Have namedtuple __replace__ return Self (#17475)

Author: max-muoto

mypy/semanal_namedtuple.py

@@ -57,6 +57,7 @@
     TYPED_NAMEDTUPLE_NAMES,
     AnyType,
     CallableType,
+    Instance,
     LiteralType,
     TupleType,
     Type,
@@ -631,9 +632,10 @@ def add_method(
             args=[Argument(var, var.type, EllipsisExpr(), ARG_NAMED_OPT) for var in vars],
         )
         if self.options.python_version >= (3, 13):
+            type_vars = [tv for tv in info.defn.type_vars]
             add_method(
                 "__replace__",
-                ret=None,
+                ret=Instance(info, type_vars),
                 args=[Argument(var, var.type, EllipsisExpr(), ARG_NAMED_OPT) for var in vars],
             )
 

test-data/unit/check-namedtuple.test

@@ -1407,9 +1407,23 @@ from typing import NamedTuple
 class A(NamedTuple):
     x: int
 
-A(x=0).__replace__(x=1)
+replaced = A(x=0).__replace__(x=1)
+reveal_type(replaced)  # N: Revealed type is "__main__.A"
+
 A(x=0).__replace__(x="asdf")  # E: Argument "x" to "__replace__" of "A" has incompatible type "str"; expected "int"
 A(x=0).__replace__(y=1)  # E: Unexpected keyword argument "y" for "__replace__" of "A"
+
+from typing import TypeVar, Generic
+
+T = TypeVar("T")
+
+class GenericA(NamedTuple, Generic[T]):
+    x: T
+
+replaced_2 = GenericA(x=0).__replace__(x=1)
+reveal_type(replaced_2)  # N: Revealed type is "__main__.GenericA"
+GenericA(x=0).__replace__(x="abc") # E: Argument "x" to "__replace__" of "GenericA" has incompatible type "str"; expected "int"
+
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-namedtuple.pyi]