Incorrect return type for synthesised __new__ methods of NamedTuple classes #2522
Description
It looks like the __new__ method we synthesize for NamedTuple classes is buggy -- here's some minimal repros of some diagnostics in the ecosystem report on this PR:
from collections import namedtuple
from typing import NamedTuple, Self
class Foo(NamedTuple):
x: int
class Bar(Foo):
def __new__(cls) -> "Bar":
return super().__new__(cls, x=42) # error[invalid-return-type] "Return type does not match returned value: expected `Bar`, found `Foo`"
class Bar2(Foo):
def __new__(cls) -> Self:
return super().__new__(cls, x=42) # error[invalid-return-type] "Return type does not match returned value: expected `Self@__new__`, found `Foo`"
Baz = namedtuple("Baz", "x y")
class Spam(Baz):
def __new__(cls) -> "Spam":
return super().__new__(cls, x=42, y=56) # error[invalid-return-type] "Return type does not match returned value: expected `Spam`, found `Baz`"
class Spam2(Baz):
def __new__(cls) -> Self:
return super().__new__(cls, x=42, y=56) # error[invalid-return-type] "Return type does not match returned value: expected `Self@__new__`, found `Baz`"I think the return type we synthesize for these methods changed in astral-sh/ruff@3e02994. We need to infer these methods as returning Self rather than an instance of the namedtuple class, I think. cc. @charliermarsh
Originally posted by @AlexWaygood in astral-sh/ruff#22584 (comment)