[GHC] #10905: Incorrect number of parameters in "role" errors

[GHC]

#10905: Incorrect number of parameters in "role" errors
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        Reporter:  crockeea          |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:  roles
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by goldfire):

 Here's my test case. It produces the bad output in 7.10, but (as noted
 above) not in HEAD.

 {{{
 {-# LANGUAGE PolyKinds #-}

 module T10905 where

 import Data.Coerce
 import Data.Functor.Identity

 data TaggedT s m b = TagT { untagT :: m b }

 foo :: TaggedT () [] Int -> TaggedT () [] (Identity Int)
 foo = coerce

 -- test the printing of TaggedT's role signature
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10905#comment:2>
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