Generate correct error message for generator expression following

keyword arguments

Author: lysnikolaou

Grammar/python.gram

@@ -625,6 +625,8 @@ incorrect_arguments:
     | a=expression for_if_clauses ',' [args | expression for_if_clauses] {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "Generator expression must be parenthesized") }
     | a=args for_if_clauses { _PyPegen_nonparen_genexp_in_call(p, a) }
+    | args ',' a=expression for_if_clauses {
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "Generator expression must be parenthesized") }
     | a=args ',' args { _PyPegen_arguments_parsing_error(p, a) }
 invalid_kwarg:
     | a=expression '=' {

Parser/pegen/parse.c

@@ -10595,6 +10595,7 @@ t_atom_rule(Parser *p)
 //     | args ',' '*'
 //     | expression for_if_clauses ',' [args | expression for_if_clauses]
 //     | args for_if_clauses
+//     | args ',' expression for_if_clauses
 //     | args ',' args
 static void *
 incorrect_arguments_rule(Parser *p)
@@ -10668,6 +10669,30 @@ incorrect_arguments_rule(Parser *p)
         }
         p->mark = _mark;
     }
+    { // args ',' expression for_if_clauses
+        Token * _literal;
+        expr_ty a;
+        expr_ty args_var;
+        asdl_seq* for_if_clauses_var;
+        if (
+            (args_var = args_rule(p))  // args
+            &&
+            (_literal = _PyPegen_expect_token(p, 12))  // token=','
+            &&
+            (a = expression_rule(p))  // expression
+            &&
+            (for_if_clauses_var = for_if_clauses_rule(p))  // for_if_clauses
+        )
+        {
+            _res = RAISE_SYNTAX_ERROR_KNOWN_LOCATION ( a , "Generator expression must be parenthesized" );
+            if (_res == NULL && PyErr_Occurred()) {
+                p->error_indicator = 1;
+                return NULL;
+            }
+            goto done;
+        }
+        p->mark = _mark;
+    }
     { // args ',' args
         Token * _literal;
         expr_ty a;