[GHC] #13549: GHC 8.2.1's typechecker rejects code generated by singletons that 8.0 accepts

[GHC]

#13549: GHC 8.2.1's typechecker rejects code generated by singletons that 8.0
accepts
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 I've no clue what's going on in that mess of code. Who would ever write
 such a thing? :)

 But I figured this out: if we force `do_kind_gen` on line 208 to be `True`
 always, the module compiles. I've now got to run, but my hunch is that the
 calculation of when types are closed is a bit off.

 Thanks for making an easy repro case and bisecting. That's invaluable!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13549#comment:4>
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