Re: crash caused by generic visitor (?)

14 May 2011

      Hi all, 

my apologies. Looks like the issue (and a fix!) is described here

  http://mistuke.wordpress.com/category/vsx/

Thanks,

Ranjit.

On May 13, 2011, at 4:34 PM, Ranjit Jhala wrote:
...
Hi all,
I'm trying to extract the set of identifiers that are read in given 
source file.  To this end, I wrote the following code (full source at end.)
------------------------------------------------------------------------
main 
 = do fname   <- (!! 0) `fmap` getArgs
      tcm     <- loadTypecheckedSource fname
      putStrLn $ showPpr tcm           -- this works fine
      putStrLn $ showPpr $ allIds tcm  -- this causes the crash
      return ()
allIds ::  Data a => a -> [Id]
allIds = listify (\x -> case (x :: Id) of _ -> True)
------------------------------------------------------------------------
and where:
loadTypecheckedSource ::  FilePath -> IO TypecheckedSource
unfortunately, when I compile and run it, I get the dreaded:
Bug: Bug: panic! (the 'impossible' happened)
  (GHC version 7.0.3 for i386-unknown-linux):
      placeHolderNames
Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Turns out that the problem is when the file contains a type annotation.
That is,
./Bug Test00.hs
crashes, when Test00.hs is:
module Test where
x :: Int
  x = 0
but does not crash when the file is:
module Test where
x = 0
Can anyone tell me why listify chokes in the latter case? (And how one might 
get around the problem?) I include the full source below (compiled with: ghc --make Bug, using ghc 7.0.3)
Thanks!
Ranjit.
------------------------------------------------------------------------------------------------------
import GHC 
import Outputable
import DynFlags (defaultDynFlags)
import GHC.Paths (libdir)
import System.Environment (getArgs)
import Control.Monad
import qualified Data.List as L
import Data.Data
import Data.Generics.Schemes (listify)
main 
 = do fname   <- (!! 0) `fmap` getArgs
      tcm     <- loadTypecheckedSource fname
      putStrLn $ showPpr tcm           -- this works fine
      putStrLn $ showPpr $ allIds tcm  -- this causes the crash
      return ()
allIds ::  Data a => a -> [Id]
allIds = listify (\x -> case (x :: Id) of _ -> True)
loadTypecheckedSource ::  FilePath -> IO TypecheckedSource
loadTypecheckedSource fname 
 = defaultErrorHandler defaultDynFlags $ 
     runGhc (Just libdir) $ do
       df  <- getSessionDynFlags
       setSessionDynFlags df
       tgt <- guessTarget fname Nothing
       setTargets [tgt]
       load LoadAllTargets 
       res <- load LoadAllTargets
       if failed res
         then pprPanic "Load Failed!!" (text "AAARGH!")
         else tm_typechecked_source `fmap` getTypecheckedModule fname
findModSummary ::  GhcMonad m => FilePath -> m ModSummary
findModSummary fname 
 = do msums <- depanal [] False
      case L.find ((fname ==) . ms_hspp_file) msums of 
        Just msum -> return msum
        Nothing   -> pprPanic "ModuleName Lookup Failed!!" (text "AARGHC!")
getTypecheckedModule :: GhcMonad m => FilePath -> m TypecheckedModule
getTypecheckedModule = findModSummary >=> parseModule >=> typecheckModule