replacing fromJust with an exception handling.

CabalApi.hs

@@ -12,7 +12,7 @@ module CabalApi (
 import Control.Applicative
 import Control.Exception (throwIO)
 import Data.List (intercalate)
-import Data.Maybe (maybeToList, listToMaybe, fromJust)
+import Data.Maybe (maybeToList, listToMaybe)
 import Data.Set (fromList, toList)
 import Distribution.Package (Dependency(Dependency), PackageName(PackageName))
 import Distribution.PackageDescription
@@ -30,19 +30,21 @@ import Types
 fromCabalFile :: [GHCOption]
               -> Cradle
               -> IO ([GHCOption],[IncludeDir],[Package])
-fromCabalFile ghcOptions cradle =
-    cookInfo ghcOptions cradle <$> cabalParseFile cfile
+fromCabalFile ghcOptions cradle = do
+    cabal <- cabalParseFile cfile
+    case cabalBuildInfo cabal of
+        Nothing    -> throwIO BrokenCabalFile
+        Just binfo -> return $ cookInfo ghcOptions cradle cabal binfo
   where
-    Just cfile = cradleCabalFile  cradle
+    Just cfile = cradleCabalFile cradle
 
-cookInfo :: [String] -> Cradle -> GenericPackageDescription
-            -> ([GHCOption],[IncludeDir],[Package])
-cookInfo ghcOptions cradle cabal = (gopts,idirs,depPkgs)
+cookInfo :: [String] -> Cradle -> GenericPackageDescription -> BuildInfo
+         -> ([GHCOption],[IncludeDir],[Package])
+cookInfo ghcOptions cradle cabal binfo = (gopts,idirs,depPkgs)
   where
     owdir      = cradleCurrentDir cradle
     Just cdir  = cradleCabalDir   cradle
     Just cfile = cradleCabalFile  cradle
-    binfo      = cabalBuildInfo cabal
     gopts      = getGHCOptions ghcOptions binfo
     idirs      = includeDirectories cdir owdir $ cabalAllSourceDirs cabal
     depPkgs    = removeMe cfile $ cabalAllDependPackages cabal
@@ -70,8 +72,8 @@ getGHCOptions ghcOptions binfo = ghcOptions ++ exts ++ [lang] ++ libs ++ libDirs
 ----------------------------------------------------------------
 
 -- Causes error, catched in the upper function.
-cabalBuildInfo :: GenericPackageDescription -> BuildInfo
-cabalBuildInfo pd = fromJust $ fromLibrary pd <|> fromExecutable pd
+cabalBuildInfo :: GenericPackageDescription -> Maybe BuildInfo
+cabalBuildInfo pd = fromLibrary pd <|> fromExecutable pd
   where
     fromLibrary c    = libBuildInfo . condTreeData <$> condLibrary c
     fromExecutable c = buildInfo . condTreeData . snd <$> listToMaybe (condExecutables c)

Debug.hs

@@ -1,7 +1,10 @@
+ {-# LANGUAGE TemplateHaskell #-}
+
 module Debug (debugInfo, debug) where
 
 import CabalApi
 import Control.Applicative
+import Control.Exception.IOChoice.TH
 import Control.Monad
 import Data.List (intercalate)
 import Data.Maybe
@@ -12,6 +15,11 @@ import Types
 
 ----------------------------------------------------------------
 
+(||>>) :: IO a -> IO a -> IO a
+(||>>) = $(newIOChoice [''BrokenCabalFile])
+
+----------------------------------------------------------------
+
 debugInfo :: Options -> Cradle -> String -> String -> IO String
 debugInfo opt cradle ver fileName = unlines <$> debug opt cradle ver fileName
 
@@ -19,7 +27,7 @@ debug :: Options -> Cradle -> String -> String -> IO [String]
 debug opt cradle ver fileName = do
     (gopts, incDir, pkgs) <-
         if cabal then
-            fromCabalFile (ghcOpts opt) cradle -- FIXME
+            fromCabalFile (ghcOpts opt) cradle ||>> return (ghcOpts opt, [], [])
           else
             return (ghcOpts opt, [], [])
     [fast] <- withGHC fileName $ do

GHCApi.hs

@@ -61,7 +61,7 @@ initializeFlagsWithCradle opt cradle ghcOptions logging
         initSession CabalPkg opt gopts idirs (Just depPkgs) logging
     withoutCabal =
         initSession SingleFile opt ghcOptions importDirs Nothing logging
-    fallback :: SomeException -> Ghc LogReader
+    fallback :: BrokenCabalFile -> Ghc LogReader
     fallback _ = withoutCabal
 
 ----------------------------------------------------------------

Types.hs

@@ -1,7 +1,11 @@
 {-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE DeriveDataTypeable #-}
 
 module Types where
 
+import Control.Exception as E
+import Data.Typeable
+
 data OutputStyle = LispStyle | PlainStyle
 
 data Options = Options {
@@ -78,3 +82,9 @@ type IncludeDir = FilePath
 type Package    = String
 
 data CheckSpeed = Slow | Fast
+
+----------------------------------------------------------------
+
+data BrokenCabalFile = BrokenCabalFile deriving (Show, Typeable)
+
+instance Exception BrokenCabalFile