Fix evaluating forward references in STRING format can 'leak' internal names in typing

Author: ByteFlowing1337

Lib/test/test_typing.py

@@ -7561,6 +7561,23 @@ def test_with_module(self):
         typing.evaluate_forward_ref(
             fwdref_module.fw,)
 
+    def test_evaluate_forward_ref_string_format(self):
+        # Test evaluating forward references in STRING format
+        # does not 'leak' internal names
+        # See https://github.com/python/cpython/issues/150641
+        from annotationlib import Format, get_annotations
+
+        def f(arg: unknown | str | int | list[str] | tuple[int, ...]): ...
+
+        ref = get_annotations(f, format=Format.FORWARDREF)['arg']
+        self.assertEqual(
+            typing.evaluate_forward_ref(ref, format=Format.STRING),
+            "unknown | str | int | list[str] | tuple[int, ...]",
+        )
+        self.assertEqual(
+            typing.evaluate_forward_ref(ref, format=Format.STRING),
+            ref.__resolved_str__
+        )
 
 class CollectionsAbcTests(BaseTestCase):
 

Lib/typing.py

@@ -1019,8 +1019,8 @@ def evaluate_forward_ref(
 
     """
     if format == annotationlib.Format.STRING:
-        return forward_ref.__forward_arg__
-    if forward_ref.__forward_arg__ in _recursive_guard:
+        return forward_ref.__resolved_str__
+    if forward_ref.__resolved_str__ in _recursive_guard:
         return forward_ref
 
     if format is None:
@@ -1044,7 +1044,7 @@ def evaluate_forward_ref(
         globals,
         locals,
         type_params,
-        recursive_guard=_recursive_guard | {forward_ref.__forward_arg__},
+        recursive_guard=_recursive_guard | {forward_ref.__resolved_str__},
         format=format,
         owner=owner,
         parent_fwdref=forward_ref,

Misc/NEWS.d/next/Library/2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst

@@ -0,0 +1,2 @@
+Fix evaluating forward references in STRING format can 'leak' internal names
+in ``typing``.