[GHC] #11027: GHC API panic (evaluated the place holder for a PostTcType)

28 Oct 2015


      #11027: GHC API panic (evaluated the place holder for a PostTcType)
-------------------------------------+-------------------------------------
           Reporter:  rubik          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHC API        |           Version:  7.8.4
           Keywords:  undefined,     |  Operating System:  Linux
  place holder, posttctype           |
       Architecture:  x86_64         |   Type of failure:  Runtime crash
  (amd64)                            |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 The same code that works for GHC 7.10.2 blows up on GHC 7.8.4, with errors
 like
 {{{
     test/ArgonSpec.hs:104: (best-effort)
       6) Argon.analyze accounts for && operator
            uncaught exception: GhcException (argon-test: panic! (the
 'impossible' happened)
              (GHC version 7.8.4 for x86_64-unknown-linux):
                 fixity

            Please report this as a GHC bug:
 http://www.haskell.org/ghc/reportabug
            )

       test/ArgonSpec.hs:106: (best-effort)
       7) Argon.analyze counts everything in a real example
            uncaught exception: GhcException (argon-test: panic! (the
 'impossible' happened)
              (GHC version 7.8.4 for x86_64-unknown-linux):
                 Evaluated the place holder for a PostTcType

            Please report this as a GHC bug:
 http://www.haskell.org/ghc/reportabug
            )
 }}}

 The responsible module is
 [https://github.com/rubik/argon/blob/master/src/Argon/Visitor.hs]
 and in particular (I think):
 {{{
 visitExp :: Exp -> Int
 visitExp (GHC.HsIf {}) = 1
 visitExp (GHC.HsMultiIf _ alts) = length alts - 1
 visitExp (GHC.HsLamCase _ alts) = length (GHC.mg_alts alts) - 1
 visitExp (GHC.HsCase _ alts)    = length (GHC.mg_alts alts) - 1
 visitExp _ = 0

 visitOp :: Exp -> Int
 visitOp (GHC.OpApp _ (GHC.L _ (GHC.HsVar op)) _ _) =
     case getName op of
       "||" -> 1
       "&&" -> 1
       _    -> 0
 visitOp _ = 0
 }}}
 somehow, even if I use wildcards, the first arguments of the type
 constructors gets evaluated and since it's undefined GHC crashes.
 What am I supposed to do?
 The documentation does not say anything on the matter.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11027
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