[GHC] #15147: Type checker plugin receives Wanteds that are not completely unflattened

[GHC]

#15147: Type checker plugin receives Wanteds that are not completely unflattened
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        Reporter:  nfrisby           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.4.1
  checker)                           |             Keywords:  type checker
      Resolution:                    |  plugins
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 nfrisby):

 Looking at `-ddump-tc-trace`, the compiler flattens the wanteds and then
 zonks them before passing them to the plugin. However, the zonking pass
 makes a substitution that re-introduces the fsk var.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15147#comment:1>
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