Reland: "Fix how Gradle resolves Android plugin" (#137115)

Relands #97823

When the tool migrated to `.flutter-plugins-dependencies`, the Gradle plugin was never changed.
Until now, the plugin had the heuristic that a plugin with a `android/build.gradle` file supported the Android platform.

Also applies schema of `getPluginDependencies` to `getPluginList` which uses a `List` of Object instead of `Properties`.

Fixes #97729
Cause of the error: https://github.com/flutter/flutter/blob/5f105a6ca7a5ac7b8bc9b241f4c2d86f4188cf5c/packages/flutter_tools/gradle/flutter.gradle#L421C25-L421C25

Fixes #98048
The deprecated line `include ":$name"` in `settings.gradle` (pluginEach) in old projects causes the `project.rootProject.findProject` to also find the plugin "project", so it is not failing on the `afterEvaluate` method. But the plugin shouldn't be included in the first place as it fails with `Could not find method implementation() for arguments` error in special cases.

Related to #48918, see [_writeFlutterPluginsListLegacy](https://github.com/flutter/flutter/blob/27bc1cf61a5b54bf655062be63050123abb617e4/packages/flutter_tools/lib/src/flutter_plugins.dart#L248).
Co-authored-by: Emmanuel Garcia <egarciad@google.com>

packages/flutter_tools/gradle/module_plugin_loader.gradle

@@ -5,41 +5,26 @@
 // This file is included from `<module>/.android/include_flutter.groovy`,
 // so it can be versioned with the Flutter SDK.
 
-import groovy.json.JsonSlurper
+import java.nio.file.Paths
+
+File pathToThisDirectory = buildscript.sourceFile.parentFile
+apply from: Paths.get(pathToThisDirectory.absolutePath, "src", "main", "groovy", "native_plugin_loader.groovy")
 
 def moduleProjectRoot = project(':flutter').projectDir.parentFile.parentFile
 
-def object = null;
-String flutterModulePath = project(':flutter').projectDir.parentFile.getAbsolutePath()
-// If this logic is changed, also change the logic in app_plugin_loader.gradle.
-def pluginsFile = new File(moduleProjectRoot, '.flutter-plugins-dependencies')
-if (pluginsFile.exists()) {
-    object = new JsonSlurper().parseText(pluginsFile.text)
-    assert object instanceof Map
-    assert object.plugins instanceof Map
-    assert object.plugins.android instanceof List
-    // Includes the Flutter plugins that support the Android platform.
-    object.plugins.android.each { androidPlugin ->
-        assert androidPlugin.name instanceof String
-        assert androidPlugin.path instanceof String
-        // Skip plugins that have no native build (such as a Dart-only
-        // implementation of a federated plugin).
-        def needsBuild = androidPlugin.containsKey('native_build') ? androidPlugin['native_build'] : true
-        if (!needsBuild) {
-            return
-        }
-        def pluginDirectory = new File(androidPlugin.path, 'android')
+List<Map<String, Object>> nativePlugins = nativePluginLoader.getPlugins(moduleProjectRoot)
+nativePlugins.each { androidPlugin ->
+    def pluginDirectory = new File(androidPlugin.path as String, 'android')
     assert pluginDirectory.exists()
     include ":${androidPlugin.name}"
     project(":${androidPlugin.name}").projectDir = pluginDirectory
-    }
 }
 
+String flutterModulePath = project(':flutter').projectDir.parentFile.getAbsolutePath()
 gradle.getGradle().projectsLoaded { g ->
     g.rootProject.beforeEvaluate { p ->
         p.subprojects { subproject ->
-            if (object != null && object.plugins != null && object.plugins.android != null
-                    && object.plugins.android.name.contains(subproject.name)) {
+            if (nativePlugins.name.contains(subproject.name)) {
                 File androidPluginBuildOutputDir = new File(flutterModulePath + File.separator
                         + "plugins_build_output" + File.separator + subproject.name);
                 if (!androidPluginBuildOutputDir.exists()) {

packages/flutter_tools/gradle/src/main/groovy/app_plugin_loader.groovy

-import groovy.json.JsonSlurper
 import org.gradle.api.Plugin
 import org.gradle.api.initialization.Settings
 
+import java.nio.file.Paths
+
 apply plugin: FlutterAppPluginLoaderPlugin
 
 class FlutterAppPluginLoaderPlugin implements Plugin<Settings> {
-    // This string must match _kFlutterPluginsHasNativeBuildKey defined in
-    // packages/flutter_tools/lib/src/flutter_plugins.dart.
-    private final String nativeBuildKey = 'native_build'
-
     @Override
     void apply(Settings settings) {
         def flutterProjectRoot = settings.settingsDir.parentFile
 
-        // If this logic is changed, also change the logic in module_plugin_loader.gradle.
-        def pluginsFile = new File(flutterProjectRoot, '.flutter-plugins-dependencies')
-        if (!pluginsFile.exists()) {
-            return
+        if(!settings.ext.hasProperty('flutterSdkPath')) {
+            def properties = new Properties()
+            def localPropertiesFile = new File(settings.rootProject.projectDir, "local.properties")
+            localPropertiesFile.withInputStream { properties.load(it) }
+            settings.ext.flutterSdkPath = properties.getProperty("flutter.sdk")
+            assert settings.ext.flutterSdkPath != null, "flutter.sdk not set in local.properties"
         }
         
-        def object = new JsonSlurper().parseText(pluginsFile.text)
-        assert object instanceof Map
-        assert object.plugins instanceof Map
-        assert object.plugins.android instanceof List
-        // Includes the Flutter plugins that support the Android platform.
-        object.plugins.android.each { androidPlugin ->
-            assert androidPlugin.name instanceof String
-            assert androidPlugin.path instanceof String
-            // Skip plugins that have no native build (such as a Dart-only implementation
-            // of a federated plugin).
-            def needsBuild = androidPlugin.containsKey(nativeBuildKey) ? androidPlugin[nativeBuildKey] : true
-            if (!needsBuild) {
-                return
-            }
-            def pluginDirectory = new File(androidPlugin.path, 'android')
+        // Load shared gradle functions
+        settings.apply from: Paths.get(settings.ext.flutterSdkPath, "packages", "flutter_tools", "gradle", "src", "main", "groovy", "native_plugin_loader.groovy")
+
+        List<Map<String, Object>> nativePlugins = settings.ext.nativePluginLoader.getPlugins(flutterProjectRoot)
+        nativePlugins.each { androidPlugin ->
+            def pluginDirectory = new File(androidPlugin.path as String, 'android')
             assert pluginDirectory.exists()
             settings.include(":${androidPlugin.name}")
             settings.project(":${androidPlugin.name}").projectDir = pluginDirectory

packages/flutter_tools/gradle/src/main/groovy/native_plugin_loader.groovy

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import groovy.json.JsonSlurper
+
+@Singleton
+class NativePluginLoader {
+
+    // This string must match _kFlutterPluginsHasNativeBuildKey defined in
+    // packages/flutter_tools/lib/src/flutter_plugins.dart.
+    static final String nativeBuildKey = "native_build"
+    static final String flutterPluginsDependenciesFile = ".flutter-plugins-dependencies"
+
+    /**
+     * Gets the list of plugins that support the Android platform.
+     * The list contains map elements with the following content:
+     * {
+     *     "name": "plugin-a",
+     *     "path": "/path/to/plugin-a",
+     *     "dependencies": ["plugin-b", "plugin-c"],
+     *     "native_build": true
+     * }
+     *
+     * Therefore the map value can either be a `String`, a `List<String>` or a `boolean`.
+     */
+    List<Map<String, Object>> getPlugins(File flutterSourceDirectory) {
+        List<Map<String, Object>> nativePlugins = []
+        def meta = getDependenciesMetadata(flutterSourceDirectory)
+        if (meta == null) {
+            return nativePlugins
+        }
+
+        assert(meta.plugins instanceof Map<String, Object>)
+        def androidPlugins = meta.plugins.android
+        assert(androidPlugins instanceof List<Map>)
+        // Includes the Flutter plugins that support the Android platform.
+        androidPlugins.each { Map<String, Object> androidPlugin ->
+            // The property types can be found in _filterPluginsByPlatform defined in
+            // packages/flutter_tools/lib/src/flutter_plugins.dart.
+            assert(androidPlugin.name instanceof String)
+            assert(androidPlugin.path instanceof String)
+            assert(androidPlugin.dependencies instanceof List<String>)
+            // Skip plugins that have no native build (such as a Dart-only implementation
+            // of a federated plugin).
+            def needsBuild = androidPlugin.containsKey(nativeBuildKey) ? androidPlugin[nativeBuildKey] : true
+            if (needsBuild) {
+                nativePlugins.add(androidPlugin)
+            }
+        }
+        return nativePlugins
+    }
+
+
+    private Map<String, Object> parsedFlutterPluginsDependencies
+
+    /**
+     * Parses <project-src>/.flutter-plugins-dependencies
+     */
+    Map<String, Object> getDependenciesMetadata(File flutterSourceDirectory) {
+        // Consider a `.flutter-plugins-dependencies` file with the following content:
+        // {
+        //     "plugins": {
+        //       "android": [
+        //         {
+        //           "name": "plugin-a",
+        //           "path": "/path/to/plugin-a",
+        //           "dependencies": ["plugin-b", "plugin-c"],
+        //           "native_build": true
+        //         },
+        //         {
+        //           "name": "plugin-b",
+        //           "path": "/path/to/plugin-b",
+        //           "dependencies": ["plugin-c"],
+        //           "native_build": true
+        //         },
+        //         {
+        //           "name": "plugin-c",
+        //           "path": "/path/to/plugin-c",
+        //           "dependencies": [],
+        //           "native_build": true
+        //         },
+        //       ],
+        //     },
+        //     "dependencyGraph": [
+        //       {
+        //         "name": "plugin-a",
+        //         "dependencies": ["plugin-b","plugin-c"]
+        //       },
+        //       {
+        //         "name": "plugin-b",
+        //         "dependencies": ["plugin-c"]
+        //       },
+        //       {
+        //         "name": "plugin-c",
+        //         "dependencies": []
+        //       }
+        //     ]
+        // }
+        // This means, `plugin-a` depends on `plugin-b` and `plugin-c`.
+        // `plugin-b` depends on `plugin-c`.
+        // `plugin-c` doesn't depend on anything.
+        if (parsedFlutterPluginsDependencies) {
+            return parsedFlutterPluginsDependencies
+        }
+        File pluginsDependencyFile = new File(flutterSourceDirectory, flutterPluginsDependenciesFile)
+        if (pluginsDependencyFile.exists()) {
+            def object = new JsonSlurper().parseText(pluginsDependencyFile.text)
+            assert(object instanceof Map<String, Object>)
+            parsedFlutterPluginsDependencies = object
+            return object
+        }
+        return null
+    }
+}
+
+// TODO(135392): Remove and use declarative form when migrated
+ext {
+    nativePluginLoader = NativePluginLoader.instance
+}

packages/flutter_tools/test/integration.shard/android_plugin_skip_unsupported_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file_testing/file_testing.dart';
+import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/io.dart';
+import 'package:flutter_tools/src/cache.dart';
+
+import '../src/common.dart';
+import 'test_data/plugin_each_settings_gradle_project.dart';
+import 'test_data/plugin_project.dart';
+import 'test_data/project.dart';
+import 'test_utils.dart';
+
+void main() {
+  late Directory tempDir;
+
+  setUp(() {
+    Cache.flutterRoot = getFlutterRoot();
+    tempDir = createResolvedTempDirectorySync('flutter_plugin_test.');
+  });
+
+  tearDown(() async {
+    tryToDelete(tempDir);
+  });
+
+  // Regression test for https://github.com/flutter/flutter/issues/97729 (#137115).
+  /// Creates a project which uses a plugin, which is not supported on Android.
+  /// This means it has no entry in pubspec.yaml for:
+  /// flutter -> plugin -> platforms -> android
+  ///
+  /// [createAndroidPluginFolder] indicates that the plugin can additionally
+  /// have a functioning `android` folder.
+  Future<ProcessResult> testUnsupportedPlugin({
+    required Project project,
+    required bool createAndroidPluginFolder,
+  }) async {
+    final String flutterBin = fileSystem.path.join(
+      getFlutterRoot(),
+      'bin',
+      'flutter',
+    );
+
+    // Create dummy plugin that supports iOS and optionally Android.
+    processManager.runSync(<String>[
+      flutterBin,
+      ...getLocalEngineArguments(),
+      'create',
+      '--template=plugin',
+      '--platforms=ios${createAndroidPluginFolder ? ',android' : ''}',
+      'test_plugin',
+    ], workingDirectory: tempDir.path);
+
+    final Directory pluginAppDir = tempDir.childDirectory('test_plugin');
+
+    final File pubspecFile = pluginAppDir.childFile('pubspec.yaml');
+    String pubspecYamlSrc =
+        pubspecFile.readAsStringSync().replaceAll('\r\n', '\n');
+    if (createAndroidPluginFolder) {
+      // Override pubspec to drop support for the Android implementation.
+      pubspecYamlSrc = pubspecYamlSrc
+          .replaceFirst(
+        RegExp(r'name:.*\n'),
+        'name: test_plugin\n',
+      )
+          .replaceFirst('''
+      android:
+        package: com.example.test_plugin
+        pluginClass: TestPlugin
+''', '''
+#      android:
+#        package: com.example.test_plugin
+#        pluginClass: TestPlugin
+''');
+
+      pubspecFile.writeAsStringSync(pubspecYamlSrc);
+
+      // Check the android directory and the build.gradle file within.
+      final File pluginGradleFile =
+          pluginAppDir.childDirectory('android').childFile('build.gradle');
+      expect(pluginGradleFile, exists);
+    } else {
+      expect(pubspecYamlSrc, isNot(contains('android:')));
+    }
+
+    // Create a project which includes the plugin to test against
+    final Directory pluginExampleAppDir =
+        pluginAppDir.childDirectory('example');
+
+    await project.setUpIn(pluginExampleAppDir);
+
+    // Run flutter build apk to build plugin example project.
+    return processManager.runSync(<String>[
+      flutterBin,
+      ...getLocalEngineArguments(),
+      'build',
+      'apk',
+      '--debug',
+    ], workingDirectory: pluginExampleAppDir.path);
+  }
+
+  test('skip plugin if it does not support the Android platform', () async {
+    final Project project = PluginWithPathAndroidProject();
+    final ProcessResult buildApkResult = await testUnsupportedPlugin(
+        project: project, createAndroidPluginFolder: false);
+    expect(buildApkResult.stderr.toString(),
+        isNot(contains('Please fix your settings.gradle.')));
+    expect(buildApkResult, const ProcessResultMatcher());
+  });
+
+  test(
+      'skip plugin with android folder if it does not support the Android platform',
+      () async {
+    final Project project = PluginWithPathAndroidProject();
+    final ProcessResult buildApkResult = await testUnsupportedPlugin(
+        project: project, createAndroidPluginFolder: true);
+    expect(buildApkResult.stderr.toString(),
+        isNot(contains('Please fix your settings.gradle.')));
+    expect(buildApkResult, const ProcessResultMatcher());
+  });
+
+  // TODO(54566): Remove test when issue is resolved.
+  /// Test project with a `settings.gradle` (PluginEach) that apps were created
+  /// with until Flutter v1.22.0.
+  /// It uses the `.flutter-plugins` file to load EACH plugin.
+  test(
+      'skip plugin if it does not support the Android platform with a _plugin.each_ settings.gradle',
+      () async {
+    final Project project = PluginEachWithPathAndroidProject();
+    final ProcessResult buildApkResult = await testUnsupportedPlugin(
+        project: project, createAndroidPluginFolder: false);
+    expect(buildApkResult.stderr.toString(),
+        isNot(contains('Please fix your settings.gradle.')));
+    expect(buildApkResult, const ProcessResultMatcher());
+  });
+
+  // TODO(54566): Remove test when issue is resolved.
+  /// Test project with a `settings.gradle` (PluginEach) that apps were created
+  /// with until Flutter v1.22.0.
+  /// It uses the `.flutter-plugins` file to load EACH plugin.
+  /// The plugin includes a functional 'android' folder.
+  test(
+      'skip plugin with android folder if it does not support the Android platform with a _plugin.each_ settings.gradle',
+      () async {
+    final Project project = PluginEachWithPathAndroidProject();
+    final ProcessResult buildApkResult = await testUnsupportedPlugin(
+        project: project, createAndroidPluginFolder: true);
+    expect(buildApkResult.stderr.toString(),
+        isNot(contains('Please fix your settings.gradle.')));
+    expect(buildApkResult, const ProcessResultMatcher());
+  });
+
+  // TODO(54566): Remove test when issue is resolved.
+  /// Test project with a `settings.gradle` (PluginEach) that apps were created
+  /// with until Flutter v1.22.0.
+  /// It is compromised by removing the 'include' statement of the plugins.
+  /// As the "'.flutter-plugins'" keyword is still present, the framework
+  /// assumes that all plugins are included, which is not the case.
+  /// Therefore it should throw an error.
+  test(
+      'skip plugin if it does not support the Android platform with a compromised _plugin.each_ settings.gradle',
+      () async {
+    final Project project = PluginCompromisedEachWithPathAndroidProject();
+    final ProcessResult buildApkResult = await testUnsupportedPlugin(
+        project: project, createAndroidPluginFolder: true);
+    expect(
+      buildApkResult,
+      const ProcessResultMatcher(
+          stderrPattern: 'Please fix your settings.gradle.'),
+    );
+  });
+}
+
+const String pubspecWithPluginPath = r'''
+name: test
+environment:
+  sdk: '>=3.2.0-0 <4.0.0'
+dependencies:
+  flutter:
+    sdk: flutter
+
+  test_plugin:
+    path: ../
+''';
+
+/// Project that load's a plugin from the specified path.
+class PluginWithPathAndroidProject extends PluginProject {
+  @override
+  String get pubspec => pubspecWithPluginPath;
+}
+
+// TODO(54566): Remove class when issue is resolved.
+/// [PluginEachSettingsGradleProject] that load's a plugin from the specified
+/// path.
+class PluginEachWithPathAndroidProject extends PluginEachSettingsGradleProject {
+  @override
+  String get pubspec => pubspecWithPluginPath;
+}
+
+// TODO(54566): Remove class when issue is resolved.
+/// [PluginCompromisedEachSettingsGradleProject] that load's a plugin from the
+/// specified path.
+class PluginCompromisedEachWithPathAndroidProject
+    extends PluginCompromisedEachSettingsGradleProject {
+  @override
+  String get pubspec => pubspecWithPluginPath;
+}

packages/flutter_tools/test/integration.shard/test_data/plugin_each_settings_gradle_project.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// TODO(54566): Remove this file when issue is resolved.
+
+import 'deferred_components_config.dart';
+import 'plugin_project.dart';
+
+/// Project to test the deprecated `settings.gradle` (PluginEach) that apps were
+/// created with until Flutter v1.22.0.
+/// It uses the `.flutter-plugins` file to load EACH plugin.
+class PluginEachSettingsGradleProject extends PluginProject {
+  @override
+  DeferredComponentsConfig get deferredComponents =>
+      PluginEachSettingsGradleDeferredComponentsConfig();
+}
+
+class PluginEachSettingsGradleDeferredComponentsConfig
+    extends PluginDeferredComponentsConfig {
+  @override
+  String get androidSettings => r'''
+include ':app'
+def flutterProjectRoot = rootProject.projectDir.parentFile.toPath()
+def plugins = new Properties()
+def pluginsFile = new File(flutterProjectRoot.toFile(), '.flutter-plugins')
+if (pluginsFile.exists()) {
+    pluginsFile.withReader('UTF-8') { reader -> plugins.load(reader) }
+}
+plugins.each { name, path ->
+    def pluginDirectory = flutterProjectRoot.resolve(path).resolve('android').toFile()
+    include ":$name"
+    project(":$name").projectDir = pluginDirectory
+}
+  ''';
+}
+
+/// Project to test the deprecated `settings.gradle` (PluginEach) that apps were
+/// created with until Flutter v1.22.0.
+/// It uses the `.flutter-plugins` file to get EACH plugin.
+/// It is compromised by removing the 'include' statement of the plugins.
+class PluginCompromisedEachSettingsGradleProject extends PluginProject {
+  @override
+  DeferredComponentsConfig get deferredComponents =>
+      PluginCompromisedEachSettingsGradleDeferredComponentsConfig();
+}
+
+class PluginCompromisedEachSettingsGradleDeferredComponentsConfig
+    extends PluginDeferredComponentsConfig {
+  @override
+  String get androidSettings => r'''
+include ':app'
+def flutterProjectRoot = rootProject.projectDir.parentFile.toPath()
+def plugins = new Properties()
+def pluginsFile = new File(flutterProjectRoot.toFile(), '.flutter-plugins')
+if (pluginsFile.exists()) {
+    pluginsFile.withReader('UTF-8') { reader -> plugins.load(reader) }
+}
+  ''';
+}

packages/flutter_tools/test/integration.shard/test_data/plugin_project.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'basic_project.dart';
+import 'deferred_components_config.dart';
+import 'deferred_components_project.dart';
+
+/// Project which can load native plugins
+class PluginProject extends BasicProject {
+  @override
+  final DeferredComponentsConfig? deferredComponents =
+      PluginDeferredComponentsConfig();
+}
+
+class PluginDeferredComponentsConfig extends BasicDeferredComponentsConfig {
+  @override
+  String get androidBuild => r'''
+buildscript {
+    ext.kotlin_version = '1.7.10'
+    repositories {
+        google()
+        mavenCentral()
+    }
+    dependencies {
+        classpath 'com.android.tools.build:gradle:7.3.0'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    }
+    configurations.classpath {
+        resolutionStrategy.activateDependencyLocking()
+    }
+}
+allprojects {
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+rootProject.buildDir = '../build'
+subprojects {
+    project.buildDir = "${rootProject.buildDir}/${project.name}"
+}
+subprojects {
+    project.evaluationDependsOn(':app')
+    dependencyLocking {
+        ignoredDependencies.add('io.flutter:*')
+        lockFile = file("${rootProject.projectDir}/project-${project.name}.lockfile")
+        if (!project.hasProperty('local-engine-repo')) {
+          lockAllConfigurations()
+        }
+    }
+}
+tasks.register("clean", Delete) {
+    delete rootProject.buildDir
+}
+''';
+
+  @override
+  String get androidSettings => r'''
+include ':app'
+
+def localPropertiesFile = new File(rootProject.projectDir, "local.properties")
+def properties = new Properties()
+
+assert localPropertiesFile.exists()
+localPropertiesFile.withReader("UTF-8") { reader -> properties.load(reader) }
+
+def flutterSdkPath = properties.getProperty("flutter.sdk")
+assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
+apply from: "$flutterSdkPath/packages/flutter_tools/gradle/app_plugin_loader.gradle"
+''';
+
+  @override
+  String get appManifest => r'''
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="com.yourcompany.flavors">
+    <uses-permission android:name="android.permission.INTERNET"/>
+    <application
+        android:name="${applicationName}"
+        android:label="flavors">
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:launchMode="singleTop"
+            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
+            android:hardwareAccelerated="true"
+            android:windowSoftInputMode="adjustResize">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN"/>
+                <category android:name="android.intent.category.LAUNCHER"/>
+            </intent-filter>
+        </activity>
+        <meta-data
+            android:name="flutterEmbedding"
+            android:value="2" />
+    </application>
+</manifest>
+''';
+}