slim-lint slow with RuboCop 1.72 and plugins

[erikaxel]

We experienced a dramatic slowdown (approx 10x) using Rubocop 1.72 compared to 1.71 for slim-lint.

With Rubocop 1.71.2:

 time bundle exec slim-lint app/**/*.slim
________________________________________________________
Executed in   33.81 secs    fish           external
   usr time   32.47 secs  587.00 micros   32.47 secs
   sys time    1.22 secs  743.00 micros    1.22 secs

With Rubocop 1.72.2:

time bundle exec slim-lint app/**/*.slim
________________________________________________________
Executed in  359.47 secs    fish           external
   usr time  306.95 secs  525.00 micros  306.95 secs
   sys time   51.91 secs  923.00 micros   51.91 secs

We have not seen a similar slowdown on our Rubocop runs, so this seems to be an issue with slim-lint.

The biggest change between 1.71 and 1.72 is the introduction of the new RuboCop plugin system which I think is the problem.

To support this hypothesis, tested the following

• Removed all plugins under the new plugin: keyword: 14 seconds
• Adding one plugin: 70 seconds
• Adding three plugins: 360 seconds

The plugins were adding using the new keyword like so:

plugins:
  - rubocop-rspec
  - rubocop-rails
  - rubocop-performance

This only seems to be a problem when using plugin because we have some plugins included using the old require: method which didn't seem to have any effect on the run time.