Leaving a generator via an exception causes it to close

src/runtime/runtime-generator.cc

 // Copyright 2014 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/arguments.h"
 #include "src/frames-inl.h"
 #include "src/runtime/runtime-utils.h"
 
@@ skipping 117 matching lines @@
       return value;
     case JSGeneratorObject::THROW:
       return isolate->Throw(value);
   }
 
   UNREACHABLE();
   return isolate->ThrowIllegalOperation();
 }
 
 
-RUNTIME_FUNCTION(Runtime_ThrowGeneratorStateError) {
+RUNTIME_FUNCTION(Runtime_GeneratorClose) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(JSGeneratorObject, generator, 0);
-  int continuation = generator->continuation();
-  const char* message = continuation == JSGeneratorObject::kGeneratorClosed
-                            ? "generator_finished"
-                            : "generator_running";
-  Vector<Handle<Object> > argv = HandleVector<Object>(NULL, 0);
-  THROW_NEW_ERROR_RETURN_FAILURE(isolate, NewError(message, argv));
+
+  generator->set_continuation(JSGeneratorObject::kGeneratorClosed);
+
+  return isolate->heap()->undefined_value();
 }
 
 
 // Returns function of generator activation.
 RUNTIME_FUNCTION(Runtime_GeneratorGetFunction) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(JSGeneratorObject, generator, 0);
 
   return generator->function();
@@ skipping 62 matching lines @@
   return NULL;
 }
 
 
 RUNTIME_FUNCTION(RuntimeReference_GeneratorThrow) {
   UNREACHABLE();  // Optimization disabled in SetUpGenerators().
   return NULL;
 }
 }
 }  // namespace v8::internal