Forward Error objects to uncaught exception handler if there is one.

shell/platform/android/BUILD.gn

@@ -458,6 +458,7 @@ action("robolectric_tests") {
     "test/io/flutter/embedding/engine/PluginComponentTest.java",
     "test/io/flutter/embedding/engine/RenderingComponentTest.java",
     "test/io/flutter/embedding/engine/dart/DartExecutorTest.java",
+    "test/io/flutter/embedding/engine/dart/DartMessengerTest.java",
     "test/io/flutter/embedding/engine/loader/ApplicationInfoLoaderTest.java",
     "test/io/flutter/embedding/engine/loader/FlutterLoaderTest.java",
     "test/io/flutter/embedding/engine/mutatorsstack/FlutterMutatorViewTest.java",

shell/platform/android/io/flutter/embedding/engine/dart/DartMessenger.java

@@ -86,6 +86,8 @@ public void handleMessageFromDart(
       } catch (Exception ex) {
         Log.e(TAG, "Uncaught exception in binary message listener", ex);
         flutterJNI.invokePlatformMessageEmptyResponseCallback(replyId);
+      } catch (Error err) {
+        handleError(err);
       }
     } else {
       Log.v(TAG, "No registered handler for message. Responding to Dart with empty reply message.");
@@ -103,6 +105,8 @@ public void handlePlatformMessageResponse(int replyId, @Nullable byte[] reply) {
         callback.reply(reply == null ? null : ByteBuffer.wrap(reply));
       } catch (Exception ex) {
         Log.e(TAG, "Uncaught exception in binary message reply handler", ex);
+      } catch (Error err) {
+        handleError(err);
       }
     }
   }
@@ -123,7 +127,19 @@ public int getPendingChannelResponseCount() {
     return pendingReplies.size();
   }
 
-  private static class Reply implements BinaryMessenger.BinaryReply {
+  // Handles `Error` objects which are not supposed to be caught.
+  //
+  // We forward them to the thread's uncaught exception handler if there is one. If not, they
+  // are rethrown.
+  private static void handleError(Error err) {
+    Thread currentThread = Thread.currentThread();
+    if (currentThread.getUncaughtExceptionHandler() == null) {
+      throw err;
+    }
+    currentThread.getUncaughtExceptionHandler().uncaughtException(currentThread, err);
+  }
+
+  static class Reply implements BinaryMessenger.BinaryReply {
     @NonNull private final FlutterJNI flutterJNI;
     private final int replyId;
     private final AtomicBoolean done = new AtomicBoolean(false);

shell/platform/android/test/io/flutter/FlutterTestSuite.java

@@ -16,6 +16,8 @@
 import io.flutter.embedding.engine.FlutterJNITest;
 import io.flutter.embedding.engine.LocalizationPluginTest;
 import io.flutter.embedding.engine.RenderingComponentTest;
+import io.flutter.embedding.engine.dart.DartExecutorTest;
+import io.flutter.embedding.engine.dart.DartMessengerTest;
 import io.flutter.embedding.engine.loader.ApplicationInfoLoaderTest;
 import io.flutter.embedding.engine.loader.FlutterLoaderTest;
 import io.flutter.embedding.engine.mutatorsstack.FlutterMutatorViewTest;
@@ -41,14 +43,14 @@
 import test.io.flutter.embedding.engine.FlutterEngineTest;
 import test.io.flutter.embedding.engine.FlutterShellArgsTest;
 import test.io.flutter.embedding.engine.PluginComponentTest;
-import test.io.flutter.embedding.engine.dart.DartExecutorTest;
 
 @RunWith(Suite.class)
 @SuiteClasses({
   AccessibilityBridgeTest.class,
   AndroidKeyProcessorTest.class,
   ApplicationInfoLoaderTest.class,
   DartExecutorTest.class,
+  DartMessengerTest.class,
   FlutterActivityAndFragmentDelegateTest.class,
   FlutterActivityTest.class,
   FlutterAndroidComponentTest.class,

shell/platform/android/test/io/flutter/embedding/engine/dart/DartExecutorTest.java

@@ -1,4 +1,4 @@
-package test.io.flutter.embedding.engine.dart;
+package io.flutter.embedding.engine.dart;
 
 import static junit.framework.TestCase.assertNotNull;
 import static org.junit.Assert.assertEquals;

shell/platform/android/test/io/flutter/embedding/engine/dart/DartMessengerTest.java

@@ -0,0 +1,55 @@
+package io.flutter.embedding.engine.dart;
+
+import static junit.framework.TestCase.assertNotNull;
+import static junit.framework.TestCase.assertTrue;
+import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.mock;
+
+import io.flutter.embedding.engine.FlutterJNI;
+import io.flutter.plugin.common.BinaryMessenger.BinaryMessageHandler;
+import java.nio.ByteBuffer;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mockito;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+@Config(manifest = Config.NONE)
+@RunWith(RobolectricTestRunner.class)
+public class DartMessengerTest {
+  private static class ReportingUncaughtExceptionHandler
+      implements Thread.UncaughtExceptionHandler {
+    public Throwable latestException;
+
+    @Override
+    public void uncaughtException(Thread t, Throwable e) {
+      latestException = e;
+    }
+  }
+
+  @Test
+  public void itHandlesErrors() {
+    // Setup test.
+    final FlutterJNI fakeFlutterJni = mock(FlutterJNI.class);
+    final Thread currentThread = Thread.currentThread();
+    final Thread.UncaughtExceptionHandler savedHandler =
+        currentThread.getUncaughtExceptionHandler();
+    final ReportingUncaughtExceptionHandler reportingHandler =
+        new ReportingUncaughtExceptionHandler();
+    currentThread.setUncaughtExceptionHandler(reportingHandler);
+
+    // Create object under test.
+    final DartMessenger messenger = new DartMessenger(fakeFlutterJni);
+    final BinaryMessageHandler throwingHandler = mock(BinaryMessageHandler.class);
+    Mockito.doThrow(AssertionError.class)
+        .when(throwingHandler)
+        .onMessage(any(ByteBuffer.class), any(DartMessenger.Reply.class));
+
+    messenger.setMessageHandler("test", throwingHandler);
+    messenger.handleMessageFromDart("test", new byte[] {}, 0);
+    assertNotNull(reportingHandler.latestException);
+    assertTrue(reportingHandler.latestException instanceof AssertionError);
+    currentThread.setUncaughtExceptionHandler(savedHandler);
+  }
+}
+