[3.13] gh-114053: Fix another edge case involving `get_type_hints`, PEP 695 and PEP 563 (GH-120272) (#121003)

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

1 files changed, 16 insertions, 7 deletions

diff --git a/Lib/typing.py b/Lib/typing.py
index d09b320..fda0b2d 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1061,15 +1061,24 @@ class ForwardRef(_Final, _root=True):
                 globalns = getattr(
                     sys.modules.get(self.__forward_module__, None), '__dict__', globalns
                 )
+
+            # type parameters require some special handling,
+            # as they exist in their own scope
+            # but `eval()` does not have a dedicated parameter for that scope.
+            # For classes, names in type parameter scopes should override
+            # names in the global scope (which here are called `localns`!),
+            # but should in turn be overridden by names in the class scope
+            # (which here are called `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
+                globalns, localns = dict(globalns), dict(localns)
+                for param in type_params:
+                    param_name = param.__name__
+                    if not self.__forward_is_class__ or param_name not in globalns:
+                        globalns[param_name] = param
+                        localns.pop(param_name, None)
+
             type_ = _type_check(
-                eval(self.__forward_code__, globalns, locals_to_pass),
+                eval(self.__forward_code__, globalns, localns),
                 "Forward references must evaluate to types.",
                 is_argument=self.__forward_is_argument__,
                 allow_special_forms=self.__forward_is_class__,