Some linters, such as flake8, will lint invalid file extensions if you explicitly pass them in. E.g,
|flake8 foobar.js| will result in flake8 attempting to lint a JS file. This is a problem because passing
in files explicitly is exactly what the --rev/--workdir options do. If a developer modifies a JS file
then runs |mach lint -l flake8 -w|, that JS file will get linted.
To prevent this, mozlint needs to handle file extensions instead of relying on the underlying linter to
do it. This patch adds an "extensions" config option to the LINTER dict, and will filter these files out
as part of the 'filterpaths' steps.
MozReview-Commit-ID: KYhC6SEySC3
f4b5bbd86c