Export dex implementation jars from prebuilt_apex

Dexpreopt and boot jars package check all require access to dex
implementation jars created for java_library and java_sdk_library. They
were available when building from source but not when building from
prebuilts, even though they are embedded within the .apex files that
are referenced from prebuilt_apex.

This changes adds support to prebuilt_apex to export the dex
implementation jars and updates java_import to use those exported dex
implementation jars.

In a source build dexpreopt/boot jars package check access the apex (or
platform) specific variant of a java_library, e.g. core-oj, from which
it retrieves the dex implementation jar path.

After this change in a prebuilt build dexpreopt/boot jars package check
behave in the same way except in this case they retrieve the dex
implementation jar path from the apex (or platform) specific variant of
the java_import, e.g. core-oj.

The work to export files from a `.apex` file for use by other modules
is performed by a new `deapexer` module type. It is not used directly
in an `Android.bp` file but instead is created implicitly by
`prebuilt_apex`,

In order to do that this contains the following changes:
* Adds a new `dexapexer` module type to handle the exporting of files
  from the `.apex` file.
* Adds an exported_java_libs property to prebuilt_apex to specify the
  set of libraries whose dex implementation jars need exporting.
* Creates apex specific variants of the libraries listed in the
  exported_java_libs property.
* Adds the set of exported files to the ApexInfo to make them available
  to the apex specific variants.
* Prevents the prebuilt_apex variants from being merged together as
  they will not be compatible.
* Modifies java_import to use the exported file for variants of a
  prebuilt_apex.
* Adds a ninja rule to unpack (using deapexer) the contents of the
  prebuilt_apex's apex file, verify that the required files are present
  and make them available as outputs for other rules to use.
* Some minor refactorings to support these changes.
* Adds tests to cover prebuilt only, prebuilt with source preferred,
  and prebuilt preferred with source.

Test: m nothing
Bug: 171061220
Change-Id: Ic9bed81fb65b92f0d59f64c0bce168a9ed44cfac

java/java.go

@@ -2859,6 +2859,7 @@ func (j *Import) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 	j.classLoaderContexts = make(dexpreopt.ClassLoaderContextMap)
 
 	var flags javaBuilderFlags
+	var deapexerModule android.Module
 
 	ctx.VisitDirectDeps(func(module android.Module) {
 		tag := ctx.OtherModuleDependencyTag(module)
@@ -2879,6 +2880,11 @@ func (j *Import) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 		}
 
 		addCLCFromDep(ctx, module, j.classLoaderContexts)
+
+		// Save away the `deapexer` module on which this depends, if any.
+		if tag == android.DeapexerTag {
+			deapexerModule = module
+		}
 	})
 
 	if Bool(j.properties.Installable) {
@@ -2888,39 +2894,60 @@ func (j *Import) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 
 	j.exportAidlIncludeDirs = android.PathsForModuleSrc(ctx, j.properties.Aidl.Export_include_dirs)
 
-	if ctx.Device() && Bool(j.dexProperties.Compile_dex) {
-		sdkDep := decodeSdkDep(ctx, sdkContext(j))
-		if sdkDep.invalidVersion {
-			ctx.AddMissingDependencies(sdkDep.bootclasspath)
-			ctx.AddMissingDependencies(sdkDep.java9Classpath)
-		} else if sdkDep.useFiles {
-			// sdkDep.jar is actually equivalent to turbine header.jar.
-			flags.classpath = append(flags.classpath, sdkDep.jars...)
+	if ctx.Device() {
+		// If this is a variant created for a prebuilt_apex then use the dex implementation jar
+		// obtained from the associated deapexer module.
+		ai := ctx.Provider(android.ApexInfoProvider).(android.ApexInfo)
+		if ai.ForPrebuiltApex {
+			if deapexerModule == nil {
+				// This should never happen as a variant for a prebuilt_apex is only created if the
+				// deapxer module has been configured to export the dex implementation jar for this module.
+				ctx.ModuleErrorf("internal error: module %q does not depend on a `deapexer` module for prebuilt_apex %q",
+					j.Name(), ai.ApexVariationName)
+			}
+
+			// Get the path of the dex implementation jar from the `deapexer` module.
+			di := ctx.OtherModuleProvider(deapexerModule, android.DeapexerProvider).(android.DeapexerInfo)
+			j.dexJarFile = di.PrebuiltExportPath(j.BaseModuleName(), ".dexjar")
+			if j.dexJarFile == nil {
+				// This should never happen as a variant for a prebuilt_apex is only created if the
+				// prebuilt_apex has been configured to export the java library dex file.
+				ctx.ModuleErrorf("internal error: no dex implementation jar available from prebuilt_apex %q", deapexerModule.Name())
+			}
+		} else if Bool(j.dexProperties.Compile_dex) {
+			sdkDep := decodeSdkDep(ctx, sdkContext(j))
+			if sdkDep.invalidVersion {
+				ctx.AddMissingDependencies(sdkDep.bootclasspath)
+				ctx.AddMissingDependencies(sdkDep.java9Classpath)
+			} else if sdkDep.useFiles {
+				// sdkDep.jar is actually equivalent to turbine header.jar.
+				flags.classpath = append(flags.classpath, sdkDep.jars...)
+			}
+
+			// Dex compilation
+
+			j.dexpreopter.installPath = android.PathForModuleInstall(ctx, "framework", jarName)
+			if j.dexProperties.Uncompress_dex == nil {
+				// If the value was not force-set by the user, use reasonable default based on the module.
+				j.dexProperties.Uncompress_dex = proptools.BoolPtr(shouldUncompressDex(ctx, &j.dexpreopter))
+			}
+			j.dexpreopter.uncompressedDex = *j.dexProperties.Uncompress_dex
+
+			var dexOutputFile android.ModuleOutPath
+			dexOutputFile = j.dexer.compileDex(ctx, flags, j.minSdkVersion(), outputFile, jarName)
+			if ctx.Failed() {
+				return
+			}
+
+			configurationName := j.BaseModuleName()
+			primary := j.Prebuilt().UsePrebuilt()
+
+			// Hidden API CSV generation and dex encoding
+			dexOutputFile = j.hiddenAPI.hiddenAPI(ctx, configurationName, primary, dexOutputFile, outputFile,
+				proptools.Bool(j.dexProperties.Uncompress_dex))
+
+			j.dexJarFile = dexOutputFile
 		}
-
-		// Dex compilation
-
-		j.dexpreopter.installPath = android.PathForModuleInstall(ctx, "framework", jarName)
-		if j.dexProperties.Uncompress_dex == nil {
-			// If the value was not force-set by the user, use reasonable default based on the module.
-			j.dexProperties.Uncompress_dex = proptools.BoolPtr(shouldUncompressDex(ctx, &j.dexpreopter))
-		}
-		j.dexpreopter.uncompressedDex = *j.dexProperties.Uncompress_dex
-
-		var dexOutputFile android.ModuleOutPath
-		dexOutputFile = j.dexer.compileDex(ctx, flags, j.minSdkVersion(), outputFile, jarName)
-		if ctx.Failed() {
-			return
-		}
-
-		configurationName := j.BaseModuleName()
-		primary := j.Prebuilt().UsePrebuilt()
-
-		// Hidden API CSV generation and dex encoding
-		dexOutputFile = j.hiddenAPI.hiddenAPI(ctx, configurationName, primary, dexOutputFile, outputFile,
-			proptools.Bool(j.dexProperties.Uncompress_dex))
-
-		j.dexJarFile = dexOutputFile
 	}
 }