Check cabal build exit code, don't try to start application if build failed

yesod/Devel.hs

@@ -24,7 +24,7 @@ import qualified Data.Map as Map
 import qualified Data.Set as Set
 
 import           System.Directory
-import           System.Exit (exitFailure, exitSuccess)
+import           System.Exit (exitFailure, exitSuccess, ExitCode (..))
 import           System.FilePath (splitDirectories, dropExtension, takeExtension)
 import           System.Posix.Types (EpochTime)
 import           System.PosixCompat.Files (modificationTime, getFileStatus)
@@ -87,10 +87,13 @@ mainLoop isCabalDev = do
        recompDeps
 
        list <- getFileList
-       _ <- if isCabalDev
+       exit <- if isCabalDev
                then rawSystem "cabal-dev" ["build"]
                else rawSystem "cabal"     ["build"]
 
+       case exit of
+         ExitFailure _ -> putStrLn "Build failure, pausing..."
+         _ -> do
                removeLock
                let pkg = pkgConfigs isCabalDev ghcVer
                let start = concat ["runghc ", pkg, " devel.hs"]
@@ -157,16 +160,12 @@ checkCabalFile gpd = case D.condLibrary gpd of
              putStrLn $ "WARNING: yesod devel may not work correctly with " ++
                         "custom hs-source-dirs"
          fl <- getFileList
-         print (allModules dLib)
          let unlisted = checkFileList fl dLib
-         print fl
          when (not . null $ unlisted) $ do
               putStrLn "WARNING: the following source files are not listed in exposed-modules or other-modules:"
               mapM_ putStrLn unlisted
          when (D.fromString "Application" `notElem` D.exposedModules dLib) $ do
               putStrLn "WARNING: no exposed module Application"
-              print (D.exposedModules dLib)
-              print dLib
 
 failWith :: String -> IO a
 failWith msg = do