gh-112618: Make `Annotated` cache typed (#112619)

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

Lib/test/test_typing.py

@@ -8675,6 +8675,40 @@ class AnnotatedTests(BaseTestCase):
         self.assertEqual(X.__mro__, (X, int, object),
                          "Annotated should be transparent.")
 
+    def test_annotated_cached_with_types(self):
+        class A(str): ...
+        class B(str): ...
+
+        field_a1 = Annotated[str, A("X")]
+        field_a2 = Annotated[str, B("X")]
+        a1_metadata = field_a1.__metadata__[0]
+        a2_metadata = field_a2.__metadata__[0]
+
+        self.assertIs(type(a1_metadata), A)
+        self.assertEqual(a1_metadata, A("X"))
+        self.assertIs(type(a2_metadata), B)
+        self.assertEqual(a2_metadata, B("X"))
+        self.assertIsNot(type(a1_metadata), type(a2_metadata))
+
+        field_b1 = Annotated[str, A("Y")]
+        field_b2 = Annotated[str, B("Y")]
+        b1_metadata = field_b1.__metadata__[0]
+        b2_metadata = field_b2.__metadata__[0]
+
+        self.assertIs(type(b1_metadata), A)
+        self.assertEqual(b1_metadata, A("Y"))
+        self.assertIs(type(b2_metadata), B)
+        self.assertEqual(b2_metadata, B("Y"))
+        self.assertIsNot(type(b1_metadata), type(b2_metadata))
+
+        field_c1 = Annotated[int, 1]
+        field_c2 = Annotated[int, 1.0]
+        field_c3 = Annotated[int, True]
+
+        self.assertIs(type(field_c1.__metadata__[0]), int)
+        self.assertIs(type(field_c2.__metadata__[0]), float)
+        self.assertIs(type(field_c3.__metadata__[0]), bool)
+
 
 class TypeAliasTests(BaseTestCase):
     def test_canonical_usage_with_variable_annotation(self):

Lib/typing.py

@@ -490,7 +490,7 @@ class _SpecialForm(_Final, _NotIterable, _root=True):
         return self._getitem(self, parameters)
 
 
-class _LiteralSpecialForm(_SpecialForm, _root=True):
+class _TypedCacheSpecialForm(_SpecialForm, _root=True):
     def __getitem__(self, parameters):
         if not isinstance(parameters, tuple):
             parameters = (parameters,)
@@ -723,7 +723,7 @@ def Optional(self, parameters):
     arg = _type_check(parameters, f"{self} requires a single type.")
     return Union[arg, type(None)]
 
-@_LiteralSpecialForm
+@_TypedCacheSpecialForm
 @_tp_cache(typed=True)
 def Literal(self, *parameters):
     """Special typing form to define literal types (a.k.a. value types).
@@ -2005,8 +2005,9 @@ class _AnnotatedAlias(_NotIterable, _GenericAlias, _root=True):
         return (self.__origin__,)
 
 
-@_SpecialForm
-def Annotated(self, params):
+@_TypedCacheSpecialForm
+@_tp_cache(typed=True)
+def Annotated(self, *params):
     """Add context-specific metadata to a type.
 
     Example: Annotated[int, runtime_check.Unsigned] indicates to the
@@ -2053,7 +2054,7 @@ def Annotated(self, params):
       where T1, T2 etc. are TypeVars, which would be invalid, because
       only one type should be passed to Annotated.
     """
-    if not isinstance(params, tuple) or len(params) < 2:
+    if len(params) < 2:
         raise TypeError("Annotated[...] should be used "
                         "with at least two arguments (a type and an "
                         "annotation).")

Misc/NEWS.d/next/Library/2023-12-02-12-55-17.gh-issue-112618.7_FT8-.rst

@@ -0,0 +1,2 @@
+Fix a caching bug relating to :data:`typing.Annotated`.
+``Annotated[str, True]`` is no longer identical to ``Annotated[str, 1]``.