct {
+	// The name of the apex.
+	Name string
+
+	// TODO: Add other properties as needed.
+}
+
+type ApexMultitreeMetadata struct {
+	// Information about the installable apexes.
+	Apexes map[string]ApexMultitreeMetadataEntry
+}
+
+func (p *multitreeAnalysisSingleton) GenerateBuildActions(context android.SingletonContext) {
+	data := ApexMultitreeMetadata{
+		Apexes: make(map[string]ApexMultitreeMetadataEntry, 0),
+	}
+	context.VisitAllModules(func(module android.Module) {
+		// If this module is not being installed, ignore it.
+		if !module.Enabled() || module.IsSkipInstall() {
+			return
+		}
+		// Actual apexes provide ApexBundleInfoProvider.
+		if _, ok := context.ModuleProvider(module, ApexBundleInfoProvider).(ApexBundleInfo); !ok {
+			return
+		}
+		bundle, ok := module.(*apexBundle)
+		if ok && !bundle.testApex && !bundle.vndkApex && bundle.primaryApexType {
+			name := module.Name()
+			entry := ApexMultitreeMetadataEntry{
+				Name: name,
+			}
+			data.Apexes[name] = entry
+		}
+	})
+	p.multitreeApexMetadataPath = android.PathForOutput(context, "multitree_apex_metadata.json")
+
+	jsonStr, err := json.Marshal(data)
+	if err != nil {
+		context.Errorf(err.Error())
+	}
+	android.WriteFileRule(context, p.multitreeApexMetadataPath, string(jsonStr))
+	// This seems cleaner, but doesn't emit the phony rule in testing.
+	// context.Phony("multitree_apex_metadata", p.multitreeApexMetadataPath)
+
+	context.Build(mtctx, android.BuildParams{
+		Rule:        blueprint.Phony,
+		Description: "phony rule for multitree_apex_metadata",
+		Inputs:      []android.Path{p.multitreeApexMetadataPath},
+		Output:      android.PathForPhony(context, "multitree_apex_metadata"),
+	})
+}
diff --git a/apex/metadata_test.go b/apex/metadata_test.go
new file mode 100644
index 0000000..f6ead42
--- /dev/null
+++ b/apex/metadata_test.go
@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * 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 apex
+
+import (
+	"strings"
+	"testing"
+
+	"android/soong/android"
+	"android/soong/java"
+)
+
+func TestModulesSingleton(t *testing.T) {
+	result := android.GroupFixturePreparers(
+		PrepareForTestWithApexMultitreeSingleton,
+		java.PrepareForTestWithDexpreopt,
+		PrepareForTestWithApexBuildComponents,
+		java.FixtureConfigureApexBootJars("myapex:foo"),
+		java.PrepareForTestWithJavaSdkLibraryFiles,
+	).RunTestWithBp(t, `
+		prebuilt_apex {
+			name: "myapex",
+			src: "myapex.apex",
+			exported_bootclasspath_fragments: ["mybootclasspath-fragment"],
+		}
+
+		// A prebuilt java_sdk_library_import that is not preferred by default but will be preferred
+		// because AlwaysUsePrebuiltSdks() is true.
+		java_sdk_library_import {
+			name: "foo",
+			prefer: false,
+			shared_library: false,
+			permitted_packages: ["foo"],
+			public: {
+				jars: ["sdk_library/public/foo-stubs.jar"],
+				stub_srcs: ["sdk_library/public/foo_stub_sources"],
+				current_api: "sdk_library/public/foo.txt",
+				removed_api: "sdk_library/public/foo-removed.txt",
+				sdk_version: "current",
+			},
+			apex_available: ["myapex"],
+		}
+
+		prebuilt_bootclasspath_fragment {
+			name: "mybootclasspath-fragment",
+			apex_available: [
+				"myapex",
+			],
+			contents: [
+				"foo",
+			],
+			hidden_api: {
+				stub_flags: "prebuilt-stub-flags.csv",
+				annotation_flags: "prebuilt-annotation-flags.csv",
+				metadata: "prebuilt-metadata.csv",
+				index: "prebuilt-index.csv",
+				all_flags: "prebuilt-all-flags.csv",
+			},
+		}
+
+		platform_bootclasspath {
+			name: "myplatform-bootclasspath",
+			fragments: [
+				{
+					apex: "myapex",
+					module:"mybootclasspath-fragment",
+				},
+			],
+		}
+`,
+	)
+
+	outputs := result.SingletonForTests("apex_multitree_singleton").AllOutputs()
+	for _, output := range outputs {
+		testingBuildParam := result.SingletonForTests("apex_multitree_singleton").Output(output)
+		switch {
+		case strings.Contains(output, "soong/multitree_apex_metadata.json"):
+			android.AssertStringEquals(t, "Invalid build rule", "android/soong/android.writeFile", testingBuildParam.Rule.String())
+			android.AssertIntEquals(t, "Invalid input", len(testingBuildParam.Inputs), 0)
+			android.AssertStringDoesContain(t, "Invalid output path", output, "soong/multitree_apex_metadata.json")
+
+		case strings.HasSuffix(output, "multitree_apex_metadata"):
+			android.AssertStringEquals(t, "Invalid build rule", "<builtin>:phony", testingBuildParam.Rule.String())
+			android.AssertStringEquals(t, "Invalid input", testingBuildParam.Inputs[0].String(), "out/soong/multitree_apex_metadata.json")
+			android.AssertStringEquals(t, "Invalid output path", output, "multitree_apex_metadata")
+			android.AssertIntEquals(t, "Invalid args", len(testingBuildParam.Args), 0)
+		}
+	}
+}
diff --git a/cmd/soong_ui/main.go b/cmd/soong_ui/main.go
index fd718c2..ae026ba 100644
--- a/cmd/soong_ui/main.go
+++ b/cmd/soong_ui/main.go
@@ -200,6 +200,7 @@
 	rbeMetricsFile := filepath.Join(logsDir, c.logsPrefix+"rbe_metrics.pb")
 	bp2buildMetricsFile := filepath.Join(logsDir, c.logsPrefix+"bp2build_metrics.pb")
 	bazelMetricsFile := filepath.Join(logsDir, c.logsPrefix+"bazel_metrics.pb")
+	soongBuildMetricsFile := filepath.Join(logsDir, c.logsPrefix+"soong_build_metrics.pb")
 
 	//the profile file generated by Bazel"
 	bazelProfileFile := filepath.Join(logsDir, c.logsPrefix+"analyzed_bazel_profile.txt")
@@ -209,6 +210,7 @@
 		bp2buildMetricsFile,      // high level metrics related to bp2build.
 		soongMetricsFile,         // high level metrics related to this build system.
 		bazelMetricsFile,         // high level metrics related to bazel execution
+		soongBuildMetricsFile,    // high level metrics related to soong build(except bp2build)
 		config.BazelMetricsDir(), // directory that contains a set of bazel metrics.
 	}
 
diff --git a/java/lint.go b/java/lint.go
index a457d44..58b43df 100644
--- a/java/lint.go
+++ b/java/lint.go
@@ -96,9 +96,10 @@
 }
 
 type lintOutputs struct {
-	html android.Path
-	text android.Path
-	xml  android.Path
+	html              android.Path
+	text              android.Path
+	xml               android.Path
+	referenceBaseline android.Path
 
 	depSets LintDepSets
 }
@@ -450,7 +451,7 @@
 	html := android.PathForModuleOut(ctx, "lint", "lint-report.html")
 	text := android.PathForModuleOut(ctx, "lint", "lint-report.txt")
 	xml := android.PathForModuleOut(ctx, "lint", "lint-report.xml")
-	baseline := android.PathForModuleOut(ctx, "lint", "lint-baseline.xml")
+	referenceBaseline := android.PathForModuleOut(ctx, "lint", "lint-baseline.xml")
 
 	depSetsBuilder := NewLintDepSetBuilder().Direct(html, text, xml)
 
@@ -513,7 +514,7 @@
 		cmd.FlagWithInput("--baseline ", lintBaseline.Path())
 	}
 
-	cmd.FlagWithOutput("--write-reference-baseline ", baseline)
+	cmd.FlagWithOutput("--write-reference-baseline ", referenceBaseline)
 
 	cmd.Text("; EXITCODE=$?; ")
 
@@ -535,9 +536,10 @@
 	rule.Build("lint", "lint")
 
 	l.outputs = lintOutputs{
-		html: html,
-		text: text,
-		xml:  xml,
+		html:              html,
+		text:              text,
+		xml:               xml,
+		referenceBaseline: referenceBaseline,
 
 		depSets: depSetsBuilder.Build(),
 	}
@@ -569,9 +571,10 @@
 }
 
 type lintSingleton struct {
-	htmlZip android.WritablePath
-	textZip android.WritablePath
-	xmlZip  android.WritablePath
+	htmlZip              android.WritablePath
+	textZip              android.WritablePath
+	xmlZip               android.WritablePath
+	referenceBaselineZip android.WritablePath
 }
 
 func (l *lintSingleton) GenerateBuildActions(ctx android.SingletonContext) {
@@ -684,12 +687,15 @@
 	l.xmlZip = android.PathForOutput(ctx, "lint-report-xml.zip")
 	zip(l.xmlZip, func(l *lintOutputs) android.Path { return l.xml })
 
-	ctx.Phony("lint-check", l.htmlZip, l.textZip, l.xmlZip)
+	l.referenceBaselineZip = android.PathForOutput(ctx, "lint-report-reference-baselines.zip")
+	zip(l.referenceBaselineZip, func(l *lintOutputs) android.Path { return l.referenceBaseline })
+
+	ctx.Phony("lint-check", l.htmlZip, l.textZip, l.xmlZip, l.referenceBaselineZip)
 }
 
 func (l *lintSingleton) MakeVars(ctx android.MakeVarsContext) {
 	if !ctx.Config().UnbundledBuild() {
-		ctx.DistForGoal("lint-check", l.htmlZip, l.textZip, l.xmlZip)
+		ctx.DistForGoal("lint-check", l.htmlZip, l.textZip, l.xmlZip, l.referenceBaselineZip)
 	}
 }
 
diff --git a/ui/build/Android.bp b/ui/build/Android.bp
index 7a8fca9..b79754c 100644
--- a/ui/build/Android.bp
+++ b/ui/build/Android.bp
@@ -50,6 +50,7 @@
         "cleanbuild.go",
         "config.go",
         "context.go",
+        "staging_snapshot.go",
         "dumpvars.go",
         "environment.go",
         "exec.go",
@@ -70,10 +71,11 @@
         "cleanbuild_test.go",
         "config_test.go",
         "environment_test.go",
+        "proc_sync_test.go",
         "rbe_test.go",
+        "staging_snapshot_test.go",
         "upload_test.go",
         "util_test.go",
-        "proc_sync_test.go",
     ],
     darwin: {
         srcs: [
diff --git a/ui/build/build.go b/ui/build/build.go
index d49a754..edc595d 100644
--- a/ui/build/build.go
+++ b/ui/build/build.go
@@ -102,9 +102,9 @@
 	// Whether to include the kati-generated ninja file in the combined ninja.
 	RunKatiNinja = 1 << iota
 	// Whether to run ninja on the combined ninja.
-	RunNinja      = 1 << iota
-	RunBuildTests = 1 << iota
-	RunAll        = RunProductConfig | RunSoong | RunKati | RunKatiNinja | RunNinja
+	RunNinja       = 1 << iota
+	RunDistActions = 1 << iota
+	RunBuildTests  = 1 << iota
 )
 
 // checkBazelMode fails the build if there are conflicting arguments for which bazel
@@ -322,34 +322,42 @@
 
 		runNinjaForBuild(ctx, config)
 	}
+
+	if what&RunDistActions != 0 {
+		runDistActions(ctx, config)
+	}
 }
 
 func evaluateWhatToRun(config Config, verboseln func(v ...interface{})) int {
 	//evaluate what to run
-	what := RunAll
+	what := 0
 	if config.Checkbuild() {
 		what |= RunBuildTests
 	}
-	if config.SkipConfig() {
+	if !config.SkipConfig() {
+		what |= RunProductConfig
+	} else {
 		verboseln("Skipping Config as requested")
-		what = what &^ RunProductConfig
 	}
-	if config.SkipKati() {
-		verboseln("Skipping Kati as requested")
-		what = what &^ RunKati
-	}
-	if config.SkipKatiNinja() {
-		verboseln("Skipping use of Kati ninja as requested")
-		what = what &^ RunKatiNinja
-	}
-	if config.SkipSoong() {
+	if !config.SkipSoong() {
+		what |= RunSoong
+	} else {
 		verboseln("Skipping use of Soong as requested")
-		what = what &^ RunSoong
 	}
-
-	if config.SkipNinja() {
+	if !config.SkipKati() {
+		what |= RunKati
+	} else {
+		verboseln("Skipping Kati as requested")
+	}
+	if !config.SkipKatiNinja() {
+		what |= RunKatiNinja
+	} else {
+		verboseln("Skipping use of Kati ninja as requested")
+	}
+	if !config.SkipNinja() {
+		what |= RunNinja
+	} else {
 		verboseln("Skipping Ninja as requested")
-		what = what &^ RunNinja
 	}
 
 	if !config.SoongBuildInvocationNeeded() {
@@ -361,6 +369,11 @@
 		what = what &^ RunNinja
 		what = what &^ RunKati
 	}
+
+	if config.Dist() {
+		what |= RunDistActions
+	}
+
 	return what
 }
 
@@ -419,3 +432,9 @@
 		}
 	}()
 }
+
+// Actions to run on every build where 'dist' is in the actions.
+// Be careful, anything added here slows down EVERY CI build
+func runDistActions(ctx Context, config Config) {
+	runStagingSnapshot(ctx, config)
+}
diff --git a/ui/build/staging_snapshot.go b/ui/build/staging_snapshot.go
new file mode 100644
index 0000000..377aa64
--- /dev/null
+++ b/ui/build/staging_snapshot.go
@@ -0,0 +1,246 @@
+// Copyright 2023 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 build
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"encoding/json"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	"android/soong/shared"
+	"android/soong/ui/metrics"
+)
+
+// Metadata about a staged file
+type fileEntry struct {
+	Name string      `json:"name"`
+	Mode fs.FileMode `json:"mode"`
+	Size int64       `json:"size"`
+	Sha1 string      `json:"sha1"`
+}
+
+func fileEntryEqual(a fileEntry, b fileEntry) bool {
+	return a.Name == b.Name && a.Mode == b.Mode && a.Size == b.Size && a.Sha1 == b.Sha1
+}
+
+func sha1_hash(filename string) (string, error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	h := sha1.New()
+	if _, err := io.Copy(h, f); err != nil {
+		return "", err
+	}
+
+	return hex.EncodeToString(h.Sum(nil)), nil
+}
+
+// Subdirs of PRODUCT_OUT to scan
+var stagingSubdirs = []string{
+	"apex",
+	"cache",
+	"coverage",
+	"data",
+	"debug_ramdisk",
+	"fake_packages",
+	"installer",
+	"oem",
+	"product",
+	"ramdisk",
+	"recovery",
+	"root",
+	"sysloader",
+	"system",
+	"system_dlkm",
+	"system_ext",
+	"system_other",
+	"testcases",
+	"test_harness_ramdisk",
+	"vendor",
+	"vendor_debug_ramdisk",
+	"vendor_kernel_ramdisk",
+	"vendor_ramdisk",
+}
+
+// Return an array of stagedFileEntrys, one for each file in the staging directories inside
+// productOut
+func takeStagingSnapshot(ctx Context, productOut string, subdirs []string) ([]fileEntry, error) {
+	var outer_err error
+	if !strings.HasSuffix(productOut, "/") {
+		productOut += "/"
+	}
+	result := []fileEntry{}
+	for _, subdir := range subdirs {
+		filepath.WalkDir(productOut+subdir,
+			func(filename string, dirent fs.DirEntry, err error) error {
+				// Ignore errors. The most common one is that one of the subdirectories
+				// hasn't been built, in which case we just report it as empty.
+				if err != nil {
+					ctx.Verbosef("scanModifiedStagingOutputs error: %s", err)
+					return nil
+				}
+				if dirent.Type().IsRegular() {
+					fileInfo, _ := dirent.Info()
+					relative := strings.TrimPrefix(filename, productOut)
+					sha, err := sha1_hash(filename)
+					if err != nil {
+						outer_err = err
+					}
+					result = append(result, fileEntry{
+						Name: relative,
+						Mode: fileInfo.Mode(),
+						Size: fileInfo.Size(),
+						Sha1: sha,
+					})
+				}
+				return nil
+			})
+	}
+
+	sort.Slice(result, func(l, r int) bool { return result[l].Name < result[r].Name })
+
+	return result, outer_err
+}
+
+// Read json into an array of fileEntry. On error return empty array.
+func readJson(filename string) ([]fileEntry, error) {
+	buf, err := os.ReadFile(filename)
+	if err != nil {
+		// Not an error, just missing, which is empty.
+		return []fileEntry{}, nil
+	}
+
+	var result []fileEntry
+	err = json.Unmarshal(buf, &result)
+	if err != nil {
+		// Bad formatting. This is an error
+		return []fileEntry{}, err
+	}
+
+	return result, nil
+}
+
+// Write obj to filename.
+func writeJson(filename string, obj interface{}) error {
+	buf, err := json.MarshalIndent(obj, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	return os.WriteFile(filename, buf, 0660)
+}
+
+type snapshotDiff struct {
+	Added   []string `json:"added"`
+	Changed []string `json:"changed"`
+	Removed []string `json:"removed"`
+}
+
+// Diff the two snapshots, returning a snapshotDiff.
+func diffSnapshots(previous []fileEntry, current []fileEntry) snapshotDiff {
+	result := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{},
+		Removed: []string{},
+	}
+
+	found := make(map[string]bool)
+
+	prev := make(map[string]fileEntry)
+	for _, pre := range previous {
+		prev[pre.Name] = pre
+	}
+
+	for _, cur := range current {
+		pre, ok := prev[cur.Name]
+		found[cur.Name] = true
+		// Added
+		if !ok {
+			result.Added = append(result.Added, cur.Name)
+			continue
+		}
+		// Changed
+		if !fileEntryEqual(pre, cur) {
+			result.Changed = append(result.Changed, cur.Name)
+		}
+	}
+
+	// Removed
+	for _, pre := range previous {
+		if !found[pre.Name] {
+			result.Removed = append(result.Removed, pre.Name)
+		}
+	}
+
+	// Sort the results
+	sort.Strings(result.Added)
+	sort.Strings(result.Changed)
+	sort.Strings(result.Removed)
+
+	return result
+}
+
+// Write a json files to dist:
+//   - A list of which files have changed in this build.
+//
+// And record in out/soong:
+//   - A list of all files in the staging directories, including their hashes.
+func runStagingSnapshot(ctx Context, config Config) {
+	ctx.BeginTrace(metrics.RunSoong, "runStagingSnapshot")
+	defer ctx.EndTrace()
+
+	snapshotFilename := shared.JoinPath(config.SoongOutDir(), "staged_files.json")
+
+	// Read the existing snapshot file. If it doesn't exist, this is a full
+	// build, so all files will be treated as new.
+	previous, err := readJson(snapshotFilename)
+	if err != nil {
+		ctx.Fatal(err)
+		return
+	}
+
+	// Take a snapshot of the current out directory
+	current, err := takeStagingSnapshot(ctx, config.ProductOut(), stagingSubdirs)
+	if err != nil {
+		ctx.Fatal(err)
+		return
+	}
+
+	// Diff the snapshots
+	diff := diffSnapshots(previous, current)
+
+	// Write the diff (use RealDistDir, not one that might have been faked for bazel)
+	err = writeJson(shared.JoinPath(config.RealDistDir(), "modified_files.json"), diff)
+	if err != nil {
+		ctx.Fatal(err)
+		return
+	}
+
+	// Update the snapshot
+	err = writeJson(snapshotFilename, current)
+	if err != nil {
+		ctx.Fatal(err)
+		return
+	}
+}
diff --git a/ui/build/staging_snapshot_test.go b/ui/build/staging_snapshot_test.go
new file mode 100644
index 0000000..7ac5443
--- /dev/null
+++ b/ui/build/staging_snapshot_test.go
@@ -0,0 +1,188 @@
+// Copyright 2023 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 build
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+func assertDeepEqual(t *testing.T, expected interface{}, actual interface{}) {
+	if !reflect.DeepEqual(actual, expected) {
+		t.Fatalf("expected:\n  %#v\n actual:\n  %#v", expected, actual)
+	}
+}
+
+// Make a temp directory containing the supplied contents
+func makeTempDir(files []string, directories []string, symlinks []string) string {
+	temp, _ := os.MkdirTemp("", "soon_staging_snapshot_test_")
+
+	for _, file := range files {
+		os.MkdirAll(temp+"/"+filepath.Dir(file), 0700)
+		os.WriteFile(temp+"/"+file, []byte(file), 0600)
+	}
+
+	for _, dir := range directories {
+		os.MkdirAll(temp+"/"+dir, 0770)
+	}
+
+	for _, symlink := range symlinks {
+		os.MkdirAll(temp+"/"+filepath.Dir(symlink), 0770)
+		os.Symlink(temp, temp+"/"+symlink)
+	}
+
+	return temp
+}
+
+// If this is a clean build, we won't have any preexisting files, make sure we get back an empty
+// list and not errors.
+func TestEmptyOut(t *testing.T) {
+	ctx := testContext()
+
+	temp := makeTempDir(nil, nil, nil)
+	defer os.RemoveAll(temp)
+
+	actual, _ := takeStagingSnapshot(ctx, temp, []string{"a", "e", "g"})
+
+	expected := []fileEntry{}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure only the listed directories are picked up, and only regular files
+func TestNoExtraSubdirs(t *testing.T) {
+	ctx := testContext()
+
+	temp := makeTempDir([]string{"a/b", "a/c", "d", "e/f"}, []string{"g/h"}, []string{"e/symlink"})
+	defer os.RemoveAll(temp)
+
+	actual, _ := takeStagingSnapshot(ctx, temp, []string{"a", "e", "g"})
+
+	expected := []fileEntry{
+		{"a/b", 0600, 3, "3ec69c85a4ff96830024afeef2d4e512181c8f7b"},
+		{"a/c", 0600, 3, "592d70e4e03ee6f6780c71b0bf3b9608dbf1e201"},
+		{"e/f", 0600, 3, "9e164bef74aceede0974b857170100409efe67f1"},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles empty lists
+func TestDiffEmpty(t *testing.T) {
+	actual := diffSnapshots(nil, []fileEntry{})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles adding
+func TestDiffAdd(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{"b"},
+		Changed: []string{},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles changing mode
+func TestDiffChangeMode(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0600, 2, "5678"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{"b"},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles changing size
+func TestDiffChangeSize(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 3, "5678"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{"b"},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles changing contents
+func TestDiffChangeContents(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "aaaa"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{"b"},
+		Removed: []string{},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}
+
+// Make sure diff handles removing
+func TestDiffRemove(t *testing.T) {
+	actual := diffSnapshots([]fileEntry{
+		{"a", 0600, 1, "1234"},
+		{"b", 0700, 2, "5678"},
+	}, []fileEntry{
+		{"a", 0600, 1, "1234"},
+	})
+
+	expected := snapshotDiff{
+		Added:   []string{},
+		Changed: []string{},
+		Removed: []string{"b"},
+	}
+
+	assertDeepEqual(t, expected, actual)
+}