Fix how Gradle resolves Android plugin (#97823)

packages/flutter_tools/gradle/app_plugin_loader.gradle

@@ -20,6 +20,7 @@ assert object instanceof Map
 assert object.plugins instanceof Map
 assert object.plugins.android instanceof List
 // Includes the Flutter plugins that support the Android platform.
+// This logic must be kept in sync with the logic in flutter.gradle.
 object.plugins.android.each { androidPlugin ->
   assert androidPlugin.name instanceof String
   assert androidPlugin.path instanceof String

packages/flutter_tools/gradle/flutter.gradle

@@ -48,7 +48,7 @@ class FlutterExtension {
      * Specifies the relative directory to the Flutter project directory.
      * In an app project, this is ../.. since the app's build.gradle is under android/app.
      */
-    String source
+    String source = '../..'
 
     /** Allows to override the target file. Otherwise, the target is lib/main.dart. */
     String target
@@ -418,7 +418,7 @@ class FlutterPlugin implements Plugin<Project> {
 
     /**
      * Compares semantic versions ignoring labels.
-     * 
+     *
      * If the versions are equal (ignoring labels), returns one of the two strings arbitrarily.
      *
      * If minor or patch are omitted (non-conformant to semantic versioning), they are considered zero.
@@ -459,6 +459,9 @@ class FlutterPlugin implements Plugin<Project> {
 
             getPluginList().each { plugin ->
                 Project pluginProject = project.rootProject.findProject(plugin.key)
+                if (pluginProject == null) {
+                    return
+                }
                 pluginProject.afterEvaluate {
                     int pluginCompileSdkVersion = pluginProject.android.compileSdkVersion.substring(8) as int
                     maxPluginCompileSdkVersion = Math.max(pluginCompileSdkVersion, maxPluginCompileSdkVersion)
@@ -476,15 +479,7 @@ class FlutterPlugin implements Plugin<Project> {
                     }
                 }
             }
-        }  
-    }
-
-    /**
-     * Returns `true` if the given path contains an `android/build.gradle` file.
-     */
-    private Boolean doesSupportAndroidPlatform(String path) {
-        File editableAndroidProject = new File(path, 'android' + File.separator + 'build.gradle')
-        return editableAndroidProject.exists()
+        }
     }
 
     /**
@@ -495,8 +490,7 @@ class FlutterPlugin implements Plugin<Project> {
     private void configurePluginDependencies(Object dependencyObject) {
         assert dependencyObject.name instanceof String
         Project pluginProject = project.rootProject.findProject(":${dependencyObject.name}")
-        if (pluginProject == null ||
-            !doesSupportAndroidPlatform(pluginProject.projectDir.parentFile.path)) {
+        if (pluginProject == null) {
             return
         }
         assert dependencyObject.dependencies instanceof List
@@ -506,8 +500,7 @@ class FlutterPlugin implements Plugin<Project> {
                 return
             }
             Project dependencyProject = project.rootProject.findProject(":$pluginDependencyName")
-            if (dependencyProject == null ||
-                !doesSupportAndroidPlatform(dependencyProject.projectDir.parentFile.path)) {
+            if (dependencyProject == null) {
                 return
             }
             // Wait for the Android plugin to load and add the dependency to the plugin project.
@@ -519,17 +512,27 @@ class FlutterPlugin implements Plugin<Project> {
         }
     }
 
+    /** Gets the list of plugins that support the Android platform. */
     private Properties getPluginList() {
-        File pluginsFile = new File(project.projectDir.parentFile.parentFile, '.flutter-plugins')
-        Properties allPlugins = readPropertiesIfExist(pluginsFile)
+        Map meta = getDependenciesMetadata()
         Properties androidPlugins = new Properties()
-        allPlugins.each { name, path ->
-            if (doesSupportAndroidPlatform(path)) {
-                androidPlugins.setProperty(name, path)
+        if (meta == null) {
+            return androidPlugins
+        }
+        assert meta.plugins instanceof Map
+        assert meta.plugins.android instanceof List
+
+        // This logic must be kept in sync with the logic in app_plugin_loader.gradle.
+        meta.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
             }
-            // TODO(amirh): log an error if this plugin was specified to be an Android
-            // plugin according to the new schema, and was missing a build.gradle file.
-            // https://github.com/flutter/flutter/issues/40784
+            androidPlugins.setProperty(androidPlugin.name, androidPlugin.path)
         }
         return androidPlugins
     }
@@ -557,14 +560,31 @@ class FlutterPlugin implements Plugin<Project> {
         // This means, `plugin-a` depends on `plugin-b` and `plugin-c`.
         // `plugin-b` depends on `plugin-c`.
         // `plugin-c` doesn't depend on anything.
-        File pluginsDependencyFile = new File(project.projectDir.parentFile.parentFile, '.flutter-plugins-dependencies')
+        Map meta = getDependenciesMetadata()
+        if (meta == null) {
+            return []
+        }
+        assert meta.dependencyGraph instanceof List
+        return meta.dependencyGraph
+    }
+
+    private Map parsedFlutterPluginsDependencies
+
+    /**
+     * Parses <project-src>/.flutter-plugins-dependencies
+     */
+    private Map getDependenciesMetadata() {
+        if (parsedFlutterPluginsDependencies) {
+            return parsedFlutterPluginsDependencies
+        }
+        File pluginsDependencyFile = new File(getFlutterSourceDirectory(), '.flutter-plugins-dependencies')
         if (pluginsDependencyFile.exists()) {
             def object = new JsonSlurper().parseText(pluginsDependencyFile.text)
             assert object instanceof Map
-            assert object.dependencyGraph instanceof List
-            return object.dependencyGraph
+            parsedFlutterPluginsDependencies = object
+            return object
         }
-        return []
+        return null
     }
 
     private static String toCammelCase(List<String> parts) {

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

@@ -0,0 +1,120 @@
+// 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_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.
+  test('skip plugin if it does not support the Android platform', () async {
+    final String flutterBin = fileSystem.path.join(
+      getFlutterRoot(),
+      'bin',
+      'flutter',
+    );
+
+    // Create dummy plugin that *only* supports iOS.
+    processManager.runSync(<String>[
+      flutterBin,
+      ...getLocalEngineArguments(),
+      'create',
+      '--template=plugin',
+      '--platforms=ios',
+      'test_plugin',
+    ], workingDirectory: tempDir.path);
+
+    final Directory pluginAppDir = tempDir.childDirectory('test_plugin');
+
+    // Create an android directory and a build.gradle file within.
+    final File pluginGradleFile = pluginAppDir
+        .childDirectory('android')
+        .childFile('build.gradle')
+      ..createSync(recursive: true);
+    expect(pluginGradleFile, exists);
+
+    pluginGradleFile.writeAsStringSync(r'''
+buildscript {
+    ext.kotlin_version = '1.5.31'
+    repositories {
+        google()
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath 'com.android.tools.build:gradle:7.0.0'
+        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')
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}
+''');
+
+    final Directory pluginExampleAppDir =
+        pluginAppDir.childDirectory('example');
+
+    // Add android support to the plugin's example app.
+    final ProcessResult addAndroidResult = processManager.runSync(<String>[
+      flutterBin,
+      ...getLocalEngineArguments(),
+      'create',
+      '--template=app',
+      '--platforms=android',
+      '.',
+    ], workingDirectory: pluginExampleAppDir.path);
+    expect(addAndroidResult.exitCode, equals(0),
+        reason:
+            'flutter create exited with non 0 code: ${addAndroidResult.stderr}');
+
+    // Run flutter build apk to build plugin example project.
+    final ProcessResult buildApkResult = processManager.runSync(<String>[
+      flutterBin,
+      ...getLocalEngineArguments(),
+      'build',
+      'apk',
+      '--debug',
+    ], workingDirectory: pluginExampleAppDir.path);
+    expect(buildApkResult.exitCode, equals(0),
+        reason:
+            'flutter build apk exited with non 0 code: ${buildApkResult.stderr}');
+  });
+}