Enable Proguard by default on release mode (#39986)

Author: Emmanuel Garcia

packages/flutter_tools/gradle/flutter.gradle

@@ -132,16 +132,6 @@ class FlutterPlugin implements Plugin<Project> {
             }
         }
 
-        // Add custom build types
-        project.android.buildTypes {
-            profile {
-                initWith debug
-                if (it.hasProperty('matchingFallbacks')) {
-                    matchingFallbacks = ['debug', 'release']
-                }
-            }
-        }
-
         String flutterRootPath = resolveProperty(project, "flutter.sdk", System.env.FLUTTER_ROOT)
         if (flutterRootPath == null) {
             throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file or with a FLUTTER_ROOT environment variable.")
@@ -154,6 +144,30 @@ class FlutterPlugin implements Plugin<Project> {
         String flutterExecutableName = Os.isFamily(Os.FAMILY_WINDOWS) ? "flutter.bat" : "flutter"
         flutterExecutable = Paths.get(flutterRoot.absolutePath, "bin", flutterExecutableName).toFile();
 
+        // Add custom build types.
+        project.android.buildTypes {
+            profile {
+                initWith debug
+                if (it.hasProperty("matchingFallbacks")) {
+                    matchingFallbacks = ["debug", "release"]
+                }
+            }
+        }
+
+        if (useProguard(project)) {
+            String flutterProguardRules = Paths.get(flutterRoot.absolutePath, "packages", "flutter_tools",
+                    "gradle", "flutter_proguard_rules.pro")
+            project.android.buildTypes {
+                release {
+                    minifyEnabled true
+                    useProguard true
+                    // Fallback to `android/app/proguard-rules.pro`.
+                    // This way, custom Proguard rules can be configured as needed.
+                    proguardFiles project.android.getDefaultProguardFile("proguard-android.txt"), flutterProguardRules, "proguard-rules.pro"
+                }
+            }
+        }
+
         if (useLocalEngine(project)) {
             String engineOutPath = project.property('localEngineOut')
             File engineOut = project.file(engineOutPath)
@@ -375,6 +389,14 @@ class FlutterPlugin implements Plugin<Project> {
         return false
     }
 
+
+    private static Boolean useProguard(Project project) {
+        if (project.hasProperty('proguard')) {
+            return project.property('proguard').toBoolean()
+        }
+        return false
+    }
+
     private static Boolean buildPluginAsAar() {
         return System.getProperty('build-plugins-as-aars') == 'true'
     }

packages/flutter_tools/gradle/flutter_proguard_rules.pro

@@ -0,0 +1,11 @@
+# Prevents `Fragment and FragmentActivity not found`.
+# TODO(blasten): Remove once we bring the Maven dependencies.
+-dontwarn io.flutter.embedding.**
+
+# Build the ephemeral app in a module project.
+# Prevents: Warning: library class <plugin-package> depends on program class io.flutter.plugin.**
+# This is due to plugins (libraries) depending on the embedding (the program jar)
+-dontwarn io.flutter.plugin.**
+
+# The android.** package is provided by the OS at runtime.
+-dontwarn android.**

packages/flutter_tools/lib/src/android/gradle.dart

@@ -10,6 +10,7 @@ import 'package:meta/meta.dart';
 import '../android/android_sdk.dart';
 import '../artifacts.dart';
 import '../base/common.dart';
+import '../base/context.dart';
 import '../base/file_system.dart';
 import '../base/logger.dart';
 import '../base/os.dart';
@@ -28,11 +29,39 @@ import '../reporting/reporting.dart';
 import 'android_sdk.dart';
 import 'android_studio.dart';
 
-final RegExp _assembleTaskPattern = RegExp(r'assemble(\S+)');
+/// Gradle utils in the current [AppContext].
+GradleUtils get gradleUtils => context.get<GradleUtils>();
+
+/// Provides utilities to run a Gradle task,
+/// such as finding the Gradle executable or constructing a Gradle project.
+class GradleUtils {
+  /// Empty constructor.
+  GradleUtils();
+
+  String _cachedExecutable;
+  /// Gets the Gradle executable path.
+  /// This is the `gradlew` or `gradlew.bat` script in the `android/` directory.
+  Future<String> getExecutable(FlutterProject project) async {
+    _cachedExecutable ??= await _initializeGradle(project);
+    return _cachedExecutable;
+  }
+
+  GradleProject _cachedAppProject;
+  /// Gets the [GradleProject] for the current [FlutterProject] if built as an app.
+  Future<GradleProject> get appProject async {
+    _cachedAppProject ??= await _readGradleProject(isLibrary: false);
+    return _cachedAppProject;
+  }
 
-GradleProject _cachedGradleAppProject;
-GradleProject _cachedGradleLibraryProject;
-String _cachedGradleExecutable;
+  GradleProject _cachedLibraryProject;
+  /// Gets the [GradleProject] for the current [FlutterProject] if built as a library.
+  Future<GradleProject> get libraryProject async {
+    _cachedLibraryProject ??= await _readGradleProject(isLibrary: true);
+    return _cachedLibraryProject;
+  }
+}
+
+final RegExp _assembleTaskPattern = RegExp(r'assemble(\S+)');
 
 enum FlutterPluginVersion {
   none,
@@ -103,29 +132,20 @@ Future<File> getGradleAppOut(AndroidProject androidProject) async {
     case FlutterPluginVersion.managed:
       // Fall through. The managed plugin matches plugin v2 for now.
     case FlutterPluginVersion.v2:
-      return fs.file((await _gradleAppProject()).apkDirectory.childFile('app.apk'));
+      final GradleProject gradleProject = await gradleUtils.appProject;
+      return fs.file(gradleProject.apkDirectory.childFile('app.apk'));
   }
   return null;
 }
 
-Future<GradleProject> _gradleAppProject() async {
-  _cachedGradleAppProject ??= await _readGradleProject(isLibrary: false);
-  return _cachedGradleAppProject;
-}
-
-Future<GradleProject> _gradleLibraryProject() async {
-  _cachedGradleLibraryProject ??= await _readGradleProject(isLibrary: true);
-  return _cachedGradleLibraryProject;
-}
-
 /// Runs `gradlew dependencies`, ensuring that dependencies are resolved and
 /// potentially downloaded.
 Future<void> checkGradleDependencies() async {
   final Status progress = logger.startProgress('Ensuring gradle dependencies are up to date...', timeout: timeoutConfiguration.slowOperation);
   final FlutterProject flutterProject = FlutterProject.current();
-  final String gradle = await _ensureGradle(flutterProject);
+  final String gradlew = await gradleUtils.getExecutable(flutterProject);
   await runCheckedAsync(
-    <String>[gradle, 'dependencies'],
+    <String>[gradlew, 'dependencies'],
     workingDirectory: flutterProject.android.hostAppGradleRoot.path,
     environment: _gradleEnv,
   );
@@ -189,7 +209,8 @@ void createSettingsAarGradle(Directory androidDirectory) {
 // of calculating the app properties using Gradle. This may take minutes.
 Future<GradleProject> _readGradleProject({bool isLibrary = false}) async {
   final FlutterProject flutterProject = FlutterProject.current();
-  final String gradle = await _ensureGradle(flutterProject);
+  final String gradlew = await gradleUtils.getExecutable(flutterProject);
+
   updateLocalProperties(project: flutterProject);
 
   final FlutterManifest manifest = flutterProject.manifest;
@@ -213,12 +234,12 @@ Future<GradleProject> _readGradleProject({bool isLibrary = false}) async {
   // flavors and build types defined in the project. If gradle fails, then check if the failure is due to t
   try {
     final RunResult propertiesRunResult = await runCheckedAsync(
-      <String>[gradle, isLibrary ? 'properties' : 'app:properties'],
+      <String>[gradlew, isLibrary ? 'properties' : 'app:properties'],
       workingDirectory: hostAppGradleRoot.path,
       environment: _gradleEnv,
     );
     final RunResult tasksRunResult = await runCheckedAsync(
-      <String>[gradle, isLibrary ? 'tasks': 'app:tasks', '--all', '--console=auto'],
+      <String>[gradlew, isLibrary ? 'tasks': 'app:tasks', '--all', '--console=auto'],
       workingDirectory: hostAppGradleRoot.path,
       environment: _gradleEnv,
     );
@@ -274,11 +295,6 @@ String _locateGradlewExecutable(Directory directory) {
   return null;
 }
 
-Future<String> _ensureGradle(FlutterProject project) async {
-  _cachedGradleExecutable ??= await _initializeGradle(project);
-  return _cachedGradleExecutable;
-}
-
 // Note: Gradle may be bootstrapped and possibly downloaded as a side-effect
 // of validating the Gradle executable. This may take several seconds.
 Future<String> _initializeGradle(FlutterProject project) async {
@@ -492,17 +508,15 @@ Future<void> buildGradleProject({
   // from the local.properties file.
   updateLocalProperties(project: project, buildInfo: androidBuildInfo.buildInfo);
 
-  final String gradle = await _ensureGradle(project);
-
   switch (getFlutterPluginVersion(project.android)) {
     case FlutterPluginVersion.none:
       // Fall through. Pretend it's v1, and just go for it.
     case FlutterPluginVersion.v1:
-      return _buildGradleProjectV1(project, gradle);
+      return _buildGradleProjectV1(project);
     case FlutterPluginVersion.managed:
       // Fall through. Managed plugin builds the same way as plugin v2.
     case FlutterPluginVersion.v2:
-      return _buildGradleProjectV2(project, gradle, androidBuildInfo, target, isBuildingBundle);
+      return _buildGradleProjectV2(project, androidBuildInfo, target, isBuildingBundle);
   }
 }
 
@@ -516,9 +530,9 @@ Future<void> buildGradleAar({
 
   GradleProject gradleProject;
   if (manifest.isModule) {
-    gradleProject = await _gradleAppProject();
+    gradleProject = await gradleUtils.appProject;
   } else if (manifest.isPlugin) {
-    gradleProject = await _gradleLibraryProject();
+    gradleProject = await gradleUtils.libraryProject;
   } else {
     throwToolExit('AARs can only be built for plugin or module projects.');
   }
@@ -538,12 +552,11 @@ Future<void> buildGradleAar({
     multilineOutput: true,
   );
 
-  final String gradle = await _ensureGradle(project);
-  final String gradlePath = fs.file(gradle).absolute.path;
+  final String gradlew = await gradleUtils.getExecutable(project);
   final String flutterRoot = fs.path.absolute(Cache.flutterRoot);
   final String initScript = fs.path.join(flutterRoot, 'packages','flutter_tools', 'gradle', 'aar_init_script.gradle');
   final List<String> command = <String>[
-    gradlePath,
+    gradlew,
     '-I=$initScript',
     '-Pflutter-root=$flutterRoot',
     '-Poutput-dir=${gradleProject.buildDirectory}',
@@ -601,7 +614,8 @@ Future<void> buildGradleAar({
   printStatus('Built ${fs.path.relative(repoDirectory.path)}.', color: TerminalColor.green);
 }
 
-Future<void> _buildGradleProjectV1(FlutterProject project, String gradle) async {
+Future<void> _buildGradleProjectV1(FlutterProject project) async {
+  final String gradlew = await gradleUtils.getExecutable(project);
   // Run 'gradlew build'.
   final Status status = logger.startProgress(
     'Running \'gradlew build\'...',
@@ -610,7 +624,7 @@ Future<void> _buildGradleProjectV1(FlutterProject project, String gradle) async
   );
   final Stopwatch sw = Stopwatch()..start();
   final int exitCode = await runCommandAndStreamOutput(
-    <String>[fs.file(gradle).absolute.path, 'build'],
+    <String>[fs.file(gradlew).absolute.path, 'build'],
     workingDirectory: project.android.hostAppGradleRoot.path,
     allowReentrantFlutter: true,
     environment: _gradleEnv,
@@ -661,12 +675,12 @@ void printUndefinedTask(GradleProject project, BuildInfo buildInfo) {
 
 Future<void> _buildGradleProjectV2(
   FlutterProject flutterProject,
-  String gradle,
   AndroidBuildInfo androidBuildInfo,
   String target,
   bool isBuildingBundle,
 ) async {
-  final GradleProject project = await _gradleAppProject();
+  final String gradlew = await gradleUtils.getExecutable(flutterProject);
+  final GradleProject project = await gradleUtils.appProject;
   final BuildInfo buildInfo = androidBuildInfo.buildInfo;
 
   String assembleTask;
@@ -685,8 +699,7 @@ Future<void> _buildGradleProjectV2(
     timeout: timeoutConfiguration.slowOperation,
     multilineOutput: true,
   );
-  final String gradlePath = fs.file(gradle).absolute.path;
-  final List<String> command = <String>[gradlePath];
+  final List<String> command = <String>[gradlew];
   if (logger.isVerbose) {
     command.add('-Pverbose=true');
   } else {
@@ -712,6 +725,8 @@ Future<void> _buildGradleProjectV2(
     command.add('-Pfilesystem-scheme=${buildInfo.fileSystemScheme}');
   if (androidBuildInfo.splitPerAbi)
     command.add('-Psplit-per-abi=true');
+  if (androidBuildInfo.proguard)
+    command.add('-Pproguard=true');
   if (androidBuildInfo.targetArchs.isNotEmpty) {
     final String targetPlatforms = androidBuildInfo.targetArchs
         .map(getPlatformNameForAndroidArch).join(',');
@@ -727,6 +742,7 @@ Future<void> _buildGradleProjectV2(
   }
   command.add(assembleTask);
   bool potentialAndroidXFailure = false;
+  bool potentialProguardFailure = false;
   final Stopwatch sw = Stopwatch()..start();
   int exitCode = 1;
   try {
@@ -743,13 +759,17 @@ Future<void> _buildGradleProjectV2(
         if (!isAndroidXPluginWarning && androidXFailureRegex.hasMatch(line)) {
           potentialAndroidXFailure = true;
         }
+        // Proguard errors include this url.
+        if (!potentialProguardFailure && androidBuildInfo.proguard &&
+            line.contains('http://proguard.sourceforge.net')) {
+          potentialProguardFailure = true;
+        }
         // Always print the full line in verbose mode.
         if (logger.isVerbose) {
           return line;
         } else if (isAndroidXPluginWarning || !ndkMessageFilter.hasMatch(line)) {
           return null;
         }
-
         return line;
       },
     );
@@ -758,7 +778,13 @@ Future<void> _buildGradleProjectV2(
   }
 
   if (exitCode != 0) {
-    if (potentialAndroidXFailure) {
+    if (potentialProguardFailure) {
+      final String exclamationMark = terminal.color('[!]', TerminalColor.red);
+      printStatus('$exclamationMark Proguard may have failed to optimize the Java bytecode.', emphasis: true);
+      printStatus('To disable proguard, pass the `--no-proguard` flag to this command.', indent: 4);
+      printStatus('To learn more about Proguard, see: https://flutter.dev/docs/deployment/android#enabling-proguard', indent: 4);
+      BuildEvent('proguard-failure').send();
+    } else if (potentialAndroidXFailure) {
       printStatus('AndroidX incompatibilities may have caused this build to fail. See https://goo.gl/CP92wY.');
       BuildEvent('android-x-failure').send();
     }

packages/flutter_tools/lib/src/build_info.dart

@@ -92,6 +92,7 @@ class AndroidBuildInfo {
       AndroidArch.arm64_v8a,
     ],
     this.splitPerAbi = false,
+    this.proguard = false,
   });
 
   // The build info containing the mode and flavor.
@@ -104,6 +105,9 @@ class AndroidBuildInfo {
   /// will be produced.
   final bool splitPerAbi;
 
+  /// Whether to enable Proguard on release mode.
+  final bool proguard;
+
   /// The target platforms for the build.
   final Iterable<AndroidArch> targetArchs;
 }

packages/flutter_tools/lib/src/commands/build_apk.dart

@@ -25,9 +25,15 @@ class BuildApkCommand extends BuildSubCommand {
     argParser
       ..addFlag('split-per-abi',
         negatable: false,
-        help: 'Whether to split the APKs per ABIs.'
+        help: 'Whether to split the APKs per ABIs. '
               'To learn more, see: https://developer.android.com/studio/build/configure-apk-splits#configure-abi-split',
       )
+      ..addFlag('proguard',
+        negatable: true,
+        defaultsTo: true,
+        help: 'Whether to enable Proguard on release mode. '
+              'To learn more, see: https://flutter.dev/docs/deployment/android#enabling-proguard',
+      )
       ..addMultiOption('target-platform',
         splitCommas: true,
         defaultsTo: <String>['android-arm', 'android-arm64'],
@@ -79,7 +85,8 @@ class BuildApkCommand extends BuildSubCommand {
     final BuildInfo buildInfo = getBuildInfo();
     final AndroidBuildInfo androidBuildInfo = AndroidBuildInfo(buildInfo,
       splitPerAbi: argResults['split-per-abi'],
-      targetArchs: argResults['target-platform'].map<AndroidArch>(getAndroidArchForName)
+      targetArchs: argResults['target-platform'].map<AndroidArch>(getAndroidArchForName),
+      proguard: argResults['proguard'],
     );
 
     if (buildInfo.isRelease && !androidBuildInfo.splitPerAbi && androidBuildInfo.targetArchs.length > 1) {