[akitoshiga]

Summary

ActiveRecord::Relation delegates some Array methods to records:
https://github.com/rails/rails/blob/v8.1.3.1/activerecord/lib/active_record/relation/delegation.rb#L100-L103

In the generated RBS, these methods are defined in ActiveRecord::Delegation as (*untyped, **untyped) ?{ (*untyped) -> untyped } -> untyped, so the element type of a relation is lost (e.g. User.all[0] is untyped).

This PR adds ActiveRecord::Delegation::_DelegateToRecords[Model] and includes it into ActiveRecord::Relation::Methods[Model, PrimaryKey], so they are typed with the model of each relation.

users = User.all
users.length    # => Integer
users[0]        # => User?
users.sample(2) # => Array[User]

The signatures follow Array in core RBS and Array extensions in activesupport. each is excluded because Relation::Methods already defines it.

Why the signatures are written one by one

RBS has no syntax for delegation, and there is no way to refer to the method types of another class or to pick only some methods of Array[Model]. So reusing Array's signatures would mean taking all of them, which does not match the actual behavior:

• Inheriting from Array[Model]: Relation is not an Array, and its methods would conflict with query methods such as select and find.
• Including an interface that covers all of Array: methods Relation does not have (e.g. push, map!) would also type-check.

The interface takes the model as a type parameter, so this single definition applies to the ActiveRecord_Relation of every model generated by rbs_rails.

Notes

ActiveRecord::Associations::CollectionProxy defines some of these methods (e.g. length) by itself, and those definitions take precedence over the included interface. So user.articles.length is still untyped, while methods not defined in CollectionProxy (e.g. user.articles[0]) are typed.