java/droidstubs.go

// Copyright 2021 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 (
	"fmt"
	"strings"

	"github.com/google/blueprint/proptools"

	"android/soong/android"
	"android/soong/java/config"
	"android/soong/remoteexec"
)

func init() {
	RegisterStubsBuildComponents(android.InitRegistrationContext)
}

func RegisterStubsBuildComponents(ctx android.RegistrationContext) {
	ctx.RegisterModuleType("stubs_defaults", StubsDefaultsFactory)

	ctx.RegisterModuleType("droidstubs", DroidstubsFactory)
	ctx.RegisterModuleType("droidstubs_host", DroidstubsHostFactory)

	ctx.RegisterModuleType("prebuilt_stubs_sources", PrebuiltStubsSourcesFactory)
}

//
// Droidstubs
//
type Droidstubs struct {
	Javadoc
	android.SdkBase

	properties              DroidstubsProperties
	apiFile                 android.WritablePath
	apiXmlFile              android.WritablePath
	lastReleasedApiXmlFile  android.WritablePath
	privateApiFile          android.WritablePath
	removedApiFile          android.WritablePath
	nullabilityWarningsFile android.WritablePath

	checkCurrentApiTimestamp      android.WritablePath
	updateCurrentApiTimestamp     android.WritablePath
	checkLastReleasedApiTimestamp android.WritablePath
	apiLintTimestamp              android.WritablePath
	apiLintReport                 android.WritablePath

	checkNullabilityWarningsTimestamp android.WritablePath

	annotationsZip android.WritablePath
	apiVersionsXml android.WritablePath

	apiFilePath        android.Path
	removedApiFilePath android.Path

	metadataZip android.WritablePath
	metadataDir android.WritablePath
}

type DroidstubsProperties struct {
	// The generated public API filename by Metalava, defaults to <module>_api.txt
	Api_filename *string

	// the generated removed API filename by Metalava, defaults to <module>_removed.txt
	Removed_api_filename *string

	Check_api struct {
		Last_released ApiToCheck

		Current ApiToCheck

		Api_lint struct {
			Enabled *bool

			// If set, performs api_lint on any new APIs not found in the given signature file
			New_since *string `android:"path"`

			// If not blank, path to the baseline txt file for approved API lint violations.
			Baseline_file *string `android:"path"`
		}
	}

	// user can specify the version of previous released API file in order to do compatibility check.
	Previous_api *string `android:"path"`

	// is set to true, Metalava will allow framework SDK to contain annotations.
	Annotations_enabled *bool

	// a list of top-level directories containing files to merge qualifier annotations (i.e. those intended to be included in the stubs written) from.
	Merge_annotations_dirs []string

	// a list of top-level directories containing Java stub files to merge show/hide annotations from.
	Merge_inclusion_annotations_dirs []string

	// a file containing a list of classes to do nullability validation for.
	Validate_nullability_from_list *string

	// a file containing expected warnings produced by validation of nullability annotations.
	Check_nullability_warnings *string

	// if set to true, allow Metalava to generate doc_stubs source files. Defaults to false.
	Create_doc_stubs *bool

	// if set to true, cause Metalava to output Javadoc comments in the stubs source files. Defaults to false.
	// Has no effect if create_doc_stubs: true.
	Output_javadoc_comments *bool

	// if set to false then do not write out stubs. Defaults to true.
	//
	// TODO(b/146727827): Remove capability when we do not need to generate stubs and API separately.
	Generate_stubs *bool

	// if set to true, provides a hint to the build system that this rule uses a lot of memory,
	// whicih can be used for scheduling purposes
	High_mem *bool

	// is set to true, Metalava will allow framework SDK to contain API levels annotations.
	Api_levels_annotations_enabled *bool

	// the dirs which Metalava extracts API levels annotations from.
	Api_levels_annotations_dirs []string

	// the filename which Metalava extracts API levels annotations from. Defaults to android.jar.
	Api_levels_jar_filename *string

	// if set to true, collect the values used by the Dev tools and
	// write them in files packaged with the SDK. Defaults to false.
	Write_sdk_values *bool
}

// Used by xsd_config
type ApiFilePath interface {
	ApiFilePath() android.Path
}

type ApiStubsSrcProvider interface {
	StubsSrcJar() android.Path
}

// Provider of information about API stubs, used by java_sdk_library.
type ApiStubsProvider interface {
	AnnotationsZip() android.Path
	ApiFilePath
	RemovedApiFilePath() android.Path

	ApiStubsSrcProvider
}

// droidstubs passes sources files through Metalava to generate stub .java files that only contain the API to be
// documented, filtering out hidden classes and methods.  The resulting .java files are intended to be passed to
// a droiddoc module to generate documentation.
func DroidstubsFactory() android.Module {
	module := &Droidstubs{}

	module.AddProperties(&module.properties,
		&module.Javadoc.properties)

	InitDroiddocModule(module, android.HostAndDeviceSupported)
	android.InitSdkAwareModule(module)
	return module
}

// droidstubs_host passes sources files through Metalava to generate stub .java files that only contain the API
// to be documented, filtering out hidden classes and methods.  The resulting .java files are intended to be
// passed to a droiddoc_host module to generate documentation.  Use a droidstubs_host instead of a droidstubs
// module when symbols needed by the source files are provided by java_library_host modules.
func DroidstubsHostFactory() android.Module {
	module := &Droidstubs{}

	module.AddProperties(&module.properties,
		&module.Javadoc.properties)

	InitDroiddocModule(module, android.HostSupported)
	return module
}

func (d *Droidstubs) OutputFiles(tag string) (android.Paths, error) {
	switch tag {
	case "":
		return android.Paths{d.stubsSrcJar}, nil
	case ".docs.zip":
		return android.Paths{d.docZip}, nil
	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
	case ".annotations.zip":
		return android.Paths{d.annotationsZip}, nil
	case ".api_versions.xml":
		return android.Paths{d.apiVersionsXml}, nil
	default:
		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
	}
}

func (d *Droidstubs) AnnotationsZip() android.Path {
	return d.annotationsZip
}

func (d *Droidstubs) ApiFilePath() android.Path {
	return d.apiFilePath
}

func (d *Droidstubs) RemovedApiFilePath() android.Path {
	return d.removedApiFilePath
}

func (d *Droidstubs) StubsSrcJar() android.Path {
	return d.stubsSrcJar
}

var metalavaMergeAnnotationsDirTag = dependencyTag{name: "metalava-merge-annotations-dir"}
var metalavaMergeInclusionAnnotationsDirTag = dependencyTag{name: "metalava-merge-inclusion-annotations-dir"}
var metalavaAPILevelsAnnotationsDirTag = dependencyTag{name: "metalava-api-levels-annotations-dir"}

func (d *Droidstubs) DepsMutator(ctx android.BottomUpMutatorContext) {
	d.Javadoc.addDeps(ctx)

	if len(d.properties.Merge_annotations_dirs) != 0 {
		for _, mergeAnnotationsDir := range d.properties.Merge_annotations_dirs {
			ctx.AddDependency(ctx.Module(), metalavaMergeAnnotationsDirTag, mergeAnnotationsDir)
		}
	}

	if len(d.properties.Merge_inclusion_annotations_dirs) != 0 {
		for _, mergeInclusionAnnotationsDir := range d.properties.Merge_inclusion_annotations_dirs {
			ctx.AddDependency(ctx.Module(), metalavaMergeInclusionAnnotationsDirTag, mergeInclusionAnnotationsDir)
		}
	}

	if len(d.properties.Api_levels_annotations_dirs) != 0 {
		for _, apiLevelsAnnotationsDir := range d.properties.Api_levels_annotations_dirs {
			ctx.AddDependency(ctx.Module(), metalavaAPILevelsAnnotationsDirTag, apiLevelsAnnotationsDir)
		}
	}
}

func (d *Droidstubs) stubsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand, stubsDir android.OptionalPath) {
	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") ||
		apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") ||
		String(d.properties.Api_filename) != "" {
		filename := proptools.StringDefault(d.properties.Api_filename, ctx.ModuleName()+"_api.txt")
		d.apiFile = android.PathForModuleOut(ctx, "metalava", filename)
		cmd.FlagWithOutput("--api ", d.apiFile)
		d.apiFilePath = d.apiFile
	} else if sourceApiFile := proptools.String(d.properties.Check_api.Current.Api_file); sourceApiFile != "" {
		// If check api is disabled then make the source file available for export.
		d.apiFilePath = android.PathForModuleSrc(ctx, sourceApiFile)
	}

	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") ||
		apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") ||
		String(d.properties.Removed_api_filename) != "" {
		filename := proptools.StringDefault(d.properties.Removed_api_filename, ctx.ModuleName()+"_removed.txt")
		d.removedApiFile = android.PathForModuleOut(ctx, "metalava", filename)
		cmd.FlagWithOutput("--removed-api ", d.removedApiFile)
		d.removedApiFilePath = d.removedApiFile
	} else if sourceRemovedApiFile := proptools.String(d.properties.Check_api.Current.Removed_api_file); sourceRemovedApiFile != "" {
		// If check api is disabled then make the source removed api file available for export.
		d.removedApiFilePath = android.PathForModuleSrc(ctx, sourceRemovedApiFile)
	}

	if Bool(d.properties.Write_sdk_values) {
		d.metadataDir = android.PathForModuleOut(ctx, "metalava", "metadata")
		cmd.FlagWithArg("--sdk-values ", d.metadataDir.String())
	}

	if stubsDir.Valid() {
		if Bool(d.properties.Create_doc_stubs) {
			cmd.FlagWithArg("--doc-stubs ", stubsDir.String())
		} else {
			cmd.FlagWithArg("--stubs ", stubsDir.String())
			if !Bool(d.properties.Output_javadoc_comments) {
				cmd.Flag("--exclude-documentation-from-stubs")
			}
		}
	}
}

func (d *Droidstubs) annotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
	if Bool(d.properties.Annotations_enabled) {
		cmd.Flag("--include-annotations")

		cmd.FlagWithArg("--exclude-annotation ", "androidx.annotation.RequiresApi")

		validatingNullability :=
			strings.Contains(String(d.Javadoc.properties.Args), "--validate-nullability-from-merged-stubs") ||
				String(d.properties.Validate_nullability_from_list) != ""

		migratingNullability := String(d.properties.Previous_api) != ""
		if migratingNullability {
			previousApi := android.PathForModuleSrc(ctx, String(d.properties.Previous_api))
			cmd.FlagWithInput("--migrate-nullness ", previousApi)
		}

		if s := String(d.properties.Validate_nullability_from_list); s != "" {
			cmd.FlagWithInput("--validate-nullability-from-list ", android.PathForModuleSrc(ctx, s))
		}

		if validatingNullability {
			d.nullabilityWarningsFile = android.PathForModuleOut(ctx, "metalava", ctx.ModuleName()+"_nullability_warnings.txt")
			cmd.FlagWithOutput("--nullability-warnings-txt ", d.nullabilityWarningsFile)
		}

		d.annotationsZip = android.PathForModuleOut(ctx, "metalava", ctx.ModuleName()+"_annotations.zip")
		cmd.FlagWithOutput("--extract-annotations ", d.annotationsZip)

		if len(d.properties.Merge_annotations_dirs) != 0 {
			d.mergeAnnoDirFlags(ctx, cmd)
		}

		// TODO(tnorbye): find owners to fix these warnings when annotation was enabled.
		cmd.FlagWithArg("--hide ", "HiddenTypedefConstant").
			FlagWithArg("--hide ", "SuperfluousPrefix").
			FlagWithArg("--hide ", "AnnotationExtraction")
	}
}

func (d *Droidstubs) mergeAnnoDirFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
	ctx.VisitDirectDepsWithTag(metalavaMergeAnnotationsDirTag, func(m android.Module) {
		if t, ok := m.(*ExportedDroiddocDir); ok {
			cmd.FlagWithArg("--merge-qualifier-annotations ", t.dir.String()).Implicits(t.deps)
		} else {
			ctx.PropertyErrorf("merge_annotations_dirs",
				"module %q is not a metalava merge-annotations dir", ctx.OtherModuleName(m))
		}
	})
}

func (d *Droidstubs) inclusionAnnotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
	ctx.VisitDirectDepsWithTag(metalavaMergeInclusionAnnotationsDirTag, func(m android.Module) {
		if t, ok := m.(*ExportedDroiddocDir); ok {
			cmd.FlagWithArg("--merge-inclusion-annotations ", t.dir.String()).Implicits(t.deps)
		} else {
			ctx.PropertyErrorf("merge_inclusion_annotations_dirs",
				"module %q is not a metalava merge-annotations dir", ctx.OtherModuleName(m))
		}
	})
}

func (d *Droidstubs) apiLevelsAnnotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
	if !Bool(d.properties.Api_levels_annotations_enabled) {
		return
	}

	d.apiVersionsXml = android.PathForModuleOut(ctx, "metalava", "api-versions.xml")

	if len(d.properties.Api_levels_annotations_dirs) == 0 {
		ctx.PropertyErrorf("api_levels_annotations_dirs",
			"has to be non-empty if api levels annotations was enabled!")
	}

	cmd.FlagWithOutput("--generate-api-levels ", d.apiVersionsXml)
	cmd.FlagWithInput("--apply-api-levels ", d.apiVersionsXml)
	cmd.FlagWithArg("--current-version ", ctx.Config().PlatformSdkVersion().String())
	cmd.FlagWithArg("--current-codename ", ctx.Config().PlatformSdkCodename())

	filename := proptools.StringDefault(d.properties.Api_levels_jar_filename, "android.jar")

	ctx.VisitDirectDepsWithTag(metalavaAPILevelsAnnotationsDirTag, func(m android.Module) {
		if t, ok := m.(*ExportedDroiddocDir); ok {
			for _, dep := range t.deps {
				if dep.Base() == filename {
					cmd.Implicit(dep)
				}
				if filename != "android.jar" && dep.Base() == "android.jar" {
					// Metalava implicitly searches these patterns:
					//  prebuilts/tools/common/api-versions/android-%/android.jar
					//  prebuilts/sdk/%/public/android.jar
					// Add android.jar files from the api_levels_annotations_dirs directories to try
					// to satisfy these patterns.  If Metalava can't find a match for an API level
					// between 1 and 28 in at least one pattern it will fail.
					cmd.Implicit(dep)
				}
			}
			cmd.FlagWithArg("--android-jar-pattern ", t.dir.String()+"/%/public/"+filename)
		} else {
			ctx.PropertyErrorf("api_levels_annotations_dirs",
				"module %q is not a metalava api-levels-annotations dir", ctx.OtherModuleName(m))
		}
	})
}

func metalavaCmd(ctx android.ModuleContext, rule *android.RuleBuilder, javaVersion javaVersion, srcs android.Paths,
	srcJarList android.Path, bootclasspath, classpath classpath, homeDir android.WritablePath) *android.RuleBuilderCommand {
	rule.Command().Text("rm -rf").Flag(homeDir.String())
	rule.Command().Text("mkdir -p").Flag(homeDir.String())

	cmd := rule.Command()
	cmd.FlagWithArg("ANDROID_PREFS_ROOT=", homeDir.String())

	if ctx.Config().UseRBE() && ctx.Config().IsEnvTrue("RBE_METALAVA") {
		rule.Remoteable(android.RemoteRuleSupports{RBE: true})
		execStrategy := ctx.Config().GetenvWithDefault("RBE_METALAVA_EXEC_STRATEGY", remoteexec.LocalExecStrategy)
		labels := map[string]string{"type": "tool", "name": "metalava"}
		// TODO: metalava pool rejects these jobs
		pool := ctx.Config().GetenvWithDefault("RBE_METALAVA_POOL", "java16")
		rule.Rewrapper(&remoteexec.REParams{
			Labels:          labels,
			ExecStrategy:    execStrategy,
			ToolchainInputs: []string{config.JavaCmd(ctx).String()},
			Platform:        map[string]string{remoteexec.PoolKey: pool},
		})
	}

	cmd.BuiltTool("metalava").ImplicitTool(ctx.Config().HostJavaToolPath(ctx, "metalava.jar")).
		Flag(config.JavacVmFlags).
		Flag("-J--add-opens=java.base/java.util=ALL-UNNAMED").
		FlagWithArg("-encoding ", "UTF-8").
		FlagWithArg("-source ", javaVersion.String()).
		FlagWithRspFileInputList("@", android.PathForModuleOut(ctx, "metalava.rsp"), srcs).
		FlagWithInput("@", srcJarList)

	if len(bootclasspath) > 0 {
		cmd.FlagWithInputList("-bootclasspath ", bootclasspath.Paths(), ":")
	}

	if len(classpath) > 0 {
		cmd.FlagWithInputList("-classpath ", classpath.Paths(), ":")
	}

	cmd.Flag("--no-banner").
		Flag("--color").
		Flag("--quiet").
		Flag("--format=v2").
		FlagWithArg("--repeat-errors-max ", "10").
		FlagWithArg("--hide ", "UnresolvedImport")

	return cmd
}

func (d *Droidstubs) GenerateAndroidBuildActions(ctx android.ModuleContext) {
	deps := d.Javadoc.collectDeps(ctx)

	javaVersion := getJavaVersion(ctx, String(d.Javadoc.properties.Java_version), android.SdkContext(d))

	// Create rule for metalava

	srcJarDir := android.PathForModuleOut(ctx, "metalava", "srcjars")

	rule := android.NewRuleBuilder(pctx, ctx)

	rule.Sbox(android.PathForModuleOut(ctx, "metalava"),
		android.PathForModuleOut(ctx, "metalava.sbox.textproto")).
		SandboxInputs()

	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.
		rule.HighMem()
	}

	generateStubs := BoolDefault(d.properties.Generate_stubs, true)
	var stubsDir android.OptionalPath
	if generateStubs {
		d.Javadoc.stubsSrcJar = android.PathForModuleOut(ctx, "metalava", ctx.ModuleName()+"-"+"stubs.srcjar")
		stubsDir = android.OptionalPathForPath(android.PathForModuleOut(ctx, "metalava", "stubsDir"))
		rule.Command().Text("rm -rf").Text(stubsDir.String())
		rule.Command().Text("mkdir -p").Text(stubsDir.String())
	}

	srcJarList := zipSyncCmd(ctx, rule, srcJarDir, d.Javadoc.srcJars)

	homeDir := android.PathForModuleOut(ctx, "metalava", "home")
	cmd := metalavaCmd(ctx, rule, javaVersion, d.Javadoc.srcFiles, srcJarList,
		deps.bootClasspath, deps.classpath, homeDir)
	cmd.Implicits(d.Javadoc.implicits)

	d.stubsFlags(ctx, cmd, stubsDir)

	d.annotationsFlags(ctx, cmd)
	d.inclusionAnnotationsFlags(ctx, cmd)
	d.apiLevelsAnnotationsFlags(ctx, cmd)

	d.expandArgs(ctx, cmd)

	for _, o := range d.Javadoc.properties.Out {
		cmd.ImplicitOutput(android.PathForModuleGen(ctx, o))
	}

	// Add options for the other optional tasks: API-lint and check-released.
	// We generate separate timestamp files for them.

	doApiLint := false
	doCheckReleased := false

	// Add API lint options.

	if BoolDefault(d.properties.Check_api.Api_lint.Enabled, false) {
		doApiLint = true

		newSince := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Api_lint.New_since)
		if newSince.Valid() {
			cmd.FlagWithInput("--api-lint ", newSince.Path())
		} else {
			cmd.Flag("--api-lint")
		}
		d.apiLintReport = android.PathForModuleOut(ctx, "metalava", "api_lint_report.txt")
		cmd.FlagWithOutput("--report-even-if-suppressed ", d.apiLintReport) // TODO:  Change to ":api-lint"

		// TODO(b/154317059): Clean up this allowlist by baselining and/or checking in last-released.
		if d.Name() != "android.car-system-stubs-docs" &&
			d.Name() != "android.car-stubs-docs" {
			cmd.Flag("--lints-as-errors")
			cmd.Flag("--warnings-as-errors") // Most lints are actually warnings.
		}

		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Api_lint.Baseline_file)
		updatedBaselineOutput := android.PathForModuleOut(ctx, "metalava", "api_lint_baseline.txt")
		d.apiLintTimestamp = android.PathForModuleOut(ctx, "metalava", "api_lint.timestamp")

		// Note this string includes a special shell quote $' ... ', which decodes the "\n"s.
		//
		// TODO: metalava also has a slightly different message hardcoded. Should we unify this
		// message and metalava's one?
		msg := `$'` + // Enclose with $' ... '
			`************************************************************\n` +
			`Your API changes are triggering API Lint warnings or errors.\n` +
			`To make these errors go away, fix the code according to the\n` +
			`error and/or warning messages above.\n` +
			`\n` +
			`If it is not possible to do so, there are workarounds:\n` +
			`\n` +
			`1. You can suppress the errors with @SuppressLint("<id>")\n`

		if baselineFile.Valid() {
			cmd.FlagWithInput("--baseline:api-lint ", baselineFile.Path())
			cmd.FlagWithOutput("--update-baseline:api-lint ", updatedBaselineOutput)

			msg += fmt.Sprintf(``+
				`2. You can update the baseline by executing the following\n`+
				`   command:\n`+
				`       (cd $ANDROID_BUILD_TOP && cp \\\n`+
				`       "%s" \\\n`+
				`       "%s")\n`+
				`   To submit the revised baseline.txt to the main Android\n`+
				`   repository, you will need approval.\n`, updatedBaselineOutput, baselineFile.Path())
		} else {
			msg += fmt.Sprintf(``+
				`2. You can add a baseline file of existing lint failures\n`+
				`   to the build rule of %s.\n`, d.Name())
		}
		// Note the message ends with a ' (single quote), to close the $' ... ' .
		msg += `************************************************************\n'`

		cmd.FlagWithArg("--error-message:api-lint ", msg)
	}

	// Add "check released" options. (Detect incompatible API changes from the last public release)

	if apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") {
		doCheckReleased = true

		if len(d.Javadoc.properties.Out) > 0 {
			ctx.PropertyErrorf("out", "out property may not be combined with check_api")
		}

		apiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Last_released.Api_file))
		removedApiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Last_released.Removed_api_file))
		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Last_released.Baseline_file)
		updatedBaselineOutput := android.PathForModuleOut(ctx, "metalava", "last_released_baseline.txt")

		d.checkLastReleasedApiTimestamp = android.PathForModuleOut(ctx, "metalava", "check_last_released_api.timestamp")

		cmd.FlagWithInput("--check-compatibility:api:released ", apiFile)
		cmd.FlagWithInput("--check-compatibility:removed:released ", removedApiFile)

		if baselineFile.Valid() {
			cmd.FlagWithInput("--baseline:compatibility:released ", baselineFile.Path())
			cmd.FlagWithOutput("--update-baseline:compatibility:released ", updatedBaselineOutput)
		}

		// Note this string includes quote ($' ... '), which decodes the "\n"s.
		msg := `$'\n******************************\n` +
			`You have tried to change the API from what has been previously released in\n` +
			`an SDK.  Please fix the errors listed above.\n` +
			`******************************\n'`

		cmd.FlagWithArg("--error-message:compatibility:released ", msg)
	}

	if generateStubs {
		rule.Command().
			BuiltTool("soong_zip").
			Flag("-write_if_changed").
			Flag("-jar").
			FlagWithOutput("-o ", d.Javadoc.stubsSrcJar).
			FlagWithArg("-C ", stubsDir.String()).
			FlagWithArg("-D ", stubsDir.String())
	}

	if Bool(d.properties.Write_sdk_values) {
		d.metadataZip = android.PathForModuleOut(ctx, "metalava", ctx.ModuleName()+"-metadata.zip")
		rule.Command().
			BuiltTool("soong_zip").
			Flag("-write_if_changed").
			Flag("-d").
			FlagWithOutput("-o ", d.metadataZip).
			FlagWithArg("-C ", d.metadataDir.String()).
			FlagWithArg("-D ", d.metadataDir.String())
	}

	// TODO: We don't really need two separate API files, but this is a reminiscence of how
	// we used to run metalava separately for API lint and the "last_released" check. Unify them.
	if doApiLint {
		rule.Command().Text("touch").Output(d.apiLintTimestamp)
	}
	if doCheckReleased {
		rule.Command().Text("touch").Output(d.checkLastReleasedApiTimestamp)
	}

	// TODO(b/183630617): rewrapper doesn't support restat rules
	// rule.Restat()

	zipSyncCleanupCmd(rule, srcJarDir)

	rule.Build("metalava", "metalava merged")

	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") {

		if len(d.Javadoc.properties.Out) > 0 {
			ctx.PropertyErrorf("out", "out property may not be combined with check_api")
		}

		apiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Current.Api_file))
		removedApiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Current.Removed_api_file))
		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Current.Baseline_file)

		if baselineFile.Valid() {
			ctx.PropertyErrorf("baseline_file", "current API check can't have a baseline file. (module %s)", ctx.ModuleName())
		}

		d.checkCurrentApiTimestamp = android.PathForModuleOut(ctx, "metalava", "check_current_api.timestamp")

		rule := android.NewRuleBuilder(pctx, ctx)

		// Diff command line.
		// -F matches the closest "opening" line, such as "package android {"
		// and "  public class Intent {".
		diff := `diff -u -F '{ *$'`

		rule.Command().Text("( true")
		rule.Command().
			Text(diff).
			Input(apiFile).Input(d.apiFile)

		rule.Command().
			Text(diff).
			Input(removedApiFile).Input(d.removedApiFile)

		msg := fmt.Sprintf(`\n******************************\n`+
			`You have tried to change the API from what has been previously approved.\n\n`+
			`To make these errors go away, you have two choices:\n`+
			`   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`+
			`         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())

		rule.Command().
			Text("touch").Output(d.checkCurrentApiTimestamp).
			Text(") || (").
			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
			Text("; exit 38").
			Text(")")

		rule.Build("metalavaCurrentApiCheck", "check current API")

		d.updateCurrentApiTimestamp = android.PathForModuleOut(ctx, "metalava", "update_current_api.timestamp")

		// update API rule
		rule = android.NewRuleBuilder(pctx, ctx)

		rule.Command().Text("( true")

		rule.Command().
			Text("cp").Flag("-f").
			Input(d.apiFile).Flag(apiFile.String())

		rule.Command().
			Text("cp").Flag("-f").
			Input(d.removedApiFile).Flag(removedApiFile.String())

		msg = "failed to update public API"

		rule.Command().
			Text("touch").Output(d.updateCurrentApiTimestamp).
			Text(") || (").
			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
			Text("; exit 38").
			Text(")")

		rule.Build("metalavaCurrentApiUpdate", "update current API")
	}

	if String(d.properties.Check_nullability_warnings) != "" {
		if d.nullabilityWarningsFile == nil {
			ctx.PropertyErrorf("check_nullability_warnings",
				"Cannot specify check_nullability_warnings unless validating nullability")
		}

		checkNullabilityWarnings := android.PathForModuleSrc(ctx, String(d.properties.Check_nullability_warnings))

		d.checkNullabilityWarningsTimestamp = android.PathForModuleOut(ctx, "metalava", "check_nullability_warnings.timestamp")

		msg := fmt.Sprintf(`\n******************************\n`+
			`The warnings encountered during nullability annotation validation did\n`+
			`not match the checked in file of expected warnings. The diffs are shown\n`+
			`above. You have two options:\n`+
			`   1. Resolve the differences by editing the nullability annotations.\n`+
			`   2. Update the file of expected warnings by running:\n`+
			`         cp %s %s\n`+
			`       and submitting the updated file as part of your change.`,
			d.nullabilityWarningsFile, checkNullabilityWarnings)

		rule := android.NewRuleBuilder(pctx, ctx)

		rule.Command().
			Text("(").
			Text("diff").Input(checkNullabilityWarnings).Input(d.nullabilityWarningsFile).
			Text("&&").
			Text("touch").Output(d.checkNullabilityWarningsTimestamp).
			Text(") || (").
			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
			Text("; exit 38").
			Text(")")

		rule.Build("nullabilityWarningsCheck", "nullability warnings check")
	}
}

func StubsDefaultsFactory() android.Module {
	module := &DocDefaults{}

	module.AddProperties(
		&JavadocProperties{},
		&DroidstubsProperties{},
	)

	android.InitDefaultsModule(module)

	return module
}

var _ android.PrebuiltInterface = (*PrebuiltStubsSources)(nil)

type PrebuiltStubsSourcesProperties struct {
	Srcs []string `android:"path"`
}

type PrebuiltStubsSources struct {
	android.ModuleBase
	android.DefaultableModuleBase
	prebuilt android.Prebuilt
	android.SdkBase

	properties PrebuiltStubsSourcesProperties

	stubsSrcJar android.ModuleOutPath
}

func (p *PrebuiltStubsSources) OutputFiles(tag string) (android.Paths, error) {
	switch tag {
	case "":
		return android.Paths{p.stubsSrcJar}, nil
	default:
		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
	}
}

func (d *PrebuiltStubsSources) StubsSrcJar() android.Path {
	return d.stubsSrcJar
}

func (p *PrebuiltStubsSources) GenerateAndroidBuildActions(ctx android.ModuleContext) {
	p.stubsSrcJar = android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"stubs.srcjar")

	if len(p.properties.Srcs) != 1 {
		ctx.PropertyErrorf("srcs", "must only specify one directory path, contains %d paths", len(p.properties.Srcs))
		return
	}

	localSrcDir := p.properties.Srcs[0]
	// Although PathForModuleSrc can return nil if either the path doesn't exist or
	// the path components are invalid it won't in this case because no components
	// are specified and the module directory must exist in order to get this far.
	srcDir := android.PathForModuleSrc(ctx).(android.SourcePath).Join(ctx, localSrcDir)

	// Glob the contents of the directory just in case the directory does not exist.
	srcGlob := localSrcDir + "/**/*"
	srcPaths := android.PathsForModuleSrc(ctx, []string{srcGlob})

	rule := android.NewRuleBuilder(pctx, ctx)
	rule.Command().
		BuiltTool("soong_zip").
		Flag("-write_if_changed").
		Flag("-jar").
		FlagWithOutput("-o ", p.stubsSrcJar).
		FlagWithArg("-C ", srcDir.String()).
		FlagWithRspFileInputList("-r ", p.stubsSrcJar.ReplaceExtension(ctx, "rsp"), srcPaths)

	rule.Restat()

	rule.Build("zip src", "Create srcjar from prebuilt source")
}

func (p *PrebuiltStubsSources) Prebuilt() *android.Prebuilt {
	return &p.prebuilt
}

func (p *PrebuiltStubsSources) Name() string {
	return p.prebuilt.Name(p.ModuleBase.Name())
}

// prebuilt_stubs_sources imports a set of java source files as if they were
// generated by droidstubs.
//
// By default, a prebuilt_stubs_sources has a single variant that expects a
// set of `.java` files generated by droidstubs.
//
// Specifying `host_supported: true` will produce two variants, one for use as a dependency of device modules and one
// for host modules.
//
// Intended only for use by sdk snapshots.
func PrebuiltStubsSourcesFactory() android.Module {
	module := &PrebuiltStubsSources{}

	module.AddProperties(&module.properties)

	android.InitPrebuiltModule(module, &module.properties.Srcs)
	android.InitSdkAwareModule(module)
	InitDroiddocModule(module, android.HostAndDeviceSupported)
	return module
}