Ah, but most of the complexity in that line is an artifact of how Haddock (egregiously badly) generates documentation. The line in the source code is

    instance (Patchy p, ApplyState p ~ Tree) => Patchy (PatchInfoAnd rt p)

I don't personally like typeclassitis, but this is actually easy to interpret:

"If 'p' is a patch-like thing, and its ApplyState is a Tree, then 'PatchInfoAnd rt p' is a patch-like thing"