Add warning for bumping Android SDK version to match plugins (#92451)

packages/flutter_tools/gradle/flutter.gradle

@@ -397,12 +397,40 @@ class FlutterPlugin implements Plugin<Project> {
               "io.flutter:flutter_embedding_$flutterBuildMode:$engineVersion"
             )
         }
+
         // Wait until the Android plugin loaded.
         pluginProject.afterEvaluate {
+            if (pluginProject.android.compileSdkVersion > project.android.compileSdkVersion) {
+                project.logger.quiet("Warning: The plugin ${pluginName} requires Android SDK version ${pluginProject.android.compileSdkVersion.substring(8)}.")
+            }
             project.android.buildTypes.all addEmbeddingDependencyToPlugin
         }
     }
 
+     /** Prints error message and fix for any plugin compileSdkVersion that are higher than the project. */
+    private void detectLowCompileSdkVersion() {
+        project.afterEvaluate {
+            int projectCompileSdkVersion = project.android.compileSdkVersion.substring(8) as int
+            int maxPluginCompileSdkVersion = projectCompileSdkVersion
+            int numProcessedPlugins = getPluginList().size()
+
+            getPluginList().each { plugin ->
+                Project pluginProject = project.rootProject.findProject(plugin.key)
+                pluginProject.afterEvaluate {
+                    int pluginCompileSdkVersion = pluginProject.android.compileSdkVersion.substring(8) as int
+                    maxPluginCompileSdkVersion = Math.max(pluginCompileSdkVersion, maxPluginCompileSdkVersion)
+
+                    numProcessedPlugins--
+                    if (numProcessedPlugins == 0) {
+                        if (maxPluginCompileSdkVersion > projectCompileSdkVersion) {
+                            project.logger.error("One or more plugins require a higher Android SDK version.\nFix this issue by adding the following to ${project.projectDir}${File.separator}build.gradle:\nandroid {\n  compileSdkVersion ${maxPluginCompileSdkVersion}\n  ...\n}\n")
+                        }
+                    }
+                }
+            }
+        }  
+    }
+
     /**
      * Returns `true` if the given path contains an `android/build.gradle` file.
      */
@@ -933,6 +961,7 @@ class FlutterPlugin implements Plugin<Project> {
                 }
             }
             configurePlugins()
+            detectLowCompileSdkVersion()
             return
         }
         // Flutter host module project (Add-to-app).
@@ -984,6 +1013,7 @@ class FlutterPlugin implements Plugin<Project> {
             }
         }
         configurePlugins()
+        detectLowCompileSdkVersion()
     }
 }
 

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

@@ -0,0 +1,92 @@
+// 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);
+  });
+
+  test('error logged when plugin Android compileSdkVersion higher than project', () async {
+    final String flutterBin = fileSystem.path.join(
+      getFlutterRoot(),
+      'bin',
+      'flutter',
+    );
+
+    // Create dummy plugin
+    processManager.runSync(<String>[
+      flutterBin,
+      ...getLocalEngineArguments(),
+      'create',
+      '--template=plugin',
+      '--platforms=android',
+      'test_plugin',
+    ], workingDirectory: tempDir.path);
+
+    final Directory pluginAppDir = tempDir.childDirectory('test_plugin');
+    final File pluginGradleFile = pluginAppDir.childDirectory('android').childFile('build.gradle');
+    expect(pluginGradleFile, exists);
+
+    final String pluginBuildGradle = pluginGradleFile.readAsStringSync();
+
+    // Bump up plugin compileSdkVersion to 31
+    final RegExp androidCompileSdkVersionRegExp = RegExp(r'compileSdkVersion ([0-9]+|flutter.compileSdkVersion)');
+    final String newPluginGradleFile = pluginBuildGradle.replaceAll(
+      androidCompileSdkVersionRegExp, 'compileSdkVersion 31');
+    pluginGradleFile.writeAsStringSync(newPluginGradleFile);
+
+    final Directory pluginExampleAppDir = pluginAppDir.childDirectory('example');
+
+    final File projectGradleFile = pluginExampleAppDir.childDirectory('android').childDirectory('app').childFile('build.gradle');
+    expect(projectGradleFile, exists);
+
+    final String projectBuildGradle = projectGradleFile.readAsStringSync();
+
+    // Bump down plugin example app compileSdkVersion to 30
+    final String newProjectGradleFile = projectBuildGradle.replaceAll(
+      androidCompileSdkVersionRegExp, 'compileSdkVersion 30');
+    projectGradleFile.writeAsStringSync(newProjectGradleFile);
+
+    // Run flutter build apk to build plugin example project
+    final ProcessResult result = processManager.runSync(<String>[
+      flutterBin,
+      ...getLocalEngineArguments(),
+      'build',
+      'apk',
+      '--target-platform=android-arm',
+    ], workingDirectory: pluginExampleAppDir.path);
+
+    // Check error message is thrown
+    expect(result.stdout,
+      contains('Warning: The plugin test_plugin requires Android SDK version 31.')
+      );
+    expect(result.stderr,
+      contains('''
+One or more plugins require a higher Android SDK version.
+Fix this issue by adding the following to ${projectGradleFile.path}:
+android {
+  compileSdkVersion 31
+  ...
+}
+
+'''
+      ));
+   });
+}

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

@@ -162,7 +162,7 @@ class MultidexProject extends Project {
   apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
   android {
-      compileSdkVersion 30
+      compileSdkVersion 31
 
       compileOptions {
           sourceCompatibility JavaVersion.VERSION_1_8