tuple constructor doesn't preserve length of iterators w/ known size

[asukaminato0721]

Describe the Bug

Sandbox Link

No response

(Only applicable for extension issues) IDE Information

No response

[javabster]

Thanks for reporting!

cc @yangdanny97

sandbox link here.

[yangdanny97]

It's because it's not a tuple comprehension, it's a generator being passed to the tuple constructor

The tuple constructor is not special-cased in the type checker, so it always produces a tuple of unknown length

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeSI%2BiABAC4CuxsA2hOrQDTVuffsC61ALzUAFAEYuAJi4BmAJQAddKWF1GsUfiXoQHEGQBOMMFFKFauALZQKAYmoAFUsdOq0WPPmoBjXOkgAc3pDVFoIf0JlBwBlGBhqAAtaWmI4RAB6DKMTM0JcQ0CMmHQMzFwfOAy-AIhg0PD-DOowAupUADdUaFRsWF9-IJCwiPRqXGJG9Dgo9DJaRP8AWg6YQzhRtUUQWUJxKW3lEABffVQfcNWAMWgYCg8cAhJyY6A

[yangdanny97]

Going strictly by the types, Pyrefly is behaving correctly here, and mypy/pyright produce the same results

Do you think this pattern is common enough to warrant a special case?

[asukaminato0721]

def f(x: tuple[int, int]) -> tuple[int, int]:
    return tuple(t for t in x)

This also err.

Not sure whether support this though.

never mind, I checked the ruff ast, this is the same way.