[GHC] #15792: TH reification prints invisible arguments to rank-2-kinded type as visible

[GHC]

#15792: TH reification prints invisible arguments to rank-2-kinded type as visible
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Template Haskell  |              Version:  8.6.1
      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:D5252
       Wiki Page:                    |
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Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"bfd93f90b6c63edf2790356e95feddf9898ec888/ghc" bfd93f9/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="bfd93f90b6c63edf2790356e95feddf9898ec888"
 Fix #15792 by not reifying invisible arguments in AppTys

 Summary:
 The `reifyType` function in `TcSplice` is carefully designed
 to avoid reifying visible arguments to `TyConApp`s. However, the same
 care was not given towards the `AppTy` case, which lead to #15792.

 This patch changes to the `AppTy` case of `reifyType` so that it
 consults the kind of the function type to determine which of the
 argument types are invisible (and therefore should be dropped) during
 reification. This required crafting a variant of `tyConArgFlags`,
 which I dubbed `appTyArgFlags`, that accept an arbitrary function
 `Type` instead of a `TyCon`.

 Test Plan: make test TEST=T15792

 Reviewers: goldfire, bgamari, simonpj

 Reviewed By: simonpj

 Subscribers: simonpj, rwbarton, carter

 GHC Trac Issues: #15792

 Differential Revision: https://phabricator.haskell.org/D5252
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15792#comment:2>
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