Deduplicate plugin registration logic and make error logs visible

shell/platform/android/io/flutter/embedding/engine/FlutterEngine.java

@@ -20,6 +20,7 @@
 import io.flutter.embedding.engine.plugins.broadcastreceiver.BroadcastReceiverControlSurface;
 import io.flutter.embedding.engine.plugins.contentprovider.ContentProviderControlSurface;
 import io.flutter.embedding.engine.plugins.service.ServiceControlSurface;
+import io.flutter.embedding.engine.plugins.util.GeneratedPluginRegister;
 import io.flutter.embedding.engine.renderer.FlutterRenderer;
 import io.flutter.embedding.engine.renderer.RenderSurface;
 import io.flutter.embedding.engine.systemchannels.AccessibilityChannel;
@@ -342,7 +343,7 @@ public FlutterEngine(
     // Only automatically register plugins if both constructor parameter and
     // loaded AndroidManifest config turn this feature on.
     if (automaticallyRegisterPlugins && flutterLoader.automaticallyRegisterPlugins()) {
-      registerPlugins();
+      GeneratedPluginRegister.registerGeneratedPlugins(this);
     }
   }
 
@@ -391,36 +392,6 @@ private boolean isAttachedToJni() {
         newFlutterJNI); // FlutterJNI.
   }
 
-  /**
-   * Registers all plugins that an app lists in its pubspec.yaml.
-   *
-   * <p>The Flutter tool generates a class called GeneratedPluginRegistrant, which includes the code
-   * necessary to register every plugin in the pubspec.yaml with a given {@code FlutterEngine}. The
-   * GeneratedPluginRegistrant must be generated per app, because each app uses different sets of
-   * plugins. Therefore, the Android embedding cannot place a compile-time dependency on this
-   * generated class. This method uses reflection to attempt to locate the generated file and then
-   * use it at runtime.
-   *
-   * <p>This method fizzles if the GeneratedPluginRegistrant cannot be found or invoked. This
-   * situation should never occur, but if any eventuality comes up that prevents an app from using
-   * this behavior, that app can still write code that explicitly registers plugins.
-   */
-  private void registerPlugins() {
-    try {
-      Class<?> generatedPluginRegistrant =
-          Class.forName("io.flutter.plugins.GeneratedPluginRegistrant");
-      Method registrationMethod =
-          generatedPluginRegistrant.getDeclaredMethod("registerWith", FlutterEngine.class);
-      registrationMethod.invoke(null, this);
-    } catch (Exception e) {
-      Log.w(
-          TAG,
-          "Tried to automatically register plugins with FlutterEngine ("
-              + this
-              + ") but could not find and invoke the GeneratedPluginRegistrant.");
-    }
-  }
-
   /**
    * Cleans up all components within this {@code FlutterEngine} and destroys the associated Dart
    * Isolate. All state held by the Dart Isolate, such as the Flutter Elements tree, is lost.

shell/platform/android/io/flutter/embedding/engine/plugins/util/GeneratedPluginRegister.java

@@ -33,11 +33,15 @@ public static void registerGeneratedPlugins(@NonNull FlutterEngine flutterEngine
           generatedPluginRegistrant.getDeclaredMethod("registerWith", FlutterEngine.class);
       registrationMethod.invoke(null, flutterEngine);
     } catch (Exception e) {
-      Log.w(
+      Log.e(
           TAG,
           "Tried to automatically register plugins with FlutterEngine ("
               + flutterEngine
               + ") but could not find and invoke the GeneratedPluginRegistrant.");
+      Log.e(
+        TAG,
+        // getCause here because the first layer of the exception would be from reflect.
+        "Received exception while registering: " + e.getCause());
     }
   }
 }

shell/platform/android/test/io/flutter/embedding/engine/FlutterEngineTest.java

@@ -35,6 +35,7 @@
 import org.robolectric.RobolectricTestRunner;
 import org.robolectric.RuntimeEnvironment;
 import org.robolectric.annotation.Config;
+import org.robolectric.shadows.ShadowLog;
 
 @Config(manifest = Config.NONE)
 @RunWith(RobolectricTestRunner.class)
@@ -63,6 +64,9 @@ public Object answer(InvocationOnMock invocation) throws Throwable {
   @After
   public void tearDown() {
     GeneratedPluginRegistrant.clearRegisteredEngines();
+    // Make sure to not forget to remove the mock exception in the generated plugin registration
+    // mock, or everything subsequent will break.
+    GeneratedPluginRegistrant.pluginRegistrationException = null;
   }
 
   @Test
@@ -78,6 +82,29 @@ public void itAutomaticallyRegistersPluginsByDefault() {
     assertEquals(flutterEngine, registeredEngines.get(0));
   }
 
+  // Helps show the root cause of MissingPluginException type errors like https://github.com/flutter/flutter/issues/78625.
+  @Test
+  public void itCatchesAndDisplaysRegistrationExceptions() {
+    assertTrue(GeneratedPluginRegistrant.getRegisteredEngines().isEmpty());
+    GeneratedPluginRegistrant.pluginRegistrationException =
+        new RuntimeException("I'm a bug in the plugin");
+    FlutterLoader mockFlutterLoader = mock(FlutterLoader.class);
+    when(mockFlutterLoader.automaticallyRegisterPlugins()).thenReturn(true);
+    FlutterEngine flutterEngine =
+        new FlutterEngine(RuntimeEnvironment.application, mockFlutterLoader, flutterJNI);
+
+    List<FlutterEngine> registeredEngines = GeneratedPluginRegistrant.getRegisteredEngines();
+    // When it crashes, it doesn't end up registering anything.
+    assertEquals(0, registeredEngines.size());
+
+    // Check the logs actually says registration failed, so a subsequent MissingPluginException
+    // isn't mysterious.
+    assertTrue(ShadowLog.getLogsForTag("GeneratedPluginsRegister").get(0).msg.contains("Tried to automatically register plugins"));
+    assertTrue(ShadowLog.getLogsForTag("GeneratedPluginsRegister").get(1).msg.contains("I'm a bug in the plugin"));
+
+    GeneratedPluginRegistrant.pluginRegistrationException = null;
+  }
+
   @Test
   public void itDoesNotAutomaticallyRegistersPluginsWhenFlutterLoaderDisablesIt() {
     assertTrue(GeneratedPluginRegistrant.getRegisteredEngines().isEmpty());
@@ -105,17 +132,7 @@ public void itDoesNotAutomaticallyRegistersPluginsWhenFlutterEngineDisablesIt()
     assertTrue(registeredEngines.isEmpty());
   }
 
-  @Test
-  public void itCanBeConfiguredToNotAutomaticallyRegisterPlugins() {
-    new FlutterEngine(
-        RuntimeEnvironment.application,
-        mock(FlutterLoader.class),
-        flutterJNI,
-        /*dartVmArgs=*/ new String[] {},
-        /*automaticallyRegisterPlugins=*/ false);
 
-    assertTrue(GeneratedPluginRegistrant.getRegisteredEngines().isEmpty());
-  }
 
   @Test
   public void itNotifiesPlatformViewsControllerWhenDevHotRestart() {

shell/platform/android/test/io/flutter/plugins/GeneratedPluginRegistrant.java

@@ -13,6 +13,7 @@
 @VisibleForTesting
 public class GeneratedPluginRegistrant {
   private static final List<FlutterEngine> registeredEngines = new ArrayList<>();
+  public static RuntimeException pluginRegistrationException;
 
   /**
    * The one and only method currently generated by the tool.
@@ -21,6 +22,9 @@ public class GeneratedPluginRegistrant {
    * all registered engines instead.
    */
   public static void registerWith(FlutterEngine engine) {
+    if (pluginRegistrationException != null) {
+      throw pluginRegistrationException;
+    }
     registeredEngines.add(engine);
   }