[GHC] #14462: deriving on associated data types fails to find constraints

[GHC]

#14462: deriving on associated data types fails to find constraints
-------------------------------------+-------------------------------------
        Reporter:  mf825             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |             Keywords:  TypeFamilies,
      Resolution:                    |  associated types, deriving
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 Looks ok to me.  There's no reason that the context of the `C`-instance
 decl for `Maybe a` should be the same as that of the `Eq`-instance decl
 for `CT (Maybe a)`.

 As the message says, a standalone deriving declaration should do the job
 nicely. Did you try that?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14462#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler