[1.19 regression] copy.replace doesn't work with NamedTuple anymore

[loic-simon]

Bug Report

Using copy.replace on a NamedTuple produces an object that is not considered assignable to the NamedTuple type by mypy 1.19.0 and newer.

To Reproduce

from copy import replace
from typing import NamedTuple

class NT(NamedTuple):
    foo: int

def mre(nt: NT) -> NT:
    return replace(nt, foo=3)

Expected Behavior

• 1.18.2 (playground) : success

Actual Behavior

• 1.19.0 (playground) : main.py:10: error: Incompatible return value type (got "NT", expected "NT") [return-value]

Some reveal_types (playground):

def mre(nt: NT) -> NT:
    reveal_type(nt)
    replaced = replace(nt, foo=3)
    reveal_type(replaced)
    return replaced

give

main.py:10: note: Revealed type is "tuple[builtins.int, fallback=__main__.NT]"
main.py:12: note: Revealed type is "__main__.NT"
main.py:13: error: Incompatible return value type (got "NT", expected "NT")  [return-value]

Your Environment

• Reproduced from 1.19.0 to master. I'll try to bisect it to the exact commit.
• Python version used: 3.14

[loic-simon]

Bisected to Sync typeshed

So it looks like a typeshed problem, upsteam commit: Refine the copy._SupportsReplace.__replace__ signature

[ilevkivskyi]

A self-contained test to reproduce this

[case testTupleTypeSelfTypeProto]
from typing import Protocol, TypeVar

R = TypeVar("R", covariant=True)

class P(Protocol[R]):
    def rep(self) -> R: ...

T = TypeVar("T")
def rep(x: P[T]) -> T: ...

class C(tuple[int, str]):
    def rep(self: T) -> T: ...

t: C
reveal_type(t)  # N: Revealed type is "tuple[builtins.int, builtins.str, fallback=__main__.C]"
reveal_type(rep(t))  # N: Revealed type is "tuple[builtins.int, builtins.str, fallback=__main__.C]"
[builtins fixtures/tuple.pyi]

(second reveal fails)