From 40d731a4c3757ad478bd1a1356b87978f4570016 Mon Sep 17 00:00:00 2001
From: Jared Duke <jdduke@google.com>
Date: Tue, 20 Sep 2022 15:32:14 -0700
Subject: [PATCH] Provide platform build flag to R8/D8

Provide the `--android-platform-build` flag to R8/D8 for targets that do
not specify a stable min SDK. This includes all targets that do not
specificy an SDK version (e.g., services.jar, SystemUI.apk) and all
targets that specify core_platform (e.g., framework.jar).

Follow-up work will expand the set of cases that qualify for this flag,
but for now this captures some of the highest priority targets.

Bug: 232073181
Test: m + presubmit + validate verbose.log
Change-Id: Idad32c80490a101c049b7f937807a615564ca8ef
---
 java/dex.go      | 10 ++++++++++
 java/dex_test.go | 26 +++++++++++++++++++++++++-
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/java/dex.go b/java/dex.go
index a44d7921f..2b787032e 100644
--- a/java/dex.go
+++ b/java/dex.go
@@ -200,6 +200,16 @@ func (d *dexer) dexCommonFlags(ctx android.ModuleContext,
 			"--verbose")
 	}
 
+	// Supplying the platform build flag disables various features like API modeling and desugaring.
+	// For targets with a stable min SDK version (i.e., when the min SDK is both explicitly specified
+	// and managed+versioned), we suppress this flag to ensure portability.
+	// Note: Targets with a min SDK kind of core_platform (e.g., framework.jar) or unspecified (e.g.,
+	// services.jar), are not classified as stable, which is WAI.
+	// TODO(b/232073181): Expand to additional min SDK cases after validation.
+	if !minSdkVersion.Stable() {
+		flags = append(flags, "--android-platform-build")
+	}
+
 	effectiveVersion, err := minSdkVersion.EffectiveVersion(ctx)
 	if err != nil {
 		ctx.PropertyErrorf("min_sdk_version", "%s", err)
diff --git a/java/dex_test.go b/java/dex_test.go
index a3e2deda4..66178732a 100644
--- a/java/dex_test.go
+++ b/java/dex_test.go
@@ -30,6 +30,19 @@ func TestR8(t *testing.T) {
 			platform_apis: true,
 		}
 
+		android_app {
+			name: "stable_app",
+			srcs: ["foo.java"],
+			sdk_version: "current",
+			min_sdk_version: "31",
+		}
+
+		android_app {
+			name: "core_platform_app",
+			srcs: ["foo.java"],
+			sdk_version: "core_platform",
+		}
+
 		java_library {
 			name: "lib",
 			srcs: ["foo.java"],
@@ -42,11 +55,15 @@ func TestR8(t *testing.T) {
 	`)
 
 	app := result.ModuleForTests("app", "android_common")
+	stableApp := result.ModuleForTests("stable_app", "android_common")
+	corePlatformApp := result.ModuleForTests("core_platform_app", "android_common")
 	lib := result.ModuleForTests("lib", "android_common")
 	staticLib := result.ModuleForTests("static_lib", "android_common")
 
 	appJavac := app.Rule("javac")
 	appR8 := app.Rule("r8")
+	stableAppR8 := stableApp.Rule("r8")
+	corePlatformAppR8 := corePlatformApp.Rule("r8")
 	libHeader := lib.Output("turbine-combined/lib.jar").Output
 	staticLibHeader := staticLib.Output("turbine-combined/static_lib.jar").Output
 
@@ -61,6 +78,12 @@ func TestR8(t *testing.T) {
 		appR8.Args["r8Flags"], staticLibHeader.String())
 	android.AssertStringDoesContain(t, "expected -ignorewarnings in app r8 flags",
 		appR8.Args["r8Flags"], "-ignorewarnings")
+	android.AssertStringDoesContain(t, "expected --android-platform-build in app r8 flags",
+		appR8.Args["r8Flags"], "--android-platform-build")
+	android.AssertStringDoesNotContain(t, "expected no --android-platform-build in stable_app r8 flags",
+		stableAppR8.Args["r8Flags"], "--android-platform-build")
+	android.AssertStringDoesContain(t, "expected --android-platform-build in core_platform_app r8 flags",
+		corePlatformAppR8.Args["r8Flags"], "--android-platform-build")
 }
 
 func TestR8Flags(t *testing.T) {
@@ -88,7 +111,8 @@ func TestR8Flags(t *testing.T) {
 		appR8.Args["r8Flags"], "-dontobfuscate")
 	android.AssertStringDoesNotContain(t, "expected no -ignorewarnings in app r8 flags",
 		appR8.Args["r8Flags"], "-ignorewarnings")
-
+	android.AssertStringDoesContain(t, "expected --android-platform-build in app r8 flags",
+		appR8.Args["r8Flags"], "--android-platform-build")
 }
 
 func TestD8(t *testing.T) {