Async/await catch prediction for "the synchronous case"

Handle the "synchronous case" by marking try/catch blocks introduced for
async functions as ASYNC_AWAIT and traversing up the stack, finding successive
Promises and returning caught if any of them are predicted to be caught.

BUG=v8:5167

Review-Url: https://codereview.chromium.org/2325813002
Cr-Commit-Position: refs/heads/master@{#39433}

src/debug/debug.cc

@@ -1682,43 +1682,33 @@ void Debug::OnThrow(Handle<Object> exception) {
   }
 }
 
-
-void Debug::OnPromiseReject(Handle<JSObject> promise, Handle<Object> value) {
+void Debug::OnPromiseReject(Handle<Object> promise, Handle<Object> value) {
   if (in_debug_scope() || ignore_events()) return;
   HandleScope scope(isolate_);
   // Check whether the promise has been marked as having triggered a message.
   Handle<Symbol> key = isolate_->factory()->promise_debug_marker_symbol();
-  if (JSReceiver::GetDataProperty(promise, key)->IsUndefined(isolate_)) {
+  if (!promise->IsJSObject() ||
+      JSReceiver::GetDataProperty(Handle<JSObject>::cast(promise), key)
+          ->IsUndefined(isolate_)) {
     OnException(value, promise);
   }
 }
 
 
-MaybeHandle<Object> Debug::PromiseHasUserDefinedRejectHandler(
-    Handle<JSObject> promise) {
-  Handle<JSFunction> fun = isolate_->promise_has_user_defined_reject_handler();
-  return Execution::Call(isolate_, fun, promise, 0, NULL);
-}
-
-
 void Debug::OnException(Handle<Object> exception, Handle<Object> promise) {
   Isolate::CatchType catch_type = isolate_->PredictExceptionCatcher();
 
   // Don't notify listener of exceptions that are internal to a desugaring.
   if (catch_type == Isolate::CAUGHT_BY_DESUGARING) return;
 
-  bool uncaught = (catch_type == Isolate::NOT_CAUGHT);
+  bool uncaught = catch_type == Isolate::NOT_CAUGHT;
   if (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).Assert();
     // 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(isolate_);
+    uncaught = !isolate_->PromiseHasUserDefinedRejectHandler(jspromise);
   }
   // Bail out if exception breaks are not active
   if (uncaught) {

src/debug/debug.h

@@ -413,7 +413,7 @@ class Debug {
   void OnDebugBreak(Handle<Object> break_points_hit, bool auto_continue);
 
   void OnThrow(Handle<Object> exception);
-  void OnPromiseReject(Handle<JSObject> promise, Handle<Object> value);
+  void OnPromiseReject(Handle<Object> promise, Handle<Object> value);
   void OnCompileError(Handle<Script> script);
   void OnBeforeCompile(Handle<Script> script);
   void OnAfterCompile(Handle<Script> script);
@@ -594,9 +594,6 @@ class Debug {
   // Mirror cache handling.
   void ClearMirrorCache();
 
-  MaybeHandle<Object> PromiseHasUserDefinedRejectHandler(
-      Handle<JSObject> promise);
-
   void CallEventCallback(v8::DebugEvent event,
                          Handle<Object> exec_state,
                          Handle<Object> event_data,

src/isolate.cc

@@ -1703,6 +1703,19 @@ void Isolate::PopPromise() {
   global_handles()->Destroy(global_promise.location());
 }
 
+bool Isolate::PromiseHasUserDefinedRejectHandler(Handle<Object> promise) {
+  Handle<JSFunction> fun = promise_has_user_defined_reject_handler();
+  Handle<Object> has_reject_handler;
+  if (Execution::TryCall(this, fun, promise, 0, NULL)
+          .ToHandle(&has_reject_handler)) {
+    return has_reject_handler->IsTrue(this);
+  }
+  // If an exception is thrown in the course of execution of this built-in
+  // function, it indicates either a bug, or a synthetic uncatchable
+  // exception in the shutdown path. In either case, it's OK to predict either
+  // way in DevTools.
+  return false;
+}
 
 Handle<Object> Isolate::GetPromiseOnStackOnThrow() {
   Handle<Object> undefined = factory()->undefined_value();
@@ -1713,19 +1726,46 @@ Handle<Object> Isolate::GetPromiseOnStackOnThrow() {
   if (prediction == NOT_CAUGHT || prediction == CAUGHT_BY_EXTERNAL) {
     return undefined;
   }
+  Handle<Object> retval = undefined;
+  PromiseOnStack* promise_on_stack = tltop->promise_on_stack_;
   for (JavaScriptFrameIterator it(this); !it.done(); it.Advance()) {
     switch (PredictException(it.frame())) {
       case HandlerTable::UNCAUGHT:
-      case HandlerTable::ASYNC_AWAIT:
-        break;
+        continue;
       case HandlerTable::CAUGHT:
       case HandlerTable::DESUGARING:
-        return undefined;
+        if (retval->IsJSObject()) {
+          // Caught the result of an inner async/await invocation.
+          // Mark the inner promise as caught in the "synchronous case" so
+          // that Debug::OnException will see. In the synchronous case,
+          // namely in the code in an async function before the first
+          // await, the function which has this exception event has not yet
+          // returned, so the generated Promise has not yet been marked
+          // by AsyncFunctionAwaitCaught with promiseHandledHintSymbol.
+          Handle<Symbol> key = factory()->promise_handled_hint_symbol();
+          JSObject::SetProperty(Handle<JSObject>::cast(retval), key,
+                                factory()->true_value(), STRICT)
+              .Assert();
+        }
+        return retval;
       case HandlerTable::PROMISE:
-        return tltop->promise_on_stack_->promise();
+        return promise_on_stack->promise();
+      case HandlerTable::ASYNC_AWAIT: {
+        // If in the initial portion of async/await, continue the loop to pop up
+        // successive async/await stack frames until an asynchronous one with
+        // dependents is found, or a non-async stack frame is encountered, in
+        // order to handle the synchronous async/await catch prediction case:
+        // assume that async function calls are awaited.
+        retval = promise_on_stack->promise();
+        if (PromiseHasUserDefinedRejectHandler(retval)) {
+          return retval;
+        }
+        promise_on_stack = promise_on_stack->prev();
+        continue;
       }
     }
-  return undefined;
+  }
+  return retval;
 }
 
 

src/isolate.h

@@ -673,8 +673,14 @@ class Isolate {
   // Push and pop a promise and the current try-catch handler.
   void PushPromise(Handle<JSObject> promise);
   void PopPromise();
+
+  // Return the relevant Promise that a throw/rejection pertains to, based
+  // on the contents of the Promise stack
   Handle<Object> GetPromiseOnStackOnThrow();
 
+  // Heuristically guess whether a Promise is handled by user catch handler
+  bool PromiseHasUserDefinedRejectHandler(Handle<Object> promise);
+
   class ExceptionScope {
    public:
     // Scope currently can only be used for regular exceptions,

src/runtime/runtime-internal.cc

@@ -274,7 +274,7 @@ RUNTIME_FUNCTION(Runtime_ThrowApplyNonFunction) {
 namespace {
 
 void PromiseRejectEvent(Isolate* isolate, Handle<JSObject> promise,
-                        Handle<JSObject> rejected_promise, Handle<Object> value,
+                        Handle<Object> rejected_promise, Handle<Object> value,
                         bool debug_event) {
   if (isolate->debug()->is_active() && debug_event) {
     isolate->debug()->OnPromiseReject(rejected_promise, value);
@@ -306,12 +306,12 @@ RUNTIME_FUNCTION(Runtime_PromiseRejectEventFromStack) {
   CONVERT_ARG_HANDLE_CHECKED(JSObject, promise, 0);
   CONVERT_ARG_HANDLE_CHECKED(Object, value, 1);
 
-  Handle<JSObject> rejected_promise = promise;
+  Handle<Object> rejected_promise = promise;
   if (isolate->debug()->is_active()) {
-    Handle<Object> promise_on_stack = isolate->GetPromiseOnStackOnThrow();
-    if (promise_on_stack->IsJSObject()) {
-      rejected_promise = Handle<JSObject>::cast(promise_on_stack);
-    }
+    // If the Promise.reject call is caught, then this will return
+    // undefined, which will be interpreted by PromiseRejectEvent
+    // as being a caught exception event.
+    rejected_promise = isolate->GetPromiseOnStackOnThrow();
   }
   PromiseRejectEvent(isolate, promise, rejected_promise, value, true);
   return isolate->heap()->undefined_value();

test/mjsunit/harmony/async-debug-caught-exception-cases.js

+// Copyright 2016 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.
+
+// Flags: --allow-natives-syntax --harmony-async-await --expose-debug-as debug
+
+Debug = debug.Debug
+
+let events = 0;
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Exception) return;
+  events++;
+}
+
+async function thrower() {
+  throw "a";  // Exception a
+}
+
+var reject = () => Promise.reject("b");  // Exception b
+
+async function awaitReturn() { await 1; return; }
+
+async function scalar() { return 1; }
+
+function nothing() { return 1; }
+
+function rejectConstructor() {
+  return new Promise((resolve, reject) => reject("c"));  // Exception c
+}
+
+async function argThrower(x = (() => { throw "d"; })()) { }  // Exception d
+
+function suppressThrow() {
+  return thrower();
+}
+
+async function caught(producer) {
+  try {
+    await producer();
+  } catch (e) {
+  }
+}
+
+async function uncaught(producer) {
+  await producer();
+}
+
+async function indirectUncaught(producer) {
+  await uncaught(producer);
+}
+
+async function indirectCaught(producer) {
+  try {
+    await uncaught(producer);
+  } catch (e) {
+  }
+}
+
+function dotCatch(producer) {
+  Promise.resolve(producer()).catch(() => {});
+}
+
+function indirectReturnDotCatch(producer) {
+  (async() => producer())().catch(() => {});
+}
+
+function indirectAwaitDotCatch(producer) {
+  (async() => await producer())().catch(() => {});
+}
+
+function nestedDotCatch(producer) {
+  Promise.resolve(producer()).then().catch(() => {});
+}
+
+async function indirectAwaitCatch(producer) {
+  try {
+    await (() => producer())();
+  } catch (e) {
+  }
+}
+
+let catches = [caught, indirectCaught, indirectAwaitCatch];
+let noncatches = [uncaught, indirectUncaught];
+let lateCatches = [dotCatch,
+                   indirectReturnDotCatch,
+                   indirectAwaitDotCatch,
+                   nestedDotCatch];
+
+let throws = [thrower, reject, argThrower, suppressThrow];
+let nonthrows = [awaitReturn, scalar, nothing];
+let uncatchable = [rejectConstructor];
+
+let cases = [];
+
+for (let producer of throws) {
+  for (let consumer of catches) {
+    cases.push({ producer, consumer, expectedEvents: 1, caught: true });
+    cases.push({ producer, consumer, expectedEvents: 0, caught: false });
+  }
+}
+
+for (let producer of throws) {
+  for (let consumer of noncatches) {
+    cases.push({ producer, consumer, expectedEvents: 1, caught: true });
+    cases.push({ producer, consumer, expectedEvents: 1, caught: false });
+  }
+}
+
+for (let producer of nonthrows) {
+  for (let consumer of catches.concat(noncatches, lateCatches)) {
+    cases.push({ producer, consumer, expectedEvents: 0, caught: true });
+    cases.push({ producer, consumer, expectedEvents: 0, caught: false });
+  }
+}
+
+for (let producer of uncatchable) {
+  for (let consumer of catches.concat(noncatches, lateCatches)) {
+    cases.push({ producer, consumer, expectedEvents: 1, caught: true });
+    cases.push({ producer, consumer, expectedEvents: 1, caught: false });
+  }
+}
+
+for (let producer of throws) {
+  for (let consumer of lateCatches) {
+    cases.push({ producer, consumer, expectedEvents: 1, caught: true });
+    cases.push({ producer, consumer, expectedEvents: 1, caught: false });
+  }
+}
+
+for (let {producer, consumer, expectedEvents, caught} of cases) {
+  Debug.setListener(listener);
+  if (caught) {
+    Debug.setBreakOnException();
+  } else {
+    Debug.setBreakOnUncaughtException();
+  }
+
+  events = 0;
+  consumer(producer);
+  %RunMicrotasks();
+
+  Debug.setListener(null);
+  if (caught) {
+    Debug.clearBreakOnException();
+  } else {
+    Debug.clearBreakOnUncaughtException();
+  }
+  if (expectedEvents != events) {
+    print(`producer ${producer} consumer ${consumer} expectedEvents ` +
+          `${expectedEvents} caught ${caught} events ${events}`);
+    quit(1);
+  }
+}