Editorial: remove context copy from AsyncFunctionStart (#1685)

spec.html

@@ -40123,8 +40123,7 @@ <h1>Async Functions Abstract Operations</h1>
       <emu-clause id="sec-async-functions-abstract-operations-async-function-start" aoid="AsyncFunctionStart">
         <h1>AsyncFunctionStart ( _promiseCapability_, _asyncFunctionBody_ )</h1>
         <emu-alg>
-          1. Let _runningContext_ be the running execution context.
-          1. Let _asyncContext_ be a copy of _runningContext_.
+          1. Let _asyncContext_ be the running execution context.
           1. Set the code evaluation state of _asyncContext_ such that when evaluation is resumed for that execution context the following steps will be performed:
             1. Let _result_ be the result of evaluating _asyncFunctionBody_.
             1. Assert: If we return here, the async function either threw an exception or performed an implicit or explicit return; all awaiting is done.
@@ -40139,7 +40138,9 @@ <h1>AsyncFunctionStart ( _promiseCapability_, _asyncFunctionBody_ )</h1>
             1. Return.
           1. Push _asyncContext_ onto the execution context stack; _asyncContext_ is now the running execution context.
           1. Resume the suspended evaluation of _asyncContext_. Let _result_ be the value returned by the resumed computation.
-          1. Assert: When we return here, _asyncContext_ has already been removed from the execution context stack and _runningContext_ is the currently running execution context.
+          1. Assert: When we return here, _asyncContext_ has been removed from the execution context stack.
+          1. Push _asyncContext_ onto the execution context stack.
+          1. NOTE: Pushing _asyncContext_ onto the execution context stack is needed to fulfill invariants of <emu-xref href="#sec-ecmascript-function-objects-call-thisargument-argumentslist">Function [[Call]]</a>.
           1. Assert: _result_ is a normal completion with a value of *undefined*. The possible sources of completion values are Await or, if the async function doesn't await anything, the step 3.g above.
           1. Return.
         </emu-alg>