[GHC] #10831: DeriveFunctor not capable of deriving when wrapping Either

[GHC]

#10831: DeriveFunctor not capable of deriving when wrapping Either
-------------------------------------+-------------------------------------
              Reporter:  htebalaka   |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  low         |         Milestone:
             Component:  Compiler    |           Version:  7.10.2
              Keywords:              |  Operating System:  MacOS X
          Architecture:              |   Type of failure:  GHC rejects
  Unknown/Multiple                   |  valid program
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
-------------------------------------+-------------------------------------
 GHC can derive Functor for Okay, but rejects the equivalent Bad.
 {{{#!hs
 {-# LANGUAGE DeriveFunctor #-}
 data Okay f g a b = Inl (f a b) | Inr (g a b) deriving (Functor)
 newtype Bad f g a b = Bad (Either (f a b) (g a b)) deriving (Functor)
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10831>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler