[GHC] #12760: Assertion failed with BuildFlavour = devel2 (yet another)

[GHC]

#12760: Assertion failed with BuildFlavour = devel2 (yet another)
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        Reporter:  pacak             |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by pacak):

 I'm compiling this: 8.0.1 + some fixes on top

 {{{
 * 3971db9 (HEAD) Get in-scope set right in top_instantiate
 simonpj at microsoft.com 4 months ago
 * eedd604 Build a correct substitution in dataConInstPat niteria at gmail.com
 6 months ago
 * 4091505 Fix the in-scope set for extendTvSubstWithClone
 simonpj at microsoft.com 4 months ago
 * 4986837 (tag: ghc-8.0.1-release) rules/build-prog: Ensure programs
 depend upon their transitive deps ben at smart-cactus.org 5 months ago
 }}}

 It is not a show stopper, but it stops me from trying devel2 compiler on
 our codebase and there we have strange compilation failures. I will try to
 build it with most recent branch and will let you know.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12760#comment:2>
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