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

[GHC]

#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
      Resolution:                    |             Keywords:  undefined,
                                     |  place holder, posttctype
Operating System:  Linux             |         Architecture:  x86_64
                                     |  (amd64)
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by rubik:

Old description:

> 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.

New description:

 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/ghc-7.8/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#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler