[Bug]: False positive for FURB142 when the loop variable determines the set

[mscheifer]

Has your issue already been fixed?

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• Have you looked at the open/closed issues to see if anyone has already reported your issue?
• If reporting a false positive/incorrect suggestion, have you double checked that the suggested fix changes the code semantics?

The Bug

The following code:

sets = {1: set(), 2: set()}

to_update = [1, 2]

for a in to_update:
    sets[a].add("abc")

Emits the following error:

$ refurb bug.py
bug.py:5:1 [FURB142]: Replace `for a in to_update: sets[a].add(...)` with `sets[a].update(... for a in to_update)`)

But it should not be emitting an error instance because the expression evaluating to a set on the left hand side depends on the loop variable. It can't be replaced by a comprehension and call to update as in the suggestion.

Version Info

Refurb: v2.0.0
Mypy: v1.15.0

Python Version

Python 3.11.0

Config File

# N/A

Extra Info

None