PSA: Semantic changes to lint 'warnings'

Andrew Halberstadt ahal at
Tue Aug 28 20:11:04 UTC 2018

As of bug 1460856, mozlint (the library underpinning our various
lint systems) will no longer display warnings by default. All
current linters which were previously emitting warnings have
been changed to the 'error' level, so this won't cause any loss
of coverage. There are different implications depending where the
lint runs.

*CI and vcs hooks*
Taskcluster lint tasks and the vcs hooks will not fail if there were
only warnings. In other words, you won't be backed out for

*Command line*
The default |mach lint| formatter will tell you if there are any
suppressed warnings, but will only display them if you pass in
`-W/--warnings`. E.g:

*$* ./mach lint -nl codespell python/mozlint
✖ 0 problems (0 errors, 1 warning)

*$* ./mach lint -nl codespell python/mozlint --warnings
  62  warning  retuns  ==> returns  (codespell)

✖ 1 problem (0 errors, 1 warning)

There is a follow-up on file
to get the Phabricator reviewbot to show warnings by default. So
warning level issues on your review can be treated as strong
suggestions, but it is fine to ignore them if you want.

This change will allow us to enable a subclass of lint issues that
might contain false positives (e.g the codespell linter), or else
aren't important enough to cause a backout (but would ideally
be fixed). This change will allow the reviewbot to be more
aggressive with the issues it raises, as well as give us a bit of
a middle ground when enabling a new linter across the tree.

Please let me know if you have any questions or concerns
about this change!

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