Avoid error if origin has a buggy __eq__ (#422)

Fixes #419

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

CHANGELOG.md

@@ -1,3 +1,9 @@
+# Unreleased
+
+- Fix regression in v4.12.0 where specialization of certain
+  generics with an overridden `__eq__` method would raise errors.
+  Patch by Jelle Zijlstra.
+
 # Release 4.12.1 (June 1, 2024)
 
 - Preliminary changes for compatibility with the draft implementation

src/test_typing_extensions.py

@@ -6617,6 +6617,22 @@ def test_allow_default_after_non_default_in_alias(self):
         a4 = Callable[[Unpack[Ts]], T]
         self.assertEqual(a4.__args__, (Unpack[Ts], T))
 
+    @skip_if_py313_beta_1
+    def test_generic_with_broken_eq(self):
+        # See https://github.com/python/typing_extensions/pull/422 for context
+        class BrokenEq(type):
+            def __eq__(self, other):
+                if other is typing_extensions.Protocol:
+                    raise TypeError("I'm broken")
+                return False
+
+        class G(Generic[T], metaclass=BrokenEq):
+            pass
+
+        alias = G[int]
+        self.assertIs(get_origin(alias), G)
+        self.assertEqual(get_args(alias), (int,))
+
     @skipIf(
         sys.version_info < (3, 11, 1),
         "Not yet backported for older versions of Python"

src/typing_extensions.py

@@ -2954,13 +2954,20 @@ def _check_generic(cls, parameters, elen):
 def _has_generic_or_protocol_as_origin() -> bool:
     try:
         frame = sys._getframe(2)
-    # not all platforms have sys._getframe()
-    except AttributeError:
+    # - Catch AttributeError: not all Python implementations have sys._getframe()
+    # - Catch ValueError: maybe we're called from an unexpected module
+    #   and the call stack isn't deep enough
+    except (AttributeError, ValueError):
         return False  # err on the side of leniency
     else:
-        return frame.f_locals.get("origin") in (
-            typing.Generic, Protocol, typing.Protocol
-        )
+        # If we somehow get invoked from outside typing.py,
+        # also err on the side of leniency
+        if frame.f_globals.get("__name__") != "typing":
+            return False
+        origin = frame.f_locals.get("origin")
+        # Cannot use "in" because origin may be an object with a buggy __eq__ that
+        # throws an error.
+        return origin is typing.Generic or origin is Protocol or origin is typing.Protocol
 
 
 _TYPEVARTUPLE_TYPES = {TypeVarTuple, getattr(typing, "TypeVarTuple", None)}