ActiveSupport::Concern and Sorbet RBI solution

all_cached_model_concern.rb

# typed: true

module AllCachedModelConcern
  extend ActiveSupport::Concern

  included do
    after_save(:clear_all_cached!)
    after_destroy(:clear_all_cached!)
  end

  def clear_all_cached!
    self.class.all_cached_backend.delete(self.class.all_cached_key) if self.class.all_cached_backend
  end

  class_methods do
    def all_cached_key
      "#{self}:all_cached"
    end

    def cached_find(id)
      cached_find_all([id]).first
    end

    def cached_find!(id)
      cached_find(id) || raise(ActiveRecord::RecordNotFound, "Couldn't find #{self} with ID=#{id}")
    end

    def cached_find_all(ids)
      all_cached.select { |record| ids.map(&:to_i).include?(record.id) }
    end

    def all_cached
      if all_cached_backend.nil?
        order("id ASC").to_a
      else
        all_cached_backend.fetch(all_cached_key, expires_in: 5.minutes) { order("id ASC").to_a }
      end
    end

    def all_cached_backend
      Rails.cache
    end
  end
end

all_cached_model_concern.rbi

# typed: true

module AllCachedModelConcern
  extend ::ActiveSupport::Concern
  extend T::Sig
  extend T::Helpers

  requires_ancestor { T.class_of(ActiveRecord::Base) }
  requires_ancestor { Kernel }

  sig { void }
  def clear_all_cached!; end

  module ClassMethods
    extend T::Sig
    extend T::Helpers
    requires_ancestor { T.class_of(ActiveRecord::Base) }
    requires_ancestor { Kernel }
    TIdParam = T.type_alias { T.any(String, Integer) }
    TSelf = T.type_alias { T.self_type }

    sig { returns(String) }
    def all_cached_key; end

    sig { params(id: TIdParam).returns(T.nilable(TSelf)) }
    def cached_find(id); end

    sig { params(id: TIdParam).returns(TSelf) }
    def cached_find!(id); end

    sig { returns(T::Array[TSelf]) }
    def all_cached; end

    sig { params(ids: T::Array[TIdParam]).returns(T::Array[TSelf]) }
    def cached_find_all(ids); end

    sig { returns(ActiveSupport::Cache::Store) }
    def all_cached_backend; end
  end

  mixes_in_class_methods(ClassMethods)
end

included do ... end does work, but there is no way for Sorbet to know what the type of self inside that block is going to be. You need to add a T.bind(self, ActiveRecord::Base) inside the block to make Sorbet understand what the binding of self is. But, you can't do that in RBI files.

As a matter of fact, you won't be able to type your application too much without having to use T.unsafe or T.let or T.cast or T.bind inside your code. That's a problem RBS also has today.

As for T.self_type, I am not sure I see that being problematic with inline signatures: https://sorbet.run/?arg=--enable-experimental-requires-ancestor#%23%20typed%3A%20true%0A%0Amodule%20Foo%0A%20%20%20%20extend%20T%3A%3AHelpers%0A%0A%20%20%20%20module%20ClassMethods%0A%20%20%20%20%20%20%20%20extend%20T%3A%3ASig%0A%0A%20%20%20%20%20%20%20%20TSelf%20%3D%20T.type_alias%20%7B%20T.self_type%20%7D%0A%20%20%20%20%20%20%20%20sig%20%7B%20returns%28T.self_type%29%20%7D%0A%20%20%20%20%20%20%20%20def%20foo%3B%20self%3B%20end%0A%0A%20%20%20%20%20%20%20%20sig%20%7B%20returns%28TSelf%29%20%7D%0A%20%20%20%20%20%20%20%20def%20bar%3B%20self%3B%20end%0A%20%20%20%20end%0A%0A%20%20%20%20mixes_in_class_methods%28ClassMethods%29%0Aend%0A%0Aclass%20Bar%0A%20%20%20%20include%20Foo%0Aend%0A%0A%0AT.reveal_type%20Bar.foo%0AT.reveal_type%20Bar.bar

nuts... I was wondering if that was the case (re: T.bind being required, and no RBI solution)

As for the T.self_type, I believe the issue is in returning an T::Array of the T.self_type. Both approaches I tried below failed:

https://sorbet.run/?arg=--enable-experimental-requires-ancestor#%23%20typed%3A%20true%0A%0Amodule%20Foo%0A%20%20%20%20extend%20T%3A%3AHelpers%0A%0A%20%20%20%20module%20ClassMethods%0A%20%20%20%20%20%20%20%20extend%20T%3A%3ASig%0A%0A%20%20%20%20%20%20%20%20TSelf%20%3D%20T.type_alias%20%7B%20T.self_type%20%7D%0A%0A%20%20%20%20%20%20%20%20sig%20%7B%20returns%28T%3A%3AArray%5BT.self_type%5D%29%20%7D%0A%20%20%20%20%20%20%20%20def%20foo%3B%20%5Bself%2C%20self%5D%3B%20end%0A%0A%20%20%20%20%20%20%20%20sig%20%7B%20returns%28T%3A%3AArray%5BTSelf%5D%29%20%7D%0A%20%20%20%20%20%20%20%20def%20bar%3B%20%5Bnew%2C%20new%5D%3B%20end%0A%20%20%20%20end%0A%0A%20%20%20%20mixes_in_class_methods%28ClassMethods%29%0Aend%0A%0Aclass%20Bar%0A%20%20%20%20include%20Foo%0Aend%0A%0A%0AT.reveal_type%20Bar.foo%0AT.reveal_type%20Bar.bar