Async/await catch prediction for "the synchronous case"

src/isolate.h

 // 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.
 
 #ifndef V8_ISOLATE_H_
 #define V8_ISOLATE_H_
 
 #include <memory>
 #include <queue>
 
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   // This method is called by the api after operations that may throw
   // exceptions.  If an exception was thrown and not handled by an external
   // handler the exception is scheduled to be rethrown when we return to running
   // JavaScript code.  If an exception is scheduled true is returned.
   bool OptionalRescheduleException(bool is_bottom_call);
 
   // 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,
     // not termination exception.
     inline explicit ExceptionScope(Isolate* isolate);
     inline ~ExceptionScope();
 
    private:
     Isolate* isolate_;
     Handle<Object> pending_exception_;
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   EmbeddedVector<char, 128> filename_;
   FILE* file_;
   int scope_depth_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ISOLATE_H_