[GHC] #11465: Eliminate check_lifted check in TcValidity

[GHC]

#11465: Eliminate check_lifted check in TcValidity
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        Reporter:  simonpj           |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.10.3
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1807
       Wiki Page:                    |
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Comment (by goldfire):

 The test case for this was as follows

 {{{
 class BoxIt (a :: TYPE 'Unlifted) where
     type Boxed a :: *
     boxed :: a -> Boxed a

 instance BoxIt Char# where
     type Boxed Char# = Char
     boxed x = C# x

 main :: IO ()
 main = print $ boxed 'c'#
 }}}

 After refactoring the levity stuff as per #11471, this test failed (of
 course). But as I look at it, it's amazing that it ever worked. The width
 to the argument of `boxed` is entirely unknowable. Anyway, it's all much
 better now. :)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11465#comment:11>
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