How to speed up Rubocop's startup time

If you have a fairly complex `.rubocop.yml` file, you may find that later versions take forever to start up or report results, and it seems like it hanging when you run it manually from the CLI.

The cause for this **may** be due to you having custom exclusion rules. When you exclude files from Rubocop ala:

```yaml
AllCops:
  Exclude:
    - 'db/fixtures/**/*'
    - 'db/migrate/*.rb'
    - 'db/schema.rb'
    - 'db/seeds.rb'
    - 'Gemfile.lock'
    - 'bin/*'
    # ... etc... etc... 
```

Rubocop will then ignore any of its own exclusion rules, and land up scanning `node_modules`, cache dirs, log dirs, and even your `.git` folder!

You can fix this by adding the following into your `.rubocop.yml` file.

```yaml
inherit_mode:
  merge:
    - Exclude
```

Rubocop will now merge in its default exclusion list alongside your own.

Why this is not the default behaviour eludes me. :|

gabrielfortuna
December 18, 2023