[GHC] #12476: Error building HList

[GHC]

#12476: Error building HList
-------------------------------------+-------------------------------------
        Reporter:  DanielWaterworth  |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by DanielWaterworth:

@@ -51,0 +51,2 @@
+
+ This may be a duplicate of https://ghc.haskell.org/trac/ghc/ticket/12242

New description:

 {{{
 [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

 This may be a duplicate of https://ghc.haskell.org/trac/ghc/ticket/12242

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12476#comment:1>
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