[GHC] #16077: AvailTC Invariant being violated

[GHC]

#16077: AvailTC Invariant being violated
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        Reporter:  harpocrates       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by harpocrates):

 I've begun to investigate this and none of this actually requires `cabal`.
 Using `A.hs` and `B.hs` from the bug summary, just run

 {{{
 $ ghc -fforce-recomp -ddump-rn-trace A.hs B.hs | grep rnExports
 rnExports: Exports: [error, C{C, T;}, T{T, TI;}]
 rnExports: Exports: [C{C, T;}, T{TI;}]
 }}}

 The asymmetry is pretty clear. Also, this is reproducible on HEAD.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16077#comment:2>
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