[GHC] #16313: Core Lint warning (Unsafe coercion: {left, right}-hand type is levity-polymorphic)

[GHC]

#16313: Core Lint warning (Unsafe coercion: {left,right}-hand type is levity-
polymorphic)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Let me ask again

 Are you really arguing that if Lint sees `3# |> UnsafeCoerce(..) :: Int`,
 which coerces an Int# to an Int, that it should remain silent?

 Maybe a compiler bug put it there; it's certainly wrong isn't it?  After
 all, if the compiler was always right we would not need Core Lint.

 I'm all for adding a user-level bug-detection thing for `unsafeCoerce` as
 well, which you are perhaps implicitly suggesting.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16313#comment:5>
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