New cop to check for 3-state booleans

[fatkodima]

https://thoughtbot.com/blog/avoid-the-threestate-boolean-problem

[koic]

This style looks good to me. Can you open a PR to the Rails Style Guide, first?
https://github.com/rubocop-hq/rails-style-guide/pulls

For implementation, it is necessary to consider a applied migration files.

[silva96]

using a default value in a large table will cause a complete rewrite.

https://github.com/ankane/strong_migrations#adding-a-column-with-a-default-value

In Postgres 11+, MySQL 8.0.12+, and MariaDB 10.3.2+, this no longer requires a table rewrite and is safe.

[tejasbubane]

For implementation, it is necessary to consider a applied migration files.

@koic We can only check schema.rb file and find offenses right?

[pirj]

Some use structure.sql. Also, schema.rb is not necessarily committed, even if exists on developer machines it might not be present on CI unless you run migrations before rubocop which would be a pretty weird requirement.

Checking migrations is the only way I can think of.