[GHC] #14121: ghc master requires -XTypeInType where 8.2.1 does not

[GHC]

#14121: ghc master requires -XTypeInType where 8.2.1 does not
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        Reporter:  duog              |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.3
  checker)                           |
      Resolution:  invalid           |             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 RyanGlScott):

 Good thought bgamari, I've
 [https://ghc.haskell.org/trac/ghc/wiki/Migration/8.4?version=4 added a
 blurb] about this to the 8.4 migration guide.

 I don't think it would hurt adding mention of the fact that `TypeInType`'s
 validity checks tightened up in the release notes. FWIW, there is
 [https://phabricator.haskell.org/D3859 another patch] in the works that
 will make `TypeInType` pickier w.r.t. GADTs as well, so it might also
 behoove us to mention that as well.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14121#comment:5>
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