[GHC] #930: ghc-6.6: panic! (the 'impossible' happened) mkWWcpr: not a product GHC-Brian-6.5.1:IdInfo.IdInfo{tc rfD}

[GHC]

#930: ghc-6.6: panic! (the 'impossible' happened) mkWWcpr: not a product GHC-
Brian-6.5.1:IdInfo.IdInfo{tc rfD}
-------------------------+--------------------------------------------------
  Reporter:  briansmith  |          Owner:         
      Type:  bug         |         Status:  new    
  Priority:  normal      |      Milestone:         
 Component:  Compiler    |        Version:  6.5    
  Severity:  normal      |     Resolution:         
  Keywords:              |             Os:  Unknown
Difficulty:  Unknown     |   Architecture:  Unknown
-------------------------+--------------------------------------------------
Comment (by simonpj):

 This is an annoying, known, but awkward-to-fix problem concerning
 mutually-recursive modules.  The problem is that when compiling the
 modules *inside* a loop, a data type that is only defined at the top of
 the loop looks opaque; but after the loop is done, the structure of the
 data type becomes apparent.

 The difficulty is then that two different bits of code have different
 notions of what the data type looks like.

 So far this bug has bitten only GHC itself and one other person.  I need
 to think carefully about how to fix it.  Thanks for reporting it.

 Unsatisfactory workaround: compile without -O.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/930>
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