ActiveRecord relations' each method block argument is T.untyped

[marknuzz]

Calling #each on a PrivateAssociationRelation, PrivateCollectionProxy, etc. will give an untyped block argument. However, #each_with_index will give a typed argument. This is difficult to work around (adding a line of code with a T.cast for each time #each is used, is not a workaround at all).

These are classes which are also valid Enumerables, but the each method on these classes will use the untyped ActiveRecord::Delegation methods from the rbi/gems path, and not a path defined in rbi/dsl, or even sorbet's T::Enumerable class. This causes the block argument to be untyped, which causes a lot of missed type checking!!

[marknuzz]

Adding these lines to my require.rb in the meantime:

# https://github.com/Shopify/tapioca/issues/2034
ActiveRecord::Delegation.undef_method(:each)

[amomchilov]

Hi Mark,

I think this list of delegated methods in ActiveRecord::Delegation is the culprit.

That module is included after Enumerable in ActiveRecord::Relation. So that (untyped) delegated method takes precedence over the inherited one from Enumerable and prevents the inheritance of the correct sig from Enumerable.

I think the fix here might be as easy as adding the correct sig to ActiveRecord::Relation in RBI central:

https://github.com/Shopify/rbi-central/blob/af4f13dd7023734deb4500018b294367a3ed1cae/rbi/annotations/activerecord.rbi#L198-L201

class ActiveRecord::Relation
  sig { returns(T::Boolean) }
  def blank?; end

+  # adapted from https://github.com/sorbet/sorbet/blob/64b1468/rbi/core/enumerable.rbi#L19-L27
+  sig do
+    abstract
+      .params(blk: T.proc.params(arg0: Elem).returns(BasicObject))
+      .returns(T.untyped)
+  end
+  sig { returns(T.self_type) }
+  def each(&blk); end
end

That would be a great first contribution. Would you like to give it a shot?

[marknuzz]

Sure, I'll give it a shot this week. I've been slammed with deadlines so I can't guarantee it but it sounds simple enough and may make it easier for me to contribute other fixes later.

My workaround ended up breaking the usage of the .each method with no arguments anyway, since there was no concrete implementation of .each in the RBI, and Sorbet's Enumerable each sig returns T.self_type if used with no block.

[marknuzz]

I think the second overload above instead of sig { returns(T.self_type) } would be sig { returns(T::Enumerator[Elem]) }