[GHC] #12168: panic! (the 'impossible' happened) with gi-gtk 3.0.4

[GHC]

#12168: panic! (the 'impossible' happened) with gi-gtk 3.0.4
-------------------------------------+-------------------------------------
           Reporter:  drb226         |             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:
-------------------------------------+-------------------------------------
 I'm able to get two different panics, depending on how I try to build gi-
 gtk.

 Firstly, on my mac:

 {{{
 brew install gtk+3
 stack unpack gi-gtk-3.0.4
 cd gi-gtk-3.0.4
 stack init --resolver nightly-2016-06-08
 PKG_CONFIG_PATH=/usr/local/opt/libffi/lib/pkgconfig/ stack build
 }}}

 This results in

 {{{
 [650 of 650] Compiling GI.Gtk           ( GI/Gtk.hs, .stack-
 work/dist/x86_64-osx/Cabal-1.24.0.0/build/GI/Gtk.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-apple-darwin):
         RnEnv.plusAvail bindingSignalWriteNext CheckButtonK{CheckButtonK}
 }}}

 Secondly, also on my mac, but within an ubuntu-based docker image:

 {{{
 docker run -it snoyberg/stackage:nightly
 cd ~
 stack unpack gi-gtk-3.0.4
 cd gi-gtk-3.0.4
 stack init --resolver nightly-2016-06-08
 stack build
 }}}

 This results in

 {{{
 [599 of 654] Compiling GI.Gtk.Objects.Widget ( GI/Gtk/Objects/Widget.hs,
 .stack-work/dist/x86_64-linux/Cabal-1.24.0.0/build/GI/Gtk/Objects/Widget.o
 )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         urk! lookup local fingerprint
   $fAttrInfoWidgetMarginTopPropertyInfo4
 }}}

 The latter panic was first observed on the stackage build server, during
 the June 8th nightly build. That's why, to use the same dependencies, I
 specified the nightly-2016-06-08 stack resolver in order to reproduce it.
 I originally recorded it here:
 https://github.com/fpco/stackage/issues/1569

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12168>
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