This is a great feature, here is some feedback

My syntax highlighter in emacs expects warnings to have the word "warning" in them.

So for the two warnings reported below, the first is highlighted as an error, and the second as a warning

Language/Haskell/Refact/Utils/TypeUtils.hs:3036:17:
    Redundant constraint: SYB.Data t
    In the type signature for:
       duplicateDecl :: SYB.Data t =>
                        [GHC.LHsBind GHC.Name]
                        -> t -> GHC.Name -> GHC.Name -> RefactGhc [GHC.LHsBind GHC.Name]

Language/Haskell/Refact/Utils/TypeUtils.hs:3045:7: Warning:
    Defined but not used: ‘toks

This is in a ghci session, and the file loads without problems, so it is indeed a warning.

Can we perhaps add the word "Warning" to the output for Redundant constraints?

I also had a situation where it asked me to remove a whole lot of constraints from different functions, I did them in batches, so did not remove them all from the file at once, and at some point I had to add at least one of them back, albeit based on an error message.

Regards

Alan