[GHC] #12476: Error building HList

[GHC]

#12476: Error building HList
-------------------------------------+-------------------------------------
           Reporter:                 |             Owner:
  DanielWaterworth                   |
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 {{{
 [21 of 28] Compiling Data.HList.Labelable ( Data/HList/Labelable.hs,
 .stack-work/dist/x86_64-linux/Cabal-1.24.0.0/build/Data/HList/Labelable.o
 )

 /home/dan/fun/HList/Data/HList/Labelable.hs:137:9: warning: [-Wredundant-
 constraints]
     • Redundant constraints: (LabeledOpticF ty f, LabeledOpticP ty p)
     • In the type signature for:
            hLens' :: (ty ~ LabelableTy LabeledR, LabeledOpticF ty f,
                       LabeledOpticP ty p, LabeledOpticTo ty x to) =>
                      Label x -> to (p a (f b)) (p (LabeledR s) (f
 (LabeledR t)))
       In the instance declaration for ‘Labelable x LabeledR s t a b’

 /home/dan/fun/HList/Data/HList/Labelable.hs:211:10: warning: [-Wredundant-
 constraints]
     • Redundant constraint: ToSym (a b c) x
     • In the instance declaration for ‘EnsureLabel (a b c) (Label x)’

 /home/dan/fun/HList/Data/HList/Labelable.hs:277:10: warning: [-Wredundant-
 constraints]
     • Redundant constraint: HRLabelSet bs
     • In the instance declaration for ‘Projected Record s t a b’

 /home/dan/fun/HList/Data/HList/Labelable.hs:332:10: warning: [-Wredundant-
 constraints]
     • Redundant constraint: ToSym (to p q) x
     • In the instance declaration for ‘HExtend (to p q) (Proxy '[])’

 /home/dan/fun/HList/Data/HList/Labelable.hs:337:10: warning: [-Wredundant-
 constraints]
     • Redundant constraint: ToSym (to p q) x
     • In the instance declaration for
         ‘HExtend (to p q) (Proxy (x : xs))’

 /home/dan/fun/HList/Data/HList/Labelable.hs:344:10: warning: [-Wredundant-
 constraints]
     • Redundant constraint: ToSym (to p q) x
     • In the instance declaration for
         ‘HExtend (to p q) (Proxy (Lbl n ns desc : xs))’
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         pprIfaceCo

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 This is the version I was building:
 https://github.com/DanielWaterworth/HList/tree/66643fb75771e71192ab380e4f2ed56e37650f07

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12476>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler