Add flag to only run flake8 on the files that were modified in the HEAD commit or the current working tree.

Idea taken from https://review.openstack.org/#/c/110746/15/run_tests.sh,cm

as for the flag name I am thinking something along the lines of 'flake --vcs' or 'flake8 --current-changes'

@joe-gordon0 a merge request would be helpful in explaining the difference between the proposed flag and the existing --diff flag (because I've honestly forgotten how it differs since we last talked about this). Relatedly, the comment in that patch set doesn't explain how what you're doing there differs from --diff.

Currently flake8 -diff takes a diff as stdin. So git diff HEAD^ | flake8 -diff Then pep8 (as part of flake8) extracts the filenames from the diff, excludes any that do not match the filename filter (so we can ignore things that aren't python files etc.) and then runs pep8/flake8 against those files (as read from the filesystem -- which isn't obvious).

The idea here is to add support to flake8 to do the same thing without having to do manually call 'git diff HEAD^' and teach flake8 to detect if its running on files in a VCS and automatically extract the right files to run against.

This would allow users to trivially run flake8 on just the changed files any time they want. Instead of just in pre-commit git hook.

Another option is to just better document how to do this in flake8's documentation. The same thing can easily be made easier via git aliases:

[alias]
    flake8 = "!git diff HEAD^ | flake8 --diff "

Thoughts on what approach is preferred?

So as you pointed out, the --diff handling is part of pep8. There's no reason flake8 couldn't detect the usage of --diff sans stdin and not try to find a vcs to pull the diff from. We already have VCS discovery code for the --install-hook option.

+1 from me.

I am using something like this https://github.com/twisted/twisted/blob/fe7853b08c78756a473c8747ce1e7bd1f4cdaa5b/bin/admin/tx-pyflakes for my private project.

The example is something proposed for Twisted... but not accepted as it better to just use flake8 and not reinvent the wheel :)

The command line option can look like

flake8 --vcs-branch=master some/path

in this way it should also work for people with different main branch names

The initial implementation can only support git and later extended to hg or other tools. VCS can be autodetected.

What do you say? Does it make sense?

Thanks!

Removed component:vcs feature:accepted labels

Milestone changed to %3.x.0