[esnext] prototype runtime implementation for async functions

src/frames.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/frames.h"
 
 #include <sstream>
 
 #include "src/ast/ast.h"
 #include "src/ast/scopeinfo.h"
@@ skipping 845 matching lines @@
 
 
 void JavaScriptFrame::GetFunctions(List<JSFunction*>* functions) const {
   DCHECK(functions->length() == 0);
   functions->Add(function());
 }
 
 void JavaScriptFrame::Summarize(List<FrameSummary>* functions) const {
   DCHECK(functions->length() == 0);
   Code* code = LookupCode();
+
+  // TODO(caitp): these builtins cause crashes here --- that's not good!
+  // Should probably be a better way to keep functions from being included in
+  // stack trace.
+  if (code == *function()->GetIsolate()->builtins()->AsyncFunctionNext() ||

[caitp (gmail), 2016/04/16 20:09:30]

other than the off-by-one bug mentioned and fixed above, this is the remaining
issue with throw resumption. 

Ideally, these functions wouldn't show up in a stack trace at all.

Currently, the stack trace for exceptions thrown within an async function are a
bit weird, since they include the "AsyncFunctionStart" stack entry, which is
serialized as the async function itself (so you can end up with duplicate stack
trace entries, which is not a good look).

+      code == *function()->GetIsolate()->builtins()->AsyncFunctionThrow())
+    return;
+
   int offset = static_cast<int>(pc() - code->instruction_start());
   AbstractCode* abstract_code = AbstractCode::cast(code);
   FrameSummary summary(receiver(), function(), abstract_code, offset,
                        IsConstructor());
   functions->Add(summary);
 }
 
 JSFunction* JavaScriptFrame::function() const {
   return JSFunction::cast(function_slot_object());
 }
@@ skipping 872 matching lines @@
   for (StackFrameIterator it(isolate); !it.done(); it.Advance()) {
     StackFrame* frame = AllocateFrameCopy(it.frame(), zone);
     list.Add(frame, zone);
   }
   return list.ToVector();
 }
 
 
 }  // namespace internal
 }  // namespace v8