Clone the parent Android engine's asset provider into a spawned engine (flutter/engine#41642)

Typically the AndroidShellHolder's apk_asset_provider_ is set by AndroidShellHolder::Launch when the DartExecutor runs the engine's entrypoint.

But if the engine was started by Spawn, then the apk_asset_provider_ was not being set.  This would cause a crash if the resulting engine was later used to spawn another engine.

Fixes https://github.com/flutter/flutter/issues/122364

engine/src/flutter/shell/platform/android/android_shell_holder.cc

@@ -180,12 +180,14 @@ AndroidShellHolder::AndroidShellHolder(
     const std::shared_ptr<PlatformViewAndroidJNI>& jni_facade,
     const std::shared_ptr<ThreadHost>& thread_host,
     std::unique_ptr<Shell> shell,
+    std::unique_ptr<APKAssetProvider> apk_asset_provider,
     const fml::WeakPtr<PlatformViewAndroid>& platform_view)
     : settings_(settings),
       jni_facade_(jni_facade),
       platform_view_(platform_view),
       thread_host_(thread_host),
-      shell_(std::move(shell)) {
+      shell_(std::move(shell)),
+      apk_asset_provider_(std::move(apk_asset_provider)) {
   FML_DCHECK(jni_facade);
   FML_DCHECK(shell_);
   FML_DCHECK(shell_->IsSetup());
@@ -270,9 +272,9 @@ std::unique_ptr<AndroidShellHolder> AndroidShellHolder::Spawn(
       shell_->Spawn(std::move(config.value()), initial_route,
                     on_create_platform_view, on_create_rasterizer);
 
-  return std::unique_ptr<AndroidShellHolder>(
-      new AndroidShellHolder(GetSettings(), jni_facade, thread_host_,
-                             std::move(shell), weak_platform_view));
+  return std::unique_ptr<AndroidShellHolder>(new AndroidShellHolder(
+      GetSettings(), jni_facade, thread_host_, std::move(shell),
+      apk_asset_provider_->Clone(), weak_platform_view));
 }
 
 void AndroidShellHolder::Launch(

engine/src/flutter/shell/platform/android/android_shell_holder.h

@@ -128,6 +128,7 @@ class AndroidShellHolder {
                      const std::shared_ptr<PlatformViewAndroidJNI>& jni_facade,
                      const std::shared_ptr<ThreadHost>& thread_host,
                      std::unique_ptr<Shell> shell,
+                     std::unique_ptr<APKAssetProvider> apk_asset_provider,
                      const fml::WeakPtr<PlatformViewAndroid>& platform_view);
   static void ThreadDestructCallback(void* value);
   std::optional<RunConfiguration> BuildRunConfiguration(

engine/src/flutter/testing/scenario_app/android/BUILD.gn

@@ -21,9 +21,11 @@ _android_sources = [
   "app/src/androidTest/java/dev/flutter/scenariosui/PlatformViewWithTextureViewUiTest.java",
   "app/src/androidTest/java/dev/flutter/scenariosui/ScreenshotUtil.java",
   "app/src/androidTest/java/dev/flutter/scenariosui/SpawnEngineTests.java",
+  "app/src/androidTest/java/dev/flutter/scenariosui/SpawnMultiEngineTest.java",
   "app/src/main/AndroidManifest.xml",
   "app/src/main/java/dev/flutter/scenarios/GetBitmapActivity.java",
   "app/src/main/java/dev/flutter/scenarios/PlatformViewsActivity.java",
+  "app/src/main/java/dev/flutter/scenarios/SpawnMultiEngineActivity.java",
   "app/src/main/java/dev/flutter/scenarios/SpawnedEngineActivity.java",
   "app/src/main/java/dev/flutter/scenarios/StrictModeFlutterActivity.java",
   "app/src/main/java/dev/flutter/scenarios/SurfacePlatformViewFactory.java",

engine/src/flutter/testing/scenario_app/android/app/src/androidTest/java/dev/flutter/scenariosui/SpawnMultiEngineTest.java

@@ -0,0 +1,37 @@
+// Copyright 2013 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.
+
+package dev.flutter.scenariosui;
+
+import android.content.Intent;
+import androidx.annotation.NonNull;
+import androidx.test.filters.LargeTest;
+import androidx.test.rule.ActivityTestRule;
+import androidx.test.runner.AndroidJUnit4;
+import dev.flutter.scenarios.SpawnMultiEngineActivity;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@RunWith(AndroidJUnit4.class)
+@LargeTest
+public class SpawnMultiEngineTest {
+  Intent intent;
+
+  @Rule @NonNull
+  public ActivityTestRule<SpawnMultiEngineActivity> activityRule =
+      new ActivityTestRule<>(
+          SpawnMultiEngineActivity.class, /*initialTouchMode=*/ false, /*launchActivity=*/ false);
+
+  @Before
+  public void setUp() {
+    intent = new Intent(Intent.ACTION_MAIN);
+  }
+
+  @Test
+  public void testSpawnedEngine() throws Exception {
+    activityRule.launchActivity(intent);
+  }
+}

engine/src/flutter/testing/scenario_app/android/app/src/main/AndroidManifest.xml

@@ -37,6 +37,18 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
+        <activity
+            android:name=".SpawnMultiEngineActivity"
+            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
+            android:hardwareAccelerated="true"
+            android:launchMode="singleTop"
+            android:windowSoftInputMode="adjustResize"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
         <activity
             android:name=".ExternalTextureFlutterActivity"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"

engine/src/flutter/testing/scenario_app/android/app/src/main/java/dev/flutter/scenarios/SpawnMultiEngineActivity.java

@@ -0,0 +1,30 @@
+// Copyright 2013 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.
+
+package dev.flutter.scenarios;
+
+import android.content.Context;
+import androidx.annotation.NonNull;
+import io.flutter.embedding.engine.FlutterEngine;
+import io.flutter.embedding.engine.FlutterEngineGroup;
+
+public class SpawnMultiEngineActivity extends TestActivity {
+  static final String TAG = "Scenarios";
+
+  @Override
+  @NonNull
+  public FlutterEngine provideFlutterEngine(@NonNull Context context) {
+    FlutterEngineGroup engineGroup = new FlutterEngineGroup(context);
+    FlutterEngine firstEngine = engineGroup.createAndRunDefaultEngine(context);
+
+    FlutterEngine secondEngine = engineGroup.createAndRunDefaultEngine(context);
+
+    // Check that a new engine can be spawned from the group even if the group's
+    // original engine has been destroyed.
+    firstEngine.destroy();
+    FlutterEngine thirdEngine = engineGroup.createAndRunDefaultEngine(context);
+
+    return thirdEngine;
+  }
+}