Re: [Haskell-cafe] Install a script with Cabal?

5 Jun 2012


      On Tue, Jun 5, 2012 at 4:28 AM, Ketil Malde  wrote:
...
Rogan Creswick  writes:
...
...
I have a small project that installs a couple of Haskell tools and a
script that uses these. Cabal will of course build and install the
Haskell programs, but how can I get Cabal to install the script as
well? There's a host of UserHooks available¹, but it'd probably be
better to have an example than to try to experiment with the right
configuration.
...
I don't have an example handy, but I think you'll want preInts,
instHook, or postInst.  I'd probably go with postInst unless you need
data provided by instHook's type that isn't passed to preInst or
postInst.
I found an example¹ using copyHook. However, this seems to be the wrong
thing, at least I am unable to get cabal to ever call this hook (or
preCopy, etc).
I'm not sure if/when copy hooks are used during the typical cabal
configure/build/install process; I suspect they are not used.  There
is, however, a `cabal copy` command, which I believe does.  Not that
that helps you right now, but that may explain the behavior you saw.
...
...
LocalBuildInfo /probably/ has the details you need (eg: installDirTemplates).
This was harder than I thought.

Here's an example (I hacked an example on to the cabal-dev Setup.hs,
so there are extra imports you won't necessarily need -- full Setup.hs
is in the linked gist, the email only contains the relevant exceprts):

Gist:  https://gist.github.com/2876277

main = defaultMainWithHooks $
       simpleUserHooks { hookedPrograms = [cabalInstallProgram]
                       , postInst = postInstCp (postInst simpleUserHooks)
                       }

type PostInstHook = Args -> InstallFlags -> PackageDescription ->
LocalBuildInfo -> IO ()

postInstCp :: PostInstHook -> Args -> InstallFlags ->
PackageDescription -> LocalBuildInfo -> IO ()
postInstCp oldHook args iflags pDesc lbi = do
  let -- The filename to copy from:
      inFile :: FilePath
      inFile = "srcFileName.sh"

      -- The filename to copy to:
      outFile :: FilePath
      outFile = "destFileName.sh"

      prefix = fromFlag $ installDistPref iflags

      -- Make a concrete binDir from the LocalBuildInfo & PackageDescription:
      instBinDir :: FilePath
      instBinDir = bindir $ absoluteInstallDirs pDesc lbi
                                           (fromFlag $ copyDest
defaultCopyFlags)

      -- layer of indirection, in case we wanted to get a specific
      -- src directory from the cabal file:
      src :: FilePath
      src = inFile

      -- qualify the destination.
      dest :: FilePath
      dest = instBinDir  outFile

  -- Do the copy, creating outFile in the bin dir:
  copyFile src dest

  -- now invoke the old hook:
  oldHook args iflags pDesc lbi


--Rogan
...
I just printed out the contents of LocalBuildInfo, but that's 33 pages
(I counted) of output.  Redirected to a file, it makes it easier to
search to find the relevant needles in this haystack.
Okay, looking at installDirTemplates, I see `bindir` can extract this
data member.  It's of course an InstallDirTemplate, not a FilePath, but
I found 'fromPathTemplate', which has the right type.  Except it only
dumps the template, with $prefix and all.
Hoogle doesn't seem to know about any of the Cabal stuff, Hayoo has a *very*
annoying behavior where it cleans out everything you did if you use the
"back" button, and the "source" links it advertises seem to point into
the wide blue 404.  But using the latter, I managed to find a link to
'substPathTemplate', worked out that the PackageIdentifier it needs is a
member of PackageDescription, and tried to use that.  Except it gives
the same result, and doesn't appear to substitute anything.  I guess the
fact that it is undocumented is a hint that it's the wrong thing to use.
Reading some more, maybe 'absoluteInstallDirs' is what I'm looking for?
In addition to the usual heap of huge config structs, it needs a
"CopyDest", though.  Since I have no idea what to use, I just put
NoCopyDest there.  Does that make sense?  Okay, it works now, in the
sense that I ran it once on my laptop, and it copied the file to
~/.cabal/bin.  Here is the code, comments welcome:
 #!/usr/bin/env runhaskell
 import Distribution.Simple (defaultMainWithHooks, simpleUserHooks,UserHooks(..))
 import Distribution.Simple.Setup (InstallFlags,CopyDest(..))
 import Distribution.Simple.Utils (rawSystemExit)
 import Distribution.PackageDescription (PackageDescription())
 import Distribution.Simple.LocalBuildInfo (LocalBuildInfo(..), InstallDirs(..), absoluteInstallDirs)
 import Distribution.Verbosity (normal)
 main :: IO ()
 main = defaultMainWithHooks simpleUserHooks
     { instHook = \pd lbi uh ifs -> myinst pd lbi uh ifs >> instHook simpleUserHooks pd lbi uh ifs }
 myinst :: PackageDescription -> LocalBuildInfo -> UserHooks -> InstallFlags -> IO ()
 myinst pd lbi _uh _fs = do
     let bin = bindir $ absoluteInstallDirs pd lbi NoCopyDest
     rawSystemExit normal "cp" ["asmeval", bin]
PS: This was a rather frustrating excercise, and after wallowing through
a wilderness of modules, types, records and functions, I can't help but
feel that Cabal is a bit overengineered. Surely including a script or
similar in a package isn't all that outlandish? Could there conceivably
have been a simpler way?  Or at least, better documented?  I suspect the
fact that - with the sole exception of the link below -- I could find *no*
examples to help me out indicates that it is a bit too complicated.
-k
¹ http://blog.ezyang.com/2010/06/setting-up-cabal-the-ffi-and-c2hs/
--
If I haven't seen further, it is by standing in the footprints of giants