[GHC] #12503: Template Haskell regression: GHC erroneously thinks a type variable is also a kind

[GHC]

#12503: Template Haskell regression: GHC erroneously thinks a type variable is also
a kind
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  goldfire
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.2.1
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeInType
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:D3022
       Wiki Page:                    |
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Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"283a346586e5bf711ecd8cc61263d87771f8f744/ghc"
 283a3465/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="283a346586e5bf711ecd8cc61263d87771f8f744"
 Prevent Template Haskell splices from throwing a spurious TypeInType error

 Summary:
 There was a rather annoying corner case where splicing poly-kinded
 Template Haskell declarations could trigger an error muttering about
 `TypeInType` not being enabled, whereas the equivalent non-TH code would
 compile without issue. This was causing by overzealous validity check in
 the
 renamer, wherein failed to distinguish between two different `Exact` names
 with the same `OccName`. As a result, it mistakenly believed some type
 variables were being used as both type and kind variables simultaneously!
 Ack.

 This avoids the issue by simply disabling the aforementioned validity
 check
 for Exact names. Fixes #12503.

 Test Plan: ./validate

 Reviewers: austin, bgamari, goldfire

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D3022
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12503#comment:11>
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