[GHC] #11589: Reexports of wired-in packages don't work.

[GHC]

#11589: Reexports of wired-in packages don't work.
-------------------------------------+-------------------------------------
        Reporter:  ezyang            |                Owner:  ezyang
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  cabal/cabal09
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1926
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * testcase:   => cabal/cabal09


Comment:

 The problem appears to be when you have something like the following in a
 cabal file,
 {{{     ​
 library
   reexported-modules:  Data.List.NonEmpty
 }}}
 which results in
 {{{
 $ runghc Setup.hs build
 Building reexport-0.1.0.0...
 Preprocessing library reexport-0.1.0.0...
 Preprocessing executable 'foo' for reexport-0.1.0.0...
 [1 of 1] Compiling Main             ( Main.hs, dist/build/foo/foo-
 tmp/Main.o )

 Main.hs:1:1: error:ghc: panic! (the 'impossible' happened)
   (GHC version 8.1.20160122 for x86_64-unknown-linux):
         expectJust mkModuleToPkgConf
 CallStack (from ImplicitParams):
   error, called at compiler/utils/Maybes.hs:45:27 in ghc:Maybes

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

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11589#comment:1>
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