[GHC] #14270: GHC HEAD's ghc-stage1 panics on Data.Typeable.Internal

[GHC]

#14270: GHC HEAD's ghc-stage1 panics on Data.Typeable.Internal
-------------------------------------+-------------------------------------
           Reporter:  hvr            |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:  8.4.1
          Component:  Compiler       |           Version:  8.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #14236
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 When doing a default build of GHC HEAD (i.e. without `mk/build.mk`), GHC
 panics:

 {{{
 $ make V=0
 ===--- building phase 0
 make --no-print-directory -f ghc.mk phase=0 phase_0_builds
 make[1]: Nothing to be done for 'phase_0_builds'.
 ===--- building phase 1
 make --no-print-directory -f ghc.mk phase=1 phase_1_builds
 make[1]: Nothing to be done for 'phase_1_builds'.
 ===--- building final phase
 make --no-print-directory -f ghc.mk phase=final all
   HC [stage 1] libraries/base/dist-install/build/Data/Typeable/Internal.o
 ghc-stage1: panic! (the 'impossible' happened)
   (GHC version 8.3.20170922 for x86_64-unknown-linux):
         Template variable unbound in rewrite rule
   Variable: cobox_a3S9
   Rule "SC:mkTrApp0"
   Rule bndrs: [k1_X4g7, b_X4gb, k1_a3RW, a_a3RX, k1_X426, b_X42a,
                b_a3RY, sc_s7Yv, sc_s7Yr, sc_s7Ys, sc_s7Yt, cobox_a3S9,
 cobox_a3RZ,
                cobox_X42x, cobox_a3S8]
   LHS args: [TYPE: TYPE (b_a3RY |> Nth:2 (Sym cobox_a3S8)),
              TYPE: TYPE (b_X42a |> Nth:2 (Sym cobox_X42x)) -> *, TYPE:
 (->),
              TYPE: (b_X4gb |> Sym (cobox_a3S9 (Coh (Sym (Coh <b_a3RY>_N
                                                              (Nth:2 (Sym
 cobox_a3S8))))
                                                    (Nth:2 (Sym
 cobox_a3S8)) ; Coh <b_a3RY>_N
 (Nth:2
 (Sym cobox_a3S8))) ; Sym cobox_a3RZ)),
              TrTyCon
                @ (TYPE (b_a3RY |> Nth:2 (Sym cobox_a3S8))
                   -> TYPE (b_X42a |> Nth:2 (Sym cobox_X42x)) -> *)
                @ (->)
                sc_s7Yr
                sc_s7Ys
                $tc(->)
                sc_s7Yt,
              sc_s7Yv]
   Actual args: [TYPE: TYPE (b_a3RY |> Nth:2 (Sym cobox_a3S8)),
                 TYPE: TYPE (b_X42a |> Nth:2 (Sym cobox_X42x)) -> *, TYPE:
 (->),
                 TYPE: (b_X4gb |> Sym (cobox_a3S9 (Coh (Sym (Coh <b_a3RY>_N
                                                                 (Nth:2
 (Sym cobox_a3S8))))
                                                       (Nth:2 (Sym
 cobox_a3S8)) ; Coh <b_a3RY>_N
 (Nth:2
 (Sym cobox_a3S8))) ; Sym cobox_a3RZ)),
                 TrTyCon
                   @ (TYPE (b_a3RY |> Nth:2 (Sym cobox_a3S8))
                      -> TYPE (b_X42a |> Nth:2 (Sym cobox_X42x)) -> *)
                   @ (->)
                   dt_a2Vb
                   dt_a2Vc
                   $tc(->)
                   kind_vars_X37r,
 ...
 }}}

 You can see a more complete error in the build log at

  https://launchpadlibrarian.net/337888338/buildlog_ubuntu-trusty-amd64
 .ghc-head_8.3.20170922+git.0.5a8b843-7~14.04_BUILDING.txt.gz


 This panic seems to be causally connected to
 cc6be3a2f23c9b2e04f9f491099149e1e1d4d20b (which addressed #14236) because
 reverting that commit allows me to avoid the panic.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14270>
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