[GHC] #14720: GHC 8.4.1-alpha regression with TypeInType

[GHC]

#14720: GHC 8.4.1-alpha regression with TypeInType
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.4.1-alpha1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
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 monoidal):

 For the record, here's a smaller test case:

 {{{#!hs
 {-# LANGUAGE AllowAmbiguousTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeInType #-}
 module SGenerics where

 import Data.Kind (Type)

 type family R :: Type
 data family Sing (z :: R)
 type family PFrom (x :: Type) :: R

 u :: forall (a :: R). Sing a
 u = u

 v :: forall (a :: Type). Sing (PFrom a)
 v = u
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14720#comment:3>
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