alba: bind class_eval'd DSL blocks to T.self_type

[mokevnin]

Type of Change

• Modify RBI for an existing gem

Changes

• Gem name: alba
• Gem version: 4.0.0
• Gem source: https://github.com/okuramasafumi/alba/blob/main/lib/alba/nested_attribute.rb#L24-L27, https://github.com/okuramasafumi/alba/blob/main/lib/alba/resource.rb#L118-L122
• Gem API doc: https://rubydoc.info/gems/alba/Alba/Resource/ClassMethods
• Tapioca version: 0.19.2
• Sorbet version: 0.6.13497

Follow-up to #422, which is mine: I typed the blocks of nested, nested_attribute and trait as T.proc.bind(T.untyped). That binding is weaker than the runtime warrants, and the erasure it causes is not local to the block's own self.

All three class_eval the block on a subclass of the resource class the macro was called on:

# lib/alba/nested_attribute.rb
resource_class = Class.new(@klass)
resource_class.class_eval(&@block)

# lib/alba/resource.rb, #hash_from_traits
resource_class = Class.new(self.class)
resource_class.class_eval(&body)

So self inside the block is exactly the receiver of the macro, which T.self_type names precisely. This differs from the ActiveSupport::Concern case in #423: a concern genuinely cannot know its includer, whereas here the type is right there in the call.

The cost of T.untyped is that it also erases what is declared inside the block. A project that types its resources (a Tapioca DSL compiler generating a per-resource attribute sig, or a hand-written shim) loses that typing for everything inside nested do ... end — the block parameter, and every value derived from it, silently becomes untyped, because attribute is now being called on an untyped self. In our app this turned a correct T.must(it.price) on a T.nilable(SubscriptionPrice) into a 7050 "redundant T.must", i.e. the annotation did not just fail to add information, it removed information Sorbet previously had. With T.self_type that typing is preserved, and inside the block plain nested/attribute calls still resolve through Alba::Resource::ClassMethods as before.

repo check index, rubocop alba, runtime alba and static alba all pass locally.

Blocks left alone deliberately: attribute, meta, on_nil and the association source blocks are instance_exec'd on a resource instance, not the class, so T.self_type would be wrong there and the honest type is a separate question.

🤖 Generated with Claude Code

[mokevnin]

Thanks for the quick review and merge!