Fix JS to Java exception conversion for UncaughtExceptionHandler

Author: zbynek

gwt-core-gwt2-tests/src/test/java/org/gwtproject/core/client/GWTTest.java

@@ -16,8 +16,14 @@
 package org.gwtproject.core.client;
 
 import com.google.gwt.junit.client.GWTTestCase;
+import elemental2.dom.DomGlobal;
+import java.util.ArrayList;
+import java.util.List;
 
 public class GWTTest extends GWTTestCase {
+
+  private List<Throwable> caught = new ArrayList<>();
+
   @Override
   public String getModuleName() {
     return "org.gwtproject.core.Core";
@@ -32,4 +38,22 @@ public void testIsClient() {
     assertTrue(GWT.isClient());
     assertTrue(org.gwtproject.core.shared.GWT.isClient());
   }
+
+  public void testReportUncaughtError() {
+    GWT.setUncaughtExceptionHandler(caught::add);
+    GWT.reportUncaughtException(new RuntimeException());
+    DomGlobal.setTimeout(
+        (ignore) -> {
+          assertEquals(1, caught.size());
+          assertEquals("java.lang.JsException", caught.get(0).getClass().getName());
+          finishTest();
+        },
+        1000);
+    delayTestFinish(3000);
+  }
+
+  @Override
+  public boolean catchExceptions() {
+    return false;
+  }
 }

gwt-core/src/main/java/org/gwtproject/core/client/GWT.java

@@ -152,7 +152,7 @@ private static void addOnErrorHandler(Window window, Window.OnerrorFn onerrorFn)
   @JsMethod
   private static native Throwable fromObject(Object obj) /*-{
     //GWT2 impl using JSNI, see GWT.native.js for the j2cl impl
-    var throwable = @java.lang.Throwable::of(*)(obj);
+    return @java.lang.Throwable::of(*)(obj);
   }-*/;
 
   @JsType(isNative = true, name = "window", namespace = "<window>")