[GHC] #14043: GHC.Stack.callStack throws exception

[GHC]

#14043: GHC.Stack.callStack throws exception
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.0.1
      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 bgamari):

 The problem appears to be that `callStack` is defined directly in terms of
 `popCallStack`, which fails on an empty stack. Presumably we should just
 return an empty stack in this case.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14043#comment:1>
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