[GHC] #12727: ghc: panic! (the 'impossible' happened) - piResultTy

[GHC]

#12727: ghc: panic! (the 'impossible' happened) - piResultTy
-------------------------------------+-------------------------------------
           Reporter:  ocharles       |             Owner:
               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:
-------------------------------------+-------------------------------------
 Oddly this only happens on our build server, not on my local machine. On
 compilation, I get:

 {{{
 [187 of 273] Compiling Query.Order      ( Query/Order.hs,
 dist/build/Query/Order.o )

 Query/Order.hs:340:1: warning: [-Wredundant-constraints]
     • Redundant constraint: MonadBaseControl IO m
     • In the type signature for:
            updateOrdersSuccess :: (MonadBaseControl IO m,
                                    MonadTransaction m) =>
                                   m ()
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         piResultTy
   Maybe Int64
   a1_a4WiL

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

 The configuration parameters are:

 {{{
 configureFlags: --verbose --prefix=/nix/store
 /qxfjd5jxr593dn43i3659s86d0rdllyv-circuithub-api-0.0.4
 --libdir=$prefix/lib/$compiler --libsubdir=$pkgid --with-gcc=gcc
 --package-db=/tmp/nix-build-circuithub-api-0.0.4.drv-0/package.conf.d
 --ghc-option=-j1 --disable-split-objs --disable-library-profiling
 --disable-profiling --disable-shared --enable-library-vanilla --disable-
 executable-dynamic --disable-tests
 }}}

 I've attached Query/Order.hs, but you won't be able to compile it stand-
 alone.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12727>
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