Kaminari pagination is not supported by Tapioca

Start with Rails' activerecord/lib/active_record/relation/delegation.rb, especially the generated relation methods and the generate_relation_method(:page) entry point described in the report. Trace Tapioca's RBI generation for ActiveRecord relations and reproduce the Kaminari page/per case; done means Tapioca generates signatures for those methods without the initializer workaround.

Trying to update tapioca from 0.12.0 to 0.13.1 results in this error:

path/to/file.rb:32: Method page does not exist on Model::PrivateAssociationRelation https://srb.help/7003
    32 |    @records = Model.all.page(params[:page]).per(25)

Investigation

The page method is defined on the class by kaminari:
https://github.com/kaminari/kaminari/blob/9182d065c144afa45c6b7cf444f810bea1fd7201/kaminari-activerecord/lib/kaminari/activerecord/active_record_model_extension.rb#L14-L23

But attempting to introspect it at runtime yields nothing:

pry(main)> Model.all.method(:page)
=> #<Method: Model::ActiveRecord_Relation#page(*)>
pry(main)> Model.all.method(:page).source_location
=> nil
pry(main)> Model.all.method(:page).owner
=> Model::ActiveRecord_Relation
pry(main)> Model.all.method(:page).owner.instance_method(:page)
NameError: undefined method `page' for class `ActiveRecord::Relation'
from (pry):1:in `instance_method'from (pry):35:in `method'
pry(main)> Model.all.methods.include?(:page)
=> false

This is because it is delegated by https://github.com/rails/rails/blob/d37c533139f70efdcd95f8dadd48c10eba429f94/activerecord/lib/active_record/relation/delegation.rb#L71-L88

Which is generated on demand when the method is missing:
https://github.com/rails/rails/blob/d37c533139f70efdcd95f8dadd48c10eba429f94/activerecord/lib/active_record/relation/delegation.rb#L115-L124

Attempting the same as above after calling the method once does yield something a bit more interesting:

pry(main)> Model.all.method(:page)
=> #<Method: Model::ActiveRecord_Relation(Model::GeneratedRelationMethods)#page(...) /Users/seb/.gem/ruby/3.2.2/gems/activerecord-7.1.3.2/lib/active_record/relation/delegation.rb:78>
pry(main)> Model.all.method(:page).source_location
=> ["/Users/seb/.gem/ruby/3.2.2/gems/activerecord-7.1.3.2/lib/active_record/relation/delegation.rb", 78]
pry(main)> Model.all.method(:page).owner
=> Model::GeneratedRelationMethods
pry(main)> Model.all.method(:page).owner.instance_method(:page)
=> #<UnboundMethod: Model::GeneratedRelationMethods#page(...) /Users/seb/.gem/ruby/3.2.2/gems/activerecord-7.1.3.2/lib/active_record/relation/delegation.rb:78>
pry(main)> Model.all.methods.include?(:page)
=> true

The same can be achieved by calling Model.generate_relation_method(:page)

Workaround

Adding this in config/initializers/kaminari.rb makes tapioca generate the methods:

if defined?(Tapioca)
  Rails.application.config.after_initialize do
    Rails.application.eager_load!

    ActiveRecord::Base.descendants.each do |model|
      model.generate_relation_method(:page)
      model.generate_relation_method(:per)
    end
  end
end