pythongh-94996: Disallow parsing pos only param with feature_version < (3, 8)

Author: hauntsaninja

Grammar/python.gram

@@ -287,9 +287,9 @@ params[arguments_ty]:
 
 parameters[arguments_ty]:
     | a=slash_no_default b[asdl_arg_seq*]=param_no_default* c=param_with_default* d=[star_etc] {
-        _PyPegen_make_arguments(p, a, NULL, b, c, d) }
+        CHECK_VERSION(arguments_ty, 8, "Positional-only parameters are", _PyPegen_make_arguments(p, a, NULL, b, c, d)) }
     | a=slash_with_default b=param_with_default* c=[star_etc] {
-        _PyPegen_make_arguments(p, NULL, a, NULL, b, c) }
+        CHECK_VERSION(arguments_ty, 8, "Positional-only parameters are", _PyPegen_make_arguments(p, NULL, a, NULL, b, c)) }
     | a[asdl_arg_seq*]=param_no_default+ b=param_with_default* c=[star_etc] {
         _PyPegen_make_arguments(p, NULL, NULL, a, b, c) }
     | a=param_with_default+ b=[star_etc] { _PyPegen_make_arguments(p, NULL, NULL, NULL, a, b)}

Lib/test/test_ast.py

@@ -738,6 +738,14 @@ def test_ast_asdl_signature(self):
         expressions[0] = f"expr = {ast.expr.__subclasses__()[0].__doc__}"
         self.assertCountEqual(ast.expr.__doc__.split("\n"), expressions)
 
+    def test_positional_only_feature_version(self):
+        ast.parse('def foo(x, /): ...', feature_version=(3, 8))
+        ast.parse('def bar(x=1, /): ...', feature_version=(3, 8))
+        with self.assertRaises(SyntaxError):
+            ast.parse('def foo(x, /): ...', feature_version=(3, 7))
+        with self.assertRaises(SyntaxError):
+            ast.parse('def bar(x=1, /): ...', feature_version=(3, 7))
+
     def test_parenthesized_with_feature_version(self):
         ast.parse('with (CtxManager() as example): ...', feature_version=(3, 10))
         # While advertised as a feature in Python 3.10, this was allowed starting 3.9
@@ -746,7 +754,7 @@ def test_parenthesized_with_feature_version(self):
             ast.parse('with (CtxManager() as example): ...', feature_version=(3, 8))
         ast.parse('with CtxManager() as example: ...', feature_version=(3, 8))
 
-    def test_issue40614_feature_version(self):
+    def test_debug_f_string_feature_version(self):
         ast.parse('f"{x=}"', feature_version=(3, 8))
         with self.assertRaises(SyntaxError):
             ast.parse('f"{x=}"', feature_version=(3, 7))