[GHC] #11554: Self quantification in GADT data declarations

[GHC]

#11554: Self quantification in GADT data declarations
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        Reporter:  Rafbill           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.2
       Component:  Compiler (Type    |              Version:  8.0.1-rc2
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 Won't `ATcTyConUnpromoted` and `ATcTyCon` be the same, always? That is, if
 (and only if) we're currently checking a mutually recursive group
 containing the tycon `T`, `T` will be registered as `ATcTyCon`. Isn't that
 the exact scenario where you're proposing to use `ATcTyConUnpromoted`? So
 my take would be to check in `tcTyVar`, just as you suggest, but use the
 existing `ATcTyCon` instead of creating something new.

 Or what am I missing?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11554#comment:9>
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