[GHC] #15871: Revamp -fprint-explicit-kinds

[GHC]

#15871: Revamp -fprint-explicit-kinds
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  task              |               Status:  patch
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D5314
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"f5d2083807a03c57f194fcc3a7baf82e34aad524/ghc" f5d2083/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="f5d2083807a03c57f194fcc3a7baf82e34aad524"
 Overhaul -fprint-explicit-kinds to use VKA

 This patch changes the behavior of `-fprint-explicit-kinds`
 so that it displays kind argument using visible kind application.
 In other words, the flag now:

 1. Prints instantiations of specified variables with `@(...)`.
 2. Prints instantiations of inferred variables with `@{...}`.

 In addition, this patch removes the `Use -fprint-explicit-kinds to
 see the kind arguments` error message that often arises when a type
 mismatch occurs due to different kinds. Instead, whenever there is a
 kind mismatch, we now enable the `-fprint-explicit-kinds` flag
 locally to help cue to the programmer where the error lies.
 (See `Note [Kind arguments in error messages]` in `TcErrors`.)
 As a result, these funny `@{...}` things can now appear to the user
 even without turning on the `-fprint-explicit-kinds` flag explicitly,
 so I took the liberty of documenting them in the users' guide.

 Test Plan: ./validate

 Reviewers: goldfire, simonpj, bgamari

 Reviewed By: simonpj

 Subscribers: rwbarton, carter

 GHC Trac Issues: #15871

 Differential Revision: https://phabricator.haskell.org/D5314
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15871#comment:6>
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