[3.12] gh-114053: Fix bad interaction of PEP-695, PEP-563 and get_type_hints (#118009) (#118104)

Co-authored-by: Jelle Zijlstra <[email protected]>

Author: AlexWaygood

Doc/library/typing.rst

@@ -2887,7 +2887,9 @@ Introspection helpers
 
    This is often the same as ``obj.__annotations__``. In addition,
    forward references encoded as string literals are handled by evaluating
-   them in ``globals`` and ``locals`` namespaces. For a class ``C``, return
+   them in ``globals``, ``locals`` and (where applicable)
+   :ref:`type parameter <type-params>` namespaces.
+   For a class ``C``, return
    a dictionary constructed by merging all the ``__annotations__`` along
    ``C.__mro__`` in reverse order.
 

Lib/test/test_typing.py

@@ -47,7 +47,7 @@
 import types
 
 from test.support import captured_stderr, cpython_only
-from test.typinganndata import mod_generics_cache, _typed_dict_helper
+from test.typinganndata import ann_module695, mod_generics_cache, _typed_dict_helper
 
 
 CANNOT_SUBCLASS_TYPE = 'Cannot subclass special typing classes'
@@ -4499,6 +4499,30 @@ def f(x: X): ...
             {'x': list[list[ForwardRef('X')]]}
         )
 
+    def test_pep695_generic_with_future_annotations(self):
+        hints_for_A = get_type_hints(ann_module695.A)
+        A_type_params = ann_module695.A.__type_params__
+        self.assertIs(hints_for_A["x"], A_type_params[0])
+        self.assertEqual(hints_for_A["y"].__args__[0], Unpack[A_type_params[1]])
+        self.assertIs(hints_for_A["z"].__args__[0], A_type_params[2])
+
+        hints_for_B = get_type_hints(ann_module695.B)
+        self.assertEqual(hints_for_B.keys(), {"x", "y", "z"})
+        self.assertEqual(
+            set(hints_for_B.values()) ^ set(ann_module695.B.__type_params__),
+            set()
+        )
+
+        hints_for_generic_function = get_type_hints(ann_module695.generic_function)
+        func_t_params = ann_module695.generic_function.__type_params__
+        self.assertEqual(
+            hints_for_generic_function.keys(), {"x", "y", "z", "zz", "return"}
+        )
+        self.assertIs(hints_for_generic_function["x"], func_t_params[0])
+        self.assertEqual(hints_for_generic_function["y"], Unpack[func_t_params[1]])
+        self.assertIs(hints_for_generic_function["z"].__origin__, func_t_params[2])
+        self.assertIs(hints_for_generic_function["zz"].__origin__, func_t_params[2])
+
     def test_extended_generic_rules_subclassing(self):
         class T1(Tuple[T, KT]): ...
         class T2(Tuple[T, ...]): ...

Lib/test/typinganndata/ann_module695.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+from typing import Callable
+
+
+class A[T, *Ts, **P]:
+    x: T
+    y: tuple[*Ts]
+    z: Callable[P, str]
+
+
+class B[T, *Ts, **P]:
+    T = int
+    Ts = str
+    P = bytes
+    x: T
+    y: Ts
+    z: P
+
+
+def generic_function[T, *Ts, **P](
+    x: T, *y: *Ts, z: P.args, zz: P.kwargs
+) -> None: ...

Lib/typing.py

@@ -403,15 +403,16 @@ def inner(*args, **kwds):
 
     return decorator
 
-def _eval_type(t, globalns, localns, recursive_guard=frozenset()):
+
+def _eval_type(t, globalns, localns, type_params, *, recursive_guard=frozenset()):
     """Evaluate all forward references in the given type t.
 
     For use of globalns and localns see the docstring for get_type_hints().
     recursive_guard is used to prevent infinite recursion with a recursive
     ForwardRef.
     """
     if isinstance(t, ForwardRef):
-        return t._evaluate(globalns, localns, recursive_guard)
+        return t._evaluate(globalns, localns, type_params, recursive_guard=recursive_guard)
     if isinstance(t, (_GenericAlias, GenericAlias, types.UnionType)):
         if isinstance(t, GenericAlias):
             args = tuple(
@@ -425,7 +426,13 @@ def _eval_type(t, globalns, localns, recursive_guard=frozenset()):
                 t = t.__origin__[args]
             if is_unpacked:
                 t = Unpack[t]
-        ev_args = tuple(_eval_type(a, globalns, localns, recursive_guard) for a in t.__args__)
+
+        ev_args = tuple(
+            _eval_type(
+                a, globalns, localns, type_params, recursive_guard=recursive_guard
+            )
+            for a in t.__args__
+        )
         if ev_args == t.__args__:
             return t
         if isinstance(t, GenericAlias):
@@ -906,7 +913,7 @@ def __init__(self, arg, is_argument=True, module=None, *, is_class=False):
         self.__forward_is_class__ = is_class
         self.__forward_module__ = module
 
-    def _evaluate(self, globalns, localns, recursive_guard):
+    def _evaluate(self, globalns, localns, type_params, *, recursive_guard):
         if self.__forward_arg__ in recursive_guard:
             return self
         if not self.__forward_evaluated__ or localns is not globalns:
@@ -920,14 +927,25 @@ def _evaluate(self, globalns, localns, recursive_guard):
                 globalns = getattr(
                     sys.modules.get(self.__forward_module__, None), '__dict__', globalns
                 )
+            if type_params:
+                # "Inject" type parameters into the local namespace
+                # (unless they are shadowed by assignments *in* the local namespace),
+                # as a way of emulating annotation scopes when calling `eval()`
+                locals_to_pass = {param.__name__: param for param in type_params} | localns
+            else:
+                locals_to_pass = localns
             type_ = _type_check(
-                eval(self.__forward_code__, globalns, localns),
+                eval(self.__forward_code__, globalns, locals_to_pass),
                 "Forward references must evaluate to types.",
                 is_argument=self.__forward_is_argument__,
                 allow_special_forms=self.__forward_is_class__,
             )
             self.__forward_value__ = _eval_type(
-                type_, globalns, localns, recursive_guard | {self.__forward_arg__}
+                type_,
+                globalns,
+                localns,
+                type_params,
+                recursive_guard=(recursive_guard | {self.__forward_arg__}),
             )
             self.__forward_evaluated__ = True
         return self.__forward_value__
@@ -2241,7 +2259,7 @@ def get_type_hints(obj, globalns=None, localns=None, include_extras=False):
                     value = type(None)
                 if isinstance(value, str):
                     value = ForwardRef(value, is_argument=False, is_class=True)
-                value = _eval_type(value, base_globals, base_locals)
+                value = _eval_type(value, base_globals, base_locals, base.__type_params__)
                 hints[name] = value
         return hints if include_extras else {k: _strip_annotations(t) for k, t in hints.items()}
 
@@ -2267,6 +2285,7 @@ def get_type_hints(obj, globalns=None, localns=None, include_extras=False):
             raise TypeError('{!r} is not a module, class, method, '
                             'or function.'.format(obj))
     hints = dict(hints)
+    type_params = getattr(obj, "__type_params__", ())
     for name, value in hints.items():
         if value is None:
             value = type(None)
@@ -2278,7 +2297,7 @@ def get_type_hints(obj, globalns=None, localns=None, include_extras=False):
                 is_argument=not isinstance(obj, types.ModuleType),
                 is_class=False,
             )
-        hints[name] = _eval_type(value, globalns, localns)
+        hints[name] = _eval_type(value, globalns, localns, type_params)
     return hints if include_extras else {k: _strip_annotations(t) for k, t in hints.items()}
 
 

Misc/NEWS.d/next/Library/2024-04-17-22-00-15.gh-issue-114053._JBV4D.rst

@@ -0,0 +1,4 @@
+Fix erroneous :exc:`NameError` when calling :func:`typing.get_type_hints` on
+a class that made use of :pep:`695` type parameters in a module that had
+``from __future__ import annotations`` at the top of the file. Patch by Alex
+Waygood.