cabal installing graphical apps on MacOS X

I have a graphical command line tool written in wxHaskell. For the longest time, my tool was relatively easy to install on Linux but a pain on MacOS X because my users had to jump through extra post-installation hoops like creating application bundles.

Thanks to some very patient help from Beelsebob, quicksilver, dcoutts on #haskell I was finally able to cobble together a Setup.hs file that lets me do just this. Now when I write install instructions for my program, I no longer need to add extra bullet points telling people to turn knobs and twiggle blops just to run the GUI. It just works.

Note that this was written with wxHaskell in mind. I hope that folks using gtk2hs and qtHaskell either do not have this problem or can make use of a similar solution.

desiderata

What I wanted was for the 'cabal install' command to work as well on MacOS X as it did under Linux. My core desiderata were:

1. Ability to call my application from the command line the same way you would under Linux with command line arguments correctly recognised
   
2. No need for the user to add extra junk to the path (besides $HOME/.cabal/bin which they'll already have added)
3. No manual intervention after cabal install (eg calling scripts to create application bundles)
   
4. No need to be super-user.

basic ideas

The basic ideas behind this solution are

• Replace "foo" with a shell script that calls "foo.app/MacOS/Contents/foo"
  MacOS X Leopard seems to want graphical applications to live in application bundles. At least for wxHaskell if you invoke "foo" you get a GUI that does not respond to input. On the other hand, if you invoke "foo.app/MacOS/Contents/foo" you get something that works.
  
• Use a Cabal postInst to create the application bundle in the bin dir.

basic solution

Here is the solution. (I'll send it as a mail to the wxhaskell-users mailing list too)

-- --------------- BEGIN Setup.hs EXAMPLE ------------------------------
import Control.Monad (foldM_, forM_)
import Data.Maybe ( fromMaybe )
import System.Cmd
import System.Exit
import System.Info (os)
import System.FilePath
import System.Directory ( doesFileExist, copyFile, removeFile, createDirectoryIfMissing )

import Distribution.PackageDescription
import Distribution.Simple.Setup
import Distribution.Simple
import Distribution.Simple.LocalBuildInfo

main :: IO ()
main = defaultMainWithHooks $ addMacHook simpleUserHooks
 where
  addMacHook h =
   case os of
    "darwin" -> h { postInst = appBundleHook } -- is it OK to treat darwin as synonymous with MacOS X?
    _        -> h

appBundleHook :: Args -> InstallFlags -> PackageDescription -> LocalBuildInfo -> IO ()
appBundleHook _ _ pkg localb =
 forM_ exes $ \app ->
   do createAppBundle theBindir (buildDir localb </> app </> app)
      customiseAppBundle (appBundlePath theBindir app) app
        `catch` \err -> putStrLn $ "Warning: could not customise bundle for " ++ app ++ ": " ++ show err
      removeFile (theBindir </> app)
      createAppBundleWrapper theBindir app
 where
  theBindir = bindir $ absoluteInstallDirs pkg localb NoCopyDest
  exes = fromMaybe (map exeName $ executables pkg) mRestrictTo

-- ----------------------------------------------------------------------
-- helper code for application bundles
-- ----------------------------------------------------------------------

-- | 'createAppBundle' @d p@ - creates an application bundle in @d@
--   for program @p@, assuming that @d@ already exists and is a directory.
--   Note that only the filename part of @p@ is used.
createAppBundle :: FilePath -> FilePath -> IO ()
createAppBundle dir p =
 do createDirectoryIfMissing False $ bundle
    createDirectoryIfMissing True  $ bundleBin
    createDirectoryIfMissing True  $ bundleRsrc
    copyFile p (bundleBin </> takeFileName p)
 where
  bundle     = appBundlePath dir p
  bundleBin  = bundle </> "Contents/MacOS"
  bundleRsrc = bundle </> "Contents/Resources"

-- | 'createAppBundleWrapper' @d p@ - creates a script in @d@ that calls
--   @p@ from the application bundle @d </> takeFileName p <.> "app"@
createAppBundleWrapper :: FilePath -> FilePath -> IO ()
createAppBundleWrapper bindir p =
  writeFile (bindir </> takeFileName p) scriptTxt
 where
  scriptTxt = "`dirname $0`" </> appBundlePath "." p </> "Contents/MacOS" </> takeFileName p ++ " \"$@\""

appBundlePath :: FilePath -> FilePath -> FilePath
appBundlePath dir p = dir </> takeFileName p <.> "app"

-- optional stupff: to be discussed later
mRestrictTo = Nothing
customiseAppBundle _ _ = return ()
-- --------------- END Setup.hs EXAMPLE ---------------------------------

fancier solution

I also have some extra wishlist items.

1. Possibility of installing in --global
2. Fancy custom app bundles with custom icons and what not

Global installation might already be working with this basic script, but I haven't tested it yet. Fancy app bundles sort of work (if I double-click it in Finder, I get a customised icon, but running it from the command line does not give me one).

Here are extra hooks I created for this:

-- ------------- BEGIN FANCY Setup.hs ADDENDUM ------------------------
-- | Put here IO actions needed to add any fancy things (eg icons)
--   you want to your application bundle.
customiseAppBundle :: FilePath -- ^ app bundle path
                   -> FilePath -- ^ full path to original binary
                   -> IO ()
customiseAppBundle bundleDir p =
 case takeFileName p of
  "geni" ->
    do hasRez <- doesFileExist "/Developer/Tools/Rez"
       if hasRez
          then do -- set the icon
                  copyFile "etc/macstuff/Info.plist" (bundleDir </> "Contents/Info.plist")
                  copyFile "etc/macstuff/wxmac.icns" (bundleDir </> "Contents/Resources/wxmac.icns")
                  -- no idea what this does
                  system ("/Developer/Tools/Rez -t APPL Carbon.r -o " ++ bundleDir </> "Contents/MacOS/geni")
                  writeFile (bundleDir </> "PkgInfo") "APPL????"
                  -- tell Finder about the icon
                  system ("/Developer/Tools/SetFile -a C " ++ bundleDir </> "Contents")
                  return ()
          else putStrLn "Developer Tools not found.  Too bad; no fancy icons for you."
  ""     -> return ()

-- | Put here the list of executables which contain a GUI.  If they all
--   contain a GUI (or you don't really care that much), just put Nothing
mRestrictTo :: Maybe [String]
mRestrictTo = Just ["geni"]
-- ------------- END FANCY Setup.hs ADDENDUM ---------------------------