Improve CabalFileSearchFailure messages

The original error constructors had zero extra information (for
debugginng) when triggered. The error message "NoCabalFileFound"
is simply not useful without further context.

All of the existing CabalFileSearchFailure constructors now include
a FilePath field.

cabal-install/Distribution/Client/ProjectConfig.hs

@@ -1189,8 +1189,8 @@ syncAndReadSourcePackagesRemoteRepos verbosity
         entries <- liftIO $ getDirectoryContents packageDir
         --TODO: wrap exceptions
         case filter (\e -> takeExtension e == ".cabal") entries of
-          []       -> liftIO $ throwIO NoCabalFileFound
-          (_:_:_)  -> liftIO $ throwIO MultipleCabalFilesFound
+          []       -> liftIO $ throwIO $ NoCabalFileFound packageDir
+          (_:_:_)  -> liftIO $ throwIO $ MultipleCabalFilesFound packageDir
           [cabalFileName] -> do
             monitorFiles [monitorFileHashed cabalFilePath]
             liftIO $ fmap (mkSpecificSourcePackage location)
@@ -1282,9 +1282,9 @@ readSourcePackageCabalFile verbosity pkgfilename content =
 -- | When looking for a package's @.cabal@ file we can find none, or several,
 -- both of which are failures.
 --
-data CabalFileSearchFailure =
-     NoCabalFileFound
-   | MultipleCabalFilesFound
+data CabalFileSearchFailure
+   = NoCabalFileFound FilePath
+   | MultipleCabalFilesFound FilePath
   deriving (Show, Typeable)
 
 instance Exception CabalFileSearchFailure
@@ -1298,7 +1298,7 @@ extractTarballPackageCabalFile :: FilePath -> IO (FilePath, BS.ByteString)
 extractTarballPackageCabalFile tarballFile =
     withBinaryFile tarballFile ReadMode $ \hnd -> do
       content <- LBS.hGetContents hnd
-      case extractTarballPackageCabalFilePure content of
+      case extractTarballPackageCabalFilePure tarballFile content of
         Left (Left  e) -> throwIO e
         Left (Right e) -> throwIO e
         Right (fileName, fileContent) ->
@@ -1307,11 +1307,12 @@ extractTarballPackageCabalFile tarballFile =
 
 -- | Scan through a tar file stream and collect the @.cabal@ file, or fail.
 --
-extractTarballPackageCabalFilePure :: LBS.ByteString
+extractTarballPackageCabalFilePure :: FilePath
+                                   -> LBS.ByteString
                                    -> Either (Either Tar.FormatError
                                                      CabalFileSearchFailure)
                                              (FilePath, LBS.ByteString)
-extractTarballPackageCabalFilePure =
+extractTarballPackageCabalFilePure tarballFile =
       check
     . accumEntryMap
     . Tar.filterEntries isCabalFile
@@ -1324,11 +1325,11 @@ extractTarballPackageCabalFilePure =
 
     check (Left (e, _m)) = Left (Left e)
     check (Right m) = case Map.elems m of
-        []     -> Left (Right NoCabalFileFound)
+        []     -> Left (Right $ NoCabalFileFound tarballFile)
         [file] -> case Tar.entryContent file of
           Tar.NormalFile content _ -> Right (Tar.entryPath file, content)
-          _                        -> Left (Right NoCabalFileFound)
-        _files -> Left (Right MultipleCabalFilesFound)
+          _                        -> Left (Right $ NoCabalFileFound tarballFile)
+        _files -> Left (Right $ MultipleCabalFilesFound tarballFile)
 
     isCabalFile e = case splitPath (Tar.entryPath e) of
       [     _dir, file] -> takeExtension file == ".cabal"