Binaries have package_datadir hardcoded to build directory, not path in Paths_hlint.hs

[essandess]

I’m trying to port IHaskell to MacPorts. IHaskell uses hlint. The issue is that both stack and cabal builds create binaries with an hlint_datadir that points to the build directory in .stack or .cabal-sandbox, not the install directory with prefix, say, /opt/local/share/hlint. After the build, these temporary build directories are discarded, and neither ihaskell nor hlint binaries work.

This issue has been opened at ndmitchell/hlint#699 and IHaskell/IHaskell#1061, and we all agree that it's an upstream issue with cabal.

Before I get to the issue, please let me recap the background:

• The cabal build of hlint hardcodes the build path into the binaries because of well-known issue with the way cabal handles data-files.
• This behavior breaks package managers like MacPorts and Brew because they cannot destroot properly.
• Brew has hacked around this by reluctantly modifying prefix. See idris: install using haskell-stack Homebrew/homebrew-core#1630 (comment).
• I hacked around this by adding a temporary symbolic link to prefix (ihaskell binary from stack install not independent of .stack root, not destroot'd IHaskell/IHaskell#1061 (comment)), and have been discussing this approach with the MacPorts maintainers for packages like this one that have the data-files issue. There's also been reasonable reluctance and push-back against this practice, which is one reason we haven't merged ihaskell yet.
• To address these reasonable concerns, I found hlint author's @ndmitchell's Paths_packagename.hs solution to the issue of hardcoded cabal data-files in the binary, for which no ugly DESTDIR hack is necessary. All that's required is to specify the path within a file called Paths_packagename.hs, which is normally automatically generated by cabal with its own paths. See stack datadir option writes to datadir during build, breaking DESTDIR, unlike cabal commercialhaskell/stack#5026
• Side note: pandoc's author addressed this issue by using file-embed. See: Add stack build --prefix option commercialhaskell/stack#848 (comment)

Now that we have a working fix to stack and cabal's data-files issues, I'd like to use it for the MacPorts port. I haven't gotten this working with ihaskell's more complicated build, including its dependencies like hlint.

Would you please help figure out an hlint (within ihaskell) build recipe that produces a relocatable, properly prefix-ed binary?

The src/Paths_*.hs approach works for the ihaskell binary, but not for hlint_datadir in either the ihaskell or hlint binaries. I’ve tried many things:

• Put a copy of Paths_hlint.hs both in src and src/IHaskell, without success.
• Tried setting Cabal’s global datadir setting in a variety ways.
• Adding the ghc option -ipathtoPaths_hlint, several different ways.
• Played around with --enable-relocatable, which I believe tickles that reloc guard in https://github.com/haskell/cabal/blob/master/Cabal/Distribution/Simple/Build/PathsModule.hs.

Nothing is working. ghc always finds the Paths_hlint.hs that Cabal generates, not the one I provided.

Would you all please indicate a Cabal build recipe that reads my version of Paths_hlint.hs—not Cabal's autogen version—so that we can get a properly DESTDIR-ed and PREFIXED-ed binary for a packaged install?

Cabal-based build recipe:

cabal update
cabal install cpphs happy
cabal sandbox init
cabal sandbox add-source . ./ghc-parser ./ipython-kernel
cabal install --only-dependencies
cabal configure --extra-lib-dir=/usr/lib
cabal install --extra-lib-dir=/usr/lib

Alternate stack-based build recipe:

rm -fr ~/.stack ./.stack-work stack.yaml.lock
stack setup
stack build

Here's aPaths_hlint.hs that should work. A successful build recipe will just stick this in a place where it will be found by ghc before the Cabal’s autogen Paths_*.hs file.

{- Cabal data-files hardcoded path in binary fix.

This file replaces the `Paths_hlint.hs` automatically created by Cabal.

See:
* https://github.com/commercialhaskell/stack/issues/848
* https://github.com/commercialhaskell/stack/issues/4857
* https://github.com/haskell/cabal/issues/462
* https://github.com/haskell/cabal/issues/3586

-}
        
{-# LANGUAGE CPP #-}
{-# LANGUAGE NoRebindableSyntax #-}
{-# OPTIONS_GHC -fno-warn-missing-import-lists #-}
module Paths_hlint (
    version,
    getBinDir, getLibDir, getDynLibDir, getDataDir, getLibexecDir,
    getDataFileName, getSysconfDir
  ) where

import qualified Control.Exception as Exception
import Data.Version (Version(..))
import System.Environment (getEnv)
import Prelude

#if defined(VERSION_base)

#if MIN_VERSION_base(4,0,0)
catchIO :: IO a -> (Exception.IOException -> IO a) -> IO a
#else
catchIO :: IO a -> (Exception.Exception -> IO a) -> IO a
#endif

#else
catchIO :: IO a -> (Exception.IOException -> IO a) -> IO a
#endif
catchIO = Exception.catch

version :: Version
version = Version [2,0,1] []
bindir, libdir, dynlibdir, datadir, libexecdir, sysconfdir :: FilePath

bindir     = "/opt/local/bin"
libdir     = "/opt/local/lib/ihaskell"
dynlibdir  = "/opt/local/lib/ihaskell"
datadir    = "/opt/local/share/ihaskell"
libexecdir = "/opt/local/lib/ihaskell"
sysconfdir = "/opt/local/etc"

getBinDir, getLibDir, getDynLibDir, getDataDir, getLibexecDir, getSysconfDir :: IO FilePath
getBinDir = catchIO (getEnv "hlint_bindir") (\_ -> return bindir)
getLibDir = catchIO (getEnv "hlint_libdir") (\_ -> return libdir)
getDynLibDir = catchIO (getEnv "hlint_dynlibdir") (\_ -> return dynlibdir)
getDataDir = catchIO (getEnv "hlint_datadir") (\_ -> return datadir)
getLibexecDir = catchIO (getEnv "hlint_libexecdir") (\_ -> return libexecdir)
getSysconfDir = catchIO (getEnv "hlint_sysconfdir") (\_ -> return sysconfdir)

getDataFileName :: FilePath -> IO FilePath
getDataFileName name = do
  dir <- getDataDir
  return (dir ++ "/" ++ name)