[various] Adds Android namespace (#3791)

Adds a `namespace` attribute to the Android build.gradle, for compatibility with Android Gradle Plugin 8.0, and adds tooling to enforce that it's there.

This is necessary for plugins now; for examples this isn't needed yet, but since it will be needed to eventually update the apps to AGP 8.0 anyway, it's easiest to just enforce it everywhere now.

script/tool/lib/src/gradle_check_command.dart

@@ -36,31 +36,169 @@ class GradleCheckCommand extends PackageLoopingCommand {
     const String exampleDirName = 'example';
     final bool isExample = package.directory.basename == exampleDirName ||
         package.directory.parent.basename == exampleDirName;
-    if (!_validateBuildGradle(package, isExample: isExample)) {
+    if (!_validateBuildGradles(package, isExample: isExample)) {
       return PackageResult.fail();
     }
     return PackageResult.success();
   }
 
-  bool _validateBuildGradle(RepositoryPackage package,
+  bool _validateBuildGradles(RepositoryPackage package,
       {required bool isExample}) {
-    // Currently the only check is not relevant to examples; checks that apply
-    // to both plugins and examples should go above here.
-    if (!isExample) {
-      print('${indentation}Validating android/build.gradle.');
-      final String contents = package
-          .platformDirectory(FlutterPlatform.android)
-          .childFile('build.gradle')
-          .readAsStringSync();
-      final List<String> lines = contents.split('\n');
+    final Directory androidDir =
+        package.platformDirectory(FlutterPlatform.android);
+    final File topLevelGradleFile = _getBuildGradleFile(androidDir);
 
-      if (!lines.any((String line) =>
-              line.contains('languageVersion') &&
-              !line.trim().startsWith('//')) &&
-          !lines.any((String line) =>
-              line.contains('sourceCompatibility') &&
-              !line.trim().startsWith('//'))) {
-        const String errorMessage = '''
+    // This is tracked as a variable rather than a sequence of &&s so that all
+    // failures are reported at once, not just the first one.
+    bool succeeded = true;
+    if (isExample) {
+      if (!_validateExampleTopLevelBuildGradle(package, topLevelGradleFile)) {
+        succeeded = false;
+      }
+
+      final File appGradleFile =
+          _getBuildGradleFile(androidDir.childDirectory('app'));
+      if (!_validateExampleAppBuildGradle(package, appGradleFile)) {
+        succeeded = false;
+      }
+    } else {
+      succeeded = _validatePluginBuildGradle(package, topLevelGradleFile);
+    }
+
+    return succeeded;
+  }
+
+  // Returns the gradle file in the given directory.
+  File _getBuildGradleFile(Directory dir) => dir.childFile('build.gradle');
+
+  // Returns the main/AndroidManifest.xml file for the given package.
+  File _getMainAndroidManifest(RepositoryPackage package,
+      {required bool isExample}) {
+    final Directory androidDir =
+        package.platformDirectory(FlutterPlatform.android);
+    final Directory baseDir =
+        isExample ? androidDir.childDirectory('app') : androidDir;
+    return baseDir
+        .childDirectory('src')
+        .childDirectory('main')
+        .childFile('AndroidManifest.xml');
+  }
+
+  /// Validates the build.gradle file for a plugin
+  /// (some_plugin/android/build.gradle).
+  bool _validatePluginBuildGradle(RepositoryPackage package, File gradleFile) {
+    print('${indentation}Validating '
+        '${getRelativePosixPath(gradleFile, from: package.directory)}.');
+    final String contents = gradleFile.readAsStringSync();
+    final List<String> lines = contents.split('\n');
+
+    // This is tracked as a variable rather than a sequence of &&s so that all
+    // failures are reported at once, not just the first one.
+    bool succeeded = true;
+    if (!_validateNamespace(package, contents, isExample: false)) {
+      succeeded = false;
+    }
+    if (!_validateSourceCompatibilityVersion(lines)) {
+      succeeded = false;
+    }
+    return succeeded;
+  }
+
+  /// Validates the top-level build.gradle for an example app (e.g.,
+  /// some_package/example/android/build.gradle).
+  bool _validateExampleTopLevelBuildGradle(
+      RepositoryPackage package, File gradleFile) {
+    print('${indentation}Validating '
+        '${getRelativePosixPath(gradleFile, from: package.directory)}.');
+    // TODO(stuartmorgan): Move the -Xlint validation from lint_android_command
+    // to here.
+    return true;
+  }
+
+  /// Validates the app-level build.gradle for an example app (e.g.,
+  /// some_package/example/android/app/build.gradle).
+  bool _validateExampleAppBuildGradle(
+      RepositoryPackage package, File gradleFile) {
+    print('${indentation}Validating '
+        '${getRelativePosixPath(gradleFile, from: package.directory)}.');
+    final String contents = gradleFile.readAsStringSync();
+
+    // This is tracked as a variable rather than a sequence of &&s so that all
+    // failures are reported at once, not just the first one.
+    bool succeeded = true;
+    if (!_validateNamespace(package, contents, isExample: true)) {
+      succeeded = false;
+    }
+    return succeeded;
+  }
+
+  /// Validates that [gradleContents] sets a namespace, which is required for
+  /// compatibility with apps that use AGP 8+.
+  bool _validateNamespace(RepositoryPackage package, String gradleContents,
+      {required bool isExample}) {
+    final RegExp namespaceRegex =
+        RegExp('^\\s*namespace\\s+[\'"](.*?)[\'"]', multiLine: true);
+    final RegExpMatch? namespaceMatch =
+        namespaceRegex.firstMatch(gradleContents);
+    if (namespaceMatch == null) {
+      const String errorMessage = '''
+build.gradle must set a "namespace":
+
+    android {
+        namespace 'dev.flutter.foo'
+    }
+
+The value must match the "package" attribute in AndroidManifest.xml, if one is
+present. For more information, see:
+https://developer.android.com/build/publish-library/prep-lib-release#choose-namespace
+''';
+
+      printError(
+          '$indentation${errorMessage.split('\n').join('\n$indentation')}');
+      return false;
+    } else {
+      return _validateNamespaceMatchesManifest(package,
+          isExample: isExample, namespace: namespaceMatch.group(1)!);
+    }
+  }
+
+  /// Validates that the given namespace matches the manifest package of
+  /// [package] (if any; a package does not need to be in the manifest in cases
+  /// where compatibility with AGP <7 is no longer required).
+  ///
+  /// Prints an error and returns false if validation fails.
+  bool _validateNamespaceMatchesManifest(RepositoryPackage package,
+      {required bool isExample, required String namespace}) {
+    final RegExp manifestPackageRegex = RegExp(r'package\s*=\s*"(.*?)"');
+    final String manifestContents =
+        _getMainAndroidManifest(package, isExample: isExample)
+            .readAsStringSync();
+    final RegExpMatch? packageMatch =
+        manifestPackageRegex.firstMatch(manifestContents);
+    if (packageMatch != null && namespace != packageMatch.group(1)) {
+      final String errorMessage = '''
+build.gradle "namespace" must match the "package" attribute in AndroidManifest.xml, if one is present.
+  build.gradle namespace: "$namespace"
+  AndroidMastifest.xml package: "${packageMatch.group(1)}"
+''';
+      printError(
+          '$indentation${errorMessage.split('\n').join('\n$indentation')}');
+      return false;
+    }
+    return true;
+  }
+
+  /// Checks for a source compatibiltiy version, so that it's explicit rather
+  /// than using whatever the client's local toolchaing defaults to (which can
+  /// lead to compile errors that show up for clients, but not in CI).
+  bool _validateSourceCompatibilityVersion(List<String> gradleLines) {
+    if (!gradleLines.any((String line) =>
+            line.contains('languageVersion') &&
+            !line.trim().startsWith('//')) &&
+        !gradleLines.any((String line) =>
+            line.contains('sourceCompatibility') &&
+            !line.trim().startsWith('//'))) {
+      const String errorMessage = '''
 build.gradle must set an explicit Java compatibility version.
 
 This can be done either via "sourceCompatibility":
@@ -81,12 +219,10 @@ See:
 https://docs.gradle.org/current/userguide/java_plugin.html#toolchain_and_compatibility
 for more details.''';
 
-        printError(
-            '$indentation${errorMessage.split('\n').join('\n$indentation')}');
-        return false;
-      }
+      printError(
+          '$indentation${errorMessage.split('\n').join('\n$indentation')}');
+      return false;
     }
-
     return true;
   }
 }