pyright hangs while using 100% CPU

[bkoropoff]

Describe the bug
pyright hangs and uses 100% CPU on particular python code.

To Reproduce
Running pyright <file.py> on the code below hangs and pegs a CPU at 100%.

Expected behavior
It doesn't do that.

Screenshots or Code
This is the most reduced test case I could produce:

from typing import Iterable, TypeVar, Union

T = TypeVar("T")
Tree = list[Union["Tree[T]", T]]

def _flatten(tree: Union[Tree[T], T]) -> Iterable[T]:
    if not isinstance(tree, list):
        yield tree
        return
    for v in tree:
        yield from _flatten(v)

def flatten(tree: Tree[T]) -> Iterable[T]:
    return _flatten(tree)

VS Code extension or command-line
Command line, latest version from pip (1.1.289), Linux.

Additional context
Originally found using pyright as LSP from neovim.

[erictraut]

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

[bkoropoff]

The latest version from git still hangs if I modify the test case to call the function:

from typing import Iterable, TypeVar, Union

T = TypeVar("T")
Tree = list[Union["Tree[T]", T]]

def _flatten(tree: Union[Tree[T], T]) -> Iterable[T]:
    if not isinstance(tree, list):
        yield tree
        return
    for v in tree:
        yield from _flatten(v)

def flatten(tree: Tree[T]) -> Iterable[T]:
    return _flatten(tree)

flatten([1,[2,3]])

[erictraut]

This is included in pyright 1.1.290, which I just published. It will also be included in a future release of pylance.