[GHC] #13585: ala from Control.Lens.Wrapped panics

[GHC]

#13585: ala from Control.Lens.Wrapped panics
-------------------------------------+-------------------------------------
        Reporter:  fumieval          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by fumieval:

@@ -46,0 +46,3 @@
+
+ Control.Lens.Wrapped is from the latest version of lens on GitHub:
+ https://github.com/ekmett/lens/blob/9c4447de7ef57f67dbe293320d45bd8a546be522/src/Control/Lens/Wrapped.hs

New description:

 Panic.hs:

 {{{
 module Panic where

 import Control.Lens.Wrapped
 import Data.Monoid

 foo :: Maybe String
 foo = ala Last foldMap [Just "foo"]
 }}}

 main.hs:
 {{{
 module Main where
 import Panic (foo)

 main :: IO ()
 main = print foo
 }}}

 {{{
 $ ghc -c -O2 Panic.hs
 $ ghc -c -O2 main.hs
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.2.0.20170404 for x86_64-unknown-linux):
         splitTyConApp
   (Exchange (Unwrapped (Last String)) (Unwrapped (Last String)) |> <*
                                                                     -> *
 -> *>_N) (Maybe
 [Char]) ((Identity |> <*
 -> *>_N) (Maybe
 [Char]))
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1134:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1138:37 in
 ghc:Outputable
         pprPanic, called at compiler/types/Type.hs:1105:34 in ghc:Type

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

 The GHC version is 8134f7d4ba2c14b2f24d2f4c1f5260fcaff3304a.

 Control.Lens.Wrapped is from the latest version of lens on GitHub:
 https://github.com/ekmett/lens/blob/9c4447de7ef57f67dbe293320d45bd8a546be522/src/Control/Lens/Wrapped.hs

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13585#comment:1>
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