Add default_to_stubs option to java_sdk_library

Previously, when a lib that doesn't have sdk_version property set
depends on a java_sdk_library, the impl library was used for linking.
This might be too permissive because the client lib might be using empty
sdk_version because it needed some private APIs from the platform, but
not from the java_sdk_library. This actually happend for some of the CTS
tests. They don't set sdk_version, but were directly depending on
android.test.[base|runner|mock].stubs libraries. If we switch the
references to the stub libraries into the corresponding java_sdk_library
modules (e.g. aandroid.test.[base|runner|mock]), then we would be
allowing private APIs to the CTS tests, which is not good.

To solve this problem, default_to_stub property is introduced. It when set
to true prevents the impl lib from being used for linking. When a module
that doesn't have sdk_version depends on it, the widest API surface that
the java_sdk_library provides is linked instead.

Bug: 157007292
Test: m
Merged-In: Id2acc3cafb71d1e90d4fdc9c0c70a73983355e0f
Change-Id: Id2acc3cafb71d1e90d4fdc9c0c70a73983355e0f
(cherry picked from commit 932cdfeb06)

java/java_test.go

@@ -1465,6 +1465,33 @@ func TestJavaSdkLibrary_FallbackScope(t *testing.T) {
 		`)
 }
 
+func TestJavaSdkLibrary_DefaultToStubs(t *testing.T) {
+	ctx, _ := testJava(t, `
+		java_sdk_library {
+			name: "foo",
+			srcs: ["a.java"],
+			system: {
+				enabled: true,
+			},
+			default_to_stubs: true,
+		}
+
+		java_library {
+			name: "baz",
+			srcs: ["a.java"],
+			libs: ["foo"],
+			// does not have sdk_version set, should fallback to module,
+			// which will then fallback to system because the module scope
+			// is not enabled.
+		}
+		`)
+	// The baz library should depend on the system stubs jar.
+	bazLibrary := ctx.ModuleForTests("baz", "android_common").Rule("javac")
+	if expected, actual := `^-classpath .*:/[^:]*/turbine-combined/foo\.stubs.system\.jar$`, bazLibrary.Args["classpath"]; !regexp.MustCompile(expected).MatchString(actual) {
+		t.Errorf("expected %q, found %#q", expected, actual)
+	}
+}
+
 var compilerFlagsTestCases = []struct {
 	in  string
 	out bool