Generic NamedTuple does appear attribute-less in match statements, and member type information is erased #21050
Description
Bug Report
If a NamedTuple is generic over T, then for some reason, inside a match statement over this NamedTuple, all information about member variables and their types are erased. Even if they are explicitly stated.
To Reproduce
from typing import NamedTuple
class Wrapper[T](NamedTuple):
wrap: T
foo: Wrapper[int] = Wrapper(123)
def bar() -> int:
match foo:
case Wrapper(wrap=w):
return w
case _: # this is only to make this error-less with `pyrefly`
raise RuntimeError("Unreachable")Expected Behavior
This function clearly matches a Wrapper[int] in its first case. It should detect it can match the internal wrap variable, and it also has to be int.
$ pyrefly check tst.py
INFO 0 errors
$ pyright tst.py
0 errors, 0 warnings, 0 informationsActual Behavior
mypy for some reason seems to say that Wrapper does not even have a wrap attribute, and also, it's saying that this is Any, even though the matched Wrapper here is Wrapper[int].
$ mypy --strict tst.py
tst.py:12: error: Class "tst.Wrapper[Any]" has no attribute "wrap" [misc]
tst.py:13: error: Returning Any from function declared to return "int" [no-any-return]Your Environment
- Mypy version used: 1.19.1
- Mypy command-line flags:
--strict - Python version used: 3.12.9