[GHC] #15517: haddock triggers panic in trimJoinCont

[GHC]

#15517: haddock triggers panic in trimJoinCont
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        Reporter:  sjakobi           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by sjakobi:

Old description:

> Running haddock on the [https://github.com/VictorCMiraldo/generics-mrsop
> `generics-mrsop`] package results in
>
> {{{
> haddock: panic! (the 'impossible' happened)
>   (GHC version 8.4.3 for x86_64-unknown-linux):
>         completeCall
>
> fail_av9P
> Select nodup wild_00
> Stop[BoringCtxt] Rep Singl (El FamRoseInt) (Lkup ix CodesRoseInt)
> Call stack:
>     CallStack (from HasCallStack):
>       callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in
> ghc:Outputable
>       pprPanic, called at compiler/simplCore/Simplify.hs:1533:9 in
> ghc:Simplify
> }}}
>
> The same problem affects 8.6.1 and HEAD, but not 8.2.2.
>
> The panic seems to stem from
> [https://github.com/ghc/ghc/blob/64c71ce956af3af593a46ef0d615c7f6fe6ecece/compiler/simplCore/Simplify.hs#L1613
> this catch-all in `trimeJoinCont`].

New description:

 Running haddock on the [https://github.com/VictorCMiraldo/generics-mrsop
 `generics-mrsop`] package results in

 {{{
 haddock: panic! (the 'impossible' happened)
   (GHC version 8.4.3 for x86_64-unknown-linux):
         completeCall

 fail_av9P
 Select nodup wild_00
 Stop[BoringCtxt] Rep Singl (El FamRoseInt) (Lkup ix CodesRoseInt)
 Call stack:
     CallStack (from HasCallStack):
       callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in
 ghc:Outputable
       pprPanic, called at compiler/simplCore/Simplify.hs:1533:9 in
 ghc:Simplify
 }}}

 The same problem affects 8.6.1 and HEAD, but not 8.2.2.

 The panic seems to stem from
 [https://github.com/ghc/ghc/blob/64c71ce956af3af593a46ef0d615c7f6fe6ecece/compiler/simplCore/Simplify.hs#L1613
 this catch-all in `trimJoinCont`].

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15517#comment:1>
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