handling of exclude configuration changed in an incompatible way in 0.930

[asottile]

#11825 seems related but slightly different as that one causes a crash -- I believe this was broken in #11329

Bug Report

for example: (this is reduced from a larger example just to demonstrate a minimal example)

# mypy.ini
[mypy]
exclude=(?x)
    ^(
        setup\.py$
    )

To Reproduce

set up a configuration above and run mypy

Expected Behavior

in mypy 0.920 this excluded all setup.py files

Actual Behavior

this appears to exclude all files:

$ mypy .
There are no .py[i] files in directory '.'

Your Environment

• Mypy version used: 0.930
• Mypy command-line flags: (see above)
• Mypy configuration options from mypy.ini (and other config files): (see above)
• Python version used: 3.8.10
• Operating system and version: ubuntu 20.04

[hauntsaninja]

cc @nipunn1313 something like #11828 should work for pyproject.toml, but curious for your opinion on what this should look like going forward for ini files

[nipunn1313]

Great question.

I think the safest option is to maintain the old behavior on .ini files - such that you cannot provide multiple --exclude inside ini files. ini files don't have support for array structures so this seems ok.

There is a simple workaround to get access to the new feature - using pyproject.toml instead of mypy.ini.

[posita]

I can try to augment #11828 (or provide a PR that depends on it) to restore the old .ini behavior. Would that work?

[posita]

I added #11881 to address #11830 by reverting to treating exclude in mypy.ini as a single string. This should be compatible with #11828.