[GHC] #11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack

[GHC]

#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack
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        Reporter:  thomie            |                Owner:  gridaphobe
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.11
      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 goldfire):

 I ran into this problem a few weeks ago. It seems that the place where
 `GHC.Stack.Types` normally gets loaded is the `dsLookupDataCon` call in
 `DsBinds.dsEvCallStack`. I found this peculiar at the time (why doesn't it
 get loaded earlier?) but the original source of the error (for me) was
 elsewhere. When I fixed that (to produce an `EvCallStack`), the problem
 went away.

 I don't know why this all is happening, but the knowledge that that
 particular call of `dsLookupDataCon` triggers loading in the successful
 case was a bit hard-won, so I thought I'd share.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11331#comment:3>
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