[3.11] pythongh-94996: Disallow lambda pos only params with feature_v…

…ersion < (3, 8) (pythonGH-95934)

(cherry picked from commit a965db3)

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

Grammar/python.gram

@@ -830,9 +830,9 @@ lambda_params[arguments_ty]:
 #
 lambda_parameters[arguments_ty]:
     | a=lambda_slash_no_default b[asdl_arg_seq*]=lambda_param_no_default* c=lambda_param_with_default* d=[lambda_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=lambda_slash_with_default b=lambda_param_with_default* c=[lambda_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*]=lambda_param_no_default+ b=lambda_param_with_default* c=[lambda_star_etc] {
         _PyPegen_make_arguments(p, NULL, NULL, a, b, c) }
     | a=lambda_param_with_default+ b=[lambda_star_etc] { _PyPegen_make_arguments(p, NULL, NULL, NULL, a, b)}

Lib/test/test_ast.py

@@ -746,6 +746,13 @@ def test_positional_only_feature_version(self):
         with self.assertRaises(SyntaxError):
             ast.parse('def bar(x=1, /): ...', feature_version=(3, 7))
 
+        ast.parse('lambda x, /: ...', feature_version=(3, 8))
+        ast.parse('lambda x=1, /: ...', feature_version=(3, 8))
+        with self.assertRaises(SyntaxError):
+            ast.parse('lambda x, /: ...', feature_version=(3, 7))
+        with self.assertRaises(SyntaxError):
+            ast.parse('lambda 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