From the failing test:

E AssertionError: Please update DEFAULT_MODULE_MAPPING to use canonical project names
E assert equals failed
E 'oslo.cache' 'oslo-cache'

In the past we've categorized these either as internal or "user api change". I think the latter is technically valid, since there is a user-facing impact? But I wouldn't call it a new feature.

None of the categories made much sense here. It doesn't break the user API and it's not a new feature. It's additional piece of config users can take advantage of... I just don't know. Feel free to change the category.

Yeah, none of the categories make much sense in this case. But we do want people to notice this in the changelog, so internal is probably not the best.

I agree it's hard to call this a new feature.. but I think it is. It is a new feature of Pants that you no longer need to declare the module mappings for these distributions in your own BUILD files any more.
We (including me) tend to consider features = functionality, but if we consider feature = behaviour this makes it a better fit, imho.

Edit: looking at some of the other user-api-changes PRs, I think that it would be helpful as a user, if changes under that name are mostly disruptive. That will have less noise to go through when upgrading to find changes that may need extra care. Maybe..?