gh-94949: Disallow parsing parenthesised ctx mgr with old feature_version (#94950)

* gh-94949: Disallow parsing parenthesised ctx manager with old feature_version

* 📜🤖 Added by blurb_it.

* Allow it with feature_version=(3, 9) as well

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

Author: hauntsaninja

Grammar/python.gram

@@ -391,7 +391,7 @@ for_stmt[stmt_ty]:
 with_stmt[stmt_ty]:
     | invalid_with_stmt_indent
     | 'with' '(' a[asdl_withitem_seq*]=','.with_item+ ','? ')' ':' b=block {
-        _PyAST_With(a, b, NULL, EXTRA) }
+        CHECK_VERSION(stmt_ty, 9, "Parenthesized context managers are", _PyAST_With(a, b, NULL, EXTRA)) }
     | 'with' a[asdl_withitem_seq*]=','.with_item+ ':' tc=[TYPE_COMMENT] b=block {
         _PyAST_With(a, b, NEW_TYPE_COMMENT(p, tc), EXTRA) }
     | ASYNC 'with' '(' a[asdl_withitem_seq*]=','.with_item+ ','? ')' ':' b=block {

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_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
+        ast.parse('with (CtxManager() as example): ...', feature_version=(3, 9))
+        with self.assertRaises(SyntaxError):
+            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):
         ast.parse('f"{x=}"', feature_version=(3, 8))
         with self.assertRaises(SyntaxError):

Misc/NEWS.d/next/Core and Builtins/2022-07-18-05-10-29.gh-issue-94949.OsZ7_s.rst

@@ -0,0 +1 @@
+:func:`ast.parse` will no longer parse parenthesized context managers when passed ``feature_version`` less than ``(3, 9)``. Patch by Shantanu Jain.