[GHC] #14086: Empty case does not detect kinds

[GHC]

#14086: Empty case does not detect kinds
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  low               |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3819
       Wiki Page:                    |
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Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"a267580e4ab37115dcc33f3b8a9af67b9364da12/ghc" a267580/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="a267580e4ab37115dcc33f3b8a9af67b9364da12"
 Don't warn when empty casing on Type

 Summary:
 `Type` (a.k.a. `TYPE LiftedRep`) can be used at the type level thanks
 to `TypeInType`. However, expressions like

 ```lang=haskell
 f :: Type -> Int
 f x = case x of {}
 ```

 were falsely claiming that the empty case on the value of type `Type` was
 non-exhaustive. The reason is a bit silly: `TYPE` is technically not an
 empty
 datatype in GHC's eyes, since it's a builtin, primitive type. To convince
 the
 pattern coverage checker otherwise, this adds a special case for `TYPE`.

 Test Plan: make test TEST=T14086

 Reviewers: gkaracha, austin, bgamari, goldfire

 Reviewed By: goldfire

 Subscribers: goldfire, rwbarton, thomie

 GHC Trac Issues: #14086

 Differential Revision: https://phabricator.haskell.org/D3819
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14086#comment:4>
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