Editorial: more explicit validation in CreateDynamicFunction (#2374)

Author: bakkot

spec.html

@@ -24956,20 +24956,24 @@ <h1>CreateDynamicFunction ( _constructor_, _newTarget_, _kind_, _args_ )</h1>
             1. If _newTarget_ is *undefined*, set _newTarget_ to _constructor_.
             1. If _kind_ is ~normal~, then
               1. Let _exprSym_ be the grammar symbol |FunctionExpression|.
-              1. Let _bodySym_ be the grammar symbol |FunctionBody|.
+              1. Let _bodySym_ be the grammar symbol |FunctionBody[~Yield, ~Await]|.
+              1. Let _parameterSym_ be the grammar symbol |FormalParameters[~Yield, ~Await]|.
               1. Let _fallbackProto_ be *"%Function.prototype%"*.
             1. Else if _kind_ is ~generator~, then
               1. Let _exprSym_ be the grammar symbol |GeneratorExpression|.
               1. Let _bodySym_ be the grammar symbol |GeneratorBody|.
+              1. Let _parameterSym_ be the grammar symbol |FormalParameters[+Yield, ~Await]|.
               1. Let _fallbackProto_ be *"%GeneratorFunction.prototype%"*.
             1. Else if _kind_ is ~async~, then
               1. Let _exprSym_ be the grammar symbol |AsyncFunctionExpression|.
               1. Let _bodySym_ be the grammar symbol |AsyncFunctionBody|.
+              1. Let _parameterSym_ be the grammar symbol |FormalParameters[~Yield, +Await]|.
               1. Let _fallbackProto_ be *"%AsyncFunction.prototype%"*.
             1. Else,
               1. Assert: _kind_ is ~asyncGenerator~.
               1. Let _exprSym_ be the grammar symbol |AsyncGeneratorExpression|.
               1. Let _bodySym_ be the grammar symbol |AsyncGeneratorBody|.
+              1. Let _parameterSym_ be the grammar symbol |FormalParameters[+Yield, +Await]|.
               1. Let _fallbackProto_ be *"%AsyncGeneratorFunction.prototype%"*.
             1. Let _argCount_ be the number of elements in _args_.
             1. Let _P_ be the empty String.
@@ -24990,10 +24994,14 @@ <h1>CreateDynamicFunction ( _constructor_, _newTarget_, _kind_, _args_ )</h1>
             1. Let _prefix_ be the prefix associated with _kind_ in <emu-xref href="#table-dynamic-function-sourcetext-prefixes"></emu-xref>.
             1. Let _sourceString_ be the string-concatenation of _prefix_, *" anonymous("*, _P_, 0x000A (LINE FEED), *") {"*, _bodyString_, and *"}"*.
             1. Let _sourceText_ be ! StringToCodePoints(_sourceString_).
+            1. Let _parameters_ be ParseText(! StringToCodePoints(_P_), _parameterSym_).
+            1. If _parameters_ is a List of errors, throw a *SyntaxError* exception.
+            1. Let _body_ be ParseText(! StringToCodePoints(_bodyString_), _bodySym_).
+            1. If _body_ is a List of errors, throw a *SyntaxError* exception.
+            1. NOTE: The parameters and body are parsed separately to ensure that each is valid alone. For example, `new Function("/*", "*/ ) {")` is not legal.
+            1. NOTE: If this step is reached, _sourceText_ must match _exprSym_ (although the reverse implication does not hold). The purpose of the next two steps is to enforce any Early Error rules which apply to _exprSym_ directly.
             1. Let _expr_ be ParseText(_sourceText_, _exprSym_).
             1. If _expr_ is a List of errors, throw a *SyntaxError* exception.
-            1. Let _parameters_ be the |FormalParameters| of _expr_.
-            1. Let _body_ be the child of _expr_ that is an instance of _bodySym_.
             1. Let _proto_ be ? GetPrototypeFromConstructor(_newTarget_, _fallbackProto_).
             1. Let _realmF_ be the current Realm Record.
             1. Let _scope_ be _realmF_.[[GlobalEnv]].