[GHC] #12550: Inconsistent unicode display for kinds

[GHC]

#12550: Inconsistent unicode display for kinds
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        Reporter:  johnleo       |                Owner:  johnleo
            Type:  bug           |               Status:  new
        Priority:  normal        |            Milestone:  8.2.1
       Component:  Compiler      |              Version:  8.0.1
      Resolution:                |             Keywords:
Operating System:  MacOS X       |         Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:                |  Differential Rev(s):
       Wiki Page:                |
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Comment (by johnleo):

 Ben's fix for #11660 handled almost all of the problems.  The sole
 remaining problem was the result of conflation between the input format of
 kind * (`*`, `★` or `Type`), the internal representation, and the output
 format.  If * was inferred it was output correctly, but if it was
 explicitly specified in the type signature it would be output in that
 form, which means the output format could be a confusing mixture of `*`,
 `★` and `Type`.  I have unified the output format to be `*` when non-
 unicode output is expected and `★` when `-fprint-unicode-syntax` is
 enabled.  Note that in the future we may output `Type` in all cases
 instead (see #12030) but this will not happen for some time; I plan to
 create a proposal for this.

 I wanted to go further and unify the internal representations of `*`, `★`
 and `Type` by setting the key of all three to be `liftedTypeKindTyConKey`
 since internally they are all fundamentally the same thing.  However this
 caused a panic in `PrelInfo.knownKeyNamesOkay` since apparently all keys
 have to be unique.  I wonder if that condition could be relaxed.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12550#comment:9>
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