[GHC] #16246: GHC HEAD-only Core Lint error with unboxed equality (Non-CoVar has coercion type)

[GHC]

#16246: GHC HEAD-only Core Lint error with unboxed equality (Non-CoVar has coercion
type)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.10.1
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15648            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 Hrm. Maybe we should just drop that test? The problem is that GHC may look
 at a type and, if it's headed by `~#`, assume that any variable of that
 type is a coercion variable. There's nothing wrong in the theory if an
 ordinary variable has type `~#`... it's just perhaps an invariant that GHC
 might rely on (not sure).

 Another possibility is to have a check in `Convert` that prevents
 conversion of verboten things, like `~#`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16246#comment:2>
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