Scalafix rule to help migration to 2.2.0

[cb372]

I'm really looking forward to upgrading to 2.2.0 and deleting all my cats.instances.* imports!

Is it worth providing an official scalafix rule to help people do this?

It could be just a simple grep to delete all import cats.instances.* lines, or it could be a bit smarter and also delete import cats.implicits._ lines that are only being used to import instances, not syntax.

[cb372]

Started work on a rule here: https://github.com/cb372/cats/tree/scalafix-rules-2.2.0

Now I just need to draw the rest of the owl...

[joroKr21]

There was an issue with Future's instances through.

[cb372]

Yes, I saw the discussion about that. I think it should be pretty simple to make the rule do special handling for Future instances.

[fthomas]

It would be great to add this migration rule to Scala Steward so that it can be used for the PRs that update Cats to 2.2.0.

[cb372]

Sure! If my PR gets merged, I'll make a PR to add it to Scala Steward.