SIM101 lint and fix is sometimes incorrect

[Zac-HD]

The SIM101 rule suggests replacing isinstance(a. b) or isinstance(a, c) with isinstance(a, (b, c)) - but the lint and autofix also trigger when there is an intermediate term in the or-expression. This is a problem because code can (and does) rely on short-circuiting evaluation in some such cases. For example, ruff --isolated --select=SIM101 --fix demo.py will break:

x = isinstance("", int) or True or isinstance("", undefined_name)
# x = isinstance("", (int, undefined_name)) or True  # incorrect fix!

I found this while experimenting with ruff in shed, which has a similar fixer.

[zanieb]

Hey, thanks for the issue! This fix as marked unsafe and will not be applied by default in the upcoming release. See #7901 and #7769 for details.

[Zac-HD]

Actual fix was in #7798 🙂