[GHC] #15163: non coercion variable in coVarKindsTypesRole

[GHC]

#15163: non coercion variable in coVarKindsTypesRole
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        Reporter:  alpmestan         |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  T14732
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"d191db48c43469ee1818887715bcbc5c0eb1d91f/ghc"
 d191db48/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="d191db48c43469ee1818887715bcbc5c0eb1d91f"
 Don't expose strictness when sm_inline is False

 This is very much a corner case, but Trac #15163 showed
 that if you have a RULE like
     forall x. f (g x) = ..x..

 and g = undefined, then the simplifier is likely to discard
 that 'x' argument. It is usually right to do so; but not here
 because then x is used on the right but not bound on the left.

 The fix is a narrow one, aimed at this rather pathalogical case.
 See Note [Do not expose strictness if sm_inline=False] in
 SimplUtils.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15163#comment:2>
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