Document using pre-commit and how --force-exclude can help

[ichard26]

Perhaps we should document this issue in the FAQ? Using pre-commit with Black is pretty common (and it's not always instantly clear it passes all of the files to the hook directly bypassing any file discovery the hook may implement). I'd suggest pre-commit's exclude configurations first, and then black's force-exclude.

Originally posted by @ichard26 in #3013 (comment)

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For context, we added the --force-exclude option as pre-commit always passes all filepaths to the hook directly via the command line. It doesn't care whether the filepath came from the CLI or was recursively discovered, unlike --exclude or --include

We could also document it here: https://black.readthedocs.io/en/stable/integrations/source_version_control.html

[mscheltienne]

That would be very helpful. It took me a while to figure out why my pre-commit hook was running on a file despite the file being ignored as part of the 'extend-exclude' configuration.

It also seems a bit sub optimal to specify --force-exclude as a (third) regular expression, it forces to duplicate the exclude and extend-exclude entries. Instead, a simple boolean flag which would ensure that the regular expressions in exclude and extend-exclude are respected could be better?