prebuilt_apex created ApexInfo must not include prebuilt_ prefix

As part of the work to modularize the hiddenAPI processing the
generation of the monolithic hidden API index file needs to be moved
to the platform_bootclasspath module type. Doing that broke the
TestBootDexJarsFromSourcesAndPrebuilts tests which checks the inputs to
the rule that creates that file. Fixing that required added a
platform_bootclasspath module to the test fixture for those tests which
highlighted an issue with the prebuilt_apex module.

Previously, when the prebuilt_apex created apex variants it would use
its own name as the apex variant name, even when that name included the
prebuilt_ prefix. That broke the platform_bootclasspath logic as it was
looking for apex variants for "myapex" but the only ones available were
"prebuilt_myapex".

This change ensures that it always uses the unprefixed name and fixes
the TestNoUpdatableJarsInBootImage to match. This also adds some
improved error reporting in platform_bootclasspath which helped debug
this problem.

Bug: 177892522
Test: m nothing
Change-Id: I3e88b5cec767f77dcc0e94b3ae38b499d07eadf0

apex/apex_test.go

@@ -4826,7 +4826,7 @@ func TestBootDexJarsFromSourcesAndPrebuilts(t *testing.T) {
 			name: "myapex",
 			enabled: false,
 			key: "myapex.key",
-			java_libs: ["libfoo"],
+			java_libs: ["libfoo", "libbar"],
 		}
 
 		apex_key {
@@ -4884,8 +4884,8 @@ func TestBootDexJarsFromSourcesAndPrebuilts(t *testing.T) {
 
 		// Make sure that the dex file from the prebuilt_apex contributes to the hiddenapi index file.
 		checkHiddenAPIIndexInputs(t, ctx, `
-.intermediates/prebuilt_libbar/android_common_prebuilt_myapex/hiddenapi/index.csv
-.intermediates/prebuilt_libfoo/android_common_prebuilt_myapex/hiddenapi/index.csv
+.intermediates/prebuilt_libbar/android_common_myapex/hiddenapi/index.csv
+.intermediates/prebuilt_libfoo/android_common_myapex/hiddenapi/index.csv
 `)
 	})
 }
@@ -6555,6 +6555,11 @@ func testDexpreoptWithApexes(t *testing.T, bp, errmsg string, preparer android.F
 		PrepareForTestWithApexBuildComponents,
 		preparer,
 		fs.AddToFixture(),
+		android.FixtureAddTextFile("frameworks/base/boot/Android.bp", `
+			platform_bootclasspath {
+				name: "platform-bootclasspath",
+			}
+		`),
 	).
 		ExtendWithErrorHandler(errorHandler).
 		RunTestWithBp(t, bp)
@@ -6657,13 +6662,13 @@ func TestNoUpdatableJarsInBootImage(t *testing.T) {
 	})
 
 	t.Run("nonexistent jar in the ART boot image => error", func(t *testing.T) {
-		err := "failed to find a dex jar path for module 'nonexistent'"
+		err := `"platform-bootclasspath" depends on undefined module "nonexistent"`
 		preparer := java.FixtureConfigureBootJars("platform:nonexistent")
 		testNoUpdatableJarsInBootImage(t, err, preparer)
 	})
 
 	t.Run("nonexistent jar in the framework boot image => error", func(t *testing.T) {
-		err := "failed to find a dex jar path for module 'nonexistent'"
+		err := `"platform-bootclasspath" depends on undefined module "nonexistent"`
 		preparer := java.FixtureConfigureBootJars("platform:nonexistent")
 		testNoUpdatableJarsInBootImage(t, err, preparer)
 	})

apex/prebuilt.go

@@ -172,7 +172,7 @@ func (p *prebuiltCommon) apexInfoMutator(mctx android.TopDownMutatorContext) {
 
 	// Create an ApexInfo for the prebuilt_apex.
 	apexInfo := android.ApexInfo{
-		ApexVariationName: mctx.ModuleName(),
+		ApexVariationName: android.RemoveOptionalPrebuiltPrefix(mctx.ModuleName()),
 		InApexes:          []string{mctx.ModuleName()},
 		ApexContents:      []*android.ApexContents{apexContents},
 		ForPrebuiltApex:   true,

java/platform_bootclasspath.go

@@ -208,7 +208,30 @@ func addDependencyOntoApexModulePair(ctx android.BottomUpMutatorContext, apex st
 	// error, unless missing dependencies are allowed. The simplest way to handle that is to add a
 	// dependency that will not be satisfied and the default behavior will handle it.
 	if !addedDep {
-		ctx.AddFarVariationDependencies(variations, tag, name)
+		// Add dependency on the unprefixed (i.e. source or renamed prebuilt) module which we know does
+		// not exist. The resulting error message will contain useful information about the available
+		// variants.
+		reportMissingVariationDependency(ctx, variations, name)
+
+		// Add dependency on the missing prefixed prebuilt variant too if a module with that name exists
+		// so that information about its available variants will be reported too.
+		if ctx.OtherModuleExists(prebuiltName) {
+			reportMissingVariationDependency(ctx, variations, prebuiltName)
+		}
+	}
+}
+
+// reportMissingVariationDependency intentionally adds a dependency on a missing variation in order
+// to generate an appropriate error message with information about the available variations.
+func reportMissingVariationDependency(ctx android.BottomUpMutatorContext, variations []blueprint.Variation, name string) {
+	modules := ctx.AddFarVariationDependencies(variations, nil, name)
+	if len(modules) != 1 {
+		panic(fmt.Errorf("Internal Error: expected one module, found %d", len(modules)))
+		return
+	}
+	if modules[0] != nil {
+		panic(fmt.Errorf("Internal Error: expected module to be missing but was found: %q", modules[0]))
+		return
 	}
 }