[GHC] #11334: GHC panic when calling typeOf on a promoted data constructor

[GHC]

#11334: GHC panic when calling typeOf on a promoted data constructor
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1757
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"65b810bdda625f2e98069c2c56ec93e1c65667a6/ghc" 65b810b/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="65b810bdda625f2e98069c2c56ec93e1c65667a6"
 Show TYPE 'Lifted/TYPE 'Unlifted as */# in Show TypeRep instance

 Kind equalities changed how `*`/`#` are represented internally, which
 means that showing a `TypeRep` that contains either of those kinds
 produces a rather gross-looking result, e.g.,

 ```
 > typeOf (Proxy :: Proxy 'Just)
 Proxy (TYPE 'Lifted -> Maybe (TYPE 'Lifted)) 'Just
 ```

 We can at least special-case the `Show` instance for `TypeRep` so that
 it prints `*` to represent `TYPE 'Lifted` and `#` to represent `TYPE
 'Unlifted`.

 Addresses one of the issues uncovered in #11334.

 Test Plan: ./validate

 Reviewers: simonpj, hvr, austin, goldfire, bgamari

 Reviewed By: bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1757

 GHC Trac Issues: #11334
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11334#comment:6>
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