content: -----------------------------------------------------------------------------
  -- |
  -- Module      :  Distribution.Simple.PreProcess
  -- Copyright   :  (c) 2003-2005, Isaac Jones, Malcolm Wallace
  --
  -- Maintainer  :  cabal-devel@haskell.org
  -- Portability :  portable
  --
  -- This defines a 'PreProcessor' abstraction which represents a pre-processor
  -- that can transform one kind of file into another. There is also a
  -- 'PPSuffixHandler' which is a combination of a file extension and a function
  -- for configuring a 'PreProcessor'. It defines a bunch of known built-in
  -- preprocessors like @cpp@, @cpphs@, @c2hs@, @hsc2hs@, @happy@, @alex@ etc and
  -- lists them in 'knownSuffixHandlers'. On top of this it provides a function
  -- for actually preprocessing some sources given a bunch of known suffix
  -- handlers. This module is not as good as it could be, it could really do with
  -- a rewrite to address some of the problems we have with pre-processors.
  
  {- Copyright (c) 2003-2005, Isaac Jones, Malcolm Wallace
  All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, 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.PreProcess (preprocessComponent, knownSuffixHandlers,
                                  ppSuffixes, PPSuffixHandler, PreProcessor(..),
                                  mkSimplePreProcessor, runSimplePreProcessor,
                                  ppCpp, ppCpp', ppGreenCard, ppC2hs, ppHsc2hs,
                                  ppHappy, ppAlex, ppUnlit
                                 )
      where
  
  
  import Control.Monad
  import Distribution.Simple.PreProcess.Unlit (unlit)
  import Distribution.Package
           ( Package(..), PackageName(..) )
  import qualified Distribution.ModuleName as ModuleName
  import Distribution.PackageDescription as PD
           ( PackageDescription(..), BuildInfo(..)
           , Executable(..)
           , Library(..), libModules
           , TestSuite(..), testModules
           , TestSuiteInterface(..)
           , Benchmark(..), benchmarkModules, BenchmarkInterface(..) )
  import qualified Distribution.InstalledPackageInfo as Installed
           ( InstalledPackageInfo_(..) )
  import qualified Distribution.Simple.PackageIndex as PackageIndex
  import Distribution.Simple.Compiler
           ( CompilerFlavor(..), Compiler(..), compilerFlavor, compilerVersion )
  import Distribution.Simple.LocalBuildInfo
           ( LocalBuildInfo(..), Component(..) )
  import Distribution.Simple.BuildPaths (autogenModulesDir,cppHeaderName)
  import Distribution.Simple.Utils
           ( createDirectoryIfMissingVerbose, withUTF8FileContents, writeUTF8File
           , die, setupMessage, intercalate, copyFileVerbose
           , findFileWithExtension, findFileWithExtension' )
  import Distribution.Simple.Program
           ( Program(..), ConfiguredProgram(..), programPath
           , lookupProgram, requireProgram, requireProgramVersion
           , rawSystemProgramConf, rawSystemProgram
           , greencardProgram, cpphsProgram, hsc2hsProgram, c2hsProgram
           , happyProgram, alexProgram, haddockProgram, ghcProgram, gccProgram )
  import Distribution.Simple.Test ( writeSimpleTestStub, stubFilePath, stubName )
  import Distribution.System
           ( OS(OSX, Windows), buildOS )
  import Distribution.Text
  import Distribution.Version
           ( Version(..), anyVersion, orLaterVersion )
  import Distribution.Verbosity
  
  import Data.Maybe (fromMaybe)
  import Data.List (nub)
  import System.Directory (getModificationTime, doesFileExist)
  import System.Info (os, arch)
  import System.FilePath (splitExtension, dropExtensions, (</>), (<.>),
                          takeDirectory, normalise, replaceExtension)
  
  -- |The interface to a preprocessor, which may be implemented using an
  -- external program, but need not be.  The arguments are the name of
  -- the input file, the name of the output file and a verbosity level.
  -- Here is a simple example that merely prepends a comment to the given
  -- source file:
  --
  -- > ppTestHandler :: PreProcessor
  -- > ppTestHandler =
  -- >   PreProcessor {
  -- >     platformIndependent = True,
  -- >     runPreProcessor = mkSimplePreProcessor $ \inFile outFile verbosity ->
  -- >       do info verbosity (inFile++" has been preprocessed to "++outFile)
  -- >          stuff <- readFile inFile
  -- >          writeFile outFile ("-- preprocessed as a test\n\n" ++ stuff)
  -- >          return ExitSuccess
  --
  -- We split the input and output file names into a base directory and the
  -- rest of the file name. The input base dir is the path in the list of search
  -- dirs that this file was found in. The output base dir is the build dir where
  -- all the generated source files are put.
  --
  -- The reason for splitting it up this way is that some pre-processors don't
  -- simply generate one output .hs file from one input file but have
  -- dependencies on other genereated files (notably c2hs, where building one
  -- .hs file may require reading other .chi files, and then compiling the .hs
  -- file may require reading a generated .h file). In these cases the generated
  -- files need to embed relative path names to each other (eg the generated .hs
  -- file mentions the .h file in the FFI imports). This path must be relative to
  -- the base directory where the genereated files are located, it cannot be
  -- relative to the top level of the build tree because the compilers do not
  -- look for .h files relative to there, ie we do not use \"-I .\", instead we
  -- use \"-I dist\/build\" (or whatever dist dir has been set by the user)
  --
  -- Most pre-processors do not care of course, so mkSimplePreProcessor and
  -- runSimplePreProcessor functions handle the simple case.
  --
  data PreProcessor = PreProcessor {
  
    -- Is the output of the pre-processor platform independent? eg happy output
    -- is portable haskell but c2hs's output is platform dependent.
    -- This matters since only platform independent generated code can be
    -- inlcuded into a source tarball.
    platformIndependent :: Bool,
  
    -- TODO: deal with pre-processors that have implementaion dependent output
    --       eg alex and happy have --ghc flags. However we can't really inlcude
    --       ghc-specific code into supposedly portable source tarballs.
  
    runPreProcessor :: (FilePath, FilePath) -- Location of the source file relative to a base dir
                    -> (FilePath, FilePath) -- Output file name, relative to an output base dir
                    -> Verbosity -- verbosity
                    -> IO ()     -- Should exit if the preprocessor fails
    }
  
  mkSimplePreProcessor :: (FilePath -> FilePath -> Verbosity -> IO ())
                        -> (FilePath, FilePath)
                        -> (FilePath, FilePath) -> Verbosity -> IO ()
  mkSimplePreProcessor simplePP
    (inBaseDir, inRelativeFile)
    (outBaseDir, outRelativeFile) verbosity = simplePP inFile outFile verbosity
    where inFile  = normalise (inBaseDir  </> inRelativeFile)
          outFile = normalise (outBaseDir </> outRelativeFile)
  
  runSimplePreProcessor :: PreProcessor -> FilePath -> FilePath -> Verbosity
                        -> IO ()
  runSimplePreProcessor pp inFile outFile verbosity =
    runPreProcessor pp (".", inFile) (".", outFile) verbosity
  
  -- |A preprocessor for turning non-Haskell files with the given extension
  -- into plain Haskell source files.
  type PPSuffixHandler
      = (String, BuildInfo -> LocalBuildInfo -> PreProcessor)
  
  -- | Apply preprocessors to the sources from 'hsSourceDirs' for a given
  -- component (lib, exe, or test suite).
  preprocessComponent :: PackageDescription
                      -> Component
                      -> LocalBuildInfo
                      -> Bool
                      -> Verbosity
                      -> [PPSuffixHandler]
                      -> IO ()
  preprocessComponent pd comp lbi isSrcDist verbosity handlers = case comp of
    (CLib lib@Library{ libBuildInfo = bi }) -> do
      let dirs = hsSourceDirs bi ++ [autogenModulesDir lbi]
      setupMessage verbosity "Preprocessing library" (packageId pd)
      forM_ (map ModuleName.toFilePath $ libModules lib) $
        pre dirs (buildDir lbi) (localHandlers bi)
    (CExe exe@Executable { buildInfo = bi, exeName = nm }) -> do
      let exeDir = buildDir lbi </> nm </> nm ++ "-tmp"
          dirs   = hsSourceDirs bi ++ [autogenModulesDir lbi]
      setupMessage verbosity ("Preprocessing executable '" ++ nm ++ "' for") (packageId pd)
      forM_ (map ModuleName.toFilePath $ otherModules bi) $
        pre dirs exeDir (localHandlers bi)
      pre (hsSourceDirs bi) exeDir (localHandlers bi) $
        dropExtensions (modulePath exe)
    CTest test@TestSuite{ testName = nm } -> do
      setupMessage verbosity ("Preprocessing test suite '" ++ nm ++ "' for") (packageId pd)
      case testInterface test of
        TestSuiteExeV10 _ f ->
            preProcessTest test f $ buildDir lbi </> testName test
                </> testName test ++ "-tmp"
        TestSuiteLibV09 _ _ -> do
            let testDir = buildDir lbi </> stubName test
                    </> stubName test ++ "-tmp"
            writeSimpleTestStub test testDir
            preProcessTest test (stubFilePath test) testDir
        TestSuiteUnsupported tt -> die $ "No support for preprocessing test "
                                      ++ "suite type " ++ display tt
    CBench bm@Benchmark{ benchmarkName = nm } -> do
      setupMessage verbosity ("Preprocessing benchmark '" ++ nm ++ "' for") (packageId pd)
      case benchmarkInterface bm of
        BenchmarkExeV10 _ f ->
            preProcessBench bm f $ buildDir lbi </> benchmarkName bm
                </> benchmarkName bm ++ "-tmp"
        BenchmarkUnsupported tt -> die $ "No support for preprocessing benchmark "
                                   ++ "type " ++ display tt
    where
      builtinSuffixes
        | NHC == compilerFlavor (compiler lbi) = ["hs", "lhs", "gc"]
        | otherwise                            = ["hs", "lhs"]
      localHandlers bi = [(ext, h bi lbi) | (ext, h) <- handlers]
      pre dirs dir lhndlrs fp =
        preprocessFile dirs dir isSrcDist fp verbosity builtinSuffixes lhndlrs
      preProcessTest test = preProcessComponent (testBuildInfo test)
                            (testModules test)
      preProcessBench bm = preProcessComponent (benchmarkBuildInfo bm)
                           (benchmarkModules bm)
      preProcessComponent bi modules exePath dir = do
          let biHandlers = localHandlers bi
              sourceDirs = hsSourceDirs bi ++ [ autogenModulesDir lbi ]
          sequence_ [ preprocessFile sourceDirs (buildDir lbi) isSrcDist
                  (ModuleName.toFilePath modu) verbosity builtinSuffixes
                  biHandlers
                  | modu <- modules ]
          preprocessFile (dir : (hsSourceDirs bi)) dir isSrcDist
              (dropExtensions $ exePath) verbosity
              builtinSuffixes biHandlers
  
  --TODO: try to list all the modules that could not be found
  --      not just the first one. It's annoying and slow due to the need
  --      to reconfigure after editing the .cabal file each time.
  
  -- |Find the first extension of the file that exists, and preprocess it
  -- if required.
  preprocessFile
      :: [FilePath]               -- ^source directories
      -> FilePath                 -- ^build directory
      -> Bool                     -- ^preprocess for sdist
      -> FilePath                 -- ^module file name
      -> Verbosity                -- ^verbosity
      -> [String]                 -- ^builtin suffixes
      -> [(String, PreProcessor)] -- ^possible preprocessors
      -> IO ()
  preprocessFile searchLoc buildLoc forSDist baseFile verbosity builtinSuffixes handlers = do
      -- look for files in the various source dirs with this module name
      -- and a file extension of a known preprocessor
      psrcFiles <- findFileWithExtension' (map fst handlers) searchLoc baseFile
      case psrcFiles of
          -- no preprocessor file exists, look for an ordinary source file
          -- just to make sure one actually exists at all for this module.
          -- Note: by looking in the target/output build dir too, we allow
          -- source files to appear magically in the target build dir without
          -- any corresponding "real" source file. This lets custom Setup.hs
          -- files generate source modules directly into the build dir without
          -- the rest of the build system being aware of it (somewhat dodgy)
        Nothing -> do
                   bsrcFiles <- findFileWithExtension builtinSuffixes (buildLoc : searchLoc) baseFile
                   case bsrcFiles of
                    Nothing -> die $ "can't find source for " ++ baseFile
                                  ++ " in " ++ intercalate ", " searchLoc
                    _       -> return ()
          -- found a pre-processable file in one of the source dirs
        Just (psrcLoc, psrcRelFile) -> do
              let (srcStem, ext) = splitExtension psrcRelFile
                  psrcFile = psrcLoc </> psrcRelFile
                  pp = fromMaybe (error "Internal error in preProcess module: Just expected")
                                 (lookup (tailNotNull ext) handlers)
              -- Preprocessing files for 'sdist' is different from preprocessing
              -- for 'build'.  When preprocessing for sdist we preprocess to
              -- avoid that the user has to have the preprocessors available.
              -- ATM, we don't have a way to specify which files are to be
              -- preprocessed and which not, so for sdist we only process
              -- platform independent files and put them into the 'buildLoc'
              -- (which we assume is set to the temp. directory that will become
              -- the tarball).
              --TODO: eliminate sdist variant, just supply different handlers
              when (not forSDist || forSDist && platformIndependent pp) $ do
                -- look for existing pre-processed source file in the dest dir to
                -- see if we really have to re-run the preprocessor.
                ppsrcFiles <- findFileWithExtension builtinSuffixes [buildLoc] baseFile
                recomp <- case ppsrcFiles of
                            Nothing -> return True
                            Just ppsrcFile -> do
                                btime <- getModificationTime ppsrcFile
                                ptime <- getModificationTime psrcFile
                                return (btime < ptime)
                when recomp $ do
                  let destDir = buildLoc </> dirName srcStem
                  createDirectoryIfMissingVerbose verbosity True destDir
                  runPreProcessorWithHsBootHack pp
                     (psrcLoc, psrcRelFile)
                     (buildLoc, srcStem <.> "hs")
  
    where
      dirName = takeDirectory
      tailNotNull [] = []
      tailNotNull x  = tail x
  
      -- FIXME: This is a somewhat nasty hack. GHC requires that hs-boot files
      -- be in the same place as the hs files, so if we put the hs file in dist/
      -- then we need to copy the hs-boot file there too. This should probably be
      -- done another way. Possibly we should also be looking for .lhs-boot
      -- files, but I think that preprocessors only produce .hs files.
      runPreProcessorWithHsBootHack pp
        (inBaseDir,  inRelativeFile)
        (outBaseDir, outRelativeFile) = do
          runPreProcessor pp
            (inBaseDir, inRelativeFile)
            (outBaseDir, outRelativeFile) verbosity
  
          exists <- doesFileExist inBoot
          when exists $ copyFileVerbose verbosity inBoot outBoot
  
        where
          inBoot  = replaceExtension inFile  "hs-boot"
          outBoot = replaceExtension outFile "hs-boot"
  
          inFile  = normalise (inBaseDir  </> inRelativeFile)
          outFile = normalise (outBaseDir </> outRelativeFile)
  
  -- ------------------------------------------------------------
  -- * known preprocessors
  -- ------------------------------------------------------------
  
  ppGreenCard :: BuildInfo -> LocalBuildInfo -> PreProcessor
  ppGreenCard _ lbi
      = PreProcessor {
          platformIndependent = False,
          runPreProcessor = mkSimplePreProcessor $ \inFile outFile verbosity ->
            rawSystemProgramConf verbosity greencardProgram (withPrograms lbi)
                (["-tffi", "-o" ++ outFile, inFile])
        }
  
  -- This one is useful for preprocessors that can't handle literate source.
  -- We also need a way to chain preprocessors.
  ppUnlit :: PreProcessor
  ppUnlit =
    PreProcessor {
      platformIndependent = True,
      runPreProcessor = mkSimplePreProcessor $ \inFile outFile _verbosity ->
        withUTF8FileContents inFile $ \contents ->
          either (writeUTF8File outFile) die (unlit inFile contents)
    }
  
  ppCpp :: BuildInfo -> LocalBuildInfo -> PreProcessor
  ppCpp = ppCpp' []
  
  ppCpp' :: [String] -> BuildInfo -> LocalBuildInfo -> PreProcessor
  ppCpp' extraArgs bi lbi =
    case compilerFlavor (compiler lbi) of
      GHC -> ppGhcCpp (cppArgs ++ extraArgs) bi lbi
      _   -> ppCpphs  (cppArgs ++ extraArgs) bi lbi
  
    where cppArgs = getCppOptions bi lbi
  
  ppGhcCpp :: [String] -> BuildInfo -> LocalBuildInfo -> PreProcessor
  ppGhcCpp extraArgs _bi lbi =
    PreProcessor {
      platformIndependent = False,
      runPreProcessor = mkSimplePreProcessor $ \inFile outFile verbosity -> do
        (ghcProg, ghcVersion, _) <- requireProgramVersion verbosity
                                      ghcProgram anyVersion (withPrograms lbi)
        rawSystemProgram verbosity ghcProg $
            ["-E", "-cpp"]
            -- This is a bit of an ugly hack. We're going to
            -- unlit the file ourselves later on if appropriate,
            -- so we need GHC not to unlit it now or it'll get
            -- double-unlitted. In the future we might switch to
            -- using cpphs --unlit instead.
         ++ (if ghcVersion >= Version [6,6] [] then ["-x", "hs"] else [])
         ++ (if use_optP_P lbi then ["-optP-P"] else [])
         ++ [ "-optP-include", "-optP"++ (autogenModulesDir lbi </> cppHeaderName) ]
         ++ ["-o", outFile, inFile]
         ++ extraArgs
    }
  
  ppCpphs :: [String] -> BuildInfo -> LocalBuildInfo -> PreProcessor
  ppCpphs extraArgs _bi lbi =
    PreProcessor {
      platformIndependent = False,
      runPreProcessor = mkSimplePreProcessor $ \inFile outFile verbosity -> do
        (cpphsProg, cpphsVersion, _) <- requireProgramVersion verbosity
                                          cpphsProgram anyVersion (withPrograms lbi)
        rawSystemProgram verbosity cpphsProg $
            ("-O" ++ outFile) : inFile
          : "--noline" : "--strip"
          : (if cpphsVersion >= Version [1,6] []
               then ["--include="++ (autogenModulesDir lbi </> cppHeaderName)]
               else [])
          ++ extraArgs
    }
  
  -- Haddock versions before 0.8 choke on #line and #file pragmas.  Those
  -- pragmas are necessary for correct links when we preprocess.  So use
  -- -optP-P only if the Haddock version is prior to 0.8.
  use_optP_P :: LocalBuildInfo -> Bool
  use_optP_P lbi
   = case lookupProgram haddockProgram (withPrograms lbi) of
       Just (ConfiguredProgram { programVersion = Just version })
         | version >= Version [0,8] [] -> False
       _                               -> True
  
  ppHsc2hs :: BuildInfo -> LocalBuildInfo -> PreProcessor
  ppHsc2hs bi lbi =
    PreProcessor {
      platformIndependent = False,
      runPreProcessor = mkSimplePreProcessor $ \inFile outFile verbosity -> do
        (gccProg, _) <- requireProgram verbosity gccProgram (withPrograms lbi)
        rawSystemProgramConf verbosity hsc2hsProgram (withPrograms lbi) $
            [ "--cc=" ++ programPath gccProg
            , "--ld=" ++ programPath gccProg ]
  
            -- Additional gcc options
         ++ [ "--cflag=" ++ opt | opt <- programDefaultArgs  gccProg
                                      ++ programOverrideArgs gccProg ]
         ++ [ "--lflag=" ++ opt | opt <- programDefaultArgs  gccProg
                                      ++ programOverrideArgs gccProg ]
  
            -- OSX frameworks:
         ++ [ what ++ "=-F" ++ opt
            | isOSX
            , opt <- nub (concatMap Installed.frameworkDirs pkgs)
            , what <- ["--cflag", "--lflag"] ]
         ++ [ "--lflag=" ++ arg
            | isOSX
            , opt <- PD.frameworks bi ++ concatMap Installed.frameworks pkgs
            , arg <- ["-framework", opt] ]
  
            -- Note that on ELF systems, wherever we use -L, we must also use -R
            -- because presumably that -L dir is not on the normal path for the
            -- system's dynamic linker. This is needed because hsc2hs works by
            -- compiling a C program and then running it.
  
         ++ [ "--cflag="   ++ opt | opt <- hcDefines (compiler lbi) ]
         ++ [ "--cflag="   ++ opt | opt <- sysDefines ]
  
            -- Options from the current package:
         ++ [ "--cflag=-I" ++ dir | dir <- PD.includeDirs  bi ]
         ++ [ "--cflag="   ++ opt | opt <- PD.ccOptions    bi
                                        ++ PD.cppOptions   bi ]
         ++ [ "--lflag=-L" ++ opt | opt <- PD.extraLibDirs bi ]
         ++ [ "--lflag=-Wl,-R," ++ opt | isELF
                                  , opt <- PD.extraLibDirs bi ]
         ++ [ "--lflag=-l" ++ opt | opt <- PD.extraLibs    bi ]
         ++ [ "--lflag="   ++ opt | opt <- PD.ldOptions    bi ]
  
            -- Options from dependent packages
         ++ [ "--cflag=" ++ opt
            | pkg <- pkgs
            , opt <- [ "-I" ++ opt | opt <- Installed.includeDirs pkg ]
                  ++ [         opt | opt <- Installed.ccOptions   pkg ]
                  ++ [ "-I" ++ autogenModulesDir lbi,
                       "-include", autogenModulesDir lbi </> cppHeaderName ] ]
         ++ [ "--lflag=" ++ opt
            | pkg <- pkgs
            , opt <- [ "-L" ++ opt | opt <- Installed.libraryDirs    pkg ]
                  ++ [ "-Wl,-R," ++ opt | isELF
                                   , opt <- Installed.libraryDirs    pkg ]
                  ++ [ "-l" ++ opt | opt <- Installed.extraLibraries pkg ]
                  ++ [         opt | opt <- Installed.ldOptions      pkg ] ]
         ++ ["-o", outFile, inFile]
    }
    where
      pkgs = PackageIndex.topologicalOrder (packageHacks (installedPkgs lbi))
      isOSX = case buildOS of OSX -> True; _ -> False
      isELF = case buildOS of OSX -> False; Windows -> False; _ -> True;
      packageHacks = case compilerFlavor (compiler lbi) of
        GHC -> hackRtsPackage
        _   -> id
      -- We don't link in the actual Haskell libraries of our dependencies, so
      -- the -u flags in the ldOptions of the rts package mean linking fails on
      -- OS X (it's ld is a tad stricter than gnu ld). Thus we remove the
      -- ldOptions for GHC's rts package:
      hackRtsPackage index =
        case PackageIndex.lookupPackageName index (PackageName "rts") of
          [(_, [rts])]
             -> PackageIndex.insert rts { Installed.ldOptions = [] } index
          _  -> error "No (or multiple) ghc rts package is registered!!"
  
  
  ppC2hs :: BuildInfo -> LocalBuildInfo -> PreProcessor
  ppC2hs bi lbi =
    PreProcessor {
      platformIndependent = False,
      runPreProcessor = \(inBaseDir, inRelativeFile)
                         (outBaseDir, outRelativeFile) verbosity -> do
        (c2hsProg, _, _) <- requireProgramVersion verbosity
                              c2hsProgram (orLaterVersion (Version [0,15] []))
                              (withPrograms lbi)
        (gccProg, _) <- requireProgram verbosity gccProgram (withPrograms lbi)
        rawSystemProgram verbosity c2hsProg $
  
            -- Options from the current package:
             [ "--cpp=" ++ programPath gccProg, "--cppopts=-E" ]
          ++ [ "--cppopts=" ++ opt | opt <- getCppOptions bi lbi ]
          ++ [ "--include=" ++ outBaseDir ]
  
            -- Options from dependent packages
         ++ [ "--cppopts=" ++ opt
            | pkg <- pkgs
            , opt <- [ "-I" ++ opt | opt <- Installed.includeDirs pkg ]
                  ++ [         opt | opt@('-':c:_) <- Installed.ccOptions pkg
                                   , c `elem` "DIU" ] ]
            --TODO: install .chi files for packages, so we can --include
            -- those dirs here, for the dependencies
  
             -- input and output files
          ++ [ "--output-dir=" ++ outBaseDir
             , "--output=" ++ outRelativeFile
             , inBaseDir </> inRelativeFile ]
    }
    where
      pkgs = PackageIndex.topologicalOrder (installedPkgs lbi)
  
  --TODO: perhaps use this with hsc2hs too
  --TODO: remove cc-options from cpphs for cabal-version: >= 1.10
  getCppOptions :: BuildInfo -> LocalBuildInfo -> [String]
  getCppOptions bi lbi
      = hcDefines (compiler lbi)
     ++ sysDefines
     ++ cppOptions bi
     ++ ["-I" ++ dir | dir <- PD.includeDirs bi]
     ++ [opt | opt@('-':c:_) <- PD.ccOptions bi, c `elem` "DIU"]
  
  sysDefines :: [String]
  sysDefines = ["-D" ++ os   ++ "_" ++ loc ++ "_OS"   | loc <- locations]
            ++ ["-D" ++ arch ++ "_" ++ loc ++ "_ARCH" | loc <- locations]
    where
      locations = ["BUILD", "HOST"]
  
  hcDefines :: Compiler -> [String]
  hcDefines comp =
    case compilerFlavor comp of
      GHC  -> ["-D__GLASGOW_HASKELL__=" ++ versionInt version]
      JHC  -> ["-D__JHC__=" ++ versionInt version]
      NHC  -> ["-D__NHC__=" ++ versionInt version]
      Hugs -> ["-D__HUGS__"]
      _    -> []
    where version = compilerVersion comp
  
  -- TODO: move this into the compiler abstraction
  -- FIXME: this forces GHC's crazy 4.8.2 -> 408 convention on all the other
  -- compilers. Check if that's really what they want.
  versionInt :: Version -> String
  versionInt (Version { versionBranch = [] }) = "1"
  versionInt (Version { versionBranch = [n] }) = show n
  versionInt (Version { versionBranch = n1:n2:_ })
    = -- 6.8.x -> 608
      -- 6.10.x -> 610
      let s1 = show n1
          s2 = show n2
          middle = case s2 of
                   _ : _ : _ -> ""
                   _         -> "0"
      in s1 ++ middle ++ s2
  
  ppHappy :: BuildInfo -> LocalBuildInfo -> PreProcessor
  ppHappy _ lbi = pp { platformIndependent = True }
    where pp = standardPP lbi happyProgram (hcFlags hc)
          hc = compilerFlavor (compiler lbi)
          hcFlags GHC = ["-agc"]
          hcFlags _ = []
  
  ppAlex :: BuildInfo -> LocalBuildInfo -> PreProcessor
  ppAlex _ lbi = pp { platformIndependent = True }
    where pp = standardPP lbi alexProgram (hcFlags hc)
          hc = compilerFlavor (compiler lbi)
          hcFlags GHC = ["-g"]
          hcFlags _ = []
  
  standardPP :: LocalBuildInfo -> Program -> [String] -> PreProcessor
  standardPP lbi prog args =
    PreProcessor {
      platformIndependent = False,
      runPreProcessor = mkSimplePreProcessor $ \inFile outFile verbosity ->
        rawSystemProgramConf verbosity prog (withPrograms lbi)
                             (args ++ ["-o", outFile, inFile])
    }
  
  -- |Convenience function; get the suffixes of these preprocessors.
  ppSuffixes :: [ PPSuffixHandler ] -> [String]
  ppSuffixes = map fst
  
  -- |Standard preprocessors: GreenCard, c2hs, hsc2hs, happy, alex and cpphs.
  knownSuffixHandlers :: [ PPSuffixHandler ]
  knownSuffixHandlers =
    [ ("gc",     ppGreenCard)
    , ("chs",    ppC2hs)
    , ("hsc",    ppHsc2hs)
    , ("x",      ppAlex)
    , ("y",      ppHappy)
    , ("ly",     ppHappy)
    , ("cpphs",  ppCpp)
    ]
  