Static Type Checking 🤔

What do you think of adding static type checking, either via RBS (which would require upgrading to Ruby 3.x RBS requires Ruby >= 2.6) or sorbet?

I love that we are putting effort in documentation and writing good Ruby to help us compensate for the lack of type checking. Those are great initiatives that we should definitely pursue but I wonder if we could augment them with the introduction of static type checking.

@jkmassel showed me a similar approach using Psalm for PHP in an internal project and I found it super useful.

Note: I never used either of those tools but I imagine seriously adopting them would be quite a process. I'm not arguing we should jump onto it right away, I'm just curious of your opinion. If there's interest, we should run an humble spike first, just to see if it's straightforward to adopt them and if type-annotated classes can coexist with non-type-annotated ones, allowing us a gradual adoption path.

No specific files or tests are named. Start by reviewing the Ruby release-toolkit code and comparing RBS with Sorbet for adoption effort; a useful spike should establish whether typed and untyped classes can coexist and whether gradual adoption is practical.