Add SCSS configuration for Hound

[croaky]

What

This change uses Bootstrap's existing scss/.scss-lint.yml file to configure Hound's hosted SCSS-Lint instance.

It leaves existing JavaScript linting as-is because Hound does not support ESLint or JSCS yet. It does support JSHint for the master branch, but I decided to focus just on v4 for this change.

How it works

On each pull request to Bootstrap, Hound will comment on any SCSS style violations in-line, like this:

If you update the pull request to adopt a suggestion, the comment will be hidden.

The same checks are maintained on pull requests. Instead of output such as this in Travis...

scss/_navbar.scss:216 [W] TrailingWhitespace: Line contains trailing whitespace

... it will be an in-line comment from Hound.

Hound is free for open source projects and is open source itself, like Travis: https://github.com/thoughtbot/hound

Why

The advantages for the Bootstrap project might be:

• Ruby does not need to be installed on developer's machines in order for grunt test to run all lint checks.
• If jekyll:docs could be removed from the build, Ruby would not need to be installed on TravisCI.
• Hound runs in parallel to Travis, speeding up the time CI finishes by about 4.6s on builds such as https://travis-ci.org/twbs/bootstrap/jobs/83432163
• For parity with your current setup, I've set the fail_on_violations: true setting, but if SCSS-Lint has false positives or false negatives, you can change the setting to false to treat its comments more as suggestions than a binary outcome that should fail the build. https://houndci.com/configuration#configuration

[cvrebert]

CC: @twbs/team

[mdo]

I'm in favor. Been using it on Primer and haven't had much issue with it.

[cvrebert]

@croaky Am I correct in assuming that Hound only lints changed files? My point being that if something failing lint gets pushed directly to master, we'd never find out about it via Hound? If yes, then I'm opposed to removing the scsslint task from the Gruntfile.

But in either case, I'm +1 on enabling Hound.

[croaky]

Am I correct in assuming that Hound only lints changed files?

Yup, that's correct. If you're interested, the security doc goes into excruciating detail of the what happens but the gist is it runs on the full file contents of non-deleted files in the pull request.

My point being that if something failing lint gets pushed directly to master, we'd never find out about it via Hound?

Yup, also correct. Hound only operates on GitHub webhook events for opening a pull request, and pushing follow-on commits to the pull request.

If yes, then I'm opposed to removing the scsslint task from the Gruntfile.

Sounds good. Want me to revert that deletion?

[cvrebert]

Sounds good. Want me to revert that deletion?

Yes please.

[croaky]

Cool, updated.

Since the existing Grunt + Travis lines are now back, I removed the fail_on_violations: true configuration line. By default, Hound will not mark the GitHub status on the PR as failed if it finds violations, it will only comment. That seemed to make sense to me since Travis should already fail in those scenarios. But, let me know if you like it to fail on violations.

Since Hound can only be enabled for the whole repo, I think we'll want a separate set of config branched off master:

https://github.com/twbs/bootstrap/compare/twbs:master...croaky:hound-master?expand=1

I can open that PR if that plan works for you. To avoid JSHint / SCSS-Lint surprises, both PRs (one branched off master, one off v4-dev) should be merged before an admin on this repo enables Hound at https://houndci.com.

[cvrebert]

SGTM. Open it.

[cvrebert]

Merged to master in d53525c

[cvrebert]

...And now activated on houndci.com
Thanks!