Type narrowing behaves oddly in presence of type.__eq__

[mniip]

Describe the bug
In some situations an x: Union[X, Y, ...] that has been previously narrowed to Y incorrectly unnarrows back to x: Union[X, Y]. This happens seemingly when we branch on something == X.

To Reproduce
Run pyright on the code from the Code section.

  a.py:12:18 - error: Cannot access member "p" for type "X"
    Member "p" is unknown (reportGeneralTypeIssues)
  a.py:11:25 - information: Type of "x" is "Y"

Expected behavior
No error.

Screenshots or Code

from typing import Union

class X:
    pass
class Y:
    p: type

def f(xs: list[Union[X, Y]]) -> None:
    for x in xs:
        if not isinstance(x, X):
            reveal_type(x)
            if x.p == X:
                pass

VS Code extension or command-line
Commandline pyright 1.1.287

Additional context
Works on pyright 1.1.285

[erictraut]

Thanks for the bug report. This will be addressed in the next release.

This was a long-time bug that was previously masked by the way the type narrowing logic was called. A change that I made in 1.1.286 caused it to come to light.

[erictraut]

This is addressed in pyright 1.1.288, which I just published. It will also be included in a future release of pylance.