Use system modules for prebuilt SDKs >=30

Prebuilt SDKs >=30 now contain core-for-system-modules.jar,
convert them to system modules and use them when compiling against
the SDK to allow using javac -source 1.9 -target 1.9.

Bug: 117069453
Test: TestClasspath
Change-Id: Iebadad5980b952ed91c3ffd56cff1ce1827d3247
Merged-In: Iebadad5980b952ed91c3ffd56cff1ce1827d3247
diff --git a/java/java.go b/java/java.go
index de38b26..a8c104e 100644
--- a/java/java.go
+++ b/java/java.go
@@ -625,13 +625,15 @@
 			}
 		} else if sdkDep.useModule {
 			ctx.AddVariationDependencies(nil, bootClasspathTag, sdkDep.bootclasspath...)
-			ctx.AddVariationDependencies(nil, systemModulesTag, sdkDep.systemModules)
 			ctx.AddVariationDependencies(nil, java9LibTag, sdkDep.java9Classpath...)
 			if j.deviceProperties.EffectiveOptimizeEnabled() && sdkDep.hasStandardLibs() {
 				ctx.AddVariationDependencies(nil, proguardRaiseTag, config.DefaultBootclasspathLibraries...)
 				ctx.AddVariationDependencies(nil, proguardRaiseTag, config.DefaultLibraries...)
 			}
 		}
+		if sdkDep.systemModules != "" {
+			ctx.AddVariationDependencies(nil, systemModulesTag, sdkDep.systemModules)
+		}
 
 		if ctx.ModuleName() == "android_stubs_current" ||
 			ctx.ModuleName() == "android_system_stubs_current" ||
@@ -1034,19 +1036,10 @@
 }
 
 func getJavaVersion(ctx android.ModuleContext, javaVersion string, sdkContext sdkContext) javaVersion {
-	sdk, err := sdkContext.sdkVersion().effectiveVersion(ctx)
-	if err != nil {
-		ctx.PropertyErrorf("sdk_version", "%s", err)
-	}
 	if javaVersion != "" {
 		return normalizeJavaVersion(ctx, javaVersion)
-	} else if ctx.Device() && sdk <= 23 {
-		return JAVA_VERSION_7
-	} else if ctx.Device() && sdk <= 29 {
-		return JAVA_VERSION_8
-	} else if ctx.Device() && ctx.Config().UnbundledBuildUsePrebuiltSdks() {
-		// TODO(b/142896162): once we have prebuilt system modules we can use 1.9 for unbundled builds
-		return JAVA_VERSION_8
+	} else if ctx.Device() {
+		return sdkContext.sdkVersion().defaultJavaLanguageVersion(ctx)
 	} else {
 		return JAVA_VERSION_9
 	}