Refine the copy._SupportsReplace.__replace__ signature (#14786)

stdlib/@tests/test_cases/check_copy.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import copy
 import sys
+from typing import Generic, TypeVar
 from typing_extensions import Self, assert_type
 
 
@@ -19,3 +20,20 @@ if sys.version_info >= (3, 13):
     obj = ReplaceableClass(42)
     cpy = copy.replace(obj, val=23)
     assert_type(cpy, ReplaceableClass)
+
+
+_T_co = TypeVar("_T_co", covariant=True)
+
+
+class Box(Generic[_T_co]):
+    def __init__(self, value: _T_co, /) -> None:
+        self.value = value
+
+    def __replace__(self, value: str) -> Box[str]:
+        return Box(value)
+
+
+if sys.version_info >= (3, 13):
+    box1: Box[int] = Box(42)
+    box2 = copy.replace(box1, val="spam")
+    assert_type(box2, Box[str])