From d93b4ac2ff7bce07fb1c8805f43838818598191c Mon Sep 17 00:00:00 2001
From: Nikita Sobolev <mail@sobolevn.me>
Date: Fri, 11 Aug 2023 22:12:11 +0300
Subject: [PATCH] gh-101162: Forbid using issubclass() with GenericAlias as the
 1st arg (GH-103369)

---
 Lib/test/test_typing.py                          | 16 ++++++++++++++++
 ...023-04-08-12-43-52.gh-issue-101162.yOCd_J.rst |  2 ++
 Objects/abstract.c                               |  2 +-
 Objects/genericaliasobject.c                     |  1 +
 4 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2023-04-08-12-43-52.gh-issue-101162.yOCd_J.rst

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 0450a87577e..fa39c796197 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -4091,6 +4091,22 @@ class GenericTests(BaseTestCase):
         with self.assertRaises(TypeError):
             C[()]
 
+    def test_generic_subclass_checks(self):
+        for typ in [list[int], List[int],
+                    tuple[int, str], Tuple[int, str],
+                    typing.Callable[..., None],
+                    collections.abc.Callable[..., None]]:
+            with self.subTest(typ=typ):
+                self.assertRaises(TypeError, issubclass, typ, object)
+                self.assertRaises(TypeError, issubclass, typ, type)
+                self.assertRaises(TypeError, issubclass, typ, typ)
+                self.assertRaises(TypeError, issubclass, object, typ)
+
+                # isinstance is fine:
+                self.assertTrue(isinstance(typ, object))
+                # but, not when the right arg is also a generic:
+                self.assertRaises(TypeError, isinstance, typ, typ)
+
     def test_init(self):
         T = TypeVar('T')
         S = TypeVar('S')
diff --git a/Misc/NEWS.d/next/Library/2023-04-08-12-43-52.gh-issue-101162.yOCd_J.rst b/Misc/NEWS.d/next/Library/2023-04-08-12-43-52.gh-issue-101162.yOCd_J.rst
new file mode 100644
index 00000000000..e9fadc8f436
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-04-08-12-43-52.gh-issue-101162.yOCd_J.rst
@@ -0,0 +1,2 @@
+Forbid using :func:`builtins.issubclass` with :class:`types.GenericAlias` as
+the first argument.
diff --git a/Objects/abstract.c b/Objects/abstract.c
index b4edcec6007..c113364a88a 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2812,7 +2812,7 @@ object_issubclass(PyThreadState *tstate, PyObject *derived, PyObject *cls)
         return -1;
     }
 
-    /* Probably never reached anymore. */
+    /* Can be reached when infinite recursion happens. */
     return recursive_issubclass(derived, cls);
 }
 
diff --git a/Objects/genericaliasobject.c b/Objects/genericaliasobject.c
index df8873454ae..faf517b66b9 100644
--- a/Objects/genericaliasobject.c
+++ b/Objects/genericaliasobject.c
@@ -626,6 +626,7 @@ ga_vectorcall(PyObject *self, PyObject *const *args,
 
 static const char* const attr_exceptions[] = {
     "__class__",
+    "__bases__",
     "__origin__",
     "__args__",
     "__unpacked__",