From bc6bd537f15e41edf73a6924bcc62b77effb62bf Mon Sep 17 00:00:00 2001
From: Ivy Xu <fakeshadow1337@gmail.com>
Date: Fri, 3 Jul 2026 16:42:06 +0800
Subject: [PATCH] gh-150641: Fix evaluating forward references in STRING format
 can 'leak' internal names in `typing` (#150648)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
(cherry picked from commit f75028f7ceebee4cbeb46bf040834e2005d57436)
---
 Lib/test/test_typing.py                              | 12 ++++++++++++
 Lib/typing.py                                        |  2 +-
 .../2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst   |  2 ++
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 1832af632de4dff..8786c1b4dfecda6 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -7446,6 +7446,18 @@ 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
+
+        def f(arg: unknown | str | int | list[str] | tuple[int, ...]): ...
+
+        ref = annotationlib.get_annotations(f, format=annotationlib.Format.FORWARDREF)['arg']
+        self.assertEqual(
+            typing.evaluate_forward_ref(ref, format=annotationlib.Format.STRING),
+            "unknown | str | int | list[str] | tuple[int, ...]",
+        )
 
 class CollectionsAbcTests(BaseTestCase):
 
diff --git a/Lib/typing.py b/Lib/typing.py
index d9a7f7210bbcdd2..9308e0820f55cb6 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -991,7 +991,7 @@ def evaluate_forward_ref(
 
     """
     if format == _lazy_annotationlib.Format.STRING:
-        return forward_ref.__forward_arg__
+        return forward_ref.__resolved_str__
     if forward_ref.__forward_arg__ in _recursive_guard:
         return forward_ref
 
diff --git a/Misc/NEWS.d/next/Library/2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst b/Misc/NEWS.d/next/Library/2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst
new file mode 100644
index 000000000000000..eba899c96fcd26b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst
@@ -0,0 +1,2 @@
+Fix bug where :func:`typing.evaluate_forward_ref` with the ``STRING`` format
+could leak internal names used by the annotation machinery.