Check for True instead of truthy for TypeVarTuple unpacking

truthy output was interpreting annotationlib _Stringifier instances as unpacked TypeVarTuples

Author: DavidCEllis

Lib/test/test_typing.py

@@ -9788,6 +9788,19 @@ class B(str): ...
         self.assertIs(type(field_c2.__metadata__[0]), float)
         self.assertIs(type(field_c3.__metadata__[0]), bool)
 
+    def test_forwardref_partial_evaluation(self):
+        # Test that Annotated partially evaluates if it contains a ForwardRef
+        # See: https://github.com/python/cpython/issues/137706
+        def f(x: Annotated[undefined, '']): pass
+
+        ann = annotationlib.get_annotations(f, format=annotationlib.Format.FORWARDREF)
+
+        # Test that the attributes are retrievable from the partially evaluated annotation
+        x_ann = ann['x']
+        self.assertIs(get_origin(x_ann), Annotated)
+        self.assertEqual(x_ann.__origin__, EqualToForwardRef('undefined', owner=f))
+        self.assertEqual(x_ann.__metadata__, ('',))
+
 
 class TypeAliasTests(BaseTestCase):
     def test_canonical_usage_with_variable_annotation(self):

Lib/typing.py

@@ -1033,8 +1033,10 @@ def evaluate_forward_ref(
 
 
 def _is_unpacked_typevartuple(x: Any) -> bool:
+    # Need to check 'is True' here
+    # See: https://github.com/python/cpython/issues/137706
     return ((not isinstance(x, type)) and
-            getattr(x, '__typing_is_unpacked_typevartuple__', False))
+            getattr(x, '__typing_is_unpacked_typevartuple__', False) is True)
 
 
 def _is_typevar_like(x: Any) -> bool: