[GHC] #11549: Add -fshow-runtime-rep

[GHC]

#11549: Add -fshow-runtime-rep
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        Reporter:  goldfire          |                Owner:  goldfire
            Type:  bug               |               Status:  closed
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.1
      Resolution:  fixed             |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1961
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Do you think it's worth special-casing this kind of behavior with
 `-XTypeApplications` as well? Currently, it's quite easy to leak
 `RuntimeRep`:

 {{{
 $ /opt/ghc/8.0.1/bin/ghci
 GHCi, version 8.0.0.20160324: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/ryanglscott/.ghci
 λ> :t undefined
 undefined :: GHC.Stack.Types.HasCallStack => a
 λ> :set -XTypeApplications
 λ> :t undefined @Int

 <interactive>:1:12: error:
     • Expected kind ‘GHC.Types.RuntimeRep’, but ‘Int’ has kind ‘*’
     • In the type ‘Int’
       In the expression: undefined @Int
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11549#comment:10>
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