forbid AST_Await in computed function arguments (#4352)

fixes #4351

lib/parse.js

@@ -653,14 +653,15 @@ function parse($TEXT, options) {
         input         : typeof $TEXT == "string"
                         ? tokenizer($TEXT, options.filename, options.html5_comments, options.shebang)
                         : $TEXT,
-        token         : null,
-        prev          : null,
-        peeked        : null,
         in_async      : false,
-        in_function   : 0,
         in_directives : true,
+        in_funarg     : -1,
+        in_function   : 0,
         in_loop       : 0,
-        labels        : []
+        labels        : [],
+        peeked        : null,
+        prev          : null,
+        token         : null,
     };
 
     S.token = next();
@@ -1053,9 +1054,12 @@ function parse($TEXT, options) {
         if (name && ctor !== AST_Accessor && !(name instanceof AST_SymbolDeclaration))
             unexpected(prev());
         expect("(");
+        var was_funarg = S.in_funarg;
+        S.in_funarg = S.in_function;
         var argnames = expr_list(")", !options.strict, false, function() {
             return maybe_destructured(AST_SymbolFunarg);
         });
+        S.in_funarg = was_funarg;
         var loop = S.in_loop;
         var labels = S.labels;
         ++S.in_function;
@@ -1638,6 +1642,7 @@ function parse($TEXT, options) {
     function maybe_await() {
         var start = S.token;
         if (!(S.in_async && is("name", "await"))) return maybe_unary();
+        if (S.in_funarg === S.in_function) croak("Invalid use of await in function argument");
         S.input.context().regex_allowed = true;
         next();
         return new AST_Await({