Give more informative error messages

[ghc-hetmet.git] / libraries / bin-package-db / Distribution / InstalledPackageInfo / Binary.hs

diff --git a/libraries/bin-package-db/Distribution/InstalledPackageInfo/Binary.hs b/libraries/bin-package-db/Distribution/InstalledPackageInfo/Binary.hs
index 0f59929..387b78f 100644 (file)
--- a/libraries/bin-package-db/Distribution/InstalledPackageInfo/Binary.hs
+++ b/libraries/bin-package-db/Distribution/InstalledPackageInfo/Binary.hs
@@ -19,9 +19,24 @@ import Distribution.Package hiding (depends)
 import Distribution.License
 import Distribution.InstalledPackageInfo as IPI
 import Data.Binary as Bin
+import Control.Exception as Exception
 
 readBinPackageDB :: Binary m => FilePath -> IO [InstalledPackageInfo_ m]
-readBinPackageDB file = Bin.decodeFile file
+readBinPackageDB file
+    = do xs <- Bin.decodeFile file
+         _ <- Exception.evaluate $ length xs
+         return xs
+      `catchUserError`
+      (\err -> error ("While parsing " ++ show file ++ ": " ++ err))
+
+catchUserError :: IO a -> (String -> IO a) -> IO a
+#ifdef BASE3
+catchUserError io f = io `Exception.catch` \e -> case e of
+                                                 ErrorCall err -> f err
+                                                 _ -> throw e
+#else
+catchUserError io f = io `Exception.catch` \(ErrorCall err) -> f err
+#endif
 
 writeBinPackageDB :: Binary m => FilePath -> [InstalledPackageInfo_ m] -> IO ()
 writeBinPackageDB file ipis = Bin.encodeFile file ipis