[GHC] #12930: DDEBUG build broken

[GHC]

#12930: DDEBUG build broken
-------------------------------------+-------------------------------------
           Reporter:  mpickering     |             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:
-------------------------------------+-------------------------------------
 {{{
 Again, Travis is failing to build master since a while. Unfortunately,
 only the author of commits get mailed by Travis, so I did not notice it so
 far. But usually, when Travis reports a build failure, this is something
 actionable! If in doubt, contact me.

 The breakage at the moment occurs only with -DDEBUG on:

     Compile failed (exit code 1) errors were:
     ghc-stage2: panic! (the 'impossible' happened)
       (GHC version 8.1.20161118 for x86_64-unknown-linux):
             No match in record selector is_iloc

     Please report this as a GHC bug:
 https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.haskell.org%2Fghc%2Freportabug&data=02%7C01%7Csimonpj%40microsoft.com%7C688619e3295e4b6e0d5d08d41b0a2104%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636163177711116020&sdata=fh8XEV4Ioaxu0KkwKjDbweFvnQiNJ0V5%2BCj%2FQAdKvsY%3D&reserved=0


 *** unexpected failure for rn017(normal) Compile failed (exit code 1)
 errors were:
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.1.20161118 for x86_64-unknown-linux):
         No match in record selector is_iloc

 Please report this as a GHC bug:
 https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.haskell.org%2Fghc%2Freportabug&data=02%7C01%7Csimonpj%40microsoft.com%7C688619e3295e4b6e0d5d08d41b0a2104%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636163177711116020&sdata=fh8XEV4Ioaxu0KkwKjDbweFvnQiNJ0V5%2BCj%2FQAdKvsY%3D&reserved=0


 *** unexpected failure for T7672(normal)

 And started appearing, unless I am mistaken, with

     From: Matthew Pickering <    matthewtpickering at gmail.com    >
     Date: Fri, 18 Nov 2016 16:28:30 +0000
     Subject: [PATCH] Optimise whole module exports

     We directly build up the correct AvailInfos rather than generating
     lots of singleton instances and combining them with expensive calls to
     unionLists.

     There are two other small changes.

     * Pushed the nubAvails call into the explicit export list
       branch as we construct them correctly and uniquely ourselves.
     * fix_faminst only needs to check the first element of the export
       list as we maintain the (yucky) invariant that the parent is the
       first thing in it.

     Reviewers: simonpj, austin, bgamari

     Reviewed By: simonpj, bgamari

     Subscribers: simonpj, thomie, niteria

     Differential Revision:     https://phabricator.haskell.org/D2657

 Matthew, can you verify that this is a regression introduce here?

 Greetings,
 Joachim
 }}}

 The failing tests are `rn017` and `T7672`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12930>
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