When did role-level library/ directories become supported?

I've looked at the documentation on the site
(https://docs.ansible.com/playbooks_roles.html) that describes this
feature, but it doesn't indicate when it became available, and the
only mention of something similar I see in the Changelog is about
library/ being relative to the playbook itself (which was introduced
in 0.5).

Does anyone know when this feature was added?

Thanks,

iirc when roles were added.

I've got one server running 1.7.1 and the playbook it's finding the
right overriden module in a role's library. It is working on 1.8.2 and
higher, so I'm guessing it's a bug in that version that was fixed.
Maybe https://github.com/ansible/ansible/issues/8633 ?