Code snippet freezes pyright

[tomhampshire]

Running pyright on the included code snippet causes pyright to run infinitely.

Describe the bug
Running pyright on the included code snippet causes pyright to run infinitely. The code itself has been minimised as much as possible, and is nonsensical.

To Reproduce
Put the code in a file and run pyright from the command line (uses pyright 1.1.287 on Arch Linux). Tested with Python 3.10.9 and Python 3.9.16.

Expected behavior
pyright should finish running.

Screenshots or Code

def function_a():
    function_b([])


def function_b(input_list):
    output_tuple = ()

    for _, value in enumerate([]):
        if value is None:
            output_tuple += (None,)
            continue
        output_tuple += (input_list[value],)

    return output_tuple

VS Code extension or command-line
pyright 1.1.287 from the Arch Linux community/pyright 1.1.287-1

[erictraut]

Thanks for the bug report. I've found the underlying cause, but I'm still working out a fix. The issue is that every time through the loop, a new tuple type is produced for output_tuple. This gets unioned with the tuple types from the previous loop passes. The type never converges to a single type. It simply adds more and more subtypes to the union.

[erictraut]

I found a reasonable fix. This will be included in the next release.

[erictraut]

This is included in pyright 1.1.289, which I just published. It will also be included in a future release of pylance.

[tomhampshire]

Thanks for looking into and fixing this!