Introduce PromiseRejectCallback.

src/debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 1244 matching lines @@
 
 bool Debug::IsBreakOnException(ExceptionBreakType type) {
   if (type == BreakUncaughtException) {
     return break_on_uncaught_exception_;
   } else {
     return break_on_exception_;
   }
 }
 
 
-bool Debug::PromiseHasRejectHandler(Handle<JSObject> promise) {
-  Handle<JSFunction> fun = Handle<JSFunction>::cast(
-      JSObject::GetDataProperty(isolate_->js_builtins_object(),
-                                isolate_->factory()->NewStringFromStaticChars(
-                                    "PromiseHasRejectHandler")));
-  Handle<Object> result =
-      Execution::Call(isolate_, fun, promise, 0, NULL).ToHandleChecked();
-  return result->IsTrue();
-}
-
-
 void Debug::PrepareStep(StepAction step_action,
                         int step_count,
                         StackFrame::Id frame_id) {
   HandleScope scope(isolate_);
 
   PrepareForBreakPoints();
 
   DCHECK(in_debug_scope());
 
   // Remember this step action and count.
@@ skipping 1228 matching lines @@
   OnException(exception, uncaught, isolate_->GetPromiseOnStackOnThrow());
   if (!scheduled_exception.is_null()) {
     isolate_->thread_local_top()->scheduled_exception_ = *scheduled_exception;
   }
 }
 
 
 void Debug::OnPromiseReject(Handle<JSObject> promise, Handle<Object> value) {
   if (in_debug_scope() || ignore_events()) return;
   HandleScope scope(isolate_);
-  OnException(value, false, promise);
+  // Check whether the promise has been marked as having triggered a message.
+  Handle<Symbol> key = isolate_->factory()->promise_debug_marker_symbol();
+  if (JSObject::GetDataProperty(promise, key)->IsUndefined()) {
+    OnException(value, false, promise);

[aandrey, 2014/09/30 14:08:24]

I think we should move to here:
  JSObject::SetProperty(jspromise, key, key, STRICT);

Also maybe move
  uncaught = has_reject_handler->IsFalse();
as well?

[Yang, 2014/09/30 14:29:47]

That would not work. When a promise is rejected via throw, we trigger the debug
event at the throw site via OnThrow. Later when the try-catch in PromiseHandle
or the Promise constructor catches that throw, the reject closure is called,
which would trigger a second debug event. To prevent such a duplicate event, we
simply mark it the first time we see it.

I moved it to OnThrow instead.

Regarding uncaught: on both code paths (OnThrow and OnPromiseReject) we could
see either caught or uncaught promise rejects. So to avoid code duplication I
would just leave the call to PromiseHasUserDefinedRejectHandler in OnException.

+  }
+}
+
+
+MaybeHandle<Object> Debug::PromiseHasUserDefinedRejectHandler(
+    Handle<JSObject> promise) {
+  Handle<JSFunction> fun = Handle<JSFunction>::cast(
+      JSObject::GetDataProperty(isolate_->js_builtins_object(),
+                                isolate_->factory()->NewStringFromStaticChars(
+                                    "PromiseHasUserDefinedRejectHandler")));
+  return Execution::Call(isolate_, fun, promise, 0, NULL);
 }
 
 
 void Debug::OnException(Handle<Object> exception, bool uncaught,
                         Handle<Object> promise) {
-  if (promise->IsJSObject()) {
-    uncaught |= !PromiseHasRejectHandler(Handle<JSObject>::cast(promise));
+  if (!uncaught && promise->IsJSObject()) {
+    Handle<JSObject> jspromise = Handle<JSObject>::cast(promise);
+    // Mark the promise as already having triggered a message.
+    Handle<Symbol> key = isolate_->factory()->promise_debug_marker_symbol();
+    JSObject::SetProperty(jspromise, key, key, STRICT);
+    // Check whether the promise reject is considered an uncaught exception.
+    Handle<Object> has_reject_handler;
+    ASSIGN_RETURN_ON_EXCEPTION_VALUE(
+        isolate_, has_reject_handler,
+        PromiseHasUserDefinedRejectHandler(jspromise), /* void */);
+    uncaught = has_reject_handler->IsFalse();
   }
   // Bail out if exception breaks are not active
   if (uncaught) {
     // Uncaught exceptions are reported by either flags.
     if (!(break_on_uncaught_exception_ || break_on_exception_)) return;
   } else {
     // Caught exceptions are reported is activated.
     if (!break_on_exception_) return;
   }
 
@@ skipping 828 matching lines @@
   logger_->DebugEvent("Put", message.text());
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   base::LockGuard<base::Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 } }  // namespace v8::internal