Add namespace to Android plugin templates (#126354)

Adds the `namespace` property necessary for AGP 8 compatibility to the plugin templates, with the conditional logic to ensure that it doesn't break AGP <4.2, so that new plugins will be maximally compatible.

Part of https://github.com/flutter/flutter/issues/125181

packages/flutter_tools/templates/plugin/android-java.tmpl/build.gradle.tmpl

@@ -22,6 +22,10 @@ rootProject.allprojects {
 apply plugin: 'com.android.library'
 
 android {
+    if (project.android.hasProperty("namespace")) {
+        namespace '{{androidIdentifier}}'
+    }
+
     compileSdkVersion {{compileSdkVersion}}
 
     compileOptions {

packages/flutter_tools/templates/plugin/android-kotlin.tmpl/build.gradle.tmpl

@@ -25,6 +25,10 @@ apply plugin: 'com.android.library'
 apply plugin: 'kotlin-android'
 
 android {
+    if (project.android.hasProperty("namespace")) {
+        namespace '{{androidIdentifier}}'
+    }
+
     compileSdkVersion 31
 
     compileOptions {

packages/flutter_tools/templates/plugin_ffi/android.tmpl/build.gradle.tmpl

@@ -25,6 +25,10 @@ rootProject.allprojects {
 apply plugin: 'com.android.library'
 
 android {
+    if (project.android.hasProperty("namespace")) {
+        namespace '{{androidIdentifier}}'
+    }
+
     // Bumping the plugin compileSdkVersion requires all clients of this plugin
     // to bump the version in their app.
     compileSdkVersion {{compileSdkVersion}}

packages/flutter_tools/test/commands.shard/permeable/create_test.dart

@@ -2848,6 +2848,77 @@ void main() {
     expect(buildContent.contains('targetSdkVersion flutter.targetSdkVersion'), true);
   });
 
+  testUsingContext('Android Java plugin contains namespace', () async {
+    Cache.flutterRoot = '../..';
+
+    final CreateCommand command = CreateCommand();
+    final CommandRunner<void> runner = createTestCommandRunner(command);
+
+    await runner.run(<String>['create', '--no-pub',
+      '-t', 'plugin',
+      '--org', 'com.bar.foo',
+      '-a', 'java',
+      '--platforms=android',
+      projectDir.path]);
+
+    final File buildGradleFile = globals.fs.file('${projectDir.path}/android/build.gradle');
+
+    expect(buildGradleFile.existsSync(), true);
+
+    final String buildGradleContent = await buildGradleFile.readAsString();
+
+    expect(buildGradleContent.contains("namespace 'com.bar.foo.flutter_project'"), true);
+    // The namespace should be conditionalized for AGP <4.2.
+    expect(buildGradleContent.contains('if (project.android.hasProperty("namespace")) {'), true);
+  });
+
+  testUsingContext('Android FFI plugin contains namespace', () async {
+    Cache.flutterRoot = '../..';
+
+    final CreateCommand command = CreateCommand();
+    final CommandRunner<void> runner = createTestCommandRunner(command);
+
+    await runner.run(<String>['create', '--no-pub',
+      '-t', 'plugin_ffi',
+      '--org', 'com.bar.foo',
+      '--platforms=android',
+      projectDir.path]);
+
+    final File buildGradleFile = globals.fs.file('${projectDir.path}/android/build.gradle');
+
+    expect(buildGradleFile.existsSync(), true);
+
+    final String buildGradleContent = await buildGradleFile.readAsString();
+
+    expect(buildGradleContent.contains("namespace 'com.bar.foo.flutter_project'"), true);
+    // The namespace should be conditionalized for AGP <4.2.
+    expect(buildGradleContent.contains('if (project.android.hasProperty("namespace")) {'), true);
+  });
+
+  testUsingContext('Android Kotlin plugin contains namespace', () async {
+    Cache.flutterRoot = '../..';
+
+    final CreateCommand command = CreateCommand();
+    final CommandRunner<void> runner = createTestCommandRunner(command);
+
+    await runner.run(<String>['create', '--no-pub',
+      '-t', 'plugin',
+      '--org', 'com.bar.foo',
+      '-a', 'kotlin',
+      '--platforms=android',
+      projectDir.path]);
+
+    final File buildGradleFile = globals.fs.file('${projectDir.path}/android/build.gradle');
+
+    expect(buildGradleFile.existsSync(), true);
+
+    final String buildGradleContent = await buildGradleFile.readAsString();
+
+    expect(buildGradleContent.contains("namespace 'com.bar.foo.flutter_project'"), true);
+    // The namespace should be conditionalized for AGP <4.2.
+    expect(buildGradleContent.contains('if (project.android.hasProperty("namespace")) {'), true);
+  });
+
   testUsingContext('Linux plugins handle partially camel-case project names correctly', () async {
     Cache.flutterRoot = '../..';