Reapply python#120272

Author: JelleZijlstra

Lib/annotationlib.py

@@ -120,8 +120,21 @@ def evaluate(self, *, globals=None, locals=None, type_params=None, owner=None):
             # (unless they are shadowed by assignments *in* the local namespace),
             # as a way of emulating annotation scopes when calling `eval()`
             type_params = getattr(self.__owner__, "__type_params__", None)
+
+        # 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 is not None:
-            locals = {param.__name__: param for param in type_params} | locals
+            globals, locals = dict(globals), dict(locals)
+            for param in type_params:
+                param_name = param.__name__
+                if not self.__forward_is_class__ or param_name not in globals:
+                    globals[param_name] = param
+                    locals.pop(param_name, None)
 
         code = self.__forward_code__
         value = eval(code, globals=globals, locals=locals)