java_sdk_library use prebuilt jars for numeric sdk_version

Previously, when a library that used a numeric sdk version also
referenced a java_sdk_library it would use the current version of its
API. That was dangerous as there is an expectation that an app building
against a numbered version will also be targeted at that version and
so building against a later version of the API could hide runtime
incompatibilities.

This change will use prebuilt versions of the java_sdk_library's api
when being built for a numbered sdk version.

Bug: 148080325
Test: m droid
Change-Id: I3fd416553950785a443c1702e495a96debc33331

java/java_test.go

@@ -1099,6 +1099,12 @@ func TestJavaSdkLibrary(t *testing.T) {
 			libs: ["foo"],
 			sdk_version: "test_current",
 		}
+		java_library {
+			name: "baz-29",
+			srcs: ["c.java"],
+			libs: ["foo"],
+			sdk_version: "system_29",
+		}
 		`)
 
 	// check the existence of the internal modules
@@ -1138,6 +1144,13 @@ func TestJavaSdkLibrary(t *testing.T) {
 			"foo.stubs.test.jar")
 	}
 
+	baz29Javac := ctx.ModuleForTests("baz-29", "android_common").Rule("javac")
+	// tests if baz-29 is actually linked to the system 29 stubs lib
+	if !strings.Contains(baz29Javac.Args["classpath"], "prebuilts/sdk/29/system/foo.jar") {
+		t.Errorf("baz-29 javac classpath %v does not contain %q", baz29Javac.Args["classpath"],
+			"prebuilts/sdk/29/system/foo.jar")
+	}
+
 	// test if baz has exported SDK lib names foo and bar to qux
 	qux := ctx.ModuleForTests("qux", "android_common")
 	if quxLib, ok := qux.Module().(*Library); ok {

java/sdk_library.go

@@ -683,8 +683,9 @@ func (module *SdkLibrary) sdkJars(
 	sdkVersion sdkSpec,
 	headerJars bool) android.Paths {
 
-	// This module is just a wrapper for the stubs.
+	// If a specific numeric version has been requested or the build is explicitly configured
-	if ctx.Config().UnbundledBuildUsePrebuiltSdks() {
+	// for it then use prebuilt versions of the sdk.
+	if sdkVersion.version.isNumbered() || ctx.Config().UnbundledBuildUsePrebuiltSdks() {
 		return module.PrebuiltJars(ctx, sdkVersion)
 	} else {
 		if !sdkVersion.specified() {

java/testing.go

@@ -61,6 +61,7 @@ func TestConfig(buildDir string, env map[string]string, bp string, fs map[string
 		"prebuilts/sdk/29/public/android.jar":         nil,
 		"prebuilts/sdk/29/public/framework.aidl":      nil,
 		"prebuilts/sdk/29/system/android.jar":         nil,
+		"prebuilts/sdk/29/system/foo.jar":             nil,
 		"prebuilts/sdk/current/core/android.jar":      nil,
 		"prebuilts/sdk/current/public/android.jar":    nil,
 		"prebuilts/sdk/current/public/framework.aidl": nil,