exclude key in mypy.ini as a single regex doesn't scale for larger code bases

[rgommers]

Feature

I'd like the exclude = in mypy.ini to have a saner way to specify a lot of paths that one huge one-line regex.

This is a follow-up to #9992 (comment)

When trying to use exclude (necessary because mypy 0.800 became much more aggressive in including paths by default) I ended up with something like:

files =
    torch,
    caffe2,
    test/test_bundled_images.py,
    test/test_bundled_inputs.py,
    test/test_complex.py,
    ... <many more paths here>

#
# `exclude` is a regex, not a list of paths like `files` (sigh)
#
exclude = torch/include/|torch/csrc/|torch/distributed/elastic/agent/server/api.py

Both the files and exclude list are likely to grow over time. I don't have a strong preference on how exclude should work exactly, any pattern that allows breaking the regex into one line per pattern will be fine. E.g.:

exclude =
    pattern1|
    pattern2|
    pattern3|

Using | or some character other than a comma to indicate that it does not work like files = seems like a good idea.

[samestep]

See also pytorch/pytorch#57967 (comment) for more context.

[emmatyping]

In #10903 I think we decided that allowing to specify --exclude multiple times would be a good compromise. In the config file this would look like:

exclude =
    pattern1
    pattern2

which would be equivalent to:

exclude =
    pattern1|pattern2

[cclauss]

Most Python practitioners know that pytest allows multiple --ignore options (strings) which are different from --ignore-glob options which support Unix shell-style wildcards. While it is probably too late for mypy to adopt this approach, it would have been the least surprising to newcomers. Also see, glob strings of flake8 --exclude and --extend-exclude.

Many people are not regex masters and regex syntax can be unintuitive for the uninitiated. Supporting both regex patterns ORed together with | as well as path string patterns separated by commas (or multiple --exclude statements) would provide a better user experience for a broader audience.

[nipunn1313]

Assign this to me! I worked on it with #11329

[JelleZijlstra]

Done, thanks @nipunn1313!