[Android] Adds `namespace` to module build file templates (#126963)

Adds `namespace` to module `build.gradle` file templates.

Fixes https://github.com/flutter/flutter/issues/126403.

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

@@ -24,6 +24,11 @@ apply plugin: 'com.android.library'
 apply plugin: 'kotlin-android'
 
 android {
+    // Conditional for compatibility with AGP <4.2.
+    if (project.android.hasProperty("namespace")) {
+        namespace '{{androidIdentifier}}'
+    }
+
     compileSdkVersion {{compileSdkVersion}}
     defaultConfig {
         minSdkVersion {{minSdkVersion}}

packages/flutter_tools/templates/module/android/host_app_common/app.tmpl/build.gradle.tmpl

@@ -3,6 +3,11 @@ def flutterPluginVersion = 'managed'
 apply plugin: 'com.android.application'
 
 android {
+    // Conditional for compatibility with AGP <4.2.
+    if (project.android.hasProperty("namespace")) {
+        namespace "{{androidIdentifier}}.host"
+    }
+
     compileSdkVersion {{compileSdkVersion}}
 
     compileOptions {

packages/flutter_tools/templates/module/android/library_new_embedding/Flutter.tmpl/build.gradle.tmpl

@@ -30,6 +30,11 @@ group '{{androidIdentifier}}'
 version '1.0'
 
 android {
+    // Conditional for compatibility with AGP <4.2.
+    if (project.android.hasProperty("namespace")) {
+        namespace '{{androidIdentifier}}'
+    }
+
     compileSdkVersion flutter.compileSdkVersion
     ndkVersion flutter.ndkVersion
 

packages/flutter_tools/templates/module/android/library_new_embedding/Flutter.tmpl/src/main/AndroidManifest.xml.tmpl

@@ -3,7 +3,8 @@
     package="{{androidIdentifier}}"
     xmlns:tools="http://schemas.android.com/tools">
   <uses-permission android:name="android.permission.INTERNET"/>
-  <application tools:node="merge">
+  <application
+    tools:node="merge">
     <meta-data
       android:name="flutterProjectType"
       android:value="module" />

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

@@ -2919,6 +2919,48 @@ void main() {
     expect(buildGradleContent.contains('if (project.android.hasProperty("namespace")) {'), true);
   });
 
+  testUsingContext('Flutter module Android project contains namespace', () async {
+    const String moduleBuildGradleFilePath = '.android/build.gradle';
+    const String moduleAppBuildGradleFlePath = '.android/app/build.gradle';
+    const String moduleFlutterBuildGradleFilePath = '.android/Flutter/build.gradle';
+    await _createProject(
+      projectDir,
+      <String>['--template=module', '--org', 'com.bar.foo'],
+      <String>[moduleBuildGradleFilePath,
+        moduleAppBuildGradleFlePath,
+        moduleFlutterBuildGradleFilePath,
+      ],
+    );
+
+    final String moduleBuildGradleFileContent = await globals.fs.file(globals.fs.path.join(projectDir.path, moduleBuildGradleFilePath)).readAsString();
+    final String moduleAppBuildGradleFileContent = await globals.fs.file(globals.fs.path.join(projectDir.path, moduleAppBuildGradleFlePath)).readAsString();
+    final String moduleFlutterBuildGradleFileContent = await globals.fs.file(globals.fs.path.join(projectDir.path, moduleFlutterBuildGradleFilePath)).readAsString();
+
+    // Each build file should contain the expected namespace.
+    const String expectedNameSpace = "namespace 'com.bar.foo.flutter_project'";
+    expect(moduleBuildGradleFileContent.contains(expectedNameSpace), true);
+    expect(moduleFlutterBuildGradleFileContent.contains(expectedNameSpace), true);
+    const String expectedHostNameSpace = 'namespace "com.bar.foo.flutter_project.host"';
+    expect(moduleAppBuildGradleFileContent.contains(expectedHostNameSpace), true);
+
+    // The namespaces should be conditionalized for AGP <4.2.
+    const String expectedConditional = 'if (project.android.hasProperty("namespace")) {';
+    expect(moduleBuildGradleFileContent.contains(expectedConditional), true);
+    expect(moduleAppBuildGradleFileContent.contains(expectedConditional), true);
+    expect(moduleFlutterBuildGradleFileContent.contains(expectedConditional), true);
+
+  }, overrides: <Type, Generator>{
+    Pub: () => Pub.test(
+      fileSystem: globals.fs,
+      logger: globals.logger,
+      processManager: globals.processManager,
+      usage: globals.flutterUsage,
+      botDetector: globals.botDetector,
+      platform: globals.platform,
+      stdio: mockStdio,
+    ),
+  });
+
   testUsingContext('Linux plugins handle partially camel-case project names correctly', () async {
     Cache.flutterRoot = '../..';