bpo-41341: Recursive evaluation of ForwardRef in get_type_hints (GH-21553)
The issue raised by recursive evaluation is infinite recursion with
recursive types. In that case, only the first recursive ForwardRef is
evaluated.
(cherry picked from commit 653f420b53a3aa87316cef59de8d3f5d9e11deb4)
Co-authored-by: wyfo <joperez@hotmail.fr>
diff --git a/Lib/typing.py b/Lib/typing.py
index fd657ca..5da032b 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -244,14 +244,16 @@
return inner
-def _eval_type(t, globalns, localns):
+def _eval_type(t, globalns, localns, recursive_guard=frozenset()):
"""Evaluate all forward reverences in the given type t.
For use of globalns and localns see the docstring for get_type_hints().
+ recursive_guard is used to prevent prevent infinite recursion
+ with recursive ForwardRef.
"""
if isinstance(t, ForwardRef):
- return t._evaluate(globalns, localns)
+ return t._evaluate(globalns, localns, recursive_guard)
if isinstance(t, (_GenericAlias, GenericAlias)):
- ev_args = tuple(_eval_type(a, globalns, localns) for a in t.__args__)
+ ev_args = tuple(_eval_type(a, globalns, localns, recursive_guard) for a in t.__args__)
if ev_args == t.__args__:
return t
if isinstance(t, GenericAlias):
@@ -477,7 +479,9 @@
self.__forward_value__ = None
self.__forward_is_argument__ = is_argument
- def _evaluate(self, globalns, localns):
+ def _evaluate(self, globalns, localns, recursive_guard):
+ if self.__forward_arg__ in recursive_guard:
+ return self
if not self.__forward_evaluated__ or localns is not globalns:
if globalns is None and localns is None:
globalns = localns = {}
@@ -485,10 +489,14 @@
globalns = localns
elif localns is None:
localns = globalns
- self.__forward_value__ = _type_check(
+ type_ =_type_check(
eval(self.__forward_code__, globalns, localns),
"Forward references must evaluate to types.",
- is_argument=self.__forward_is_argument__)
+ is_argument=self.__forward_is_argument__,
+ )
+ self.__forward_value__ = _eval_type(
+ type_, globalns, localns, recursive_guard | {self.__forward_arg__}
+ )
self.__forward_evaluated__ = True
return self.__forward_value__