gh-94996: Disallow lambda pos only params with feature_version < (3, 8) (GH-95934)

3 files changed, 11 insertions, 4 deletions

diff --git a/Grammar/python.gram b/Grammar/python.gram
index afae85d..d4df78b 100644
--- a/Grammar/python.gram
+++ b/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)}
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index 2f3e9d5..4cfefe4 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -746,6 +746,13 @@ class AST_Tests(unittest.TestCase):
         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
diff --git a/Parser/parser.c b/Parser/parser.c
index 15e833a..c9366d5 100644
--- a/Parser/parser.c
+++ b/Parser/parser.c
@@ -14659,7 +14659,7 @@ lambda_parameters_rule(Parser *p)
         )
         {
             D(fprintf(stderr, "%*c+ lambda_parameters[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "lambda_slash_no_default lambda_param_no_default* lambda_param_with_default* lambda_star_etc?"));
-            _res = _PyPegen_make_arguments ( p , a , NULL , b , c , d );
+            _res = CHECK_VERSION ( arguments_ty , 8 , "Positional-only parameters are" , _PyPegen_make_arguments ( p , a , NULL , b , c , d ) );
             if (_res == NULL && PyErr_Occurred()) {
                 p->error_indicator = 1;
                 p->level--;
@@ -14689,7 +14689,7 @@ lambda_parameters_rule(Parser *p)
         )
         {
             D(fprintf(stderr, "%*c+ lambda_parameters[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "lambda_slash_with_default lambda_param_with_default* lambda_star_etc?"));
-            _res = _PyPegen_make_arguments ( p , NULL , a , NULL , b , c );
+            _res = CHECK_VERSION ( arguments_ty , 8 , "Positional-only parameters are" , _PyPegen_make_arguments ( p , NULL , a , NULL , b , c ) );
             if (_res == NULL && PyErr_Occurred()) {
                 p->error_indicator = 1;
                 p->level--;