[GHC] #10931: layers-0.1 does not compile with ghc-7.10 (likely a regression from ghc-7.8)

[GHC]

#10931: layers-0.1 does not compile with ghc-7.10 (likely a regression from
ghc-7.8)
-------------------------------------+-------------------------------------
        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.10.2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
-------------------------------------+-------------------------------------

Comment (by slyfox):

 Oh that's good! ghc-7.10 branch doesn't work though. I wonder when it was
 fixed.

 {{{
 $ inplace/bin/ghc-stage2 --interactive T10931.hs

 GHCi, version 7.10.2.20151003: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling L                ( T10931.hs, interpreted )

 T10931.hs:28:17:
     Couldn't match type ‘m’ with ‘Inner (IdT m)’
       ‘m’ is a rigid type variable bound by
           the instance declaration at T10931.hs:24:10
     Expected type: Outer (IdT m) (Inner (IdT m))
       Actual type: IdT m
     Relevant bindings include
       f :: forall (n :: * -> *).
            (n ~ Outer n (Inner n), Outer n ~ Outer (IdT m)) =>
            Inner n a
         (bound at T10931.hs:28:9)
       bug :: (forall (n :: * -> *).
               (n ~ Outer n (Inner n), Outer n ~ Outer (IdT m)) =>
               Inner n a)
              -> IdT m a
         (bound at T10931.hs:28:5)
     In the first argument of ‘IdC’, namely ‘f’
     In the expression: IdC f
     In an equation for ‘bug’: bug f = IdC f
 Failed, modules loaded: none.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10931#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler