Fix unhandled promise rejection handler after a .then

If we have a promise `p1` that is rejected, and invoke `then` on it,
we create a new promise `p2` (as it should be, per the spec) and mark
`p1` as handled. However, if we call `.catch` on `p2`, we are _not_
marking `p1` as handled correctly since its status is "pending" and
not "rejected". This patch fixes it and adds some tests.

Fixes #1461

src/org/mozilla/javascript/NativePromise.java

@@ -306,15 +306,19 @@ private Object then(
             cx.enqueueMicrotask(() -> fulfillReaction.invoke(cx, scope, result));
         } else {
             assert (state == State.REJECTED);
-            if (!handled) {
-                cx.getUnhandledPromiseTracker().promiseHandled(this);
-            }
+            markHandled(cx);
             cx.enqueueMicrotask(() -> rejectReaction.invoke(cx, scope, result));
         }
-        handled = true;
         return capability.promise;
     }
 
+    private void markHandled(Context cx) {
+        if (!handled) {
+            cx.getUnhandledPromiseTracker().promiseHandled(this);
+            handled = true;
+        }
+    }
+
     // Promise.prototype.catch
     private static Object doCatch(Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
         Object arg = (args.length > 0 ? args[0] : Undefined.instance);
@@ -446,6 +450,9 @@ private Object rejectPromise(Context cx, Scriptable scope, Object reason) {
         for (Reaction r : reactions) {
             cx.enqueueMicrotask(() -> r.invoke(cx, scope, reason));
         }
+        if (!reactions.isEmpty()) {
+            markHandled(cx);
+        }
         return Undefined.instance;
     }
 

testsrc/org/mozilla/javascript/tests/es6/UnhandledPromiseTest.java

@@ -64,6 +64,46 @@ public void simpleRejectionHandled() {
         assertTrue(Context.toBoolean(scope.get("caught", scope)));
     }
 
+    @Test
+    public void rejectionHandledAfterThen() {
+        scope.put("caught", scope, Boolean.FALSE);
+        exec(
+                "new Promise((resolve, reject) => { reject(); })."
+                        + "then(() => {})."
+                        + "catch((e) => { caught = true; });\n");
+        assertTrue(cx.getUnhandledPromiseTracker().enumerate().isEmpty());
+        AtomicBoolean handled = new AtomicBoolean();
+        // We should actually never see anything in the tracker here
+        cx.getUnhandledPromiseTracker()
+                .process(
+                        (Object o) -> {
+                            assertFalse(handled.get());
+                            handled.set(true);
+                        });
+        assertFalse(handled.get());
+        assertTrue(Context.toBoolean(scope.get("caught", scope)));
+    }
+
+    @Test
+    public void thenRejectsButCatchHandles() {
+        scope.put("caught", scope, Boolean.FALSE);
+        exec(
+                "new Promise((resolve, reject) => { resolve(); })."
+                        + "then((e) => { return Promise.reject(); })."
+                        + "catch((e) => { caught = true; });\n");
+        assertTrue(cx.getUnhandledPromiseTracker().enumerate().isEmpty());
+        AtomicBoolean handled = new AtomicBoolean();
+        // We should actually never see anything in the tracker here
+        cx.getUnhandledPromiseTracker()
+                .process(
+                        (Object o) -> {
+                            assertFalse(handled.get());
+                            handled.set(true);
+                        });
+        assertFalse(handled.get());
+        assertTrue(Context.toBoolean(scope.get("caught", scope)));
+    }
+
     @Test
     public void rejectionObject() {
         exec("new Promise((resolve, reject) => { reject('rejected'); });");
@@ -115,6 +155,22 @@ public void throwInThen() {
         assertTrue(handled.get());
     }
 
+    @Test
+    public void thenReturnsRejectedPromise() {
+        exec(
+                "new Promise((resolve, reject) => { resolve() }).then(() => { return Promise.reject('rejected'); });");
+        assertEquals(1, cx.getUnhandledPromiseTracker().enumerate().size());
+        AtomicBoolean handled = new AtomicBoolean();
+        cx.getUnhandledPromiseTracker()
+                .process(
+                        (Object o) -> {
+                            assertFalse(handled.get());
+                            handled.set(true);
+                            assertEquals("rejected", o);
+                        });
+        assertTrue(handled.get());
+    }
+
     private void exec(String script) {
         cx.evaluateString(scope, "load('./testsrc/assert.js'); " + script, "test.js", 0, null);
     }