How to detect unused instances?

[ian]

I’d like to detect unused instances in my application, or even better for a particular instance get a list of each place where it’s used. Is there a way to do this?

It doesn’t have to be built into GHC, I’m fine installing something else like hlint or an IDE tool.

[adamse]

I wonder if this is something Neil Mitchell’s weeder is able to do: https://github.com/ndmitchell/weeder