[GHC] #14343: bad pretty-printing of types with promoted data types

[GHC]

#14343: bad pretty-printing of types with promoted data types
-------------------------------------+-------------------------------------
        Reporter:  lspitzner         |                Owner:  andreash
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4746
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"767536ccf95d8352d146b6544857b28d9c42937e/ghc" 767536c/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="767536ccf95d8352d146b6544857b28d9c42937e"
 Fix unparseable pretty-printing of promoted data cons

 Previously we would print code which would not round-trip:
 ```
 > :set -XDataKinds
 > :set -XPolyKinds
 > data Proxy k = Proxy
 > _ :: Proxy '[ 'True ]
 error:
   Found hole: _ :: Proxy '['True]
 > _ :: Proxy '['True]
 error:
     Invalid type signature: _ :: ...
     Should be of form <variable> :: <type>
 ```

 Test Plan: Validate with T14343

 Reviewers: RyanGlScott, goldfire, bgamari, tdammers

 Reviewed By: RyanGlScott, bgamari

 Subscribers: tdammers, rwbarton, thomie, carter

 GHC Trac Issues: #14343

 Differential Revision: https://phabricator.haskell.org/D4746
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14343#comment:7>
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