[GHC] #12444: Regression: panic! on inaccessible code with constraint

[GHC]

#12444: Regression: panic! on inaccessible code with constraint
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        Reporter:  zilinc            |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Compile-time      |            Test Case:
  crash                              |  polykinds/T12444
      Blocked By:                    |             Blocking:
 Related Tickets:  #12526            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"c48595eef2bca6d91ec0a649839f8066f269e6a4/ghc"
 c48595ee/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="c48595eef2bca6d91ec0a649839f8066f269e6a4"
 Never apply worker/wrapper to DFuns

 While fixing Trac #12444 I found an occasion on which we applied
 worker/wrapper to a DFunId.  This is bad: it destroys the magic
 DFunUnfolding.

 This patch is a minor refactoring that stops this corner case
 happening, and tidies up the code a bit too.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12444#comment:7>
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