skip ignored files at discovery

[james-powis]

Fixes: #399

Not sure how coverage decreased, I did not touch that file ;)

ignored files should be skipped early on to prevent other issues such as tripping on intentionally ignored broken symlinks.

There are many reasons that a file is ignored, one of those reasons is that it is a symlink which for valid reasons is broken. Without this change, this results in an [Errno 2] No such file or directory: error which can cause CI/CD to fail.

There likely is efficiencies by skipping to read in the skipped files at startup, but that is not the point of this PR.

[coveralls]

coverage: 99.797% (-0.03%) from 99.822%
when pulling 5417f96 on james-powis:skip-ignored-files-on-load
into 0d7ae7b on adrienverge:master.

[adrienverge]

Thanks for contributing!

Not sure how coverage decreased, I did not touch that file ;)

Coverage decreased indeed, because changes to yamllint source code should come with tests, to make sure there won't be regression. It was requested in the original issue #399 ;)
A new test simulating the scenario of the initial message of #399 should be fine. See tests/test_config.py for how existing tests look like.

If you add a check not conf.is_file_ignored(filepath) early, should this check be removed later in yamllint execution? (I'm not 100% sure, but I remember that touching find_files_recursively() + conf.is_file_ignored() is tricky and could create problems, it needs special attention)

[james-powis]

@adrienverge I did not touch linter.py so its coverage decreasing is not related to my change to cli.py and likely a related to something else....

Furthermore there is a pretty significant gordian knot related to these checks inside and out within the code. Refactoring your code is not my interest. I was just trying to contribute a fix, which this does, and your users have been complaining about for over 2 years, which I also was impacted by. I have a monkey patch in place and do not need you to accept this. I just figured I would try and help out. This is an exceptionally trivial change, and one which is exceptionally difficult to write a test for. Its just not that valuable for me to deal with that silly difficulty. However I am sure you could piece together the test modifications in my other PR if you need inspiration.