panic parsing a stmt in ghc 7 (possible regression?)

[Daniel Gorín]

Hi

I'm trying to make the hint library work also with ghc 7 and I'm having problems with some test-cases that are now raising exceptions. I've been able to reduce the problem to a small example. The program below runs ghc in interpreter-mode and attempts to parse an statement using ghc's parseStmt function; the particular statement is a let-expression with a \n in the middle. The observed behaviour is:

> $ ghc-6.12.1 -fforce-recomp --make -package ghc -cpp -Wall d.hs && ./d 
> [1 of 1] Compiling Main             ( d.hs, d.o )
> Linking d ...
> let {e = let x = ()
> in x ;} in e
> Ok
> $ ghc-7.0.1 -fforce-recomp --make -package ghc -cpp -Wall d.hs && ./d 
> [1 of 1] Compiling Main             ( d.hs, d.o )
> Linking d ...
> let {e = let x = ()
> in x ;} in e
> d: d: panic! (the 'impossible' happened)
>   (GHC version 7.0.1 for i386-apple-darwin):
> 	srcLocCol <no location info>
> 
> Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Is it a regression or should I be doing this some other way?

Thanks,
Daniel

-- d.hs
import qualified GHC
import qualified MonadUtils as GHC ( liftIO )
import qualified StringBuffer as GHC
import qualified Lexer as GHC
import qualified Parser as GHC
import qualified GHC.Paths

main :: IO ()
main = GHC.runGhcT (Just GHC.Paths.libdir) $ do
       -- initialize
       df0 <- GHC.getSessionDynFlags
       _ <- GHC.setSessionDynFlags df0{GHC.ghcMode    = GHC.CompManager,
                                       GHC.hscTarget  = GHC.HscInterpreted,
                                       GHC.ghcLink    = GHC.LinkInMemory,
                                       GHC.verbosity  = 0}
       df1 <- GHC.getSessionDynFlags
      -- runParser
       let expr = "let {e = let x = ()\nin x ;} in e"
       GHC.liftIO $ putStrLn expr
       buf <- GHC.liftIO $ GHC.stringToStringBuffer expr
       let p_res = GHC.unP GHC.parseStmt (mkPState df1 buf GHC.noSrcLoc)
       case  p_res of
         GHC.POk{} -> GHC.liftIO $ putStrLn "Ok"
         GHC.PFailed{} -> GHC.liftIO $ putStrLn "Failed"
    where
#if __GLASGOW_HASKELL__ >= 700
          mkPState = GHC.mkPState
#else
          mkPState = \a b c -> GHC.mkPState b c a
#endif