    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Simple.GHC
    -- Copyright   :  Isaac Jones 2003-2007
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- This is a fairly large module. It contains most of the GHC-specific code for
    -- configuring, building and installing packages. It also exports a function
    -- for finding out what packages are already installed. Configuring involves
    -- finding the @ghc@ and @ghc-pkg@ programs, finding what language extensions
    -- this version of ghc supports and returning a 'Compiler' value.
    --
    -- 'getInstalledPackages' involves calling the @ghc-pkg@ program to find out
    -- what packages are installed.
    --
    -- Building is somewhat complex as there is quite a bit of information to take
    -- into account. We have to build libs and programs, possibly for profiling and
    -- shared libs. We have to support building libraries that will be usable by
    -- GHCi and also ghc's @-split-objs@ feature. We have to compile any C files
    -- using ghc. Linking, especially for @split-objs@ is remarkably complex,
    -- partly because there tend to be 1,000's of @.o@ files and this can often be
    -- more than we can pass to the @ld@ or @ar@ programs in one go.
    --
    -- Installing for libs and exes involves finding the right files and copying
    -- them to the right places. One of the more tricky things about this module is
    -- remembering the layout of files in the build directory (which is not
    -- explicitly documented) and thus what search dirs are used for various kinds
    -- of files.

    {- Copyright (c) 2003-2005, Isaac Jones
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modiication, are permitted provided that the following conditions are
    met:

        * Redistributions of source code must retain the above copyright
          notice, this list of conditions and the following disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials provided
          with the distribution.

        * Neither the name of Isaac Jones nor the names of other
          contributors may be used to endorse or promote products derived
          from this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
    A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. -}

    module Distribution.Simple.GHC (
            configure, getInstalledPackages,
            buildLib, buildExe,
            installLib, installExe,
            libAbiHash,
            registerPackage,
            ghcOptions,
            ghcVerbosityOptions,
            ghcPackageDbOptions,
            ghcLibDir,
     ) where

    import qualified Distribution.Simple.GHC.IPI641 as IPI641
    import qualified Distribution.Simple.GHC.IPI642 as IPI642
    import Distribution.PackageDescription as PD
             ( PackageDescription(..), BuildInfo(..), Executable(..)
             , Library(..), libModules, hcOptions, usedExtensions, allExtensions )
    import Distribution.InstalledPackageInfo
             ( InstalledPackageInfo )
    import qualified Distribution.InstalledPackageInfo as InstalledPackageInfo
                                    ( InstalledPackageInfo_(..) )
    import Distribution.Simple.PackageIndex (PackageIndex)
    import qualified Distribution.Simple.PackageIndex as PackageIndex
    import Distribution.Simple.LocalBuildInfo
             ( LocalBuildInfo(..), ComponentLocalBuildInfo(..)
             , absoluteInstallDirs )
    import Distribution.Simple.InstallDirs hiding ( absoluteInstallDirs )
    import Distribution.Simple.BuildPaths
    import Distribution.Simple.Utils
    import Distribution.Package
             ( PackageIdentifier, Package(..), PackageName(..) )
    import qualified Distribution.ModuleName as ModuleName
    import Distribution.Simple.Program
             ( Program(..), ConfiguredProgram(..), ProgramConfiguration, ProgArg
             , ProgramLocation(..), rawSystemProgram, rawSystemProgramConf
             , rawSystemProgramStdout, rawSystemProgramStdoutConf
             , requireProgramVersion, requireProgram, getProgramOutput
             , userMaybeSpecifyPath, programPath, lookupProgram, addKnownProgram
             , ghcProgram, ghcPkgProgram, hsc2hsProgram
             , arProgram, ranlibProgram, ldProgram
             , gccProgram, stripProgram )
    import qualified Distribution.Simple.Program.HcPkg as HcPkg
    import qualified Distribution.Simple.Program.Ar    as Ar
    import qualified Distribution.Simple.Program.Ld    as Ld
    import Distribution.Simple.Compiler
             ( CompilerFlavor(..), CompilerId(..), Compiler(..), compilerVersion
             , OptimisationLevel(..), PackageDB(..), PackageDBStack
             , Flag, languageToFlags, extensionsToFlags )
    import Distribution.Version
             ( Version(..), anyVersion, orLaterVersion )
    import Distribution.System
             ( OS(..), buildOS )
    import Distribution.Verbosity
    import Distribution.Text
             ( display, simpleParse )
    import Language.Haskell.Extension (Language(..), Extension(..))

    import Control.Monad            ( unless, when, liftM )
    import Data.Char                ( isSpace )
    import Data.List
    import Data.Maybe               ( catMaybes )
    import Data.Monoid              ( Monoid(..) )
    import System.Directory
             ( removeFile, getDirectoryContents, doesFileExist
             , getTemporaryDirectory )
    import System.FilePath          ( (</>), (<.>), takeExtension,
                                      takeDirectory, replaceExtension, splitExtension )
    import System.IO (hClose, hPutStrLn)
    import Distribution.Compat.Exception (catchExit, catchIO)

    -- -----------------------------------------------------------------------------
    -- Configuring

    configure :: Verbosity -> Maybe FilePath -> Maybe FilePath
              -> ProgramConfiguration -> IO (Compiler, ProgramConfiguration)
    configure verbosity hcPath hcPkgPath conf0 = do

      (ghcProg, ghcVersion, conf1) <-
        requireProgramVersion verbosity ghcProgram
          (orLaterVersion (Version [6,4] []))
          (userMaybeSpecifyPath "ghc" hcPath conf0)

      -- This is slightly tricky, we have to configure ghc first, then we use the
      -- location of ghc to help find ghc-pkg in the case that the user did not
      -- specify the location of ghc-pkg directly:
      (ghcPkgProg, ghcPkgVersion, conf2) <-
        requireProgramVersion verbosity ghcPkgProgram {
          programFindLocation = guessGhcPkgFromGhcPath ghcProg
        }
        anyVersion (userMaybeSpecifyPath "ghc-pkg" hcPkgPath conf1)

      when (ghcVersion /= ghcPkgVersion) $ die $
           "Version mismatch between ghc and ghc-pkg: "
        ++ programPath ghcProg ++ " is version " ++ display ghcVersion ++ " "
        ++ programPath ghcPkgProg ++ " is version " ++ display ghcPkgVersion

      -- Likewise we try to find the matching hsc2hs program.
      let hsc2hsProgram' = hsc2hsProgram {
                               programFindLocation = guessHsc2hsFromGhcPath ghcProg
                           }
          conf3 = addKnownProgram hsc2hsProgram' conf2

      languages  <- getLanguages verbosity ghcProg
      extensions <- getExtensions verbosity ghcProg

      ghcInfo <- if ghcVersion >= Version [6,7] []
                 then do xs <- getProgramOutput verbosity ghcProg ["--info"]
                         case reads xs of
                             [(i, ss)]
                              | all isSpace ss ->
                                 return i
                             _ ->
                                 die "Can't parse --info output of GHC"
                 else return []

      let comp = Compiler {
            compilerId             = CompilerId GHC ghcVersion,
            compilerLanguages      = languages,
            compilerExtensions     = extensions
          }
          conf4 = configureToolchain ghcProg ghcInfo conf3 -- configure gcc and ld
      return (comp, conf4)

    -- | Given something like /usr/local/bin/ghc-6.6.1(.exe) we try and find
    -- the corresponding tool; e.g. if the tool is ghc-pkg, we try looking
    -- for a versioned or unversioned ghc-pkg in the same dir, that is:
    --
    -- > /usr/local/bin/ghc-pkg-ghc-6.6.1(.exe)
    -- > /usr/local/bin/ghc-pkg-6.6.1(.exe)
    -- > /usr/local/bin/ghc-pkg(.exe)
    --
    guessToolFromGhcPath :: FilePath -> ConfiguredProgram -> Verbosity
                         -> IO (Maybe FilePath)
    guessToolFromGhcPath tool ghcProg verbosity
      = do let path              = programPath ghcProg
               dir               = takeDirectory path
               versionSuffix     = takeVersionSuffix (dropExeExtension path)
               guessNormal       = dir </> tool <.> exeExtension
               guessGhcVersioned = dir </> (tool ++ "-ghc" ++ versionSuffix) <.> exeExtension
               guessVersioned    = dir </> (tool ++ versionSuffix) <.> exeExtension
               guesses | null versionSuffix = [guessNormal]
                       | otherwise          = [guessGhcVersioned,
                                               guessVersioned,
                                               guessNormal]
           info verbosity $ "looking for tool " ++ show tool ++ " near compiler in " ++ dir
           exists <- mapM doesFileExist guesses
           case [ file | (file, True) <- zip guesses exists ] of
             [] -> return Nothing
             (fp:_) -> do info verbosity $ "found " ++ tool ++ " in " ++ fp
                          return (Just fp)

      where takeVersionSuffix :: FilePath -> String
            takeVersionSuffix = reverse . takeWhile (`elem ` "0123456789.-") . reverse

            dropExeExtension :: FilePath -> FilePath
            dropExeExtension filepath =
              case splitExtension filepath of
                (filepath', extension) | extension == exeExtension -> filepath'
                                       | otherwise                 -> filepath

    -- | Given something like /usr/local/bin/ghc-6.6.1(.exe) we try and find a
    -- corresponding ghc-pkg, we try looking for both a versioned and unversioned
    -- ghc-pkg in the same dir, that is:
    --
    -- > /usr/local/bin/ghc-pkg-ghc-6.6.1(.exe)
    -- > /usr/local/bin/ghc-pkg-6.6.1(.exe)
    -- > /usr/local/bin/ghc-pkg(.exe)
    --
    guessGhcPkgFromGhcPath :: ConfiguredProgram -> Verbosity -> IO (Maybe FilePath)
    guessGhcPkgFromGhcPath = guessToolFromGhcPath "ghc-pkg"

    -- | Given something like /usr/local/bin/ghc-6.6.1(.exe) we try and find a
    -- corresponding hsc2hs, we try looking for both a versioned and unversioned
    -- hsc2hs in the same dir, that is:
    --
    -- > /usr/local/bin/hsc2hs-ghc-6.6.1(.exe)
    -- > /usr/local/bin/hsc2hs-6.6.1(.exe)
    -- > /usr/local/bin/hsc2hs(.exe)
    --
    guessHsc2hsFromGhcPath :: ConfiguredProgram -> Verbosity -> IO (Maybe FilePath)
    guessHsc2hsFromGhcPath = guessToolFromGhcPath "hsc2hs"

    -- | Adjust the way we find and configure gcc and ld
    --
    configureToolchain :: ConfiguredProgram -> [(String, String)]
                                            -> ProgramConfiguration
                                            -> ProgramConfiguration
    configureToolchain ghcProg ghcInfo =
        addKnownProgram gccProgram {
          programFindLocation = findProg gccProgram
                                  [ if ghcVersion >= Version [6,12] []
                                      then mingwBinDir </> "gcc.exe"
                                      else baseDir     </> "gcc.exe" ],
          programPostConf     = configureGcc
        }
      . addKnownProgram ldProgram {
          programFindLocation = findProg ldProgram
                                  [ if ghcVersion >= Version [6,12] []
                                      then mingwBinDir </> "ld.exe"
                                      else libDir      </> "ld.exe" ],
          programPostConf     = configureLd
        }
      . addKnownProgram arProgram {
          programFindLocation = findProg arProgram
                                  [ if ghcVersion >= Version [6,12] []
                                      then mingwBinDir </> "ar.exe"
                                      else libDir      </> "ar.exe" ]
        }
      where
        Just ghcVersion = programVersion ghcProg
        compilerDir = takeDirectory (programPath ghcProg)
        baseDir     = takeDirectory compilerDir
        mingwBinDir = baseDir </> "mingw" </> "bin"
        libDir      = baseDir </> "gcc-lib"
        includeDir  = baseDir </> "include" </> "mingw"
        isWindows   = case buildOS of Windows -> True; _ -> False

        -- on Windows finding and configuring ghc's gcc and ld is a bit special
        findProg :: Program -> [FilePath] -> Verbosity -> IO (Maybe FilePath)
        findProg prog locations
          | isWindows = \verbosity -> look locations verbosity
          | otherwise = programFindLocation prog
          where
            look [] verbosity = do
              warn verbosity ("Couldn't find " ++ programName prog ++ " where I expected it. Trying the search path.")
              programFindLocation prog verbosity
            look (f:fs) verbosity = do
              exists <- doesFileExist f
              if exists then return (Just f)
                        else look fs verbosity

        ccFlags        = getFlags "C compiler flags"
        gccLinkerFlags = getFlags "Gcc Linker flags"
        ldLinkerFlags  = getFlags "Ld Linker flags"

        getFlags key = case lookup key ghcInfo of
                       Nothing -> []
                       Just flags ->
                           case reads flags of
                           [(args, "")] -> args
                           _ -> [] -- XXX Should should be an error really

        configureGcc :: Verbosity -> ConfiguredProgram -> IO [ProgArg]
        configureGcc v cp = liftM (++ (ccFlags ++ gccLinkerFlags))
                          $ configureGcc' v cp

        configureGcc' :: Verbosity -> ConfiguredProgram -> IO [ProgArg]
        configureGcc'
          | isWindows = \_ gccProg -> case programLocation gccProg of
              -- if it's found on system then it means we're using the result
              -- of programFindLocation above rather than a user-supplied path
              -- Pre GHC 6.12, that meant we should add these flags to tell
              -- ghc's gcc where it lives and thus where gcc can find its
              -- various files:
              FoundOnSystem {}
               | ghcVersion < Version [6,11] [] ->
                  return ["-B" ++ libDir, "-I" ++ includeDir]
              _ -> return []
          | otherwise = \_ _   -> return []

        configureLd :: Verbosity -> ConfiguredProgram -> IO [ProgArg]
        configureLd v cp = liftM (++ ldLinkerFlags) $ configureLd' v cp

        -- we need to find out if ld supports the -x flag
        configureLd' :: Verbosity -> ConfiguredProgram -> IO [ProgArg]
        configureLd' verbosity ldProg = do
          tempDir <- getTemporaryDirectory
          ldx <- withTempFile tempDir ".c" $ \testcfile testchnd ->
                 withTempFile tempDir ".o" $ \testofile testohnd -> do
                   hPutStrLn testchnd "int foo() {}"
                   hClose testchnd; hClose testohnd
                   rawSystemProgram verbosity ghcProg ["-c", testcfile,
                                                       "-o", testofile]
                   withTempFile tempDir ".o" $ \testofile' testohnd' ->
                     do
                       hClose testohnd'
                       _ <- rawSystemProgramStdout verbosity ldProg
                         ["-x", "-r", testofile, "-o", testofile']
                       return True
                     `catchIO`   (\_ -> return False)
                     `catchExit` (\_ -> return False)
          if ldx
            then return ["-x"]
            else return []

    getLanguages :: Verbosity -> ConfiguredProgram -> IO [(Language, Flag)]
    getLanguages _ ghcProg
      -- TODO: should be using --supported-languages rather than hard coding
      | ghcVersion >= Version [7] [] = return [(Haskell98,   "-XHaskell98")
                                              ,(Haskell2010, "-XHaskell2010")]
      | otherwise                    = return [(Haskell98,   "")]
      where
        Just ghcVersion = programVersion ghcProg

    getExtensions :: Verbosity -> ConfiguredProgram -> IO [(Extension, Flag)]
    getExtensions verbosity ghcProg
      | ghcVersion >= Version [6,7] [] = do

        exts <- rawSystemStdout verbosity (programPath ghcProg)
                  ["--supported-languages"]
        -- GHC has the annoying habit of inverting some of the extensions
        -- so we have to try parsing ("No" ++ ghcExtensionName) first
        let readExtension str = do
              ext <- simpleParse ("No" ++ str)
              case ext of
                UnknownExtension _ -> simpleParse str
                _                  -> return ext
        return $ extensionHacks
              ++ [ (ext, "-X" ++ display ext)
                 | Just ext <- map readExtension (lines exts) ]

      | otherwise = return oldLanguageExtensions

      where
        Just ghcVersion = programVersion ghcProg

        -- ghc-6.8 intorduced RecordPuns however it should have been
        -- NamedFieldPuns. We now encourage packages to use NamedFieldPuns so for
        -- compatability we fake support for it in ghc-6.8 by making it an alias
        -- for the old RecordPuns extension.
        extensionHacks = [ (NamedFieldPuns, "-XRecordPuns")
                         | ghcVersion >= Version [6,8]  []
                        && ghcVersion <  Version [6,10] [] ]

    -- | For GHC 6.6.x and earlier, the mapping from supported extensions to flags
    oldLanguageExtensions :: [(Extension, Flag)]
    oldLanguageExtensions =
        [(OverlappingInstances       , "-fallow-overlapping-instances")
        ,(TypeSynonymInstances       , "-fglasgow-exts")
        ,(TemplateHaskell            , "-fth")
        ,(ForeignFunctionInterface   , "-fffi")
        ,(NoMonomorphismRestriction  , "-fno-monomorphism-restriction")
        ,(NoMonoPatBinds             , "-fno-mono-pat-binds")
        ,(UndecidableInstances       , "-fallow-undecidable-instances")
        ,(IncoherentInstances        , "-fallow-incoherent-instances")
        ,(Arrows                     , "-farrows")
        ,(Generics                   , "-fgenerics")
        ,(NoImplicitPrelude          , "-fno-implicit-prelude")
        ,(ImplicitParams             , "-fimplicit-params")
        ,(CPP                        , "-cpp")
        ,(BangPatterns               , "-fbang-patterns")
        ,(KindSignatures             , fglasgowExts)
        ,(RecursiveDo                , fglasgowExts)
        ,(ParallelListComp           , fglasgowExts)
        ,(MultiParamTypeClasses      , fglasgowExts)
        ,(FunctionalDependencies     , fglasgowExts)
        ,(Rank2Types                 , fglasgowExts)
        ,(RankNTypes                 , fglasgowExts)
        ,(PolymorphicComponents      , fglasgowExts)
        ,(ExistentialQuantification  , fglasgowExts)
        ,(ScopedTypeVariables        , "-fscoped-type-variables")
        ,(FlexibleContexts           , fglasgowExts)
        ,(FlexibleInstances          , fglasgowExts)
        ,(EmptyDataDecls             , fglasgowExts)
        ,(PatternGuards              , fglasgowExts)
        ,(GeneralizedNewtypeDeriving , fglasgowExts)
        ,(MagicHash                  , fglasgowExts)
        ,(UnicodeSyntax              , fglasgowExts)
        ,(PatternSignatures          , fglasgowExts)
        ,(UnliftedFFITypes           , fglasgowExts)
        ,(LiberalTypeSynonyms        , fglasgowExts)
        ,(TypeOperators              , fglasgowExts)
        ,(GADTs                      , fglasgowExts)
        ,(RelaxedPolyRec             , fglasgowExts)
        ,(ExtendedDefaultRules       , "-fextended-default-rules")
        ,(UnboxedTuples              , fglasgowExts)
        ,(DeriveDataTypeable         , fglasgowExts)
        ,(ConstrainedClassMethods    , fglasgowExts)
        ]
        where
          fglasgowExts = "-fglasgow-exts"

    getInstalledPackages :: Verbosity -> PackageDBStack -> ProgramConfiguration
                         -> IO PackageIndex
    getInstalledPackages verbosity packagedbs conf = do
      checkPackageDbStack packagedbs
      pkgss <- getInstalledPackages' verbosity packagedbs conf
      topDir <- ghcLibDir' verbosity ghcProg
      let indexes = [ PackageIndex.fromList (map (substTopDir topDir) pkgs)
                    | (_, pkgs) <- pkgss ]
      return $! hackRtsPackage (mconcat indexes)

      where
        -- On Windows, various fields have $topdir/foo rather than full
        -- paths. We need to substitute the right value in so that when
        -- we, for example, call gcc, we have proper paths to give it
        Just ghcProg = lookupProgram ghcProgram conf

        hackRtsPackage index =
          case PackageIndex.lookupPackageName index (PackageName "rts") of
            [(_,[rts])]
               -> PackageIndex.insert (removeMingwIncludeDir rts) index
            _  -> index -- No (or multiple) ghc rts package is registered!!
                        -- Feh, whatever, the ghc testsuite does some crazy stuff.

    ghcLibDir :: Verbosity -> LocalBuildInfo -> IO FilePath
    ghcLibDir verbosity lbi =
        (reverse . dropWhile isSpace . reverse) `fmap`
         rawSystemProgramStdoutConf verbosity ghcProgram (withPrograms lbi) ["--print-libdir"]

    ghcLibDir' :: Verbosity -> ConfiguredProgram -> IO FilePath
    ghcLibDir' verbosity ghcProg =
        (reverse . dropWhile isSpace . reverse) `fmap`
         rawSystemProgramStdout verbosity ghcProg ["--print-libdir"]

    checkPackageDbStack :: PackageDBStack -> IO ()
    checkPackageDbStack (GlobalPackageDB:rest)
      | GlobalPackageDB `notElem` rest = return ()
    checkPackageDbStack _ =
      die $ "GHC.getInstalledPackages: the global package db must be "
         ++ "specified first and cannot be specified multiple times"

    -- GHC < 6.10 put "$topdir/include/mingw" in rts's installDirs. This
    -- breaks when you want to use a different gcc, so we need to filter
    -- it out.
    removeMingwIncludeDir :: InstalledPackageInfo -> InstalledPackageInfo
    removeMingwIncludeDir pkg =
        let ids = InstalledPackageInfo.includeDirs pkg
            ids' = filter (not . ("mingw" `isSuffixOf`)) ids
        in pkg { InstalledPackageInfo.includeDirs = ids' }

    -- | Get the packages from specific PackageDBs, not cumulative.
    --
    getInstalledPackages' :: Verbosity -> [PackageDB] -> ProgramConfiguration
                         -> IO [(PackageDB, [InstalledPackageInfo])]
    getInstalledPackages' verbosity packagedbs conf
      | ghcVersion >= Version [6,9] [] =
      sequence
        [ do pkgs <- HcPkg.dump verbosity ghcPkgProg packagedb
             return (packagedb, pkgs)
        | packagedb <- packagedbs ]

      where
        Just ghcPkgProg = lookupProgram ghcPkgProgram conf
        Just ghcProg    = lookupProgram ghcProgram conf
        Just ghcVersion = programVersion ghcProg

    getInstalledPackages' verbosity packagedbs conf = do
        str <- rawSystemProgramStdoutConf verbosity ghcPkgProgram conf ["list"]
        let pkgFiles = [ init line | line <- lines str, last line == ':' ]
            dbFile packagedb = case (packagedb, pkgFiles) of
              (GlobalPackageDB, global:_)      -> return $ Just global
              (UserPackageDB,  _global:user:_) -> return $ Just user
              (UserPackageDB,  _global:_)      -> return $ Nothing
              (SpecificPackageDB specific, _)  -> return $ Just specific
              _ -> die "cannot read ghc-pkg package listing"
        pkgFiles' <- mapM dbFile packagedbs
        sequence [ withFileContents file $ \content -> do
                      pkgs <- readPackages file content
                      return (db, pkgs)
                 | (db , Just file) <- zip packagedbs pkgFiles' ]
      where
        -- Depending on the version of ghc we use a different type's Read
        -- instance to parse the package file and then convert.
        -- It's a bit yuck. But that's what we get for using Read/Show.
        readPackages
          | ghcVersion >= Version [6,4,2] []
          = \file content -> case reads content of
              [(pkgs, _)] -> return (map IPI642.toCurrent pkgs)
              _           -> failToRead file
          | otherwise
          = \file content -> case reads content of
              [(pkgs, _)] -> return (map IPI641.toCurrent pkgs)
              _           -> failToRead file
        Just ghcProg = lookupProgram ghcProgram conf
        Just ghcVersion = programVersion ghcProg
        failToRead file = die $ "cannot read ghc package database " ++ file

    substTopDir :: FilePath -> InstalledPackageInfo -> InstalledPackageInfo
    substTopDir topDir ipo
     = ipo {
           InstalledPackageInfo.importDirs
               = map f (InstalledPackageInfo.importDirs ipo),
           InstalledPackageInfo.libraryDirs
               = map f (InstalledPackageInfo.libraryDirs ipo),
           InstalledPackageInfo.includeDirs
               = map f (InstalledPackageInfo.includeDirs ipo),
           InstalledPackageInfo.frameworkDirs
               = map f (InstalledPackageInfo.frameworkDirs ipo),
           InstalledPackageInfo.haddockInterfaces
               = map f (InstalledPackageInfo.haddockInterfaces ipo),
           InstalledPackageInfo.haddockHTMLs
               = map f (InstalledPackageInfo.haddockHTMLs ipo)
       }
        where f ('$':'t':'o':'p':'d':'i':'r':rest) = topDir ++ rest
              f x = x

    -- -----------------------------------------------------------------------------
    -- Building

    -- | Build a library with GHC.
    --
    buildLib :: Verbosity -> PackageDescription -> LocalBuildInfo
                          -> Library            -> ComponentLocalBuildInfo -> IO ()
    buildLib verbosity pkg_descr lbi lib clbi = do
      let pref = buildDir lbi
          pkgid = packageId pkg_descr
          runGhcProg = rawSystemProgramConf verbosity ghcProgram (withPrograms lbi)
          ifVanillaLib forceVanilla = when (forceVanilla || withVanillaLib lbi)
          ifProfLib = when (withProfLib lbi)
          ifSharedLib = when (withSharedLib lbi)
          ifGHCiLib = when (withGHCiLib lbi && withVanillaLib lbi)
          comp = compiler lbi

      libBi <- hackThreadedFlag verbosity
                 comp (withProfLib lbi) (libBuildInfo lib)

      let libTargetDir = pref
          forceVanillaLib = TemplateHaskell `elem` allExtensions libBi
          -- TH always needs vanilla libs, even when building for profiling

      createDirectoryIfMissingVerbose verbosity True libTargetDir
      -- TODO: do we need to put hs-boot files into place for mutually recurive modules?
      let ghcArgs =
                 "--make"
              :  ["-package-name", display pkgid ]
              ++ constructGHCCmdLine lbi libBi clbi libTargetDir verbosity
              ++ map display (libModules lib)
          ghcArgsProf = ghcArgs
              ++ ["-prof",
                  "-hisuf", "p_hi",
                  "-osuf", "p_o"
                 ]
              ++ ghcProfOptions libBi
          ghcArgsShared = ghcArgs
              ++ ["-dynamic",
                  "-hisuf", "dyn_hi",
                  "-osuf", "dyn_o", "-fPIC"
                 ]
              ++ ghcSharedOptions libBi
      unless (null (libModules lib)) $
        do ifVanillaLib forceVanillaLib (runGhcProg ghcArgs)
           ifProfLib (runGhcProg ghcArgsProf)
           ifSharedLib (runGhcProg ghcArgsShared)

      -- build any C sources
      unless (null (cSources libBi)) $ do
         info verbosity "Building C Sources..."
         sequence_ [do let (odir,args) = constructCcCmdLine lbi libBi clbi pref
                                                            filename verbosity
                                                            (withProfLib lbi)
                       createDirectoryIfMissingVerbose verbosity True odir
                       runGhcProg args
                       ifSharedLib (runGhcProg (args ++ ["-fPIC", "-osuf dyn_o"]))
                   | filename <- cSources libBi]

      -- link:
      info verbosity "Linking..."
      let cObjs = map (`replaceExtension` objExtension) (cSources libBi)
          cSharedObjs = map (`replaceExtension` ("dyn_" ++ objExtension)) (cSources libBi)
          vanillaLibFilePath = libTargetDir </> mkLibName pkgid
          profileLibFilePath = libTargetDir </> mkProfLibName pkgid
          sharedLibFilePath  = libTargetDir </> mkSharedLibName pkgid
                                                  (compilerId (compiler lbi))
          ghciLibFilePath    = libTargetDir </> mkGHCiLibName pkgid
          libInstallPath = libdir $ absoluteInstallDirs pkg_descr lbi NoCopyDest
          sharedLibInstallPath = libInstallPath </> mkSharedLibName pkgid
                                                  (compilerId (compiler lbi))

      stubObjs <- fmap catMaybes $ sequence
        [ findFileWithExtension [objExtension] [libTargetDir]
            (ModuleName.toFilePath x ++"_stub")
        | x <- libModules lib ]
      stubProfObjs <- fmap catMaybes $ sequence
        [ findFileWithExtension ["p_" ++ objExtension] [libTargetDir]
            (ModuleName.toFilePath x ++"_stub")
        | x <- libModules lib ]
      stubSharedObjs <- fmap catMaybes $ sequence
        [ findFileWithExtension ["dyn_" ++ objExtension] [libTargetDir]
            (ModuleName.toFilePath x ++"_stub")
        | x <- libModules lib ]

      hObjs     <- getHaskellObjects lib lbi
                        pref objExtension True
      hProfObjs <-
        if (withProfLib lbi)
                then getHaskellObjects lib lbi
                        pref ("p_" ++ objExtension) True
                else return []
      hSharedObjs <-
        if (withSharedLib lbi)
                then getHaskellObjects lib lbi
                        pref ("dyn_" ++ objExtension) False
                else return []

      unless (null hObjs && null cObjs && null stubObjs) $ do
        -- first remove library files if they exists
        sequence_
          [ removeFile libFilePath `catchIO` \_ -> return ()
          | libFilePath <- [vanillaLibFilePath, profileLibFilePath
                           ,sharedLibFilePath,  ghciLibFilePath] ]

        let staticObjectFiles =
                   hObjs
                ++ map (pref </>) cObjs
                ++ stubObjs
            profObjectFiles =
                   hProfObjs
                ++ map (pref </>) cObjs
                ++ stubProfObjs
            ghciObjFiles =
                   hObjs
                ++ map (pref </>) cObjs
                ++ stubObjs
            dynamicObjectFiles =
                   hSharedObjs
                ++ map (pref </>) cSharedObjs
                ++ stubSharedObjs
            -- After the relocation lib is created we invoke ghc -shared
            -- with the dependencies spelled out as -package arguments
            -- and ghc invokes the linker with the proper library paths
            ghcSharedLinkArgs =
                [ "-no-auto-link-packages",
                  "-shared",
                  "-dynamic",
                  "-o", sharedLibFilePath ]
                -- For dynamic libs, Mac OS/X needs to know the install location
                -- at build time.
                ++ (if buildOS == OSX
                    then ["-dylib-install-name", sharedLibInstallPath]
                    else [])
                ++ dynamicObjectFiles
                ++ ["-package-name", display pkgid ]
                ++ ghcPackageFlags lbi clbi
                ++ ["-l"++extraLib | extraLib <- extraLibs libBi]
                ++ ["-L"++extraLibDir | extraLibDir <- extraLibDirs libBi]

        ifVanillaLib False $ do
          (arProg, _) <- requireProgram verbosity arProgram (withPrograms lbi)
          Ar.createArLibArchive verbosity arProg
            vanillaLibFilePath staticObjectFiles

        ifProfLib $ do
          (arProg, _) <- requireProgram verbosity arProgram (withPrograms lbi)
          Ar.createArLibArchive verbosity arProg
            profileLibFilePath profObjectFiles

        ifGHCiLib $ do
          (ldProg, _) <- requireProgram verbosity ldProgram (withPrograms lbi)
          Ld.combineObjectFiles verbosity ldProg
            ghciLibFilePath ghciObjFiles

        ifSharedLib $
          runGhcProg ghcSharedLinkArgs

    -- | Build an executable with GHC.
    --
    buildExe :: Verbosity -> PackageDescription -> LocalBuildInfo
                          -> Executable         -> ComponentLocalBuildInfo -> IO ()
    buildExe verbosity _pkg_descr lbi
      exe@Executable { exeName = exeName', modulePath = modPath } clbi = do
      let pref = buildDir lbi
          runGhcProg = rawSystemProgramConf verbosity ghcProgram (withPrograms lbi)

      exeBi <- hackThreadedFlag verbosity
                 (compiler lbi) (withProfExe lbi) (buildInfo exe)

      -- exeNameReal, the name that GHC really uses (with .exe on Windows)
      let exeNameReal = exeName' <.>
                        (if null $ takeExtension exeName' then exeExtension else "")

      let targetDir = pref </> exeName'
      let exeDir    = targetDir </> (exeName' ++ "-tmp")
      createDirectoryIfMissingVerbose verbosity True targetDir
      createDirectoryIfMissingVerbose verbosity True exeDir
      -- TODO: do we need to put hs-boot files into place for mutually recursive modules?
      -- FIX: what about exeName.hi-boot?

      -- build executables
      unless (null (cSources exeBi)) $ do
       info verbosity "Building C Sources."
       sequence_ [do let (odir,args) = constructCcCmdLine lbi exeBi clbi
                                              exeDir filename verbosity
                                              (withProfExe lbi)
                     createDirectoryIfMissingVerbose verbosity True odir
                     runGhcProg args
                 | filename <- cSources exeBi]

      srcMainFile <- findFile (exeDir : hsSourceDirs exeBi) modPath

      let cObjs = map (`replaceExtension` objExtension) (cSources exeBi)
      let binArgs linkExe profExe =
                 "--make"
              :  (if linkExe
                     then ["-o", targetDir </> exeNameReal]
                     else ["-c"])
              ++ constructGHCCmdLine lbi exeBi clbi exeDir verbosity
              ++ [exeDir </> x | x <- cObjs]
              ++ [srcMainFile]
              ++ ["-optl" ++ opt | opt <- PD.ldOptions exeBi]
              ++ ["-l"++lib | lib <- extraLibs exeBi]
              ++ ["-L"++libDir | libDir <- extraLibDirs exeBi]
              ++ concat [["-framework", f] | f <- PD.frameworks exeBi]
              ++ if profExe
                    then ["-prof",
                          "-hisuf", "p_hi",
                          "-osuf", "p_o"
                         ] ++ ghcProfOptions exeBi
                    else []

      -- For building exe's for profiling that use TH we actually
      -- have to build twice, once without profiling and the again
      -- with profiling. This is because the code that TH needs to
      -- run at compile time needs to be the vanilla ABI so it can
      -- be loaded up and run by the compiler.
      when (withProfExe lbi && TemplateHaskell `elem` allExtensions exeBi)
         (runGhcProg (binArgs False False))

      runGhcProg (binArgs True (withProfExe lbi))

    -- | Filter the "-threaded" flag when profiling as it does not
    --   work with ghc-6.8 and older.
    hackThreadedFlag :: Verbosity -> Compiler -> Bool -> BuildInfo -> IO BuildInfo
    hackThreadedFlag verbosity comp prof bi
      | not mustFilterThreaded = return bi
      | otherwise              = do
        warn verbosity $ "The ghc flag '-threaded' is not compatible with "
                      ++ "profiling in ghc-6.8 and older. It will be disabled."
        return bi { options = filterHcOptions (/= "-threaded") (options bi) }
      where
        mustFilterThreaded = prof && compilerVersion comp < Version [6, 10] []
                          && "-threaded" `elem` hcOptions GHC bi
        filterHcOptions p hcoptss =
          [ (hc, if hc == GHC then filter p opts else opts)
          | (hc, opts) <- hcoptss ]

    -- when using -split-objs, we need to search for object files in the
    -- Module_split directory for each module.
    getHaskellObjects :: Library -> LocalBuildInfo
                      -> FilePath -> String -> Bool -> IO [FilePath]
    getHaskellObjects lib lbi pref wanted_obj_ext allow_split_objs
      | splitObjs lbi && allow_split_objs = do
            let splitSuffix = if compilerVersion (compiler lbi) <
                                 Version [6, 11] []
                              then "_split"
                              else "_" ++ wanted_obj_ext ++ "_split"
                dirs = [ pref </> (ModuleName.toFilePath x ++ splitSuffix)
                       | x <- libModules lib ]
            objss <- mapM getDirectoryContents dirs
            let objs = [ dir </> obj
                       | (objs',dir) <- zip objss dirs, obj <- objs',
                         let obj_ext = takeExtension obj,
                         '.':wanted_obj_ext == obj_ext ]
            return objs
      | otherwise  =
            return [ pref </> ModuleName.toFilePath x <.> wanted_obj_ext
                   | x <- libModules lib ]

    -- | Extracts a String representing a hash of the ABI of a built
    -- library.  It can fail if the library has not yet been built.
    --
    libAbiHash :: Verbosity -> PackageDescription -> LocalBuildInfo
               -> Library -> ComponentLocalBuildInfo -> IO String
    libAbiHash verbosity pkg_descr lbi lib clbi = do
      libBi <- hackThreadedFlag verbosity
                 (compiler lbi) (withProfLib lbi) (libBuildInfo lib)
      let
          ghcArgs =
                 "--abi-hash"
              :  ["-package-name", display (packageId pkg_descr) ]
              ++ constructGHCCmdLine lbi libBi clbi (buildDir lbi) verbosity
              ++ map display (exposedModules lib)
      --
      rawSystemProgramStdoutConf verbosity ghcProgram (withPrograms lbi) ghcArgs

    constructGHCCmdLine
            :: LocalBuildInfo
            -> BuildInfo
            -> ComponentLocalBuildInfo
            -> FilePath
            -> Verbosity
            -> [String]
    constructGHCCmdLine lbi bi clbi odir verbosity =
            ghcVerbosityOptions verbosity
            -- Unsupported extensions have already been checked by configure
         ++ ghcOptions lbi bi clbi odir

    ghcVerbosityOptions :: Verbosity -> [String]
    ghcVerbosityOptions verbosity
         | verbosity >= deafening = ["-v"]
         | verbosity >= normal    = []
         | otherwise              = ["-w", "-v0"]

    ghcOptions :: LocalBuildInfo -> BuildInfo -> ComponentLocalBuildInfo
               -> FilePath -> [String]
    ghcOptions lbi bi clbi odir
         =  ["-hide-all-packages"]
         ++ ["-fbuilding-cabal-package" | ghcVer >= Version [6,11] [] ]
         ++ ghcPackageDbOptions (withPackageDB lbi)
         ++ ["-split-objs" | splitObjs lbi ]
         ++ ["-i"]
         ++ ["-i" ++ odir]
         ++ ["-i" ++ l | l <- nub (hsSourceDirs bi)]
         ++ ["-i" ++ autogenModulesDir lbi]
         ++ ["-I" ++ autogenModulesDir lbi]
         ++ ["-I" ++ odir]
         ++ ["-I" ++ dir | dir <- PD.includeDirs bi]
         ++ ["-optP" ++ opt | opt <- cppOptions bi]
         ++ [ "-optP-include", "-optP"++ (autogenModulesDir lbi </> cppHeaderName) ]
         ++ [ "-#include \"" ++ inc ++ "\"" | ghcVer < Version [6,11] []
                                            , inc <- PD.includes bi ]
         ++ [ "-odir",  odir, "-hidir", odir ]
         ++ concat [ ["-stubdir", odir] | ghcVer >=  Version [6,8] [] ]
         ++ ghcPackageFlags lbi clbi
         ++ (case withOptimization lbi of
               NoOptimisation      -> []
               NormalOptimisation  -> ["-O"]
               MaximumOptimisation -> ["-O2"])
         ++ hcOptions GHC bi
         ++ languageToFlags   (compiler lbi) (defaultLanguage bi)
         ++ extensionsToFlags (compiler lbi) (usedExtensions bi)
        where
          ghcVer = compilerVersion (compiler lbi)

    ghcPackageFlags :: LocalBuildInfo -> ComponentLocalBuildInfo -> [String]
    ghcPackageFlags lbi clbi
      | ghcVer >= Version [6,11] []
                  = concat [ ["-package-id", display ipkgid]
                           | (ipkgid, _) <- componentPackageDeps clbi ]

      | otherwise = concat [ ["-package", display pkgid]
                           | (_, pkgid)  <- componentPackageDeps clbi ]
        where
          ghcVer = compilerVersion (compiler lbi)

    ghcPackageDbOptions :: PackageDBStack -> [String]
    ghcPackageDbOptions dbstack = case dbstack of
      (GlobalPackageDB:UserPackageDB:dbs) -> concatMap specific dbs
      (GlobalPackageDB:dbs)               -> "-no-user-package-conf"
                                           : concatMap specific dbs
      _                                   -> ierror
      where
        specific (SpecificPackageDB db) = [ "-package-conf", db ]
        specific _ = ierror
        ierror     = error ("internal error: unexpected package db stack: " ++ show dbstack)

    constructCcCmdLine :: LocalBuildInfo -> BuildInfo -> ComponentLocalBuildInfo
                       -> FilePath -> FilePath -> Verbosity -> Bool
                       ->(FilePath,[String])
    constructCcCmdLine lbi bi clbi pref filename verbosity profiling
      =  let odir | compilerVersion (compiler lbi) >= Version [6,4,1] []  = pref
                  | otherwise = pref </> takeDirectory filename
                            -- ghc 6.4.1 fixed a bug in -odir handling
                            -- for C compilations.
         in
            (odir,
             ghcCcOptions lbi bi clbi odir
             ++ (if verbosity >= deafening then ["-v"] else [])
             ++ ["-c",filename]
             -- Note: When building with profiling enabled, we pass the -prof
             -- option to ghc here when compiling C code, so that the PROFILING
             -- macro gets defined. The macro is used in ghc's Rts.h in the
             -- definitions of closure layouts (Closures.h).
             ++ ["-prof" | profiling])

    ghcCcOptions :: LocalBuildInfo -> BuildInfo -> ComponentLocalBuildInfo
                 -> FilePath -> [String]
    ghcCcOptions lbi bi clbi odir
         =  ["-I" ++ dir | dir <- odir : PD.includeDirs bi]
         ++ ghcPackageDbOptions (withPackageDB lbi)
         ++ ghcPackageFlags lbi clbi
         ++ ["-optc" ++ opt | opt <- PD.ccOptions bi]
         ++ (case withOptimization lbi of
               NoOptimisation -> []
               _              -> ["-optc-O2"])
         ++ ["-odir", odir]

    mkGHCiLibName :: PackageIdentifier -> String
    mkGHCiLibName lib = "HS" ++ display lib <.> "o"

    -- -----------------------------------------------------------------------------
    -- Installing

    -- |Install executables for GHC.
    installExe :: Verbosity
               -> LocalBuildInfo
               -> InstallDirs FilePath -- ^Where to copy the files to
               -> FilePath  -- ^Build location
               -> (FilePath, FilePath)  -- ^Executable (prefix,suffix)
               -> PackageDescription
               -> Executable
               -> IO ()
    installExe verbosity lbi installDirs buildPref (progprefix, progsuffix) _pkg exe = do
      let binDir = bindir installDirs
      createDirectoryIfMissingVerbose verbosity True binDir
      let exeFileName = exeName exe <.> exeExtension
          fixedExeBaseName = progprefix ++ exeName exe ++ progsuffix
          installBinary dest = do
              installExecutableFile verbosity
                (buildPref </> exeName exe </> exeFileName)
                (dest <.> exeExtension)
              stripExe verbosity lbi exeFileName (dest <.> exeExtension)
      installBinary (binDir </> fixedExeBaseName)

    stripExe :: Verbosity -> LocalBuildInfo -> FilePath -> FilePath -> IO ()
    stripExe verbosity lbi name path = when (stripExes lbi) $
      case lookupProgram stripProgram (withPrograms lbi) of
        Just strip -> rawSystemProgram verbosity strip args
        Nothing    -> unless (buildOS == Windows) $
                      -- Don't bother warning on windows, we don't expect them to
                      -- have the strip program anyway.
                      warn verbosity $ "Unable to strip executable '" ++ name
                                    ++ "' (missing the 'strip' program)"
      where
        args = path : case buildOS of
           OSX -> ["-x"] -- By default, stripping the ghc binary on at least
                         -- some OS X installations causes:
                         --     HSbase-3.0.o: unknown symbol `_environ'"
                         -- The -x flag fixes that.
           _   -> []

    -- |Install for ghc, .hi, .a and, if --with-ghci given, .o
    installLib    :: Verbosity
                  -> LocalBuildInfo
                  -> FilePath  -- ^install location
                  -> FilePath  -- ^install location for dynamic librarys
                  -> FilePath  -- ^Build location
                  -> PackageDescription
                  -> Library
                  -> IO ()
    installLib verbosity lbi targetDir dynlibTargetDir builtDir pkg lib = do
      -- copy .hi files over:
      let copyHelper installFun src dst n = do
            createDirectoryIfMissingVerbose verbosity True dst
            installFun verbosity (src </> n) (dst </> n)
          copy       = copyHelper installOrdinaryFile
          copyShared = copyHelper installExecutableFile
          copyModuleFiles ext =
            findModuleFiles [builtDir] [ext] (libModules lib)
              >>= installOrdinaryFiles verbosity targetDir
      ifVanilla $ copyModuleFiles "hi"
      ifProf    $ copyModuleFiles "p_hi"
      ifShared  $ copyModuleFiles "dyn_hi"

      -- copy the built library files over:
      ifVanilla $ copy builtDir targetDir vanillaLibName
      ifProf    $ copy builtDir targetDir profileLibName
      ifGHCi    $ copy builtDir targetDir ghciLibName
      ifShared  $ copyShared builtDir dynlibTargetDir sharedLibName

      -- run ranlib if necessary:
      ifVanilla $ updateLibArchive verbosity lbi
                                   (targetDir </> vanillaLibName)
      ifProf    $ updateLibArchive verbosity lbi
                                   (targetDir </> profileLibName)

      where
        vanillaLibName = mkLibName pkgid
        profileLibName = mkProfLibName pkgid
        ghciLibName    = mkGHCiLibName pkgid
        sharedLibName  = mkSharedLibName pkgid (compilerId (compiler lbi))

        pkgid          = packageId pkg

        hasLib    = not $ null (libModules lib)
                       && null (cSources (libBuildInfo lib))
        ifVanilla = when (hasLib && withVanillaLib lbi)
        ifProf    = when (hasLib && withProfLib    lbi)
        ifGHCi    = when (hasLib && withGHCiLib    lbi)
        ifShared  = when (hasLib && withSharedLib  lbi)

    -- | On MacOS X we have to call @ranlib@ to regenerate the archive index after
    -- copying. This is because the silly MacOS X linker checks that the archive
    -- index is not older than the file itself, which means simply
    -- copying/installing the file breaks it!!
    --
    updateLibArchive :: Verbosity -> LocalBuildInfo -> FilePath -> IO ()
    updateLibArchive verbosity lbi path
      | buildOS == OSX = do
        (ranlib, _) <- requireProgram verbosity ranlibProgram (withPrograms lbi)
        rawSystemProgram verbosity ranlib [path]
      | otherwise = return ()

    -- -----------------------------------------------------------------------------
    -- Registering

    registerPackage
      :: Verbosity
      -> InstalledPackageInfo
      -> PackageDescription
      -> LocalBuildInfo
      -> Bool
      -> PackageDBStack
      -> IO ()
    registerPackage verbosity installedPkgInfo _pkg lbi _inplace packageDbs = do
      let Just ghcPkg = lookupProgram ghcPkgProgram (withPrograms lbi)
      HcPkg.reregister verbosity ghcPkg packageDbs (Right installedPkgInfo)