Install haml-lint:
bundle install
Run haml-lint against the example file
bundle exec haml-lint
$ bundle exec haml-lint
1 file inspected, 0 lints detected
$ bundle exec haml-lint
example.html.haml:1 [W] RuboCop: Layout/LineLength: Line is too long. [132/120]
1 file inspected, 1 lint detected