[GHC] #14579: GeneralizedNewtypeDeriving produces ambiguously-kinded code

[GHC]

#14579: GeneralizedNewtypeDeriving produces ambiguously-kinded code
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |
      Resolution:                    |             Keywords:  deriving
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4264
       Wiki Page:                    |
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Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"649e777211fe08432900093002547d7358f92d82/ghc" 649e777/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="649e777211fe08432900093002547d7358f92d82"
 Make typeToLHsType produce kind signatures for tycon applications

 Summary:
 `GeneralizedNewtypeDeriving` generates calls to `coerce`
 which take visible type arguments. These types must be produced by
 way of `typeToLHsType`, which converts a `Type` to an `LHsType`.
 However, `typeToLHsType` was leaving off important kind information
 when a `Type` contained a poly-kinded tycon application, leading to
 incorrectly generated code in #14579.

 This fixes the issue by tweaking `typeToLHsType` to generate
 explicit kind signatures for tycon applications. This makes the
 generated code noisier, but at least the program from #14579 now
 works correctly.

 Test Plan: make test TEST=T14579

 Reviewers: simonpj, bgamari

 Reviewed By: simonpj

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #14579

 Differential Revision: https://phabricator.haskell.org/D4264
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14579#comment:9>
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