platform_build_soong/java/hiddenapi_modular.go

// Copyright (C) 2021 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 java

import (
	"fmt"
	"strings"

	"android/soong/android"
	"github.com/google/blueprint"
	"github.com/google/blueprint/proptools"
)

// Contains support for processing hiddenAPI in a modular fashion.

type hiddenAPIStubsDependencyTag struct {
	blueprint.BaseDependencyTag
	sdkKind android.SdkKind
}

func (b hiddenAPIStubsDependencyTag) ExcludeFromApexContents() {
}

func (b hiddenAPIStubsDependencyTag) ReplaceSourceWithPrebuilt() bool {
	return false
}

func (b hiddenAPIStubsDependencyTag) SdkMemberType(child android.Module) android.SdkMemberType {
	// If the module is a java_sdk_library then treat it as if it was specific in the java_sdk_libs
	// property, otherwise treat if it was specified in the java_header_libs property.
	if javaSdkLibrarySdkMemberType.IsInstance(child) {
		return javaSdkLibrarySdkMemberType
	}

	return javaHeaderLibsSdkMemberType
}

func (b hiddenAPIStubsDependencyTag) ExportMember() bool {
	// Export the module added via this dependency tag from the sdk.
	return true
}

// Avoid having to make stubs content explicitly visible to dependent modules.
//
// This is a temporary workaround to make it easier to migrate to bootclasspath_fragment modules
// with proper dependencies.
// TODO(b/177892522): Remove this and add needed visibility.
func (b hiddenAPIStubsDependencyTag) ExcludeFromVisibilityEnforcement() {
}

var _ android.ExcludeFromVisibilityEnforcementTag = hiddenAPIStubsDependencyTag{}
var _ android.ReplaceSourceWithPrebuilt = hiddenAPIStubsDependencyTag{}
var _ android.ExcludeFromApexContentsTag = hiddenAPIStubsDependencyTag{}
var _ android.SdkMemberTypeDependencyTag = hiddenAPIStubsDependencyTag{}

// hiddenAPIRelevantSdkKinds lists all the android.SdkKind instances that are needed by the hidden
// API processing.
//
// These are in order from narrowest API surface to widest. Widest means the API stubs with the
// biggest API surface, e.g. test is wider than system is wider than public. Core platform is
// considered wider than test even though it has no relationship with test because the libraries
// that provide core platform API don't provide test. While the core platform API is being converted
// to a system API the system API is still a subset of core platform.
var hiddenAPIRelevantSdkKinds = []android.SdkKind{
	android.SdkPublic,
	android.SdkSystem,
	android.SdkTest,
	android.SdkCorePlatform,
}

// hiddenAPIComputeMonolithicStubLibModules computes the set of module names that provide stubs
// needed to produce the hidden API monolithic stub flags file.
func hiddenAPIComputeMonolithicStubLibModules(config android.Config) map[android.SdkKind][]string {
	var publicStubModules []string
	var systemStubModules []string
	var testStubModules []string
	var corePlatformStubModules []string

	if config.AlwaysUsePrebuiltSdks() {
		// Build configuration mandates using prebuilt stub modules
		publicStubModules = append(publicStubModules, "sdk_public_current_android")
		systemStubModules = append(systemStubModules, "sdk_system_current_android")
		testStubModules = append(testStubModules, "sdk_test_current_android")
	} else {
		// Use stub modules built from source
		publicStubModules = append(publicStubModules, "android_stubs_current")
		systemStubModules = append(systemStubModules, "android_system_stubs_current")
		testStubModules = append(testStubModules, "android_test_stubs_current")
	}
	// We do not have prebuilts of the core platform api yet
	corePlatformStubModules = append(corePlatformStubModules, "legacy.core.platform.api.stubs")

	// Allow products to define their own stubs for custom product jars that apps can use.
	publicStubModules = append(publicStubModules, config.ProductHiddenAPIStubs()...)
	systemStubModules = append(systemStubModules, config.ProductHiddenAPIStubsSystem()...)
	testStubModules = append(testStubModules, config.ProductHiddenAPIStubsTest()...)
	if config.IsEnvTrue("EMMA_INSTRUMENT") {
		// Add jacoco-stubs to public, system and test. It doesn't make any real difference as public
		// allows everyone access but it is needed to ensure consistent flags between the
		// bootclasspath fragment generated flags and the platform_bootclasspath generated flags.
		publicStubModules = append(publicStubModules, "jacoco-stubs")
		systemStubModules = append(systemStubModules, "jacoco-stubs")
		testStubModules = append(testStubModules, "jacoco-stubs")
	}

	m := map[android.SdkKind][]string{}
	m[android.SdkPublic] = publicStubModules
	m[android.SdkSystem] = systemStubModules
	m[android.SdkTest] = testStubModules
	m[android.SdkCorePlatform] = corePlatformStubModules
	return m
}

// hiddenAPIAddStubLibDependencies adds dependencies onto the modules specified in
// sdkKindToStubLibModules. It adds them in a well known order and uses an SdkKind specific tag to
// identify the source of the dependency.
func hiddenAPIAddStubLibDependencies(ctx android.BottomUpMutatorContext, sdkKindToStubLibModules map[android.SdkKind][]string) {
	module := ctx.Module()
	for _, sdkKind := range hiddenAPIRelevantSdkKinds {
		modules := sdkKindToStubLibModules[sdkKind]
		ctx.AddDependency(module, hiddenAPIStubsDependencyTag{sdkKind: sdkKind}, modules...)
	}
}

// hiddenAPIRetrieveDexJarBuildPath retrieves the DexJarBuildPath from the specified module, if
// available, or reports an error.
func hiddenAPIRetrieveDexJarBuildPath(ctx android.ModuleContext, module android.Module, kind android.SdkKind) android.Path {
	var dexJar android.Path
	if sdkLibrary, ok := module.(SdkLibraryDependency); ok {
		dexJar = sdkLibrary.SdkApiStubDexJar(ctx, kind)
	} else if j, ok := module.(UsesLibraryDependency); ok {
		dexJar = j.DexJarBuildPath()
	} else {
		ctx.ModuleErrorf("dependency %s of module type %s does not support providing a dex jar", module, ctx.OtherModuleType(module))
		return nil
	}

	if dexJar == nil {
		ctx.ModuleErrorf("dependency %s does not provide a dex jar, consider setting compile_dex: true", module)
	}
	return dexJar
}

var sdkKindToHiddenapiListOption = map[android.SdkKind]string{
	android.SdkPublic:       "public-stub-classpath",
	android.SdkSystem:       "system-stub-classpath",
	android.SdkTest:         "test-stub-classpath",
	android.SdkCorePlatform: "core-platform-stub-classpath",
}

// ruleToGenerateHiddenAPIStubFlagsFile creates a rule to create a hidden API stub flags file.
//
// The rule is initialized but not built so that the caller can modify it and select an appropriate
// name.
func ruleToGenerateHiddenAPIStubFlagsFile(ctx android.BuilderContext, outputPath android.WritablePath, bootDexJars android.Paths, input HiddenAPIFlagInput) *android.RuleBuilder {
	// Singleton rule which applies hiddenapi on all boot class path dex files.
	rule := android.NewRuleBuilder(pctx, ctx)

	tempPath := tempPathForRestat(ctx, outputPath)

	// Find the widest API stubs provided by the fragments on which this depends, if any.
	var dependencyStubDexJars android.Paths
	for i := len(hiddenAPIRelevantSdkKinds) - 1; i >= 0; i-- {
		kind := hiddenAPIRelevantSdkKinds[i]
		stubsForKind := input.DependencyStubDexJarsByKind[kind]
		if len(stubsForKind) != 0 {
			dependencyStubDexJars = stubsForKind
			break
		}
	}

	command := rule.Command().
		Tool(ctx.Config().HostToolPath(ctx, "hiddenapi")).
		Text("list").
		FlagForEachInput("--dependency-stub-dex=", dependencyStubDexJars).
		FlagForEachInput("--boot-dex=", bootDexJars)

	// Iterate over the sdk kinds in a fixed order.
	for _, sdkKind := range hiddenAPIRelevantSdkKinds {
		// Merge in the stub dex jar paths for this kind from the fragments on which it depends. They
		// will be needed to resolve dependencies from this fragment's stubs to classes in the other
		// fragment's APIs.
		dependencyPaths := input.DependencyStubDexJarsByKind[sdkKind]
		paths := append(dependencyPaths, input.StubDexJarsByKind[sdkKind]...)
		if len(paths) > 0 {
			option := sdkKindToHiddenapiListOption[sdkKind]
			command.FlagWithInputList("--"+option+"=", paths, ":")
		}
	}

	// Add the output path.
	command.FlagWithOutput("--out-api-flags=", tempPath)

	commitChangeForRestat(rule, tempPath, outputPath)
	return rule
}

// HiddenAPIFlagFileProperties contains paths to the flag files that can be used to augment the
// information obtained from annotations within the source code in order to create the complete set
// of flags that should be applied to the dex implementation jars on the bootclasspath.
//
// Each property contains a list of paths. With the exception of the Unsupported_packages the paths
// of each property reference a plain text file that contains a java signature per line. The flags
// for each of those signatures will be updated in a property specific way.
//
// The Unsupported_packages property contains a list of paths, each of which is a plain text file
// with one Java package per line. All members of all classes within that package (but not nested
// packages) will be updated in a property specific way.
type HiddenAPIFlagFileProperties struct {
	// Marks each signature in the referenced files as being unsupported.
	Unsupported []string `android:"path"`

	// Marks each signature in the referenced files as being unsupported because it has been removed.
	// Any conflicts with other flags are ignored.
	Removed []string `android:"path"`

	// Marks each signature in the referenced files as being supported only for targetSdkVersion <= R
	// and low priority.
	Max_target_r_low_priority []string `android:"path"`

	// Marks each signature in the referenced files as being supported only for targetSdkVersion <= Q.
	Max_target_q []string `android:"path"`

	// Marks each signature in the referenced files as being supported only for targetSdkVersion <= P.
	Max_target_p []string `android:"path"`

	// Marks each signature in the referenced files as being supported only for targetSdkVersion <= O
	// and low priority. Any conflicts with other flags are ignored.
	Max_target_o_low_priority []string `android:"path"`

	// Marks each signature in the referenced files as being blocked.
	Blocked []string `android:"path"`

	// Marks each signature in every package in the referenced files as being unsupported.
	Unsupported_packages []string `android:"path"`
}

type hiddenAPIFlagFileCategory struct {
	// PropertyName is the name of the property for this category.
	PropertyName string

	// propertyValueReader retrieves the value of the property for this category from the set of
	// properties.
	propertyValueReader func(properties *HiddenAPIFlagFileProperties) []string

	// commandMutator adds the appropriate command line options for this category to the supplied
	// command
	commandMutator func(command *android.RuleBuilderCommand, path android.Path)
}

// The flag file category for removed members of the API.
//
// This is extracted from HiddenAPIFlagFileCategories as it is needed to add the dex signatures
// list of removed API members that are generated automatically from the removed.txt files provided
// by API stubs.
var hiddenAPIRemovedFlagFileCategory = &hiddenAPIFlagFileCategory{
	// See HiddenAPIFlagFileProperties.Removed
	PropertyName: "removed",
	propertyValueReader: func(properties *HiddenAPIFlagFileProperties) []string {
		return properties.Removed
	},
	commandMutator: func(command *android.RuleBuilderCommand, path android.Path) {
		command.FlagWithInput("--unsupported ", path).Flag("--ignore-conflicts ").FlagWithArg("--tag ", "removed")
	},
}

var HiddenAPIFlagFileCategories = []*hiddenAPIFlagFileCategory{
	// See HiddenAPIFlagFileProperties.Unsupported
	{
		PropertyName: "unsupported",
		propertyValueReader: func(properties *HiddenAPIFlagFileProperties) []string {
			return properties.Unsupported
		},
		commandMutator: func(command *android.RuleBuilderCommand, path android.Path) {
			command.FlagWithInput("--unsupported ", path)
		},
	},
	hiddenAPIRemovedFlagFileCategory,
	// See HiddenAPIFlagFileProperties.Max_target_r_low_priority
	{
		PropertyName: "max_target_r_low_priority",
		propertyValueReader: func(properties *HiddenAPIFlagFileProperties) []string {
			return properties.Max_target_r_low_priority
		},
		commandMutator: func(command *android.RuleBuilderCommand, path android.Path) {
			command.FlagWithInput("--max-target-r ", path).FlagWithArg("--tag ", "lo-prio")
		},
	},
	// See HiddenAPIFlagFileProperties.Max_target_q
	{
		PropertyName: "max_target_q",
		propertyValueReader: func(properties *HiddenAPIFlagFileProperties) []string {
			return properties.Max_target_q
		},
		commandMutator: func(command *android.RuleBuilderCommand, path android.Path) {
			command.FlagWithInput("--max-target-q ", path)
		},
	},
	// See HiddenAPIFlagFileProperties.Max_target_p
	{
		PropertyName: "max_target_p",
		propertyValueReader: func(properties *HiddenAPIFlagFileProperties) []string {
			return properties.Max_target_p
		},
		commandMutator: func(command *android.RuleBuilderCommand, path android.Path) {
			command.FlagWithInput("--max-target-p ", path)
		},
	},
	// See HiddenAPIFlagFileProperties.Max_target_o_low_priority
	{
		PropertyName: "max_target_o_low_priority",
		propertyValueReader: func(properties *HiddenAPIFlagFileProperties) []string {
			return properties.Max_target_o_low_priority
		},
		commandMutator: func(command *android.RuleBuilderCommand, path android.Path) {
			command.FlagWithInput("--max-target-o ", path).Flag("--ignore-conflicts ").FlagWithArg("--tag ", "lo-prio")
		},
	},
	// See HiddenAPIFlagFileProperties.Blocked
	{
		PropertyName: "blocked",
		propertyValueReader: func(properties *HiddenAPIFlagFileProperties) []string {
			return properties.Blocked
		},
		commandMutator: func(command *android.RuleBuilderCommand, path android.Path) {
			command.FlagWithInput("--blocked ", path)
		},
	},
	// See HiddenAPIFlagFileProperties.Unsupported_packages
	{
		PropertyName: "unsupported_packages",
		propertyValueReader: func(properties *HiddenAPIFlagFileProperties) []string {
			return properties.Unsupported_packages
		},
		commandMutator: func(command *android.RuleBuilderCommand, path android.Path) {
			command.FlagWithInput("--unsupported ", path).Flag("--packages ")
		},
	},
}

// FlagFilesByCategory maps a hiddenAPIFlagFileCategory to the paths to the files in that category.
type FlagFilesByCategory map[*hiddenAPIFlagFileCategory]android.Paths

// append appends the supplied flags files to the corresponding category in this map.
func (s FlagFilesByCategory) append(other FlagFilesByCategory) {
	for _, category := range HiddenAPIFlagFileCategories {
		s[category] = append(s[category], other[category]...)
	}
}

// dedup removes duplicates in the flag files, while maintaining the order in which they were
// appended.
func (s FlagFilesByCategory) dedup() {
	for category, paths := range s {
		s[category] = android.FirstUniquePaths(paths)
	}
}

// HiddenAPIInfo contains information provided by the hidden API processing.
//
// That includes paths resolved from HiddenAPIFlagFileProperties and also generated by hidden API
// processing.
type HiddenAPIInfo struct {
	// FlagFilesByCategory maps from the flag file category to the paths containing information for
	// that category.
	FlagFilesByCategory FlagFilesByCategory

	// The paths to the stub dex jars for each of the android.SdkKind in hiddenAPIRelevantSdkKinds.
	TransitiveStubDexJarsByKind StubDexJarsByKind

	// The output from the hidden API processing needs to be made available to other modules.
	HiddenAPIFlagOutput
}

func newHiddenAPIInfo() *HiddenAPIInfo {
	info := HiddenAPIInfo{
		FlagFilesByCategory:         FlagFilesByCategory{},
		TransitiveStubDexJarsByKind: StubDexJarsByKind{},
	}
	return &info
}

func (i *HiddenAPIInfo) mergeFromFragmentDeps(ctx android.ModuleContext, fragments []android.Module) {
	// Merge all the information from the fragments. The fragments form a DAG so it is possible that
	// this will introduce duplicates so they will be resolved after processing all the fragments.
	for _, fragment := range fragments {
		if ctx.OtherModuleHasProvider(fragment, HiddenAPIInfoProvider) {
			info := ctx.OtherModuleProvider(fragment, HiddenAPIInfoProvider).(HiddenAPIInfo)
			i.TransitiveStubDexJarsByKind.append(info.TransitiveStubDexJarsByKind)
		}
	}

	// Dedup and sort paths.
	i.TransitiveStubDexJarsByKind.dedupAndSort()
}

var HiddenAPIInfoProvider = blueprint.NewProvider(HiddenAPIInfo{})

// StubDexJarsByKind maps an android.SdkKind to the paths to stub dex jars appropriate for that
// level. See hiddenAPIRelevantSdkKinds for a list of the acceptable android.SdkKind values.
type StubDexJarsByKind map[android.SdkKind]android.Paths

// append appends the supplied kind specific stub dex jar pargs to the corresponding kind in this
// map.
func (s StubDexJarsByKind) append(other StubDexJarsByKind) {
	for _, kind := range hiddenAPIRelevantSdkKinds {
		s[kind] = append(s[kind], other[kind]...)
	}
}

// dedupAndSort removes duplicates in the stub dex jar paths and sorts them into a consistent and
// deterministic order.
func (s StubDexJarsByKind) dedupAndSort() {
	for kind, paths := range s {
		s[kind] = android.SortedUniquePaths(paths)
	}
}

// HiddenAPIFlagInput encapsulates information obtained from a module and its dependencies that are
// needed for hidden API flag generation.
type HiddenAPIFlagInput struct {
	// FlagFilesByCategory contains the flag files that override the initial flags that are derived
	// from the stub dex files.
	FlagFilesByCategory FlagFilesByCategory

	// StubDexJarsByKind contains the stub dex jars for different android.SdkKind and which determine
	// the initial flags for each dex member.
	StubDexJarsByKind StubDexJarsByKind

	// DependencyStubDexJarsByKind contains the stub dex jars provided by the fragments on which this
	// depends. It is the result of merging HiddenAPIInfo.TransitiveStubDexJarsByKind from each
	// fragment on which this depends.
	DependencyStubDexJarsByKind StubDexJarsByKind

	// RemovedTxtFiles is the list of removed.txt files provided by java_sdk_library modules that are
	// specified in the bootclasspath_fragment's stub_libs and contents properties.
	RemovedTxtFiles android.Paths
}

// newHiddenAPIFlagInput creates a new initialize HiddenAPIFlagInput struct.
func newHiddenAPIFlagInput() HiddenAPIFlagInput {
	input := HiddenAPIFlagInput{
		FlagFilesByCategory: FlagFilesByCategory{},
		StubDexJarsByKind:   StubDexJarsByKind{},
	}

	return input
}

// canPerformHiddenAPIProcessing determines whether hidden API processing should be performed.
//
// A temporary workaround to avoid existing bootclasspath_fragments that do not provide the
// appropriate information needed for hidden API processing breaking the build.
// TODO(b/179354495): Remove this workaround.
func (i *HiddenAPIFlagInput) canPerformHiddenAPIProcessing(ctx android.ModuleContext, properties bootclasspathFragmentProperties) bool {
	// Performing hidden API processing without stubs is not supported and it is unlikely to ever be
	// required as the whole point of adding something to the bootclasspath fragment is to add it to
	// the bootclasspath in order to be used by something else in the system. Without any stubs it
	// cannot do that.
	if len(i.StubDexJarsByKind) == 0 {
		return false
	}

	// Hidden API processing is always enabled in tests.
	if ctx.Config().TestProductVariables != nil {
		return true
	}

	// A module that has fragments should have access to the information it needs in order to perform
	// hidden API processing.
	if len(properties.Fragments) != 0 {
		return true
	}

	// The art bootclasspath fragment does not depend on any other fragments but already supports
	// hidden API processing.
	imageName := proptools.String(properties.Image_name)
	if imageName == "art" {
		return true
	}

	// Disable it for everything else.
	return false
}

// gatherStubLibInfo gathers information from the stub libs needed by hidden API processing from the
// dependencies added in hiddenAPIAddStubLibDependencies.
//
// That includes paths to the stub dex jars as well as paths to the *removed.txt files.
func (i *HiddenAPIFlagInput) gatherStubLibInfo(ctx android.ModuleContext, contents []android.Module) {
	addFromModule := func(ctx android.ModuleContext, module android.Module, kind android.SdkKind) {
		dexJar := hiddenAPIRetrieveDexJarBuildPath(ctx, module, kind)
		if dexJar != nil {
			i.StubDexJarsByKind[kind] = append(i.StubDexJarsByKind[kind], dexJar)
		}

		if sdkLibrary, ok := module.(SdkLibraryDependency); ok {
			removedTxtFile := sdkLibrary.SdkRemovedTxtFile(ctx, kind)
			i.RemovedTxtFiles = append(i.RemovedTxtFiles, removedTxtFile.AsPaths()...)
		}
	}

	// If the contents includes any java_sdk_library modules then add them to the stubs.
	for _, module := range contents {
		if _, ok := module.(SdkLibraryDependency); ok {
			// Add information for every possible kind needed by hidden API. SdkCorePlatform is not used
			// as the java_sdk_library does not have special support for core_platform API, instead it is
			// implemented as a customized form of SdkPublic.
			for _, kind := range []android.SdkKind{android.SdkPublic, android.SdkSystem, android.SdkTest} {
				addFromModule(ctx, module, kind)
			}
		}
	}

	ctx.VisitDirectDepsIf(isActiveModule, func(module android.Module) {
		tag := ctx.OtherModuleDependencyTag(module)
		if hiddenAPIStubsTag, ok := tag.(hiddenAPIStubsDependencyTag); ok {
			kind := hiddenAPIStubsTag.sdkKind
			addFromModule(ctx, module, kind)
		}
	})

	// Normalize the paths, i.e. remove duplicates and sort.
	i.StubDexJarsByKind.dedupAndSort()
	i.RemovedTxtFiles = android.SortedUniquePaths(i.RemovedTxtFiles)
}

// extractFlagFilesFromProperties extracts the paths to flag files that are specified in the
// supplied properties and stores them in this struct.
func (i *HiddenAPIFlagInput) extractFlagFilesFromProperties(ctx android.ModuleContext, p *HiddenAPIFlagFileProperties) {
	for _, category := range HiddenAPIFlagFileCategories {
		paths := android.PathsForModuleSrc(ctx, category.propertyValueReader(p))
		i.FlagFilesByCategory[category] = paths
	}
}

func (i *HiddenAPIFlagInput) transitiveStubDexJarsByKind() StubDexJarsByKind {
	transitive := i.DependencyStubDexJarsByKind
	transitive.append(i.StubDexJarsByKind)
	return transitive
}

// HiddenAPIFlagOutput contains paths to output files from the hidden API flag generation for a
// bootclasspath_fragment module.
type HiddenAPIFlagOutput struct {
	// The path to the generated stub-flags.csv file.
	StubFlagsPath android.Path

	// The path to the generated annotation-flags.csv file.
	AnnotationFlagsPath android.Path

	// The path to the generated metadata.csv file.
	MetadataPath android.Path

	// The path to the generated index.csv file.
	IndexPath android.Path

	// The path to the generated all-flags.csv file.
	AllFlagsPath android.Path
}

// bootDexJarByModule is a map from base module name (without prebuilt_ prefix) to the boot dex
// path.
type bootDexJarByModule map[string]android.Path

// addPath adds the path for a module to the map.
func (b bootDexJarByModule) addPath(module android.Module, path android.Path) {
	b[android.RemoveOptionalPrebuiltPrefix(module.Name())] = path
}

// bootDexJars returns the boot dex jar paths sorted by their keys.
func (b bootDexJarByModule) bootDexJars() android.Paths {
	paths := android.Paths{}
	for _, k := range android.SortedStringKeys(b) {
		paths = append(paths, b[k])
	}
	return paths
}

// HiddenAPIOutput encapsulates the output from the hidden API processing.
type HiddenAPIOutput struct {
	HiddenAPIFlagOutput

	// The map from base module name to the path to the encoded boot dex file.
	EncodedBootDexFilesByModule bootDexJarByModule
}

// pathForValidation creates a path of the same type as the supplied type but with a name of
// <path>.valid.
//
// e.g. If path is an OutputPath for out/soong/hiddenapi/hiddenapi-flags.csv then this will return
// an OutputPath for out/soong/hiddenapi/hiddenapi-flags.csv.valid
func pathForValidation(ctx android.PathContext, path android.WritablePath) android.WritablePath {
	extWithoutLeadingDot := strings.TrimPrefix(path.Ext(), ".")
	return path.ReplaceExtension(ctx, extWithoutLeadingDot+".valid")
}

// buildRuleToGenerateHiddenApiFlags creates a rule to create the monolithic hidden API flags from
// the flags from all the modules, the stub flags, augmented with some additional configuration
// files.
//
// baseFlagsPath is the path to the flags file containing all the information from the stubs plus
// an entry for every single member in the dex implementation jars of the individual modules. Every
// signature in any of the other files MUST be included in this file.
//
// annotationFlags is the path to the annotation flags file generated from annotation information
// in each module.
//
// hiddenAPIInfo is a struct containing paths to files that augment the information provided by
// the annotationFlags.
func buildRuleToGenerateHiddenApiFlags(ctx android.BuilderContext, name, desc string,
	outputPath android.WritablePath, baseFlagsPath android.Path, annotationFlags android.Path,
	flagFilesByCategory FlagFilesByCategory, allFlagsPaths android.Paths, generatedRemovedDexSignatures android.OptionalPath) {

	// The file which is used to record that the flags file is valid.
	var validFile android.WritablePath

	// If there are flag files that have been generated by fragments on which this depends then use
	// them to validate the flag file generated by the rules created by this method.
	if len(allFlagsPaths) > 0 {
		// The flags file generated by the rule created by this method needs to be validated to ensure
		// that it is consistent with the flag files generated by the individual fragments.

		validFile = pathForValidation(ctx, outputPath)

		// Create a rule to validate the output from the following rule.
		rule := android.NewRuleBuilder(pctx, ctx)
		rule.Command().
			BuiltTool("verify_overlaps").
			Input(outputPath).
			Inputs(allFlagsPaths).
			// If validation passes then update the file that records that.
			Text("&& touch").Output(validFile)
		rule.Build(name+"Validation", desc+" validation")
	}

	// Create the rule that will generate the flag files.
	tempPath := tempPathForRestat(ctx, outputPath)
	rule := android.NewRuleBuilder(pctx, ctx)
	command := rule.Command().
		BuiltTool("generate_hiddenapi_lists").
		FlagWithInput("--csv ", baseFlagsPath).
		Input(annotationFlags).
		FlagWithOutput("--output ", tempPath)

	// Add the options for the different categories of flag files.
	for _, category := range HiddenAPIFlagFileCategories {
		paths := flagFilesByCategory[category]
		for _, path := range paths {
			category.commandMutator(command, path)
		}
	}

	// If available then pass the automatically generated file containing dex signatures of removed
	// API members to the rule so they can be marked as removed.
	if generatedRemovedDexSignatures.Valid() {
		hiddenAPIRemovedFlagFileCategory.commandMutator(command, generatedRemovedDexSignatures.Path())
	}

	commitChangeForRestat(rule, tempPath, outputPath)

	if validFile != nil {
		// Add the file that indicates that the file generated by this is valid.
		//
		// This will cause the validation rule above to be run any time that the output of this rule
		// changes but the validation will run in parallel with other rules that depend on this file.
		command.Validation(validFile)
	}

	rule.Build(name, desc)
}

// hiddenAPIRulesForBootclasspathFragment will generate all the flags for a fragment of the
// bootclasspath and then encode the flags into the boot dex files.
//
// It takes:
// * Map from android.SdkKind to stub dex jar paths defining the API for that sdk kind.
// * The list of modules that are the contents of the fragment.
// * The additional manually curated flag files to use.
//
// It generates:
// * stub-flags.csv
// * annotation-flags.csv
// * metadata.csv
// * index.csv
// * all-flags.csv
// * encoded boot dex files
func hiddenAPIRulesForBootclasspathFragment(ctx android.ModuleContext, contents []android.Module, input HiddenAPIFlagInput) *HiddenAPIOutput {
	hiddenApiSubDir := "modular-hiddenapi"

	// Gather information about the boot dex files for the boot libraries provided by this fragment.
	bootDexInfoByModule := extractBootDexInfoFromModules(ctx, contents)

	// Generate the stub-flags.csv.
	stubFlagsCSV := android.PathForModuleOut(ctx, hiddenApiSubDir, "stub-flags.csv")
	rule := ruleToGenerateHiddenAPIStubFlagsFile(ctx, stubFlagsCSV, bootDexInfoByModule.bootDexJars(), input)
	rule.Build("modularHiddenAPIStubFlagsFile", "modular hiddenapi stub flags")

	// Extract the classes jars from the contents.
	classesJars := extractClassesJarsFromModules(contents)

	// Generate the set of flags from the annotations in the source code.
	annotationFlagsCSV := android.PathForModuleOut(ctx, hiddenApiSubDir, "annotation-flags.csv")
	buildRuleToGenerateAnnotationFlags(ctx, "modular hiddenapi annotation flags", classesJars, stubFlagsCSV, annotationFlagsCSV)

	// Generate the metadata from the annotations in the source code.
	metadataCSV := android.PathForModuleOut(ctx, hiddenApiSubDir, "metadata.csv")
	buildRuleToGenerateMetadata(ctx, "modular hiddenapi metadata", classesJars, stubFlagsCSV, metadataCSV)

	// Generate the index file from the CSV files in the classes jars.
	indexCSV := android.PathForModuleOut(ctx, hiddenApiSubDir, "index.csv")
	buildRuleToGenerateIndex(ctx, "modular hiddenapi index", classesJars, indexCSV)

	// Removed APIs need to be marked and in order to do that the hiddenAPIInfo needs to specify files
	// containing dex signatures of all the removed APIs. In the monolithic files that is done by
	// manually combining all the removed.txt files for each API and then converting them to dex
	// signatures, see the combined-removed-dex module. This does that automatically by using the
	// *removed.txt files retrieved from the java_sdk_library modules that are specified in the
	// stub_libs and contents properties of a bootclasspath_fragment.
	removedDexSignatures := buildRuleToGenerateRemovedDexSignatures(ctx, input.RemovedTxtFiles)

	// Generate the all-flags.csv which are the flags that will, in future, be encoded into the dex
	// files.
	allFlagsCSV := android.PathForModuleOut(ctx, hiddenApiSubDir, "all-flags.csv")
	buildRuleToGenerateHiddenApiFlags(ctx, "modularHiddenApiAllFlags", "modular hiddenapi all flags", allFlagsCSV, stubFlagsCSV, annotationFlagsCSV, input.FlagFilesByCategory, nil, removedDexSignatures)

	// Encode the flags into the boot dex files.
	encodedBootDexJarsByModule := map[string]android.Path{}
	outputDir := android.PathForModuleOut(ctx, "hiddenapi-modular/encoded").OutputPath
	for _, name := range android.SortedStringKeys(bootDexInfoByModule) {
		bootDexInfo := bootDexInfoByModule[name]
		unencodedDex := bootDexInfo.path
		encodedDex := hiddenAPIEncodeDex(ctx, unencodedDex, allFlagsCSV, bootDexInfo.uncompressDex, outputDir)
		encodedBootDexJarsByModule[name] = encodedDex
	}

	// Store the paths in the info for use by other modules and sdk snapshot generation.
	output := HiddenAPIOutput{
		HiddenAPIFlagOutput: HiddenAPIFlagOutput{
			StubFlagsPath:       stubFlagsCSV,
			AnnotationFlagsPath: annotationFlagsCSV,
			MetadataPath:        metadataCSV,
			IndexPath:           indexCSV,
			AllFlagsPath:        allFlagsCSV,
		},
		EncodedBootDexFilesByModule: encodedBootDexJarsByModule,
	}
	return &output
}

func buildRuleToGenerateRemovedDexSignatures(ctx android.ModuleContext, removedTxtFiles android.Paths) android.OptionalPath {
	if len(removedTxtFiles) == 0 {
		return android.OptionalPath{}
	}

	output := android.PathForModuleOut(ctx, "modular-hiddenapi/removed-dex-signatures.txt")

	rule := android.NewRuleBuilder(pctx, ctx)
	rule.Command().
		BuiltTool("metalava").
		Flag("--no-banner").
		Inputs(removedTxtFiles).
		FlagWithOutput("--dex-api ", output)
	rule.Build("modular-hiddenapi-removed-dex-signatures", "modular hiddenapi removed dex signatures")
	return android.OptionalPathForPath(output)
}

// extractBootDexJarsFromModules extracts the boot dex jars from the supplied modules.
func extractBootDexJarsFromModules(ctx android.ModuleContext, contents []android.Module) bootDexJarByModule {
	bootDexJars := bootDexJarByModule{}
	for _, module := range contents {
		hiddenAPIModule := hiddenAPIModuleFromModule(ctx, module)
		if hiddenAPIModule == nil {
			continue
		}
		bootDexJar := retrieveBootDexJarFromHiddenAPIModule(ctx, hiddenAPIModule)
		bootDexJars.addPath(module, bootDexJar)
	}
	return bootDexJars
}

func hiddenAPIModuleFromModule(ctx android.BaseModuleContext, module android.Module) hiddenAPIModule {
	if hiddenAPIModule, ok := module.(hiddenAPIModule); ok {
		return hiddenAPIModule
	} else if _, ok := module.(*DexImport); ok {
		// Ignore this for the purposes of hidden API processing
	} else {
		ctx.ModuleErrorf("module %s does not implement hiddenAPIModule", module)
	}

	return nil
}

// bootDexInfo encapsulates both the path and uncompressDex status retrieved from a hiddenAPIModule.
type bootDexInfo struct {
	// The path to the dex jar that has not had hidden API flags encoded into it.
	path android.Path

	// Indicates whether the dex jar needs uncompressing before encoding.
	uncompressDex bool
}

// bootDexInfoByModule is a map from module name (as returned by module.Name()) to the boot dex
// path (as returned by hiddenAPIModule.bootDexJar()) and the uncompressDex flag.
type bootDexInfoByModule map[string]bootDexInfo

// bootDexJars returns the boot dex jar paths sorted by their keys.
func (b bootDexInfoByModule) bootDexJars() android.Paths {
	paths := android.Paths{}
	for _, m := range android.SortedStringKeys(b) {
		paths = append(paths, b[m].path)
	}
	return paths
}

// extractBootDexInfoFromModules extracts the boot dex jar and uncompress dex state from
// each of the supplied modules which must implement hiddenAPIModule.
func extractBootDexInfoFromModules(ctx android.ModuleContext, contents []android.Module) bootDexInfoByModule {
	bootDexJarsByModule := bootDexInfoByModule{}
	for _, module := range contents {
		hiddenAPIModule := module.(hiddenAPIModule)
		bootDexJar := retrieveBootDexJarFromHiddenAPIModule(ctx, hiddenAPIModule)
		bootDexJarsByModule[module.Name()] = bootDexInfo{
			path:          bootDexJar,
			uncompressDex: *hiddenAPIModule.uncompressDex(),
		}
	}

	return bootDexJarsByModule
}

// retrieveBootDexJarFromHiddenAPIModule retrieves the boot dex jar from the hiddenAPIModule.
//
// If the module does not provide a boot dex jar, i.e. the returned boot dex jar is nil, then  that
// create a fake path and either report an error immediately or defer reporting of the error until
// the path is actually used.
func retrieveBootDexJarFromHiddenAPIModule(ctx android.ModuleContext, module hiddenAPIModule) android.Path {
	bootDexJar := module.bootDexJar()
	if bootDexJar == nil {
		fake := android.PathForModuleOut(ctx, fmt.Sprintf("fake/boot-dex/%s.jar", module.Name()))
		bootDexJar = fake

		handleMissingDexBootFile(ctx, module, fake)
	}
	return bootDexJar
}

// extractClassesJarsFromModules extracts the class jars from the supplied modules.
func extractClassesJarsFromModules(contents []android.Module) android.Paths {
	classesJars := android.Paths{}
	for _, module := range contents {
		classesJars = append(classesJars, retrieveClassesJarsFromModule(module)...)
	}
	return classesJars
}

// retrieveClassesJarsFromModule retrieves the classes jars from the supplied module.
func retrieveClassesJarsFromModule(module android.Module) android.Paths {
	if hiddenAPIModule, ok := module.(hiddenAPIModule); ok {
		return hiddenAPIModule.classesJars()
	}

	return nil
}

// deferReportingMissingBootDexJar returns true if a missing boot dex jar should not be reported by
// Soong but should instead only be reported in ninja if the file is actually built.
func deferReportingMissingBootDexJar(ctx android.ModuleContext, module android.Module) bool {
	// TODO(b/179354495): Remove this workaround when it is unnecessary.
	// Prebuilt modules like framework-wifi do not yet provide dex implementation jars. So,
	// create a fake one that will cause a build error only if it is used.
	if ctx.Config().AlwaysUsePrebuiltSdks() {
		return true
	}

	// Any missing dependency should be allowed.
	if ctx.Config().AllowMissingDependencies() {
		return true
	}

	// This is called for both platform_bootclasspath and bootclasspath_fragment modules.
	//
	// A bootclasspath_fragment module should only use the APEX variant of source or prebuilt modules.
	// Ideally, a bootclasspath_fragment module should never have a platform variant created for it
	// but unfortunately, due to b/187910671 it does.
	//
	// That causes issues when obtaining a boot dex jar for a prebuilt module as a prebuilt module
	// used by a bootclasspath_fragment can only provide a boot dex jar when it is part of APEX, i.e.
	// has an APEX variant not a platform variant.
	//
	// There are some other situations when a prebuilt module used by a bootclasspath_fragment cannot
	// provide a boot dex jar:
	// 1. If the bootclasspath_fragment is not exported by the prebuilt_apex/apex_set module then it
	//    does not have an APEX variant and only has a platform variant and neither do its content
	//    modules.
	// 2. Some build configurations, e.g. setting TARGET_BUILD_USE_PREBUILT_SDKS causes all
	//    java_sdk_library_import modules to be treated as preferred and as many of them are not part
	//    of an apex they cannot provide a boot dex jar.
	//
	// The first case causes problems when the affected prebuilt modules are preferred but that is an
	// invalid configuration and it is ok for it to fail as the work to enable that is not yet
	// complete. The second case is used for building targets that do not use boot dex jars and so
	// deferring error reporting to ninja is fine as the affected ninja targets should never be built.
	// That is handled above.
	//
	// A platform_bootclasspath module can use libraries from both platform and APEX variants. Unlike
	// the bootclasspath_fragment it supports dex_import modules which provides the dex file. So, it
	// can obtain a boot dex jar from a prebuilt that is not part of an APEX. However, it is assumed
	// that if the library can be part of an APEX then it is the APEX variant that is used.
	//
	// This check handles the slightly different requirements of the bootclasspath_fragment and
	// platform_bootclasspath modules by only deferring error reporting for the platform variant of
	// a prebuilt modules that has other variants which are part of an APEX.
	//
	// TODO(b/187910671): Remove this once platform variants are no longer created unnecessarily.
	if android.IsModulePrebuilt(module) {
		if am, ok := module.(android.ApexModule); ok && am.InAnyApex() {
			apexInfo := ctx.OtherModuleProvider(module, android.ApexInfoProvider).(android.ApexInfo)
			if apexInfo.IsForPlatform() {
				return true
			}
		}
	}

	// A bootclasspath module that is part of a versioned sdk never provides a boot dex jar as there
	// is no equivalently versioned prebuilt APEX file from which it can be obtained. However,
	// versioned bootclasspath modules are processed by Soong so in order to avoid them causing build
	// failures missing boot dex jars need to be deferred.
	if android.IsModuleInVersionedSdk(ctx.Module()) {
		return true
	}

	return false
}

// handleMissingDexBootFile will either log a warning or create an error rule to create the fake
// file depending on the value returned from deferReportingMissingBootDexJar.
func handleMissingDexBootFile(ctx android.ModuleContext, module android.Module, fake android.WritablePath) {
	if deferReportingMissingBootDexJar(ctx, module) {
		// Create an error rule that pretends to create the output file but will actually fail if it
		// is run.
		ctx.Build(pctx, android.BuildParams{
			Rule:   android.ErrorRule,
			Output: fake,
			Args: map[string]string{
				"error": fmt.Sprintf("missing dependencies: boot dex jar for %s", module),
			},
		})
	} else {
		ctx.ModuleErrorf("module %s does not provide a dex jar", module)
	}
}

// retrieveEncodedBootDexJarFromModule returns a path to the boot dex jar from the supplied module's
// DexJarBuildPath() method.
//
// The returned path will usually be to a dex jar file that has been encoded with hidden API flags.
// However, under certain conditions, e.g. errors, or special build configurations it will return
// a path to a fake file.
func retrieveEncodedBootDexJarFromModule(ctx android.ModuleContext, module android.Module) android.Path {
	bootDexJar := module.(interface{ DexJarBuildPath() android.Path }).DexJarBuildPath()
	if bootDexJar == nil {
		fake := android.PathForModuleOut(ctx, fmt.Sprintf("fake/encoded-dex/%s.jar", module.Name()))
		bootDexJar = fake

		handleMissingDexBootFile(ctx, module, fake)
	}
	return bootDexJar
}

// extractEncodedDexJarsFromModules extracts the encoded dex jars from the supplied modules.
func extractEncodedDexJarsFromModules(ctx android.ModuleContext, contents []android.Module) bootDexJarByModule {
	encodedDexJarsByModuleName := bootDexJarByModule{}
	for _, module := range contents {
		path := retrieveEncodedBootDexJarFromModule(ctx, module)
		encodedDexJarsByModuleName.addPath(module, path)
	}
	return encodedDexJarsByModuleName
}