Disallow 'yield' in async arrow parameter lists inside generators

R=littledan@chromium.org
BUG=v8:4483

Review-Url: https://codereview.chromium.org/2270223002
Cr-Commit-Position: refs/heads/master@{#38846}

src/parsing/parser-base.h

@@ -2897,6 +2897,7 @@ ParserBase<Impl>::ParseLeftHandSideExpression(ExpressionClassifier* classifier,
               fni_->RemoveAsyncKeywordFromEnd();
             }
             ValidateBindingPattern(&async_classifier, CHECK_OK);
+            ValidateFormalParameterInitializer(&async_classifier, CHECK_OK);
             if (!async_classifier.is_valid_async_arrow_formal_parameters()) {
               ReportClassifierError(
                   async_classifier.async_arrow_formal_parameters_error());

test/cctest/test-parsing.cc

@@ -7685,6 +7685,9 @@ TEST(AsyncAwait) {
 
     "var asyncFn = async({ foo = 1 }) => foo;",
     "var asyncFn = async({ foo = 1 } = {}) => foo;",
+
+    "function* g() { var f = async(yield); }",
+    "function* g() { var f = async(x = yield); }",
     NULL
   };
   // clang-format on
@@ -7792,6 +7795,11 @@ TEST(AsyncAwaitErrors) {
 
     "var f = async(x = await) => 1;",
 
+    "function* g() { var f = async yield => 1; }",
+    "function* g() { var f = async(yield) => 1; }",
+    "function* g() { var f = async(x = yield) => 1; }",
+    "function* g() { var f = async({x = yield}) => 1; }",
+
     "class C { async constructor() {} }",
     "class C {}; class C2 extends C { async constructor() {} }",
     "class C { static async prototype() {} }",