    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Simple.PreProcess
    -- Copyright   :  (c) 2003-2005, Isaac Jones, Malcolm Wallace
    -- License     :  BSD3
    --
    -- 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.

    module Distribution.Simple.PreProcess (preprocessComponent, preprocessExtras,
                                    knownSuffixHandlers, ppSuffixes,
                                    PPSuffixHandler, PreProcessor(..),
                                    mkSimplePreProcessor, runSimplePreProcessor,
                                    ppCpp, ppCpp', ppGreenCard, ppC2hs, ppHsc2hs,
                                    ppHappy, ppAlex, ppUnlit, platformDefines
                                   )
        where

    import Distribution.Simple.PreProcess.Unlit
    import Distribution.Package
    import qualified Distribution.ModuleName as ModuleName
    import Distribution.PackageDescription as PD
    import qualified Distribution.InstalledPackageInfo as Installed
    import qualified Distribution.Simple.PackageIndex as PackageIndex
    import Distribution.Simple.CCompiler
    import Distribution.Simple.Compiler
    import Distribution.Simple.LocalBuildInfo
    import Distribution.Simple.BuildPaths
    import Distribution.Simple.Utils
    import Distribution.Simple.Program
    import Distribution.Simple.Test.LibV09
    import Distribution.System
    import Distribution.Text
    import Distribution.Version
    import Distribution.Verbosity

    import Control.Monad
    import Data.Maybe (fromMaybe)
    import Data.List (nub, isSuffixOf)
    import System.Directory (doesFileExist)
    import System.Info (os, arch)
    import System.FilePath (splitExtension, dropExtensions, (</>), (<.>),
                            takeDirectory, normalise, replaceExtension,
                            takeExtensions)

    -- |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 generated 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 generated 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
      }

    -- | Function to determine paths to possible extra C sources for a
    -- preprocessor: just takes the path to the build directory and uses
    -- this to search for C sources with names that match the
    -- preprocessor's output name format.
    type PreProcessorExtras = FilePath -> IO [FilePath]

    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
        builtinHaskellSuffixes = ["hs", "lhs", "hsig", "lhsig"]
        builtinCSuffixes       = cSourceExtensions
        builtinSuffixes        = builtinHaskellSuffixes ++ builtinCSuffixes
        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 dir 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 "Distribution.Simple.PreProcess: 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 ->
                                  psrcFile `moreRecentFile` ppsrcFile
                  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 ghcProgram   (>= Version [6,6] []) args bi lbi
        GHCJS -> ppGhcCpp ghcjsProgram (const True)          args bi lbi
        _     -> ppCpphs  args bi lbi
      where cppArgs = getCppOptions bi lbi
            args    = cppArgs ++ extraArgs

    ppGhcCpp :: Program -> (Version -> Bool)
             -> [String] -> BuildInfo -> LocalBuildInfo -> PreProcessor
    ppGhcCpp program xHs extraArgs _bi lbi =
      PreProcessor {
        platformIndependent = False,
        runPreProcessor = mkSimplePreProcessor $ \inFile outFile verbosity -> do
          (prog, version, _) <- requireProgramVersion verbosity
                                  program anyVersion (withPrograms lbi)
          rawSystemProgram verbosity prog $
              ["-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 xHs version then ["-x", "hs"] 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
      }

    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 <- platformDefines lbi ]

              -- Options from the current package:
           ++ [ "--cflag=-I" ++ dir | dir <- PD.includeDirs  bi ]
           ++ [ "--cflag="   ++ opt | opt <- PD.ccOptions    bi
                                          ++ PD.cppOptions   bi ]
           ++ [ "--cflag="   ++ opt | opt <-
                   [ "-I" ++ autogenModulesDir lbi,
                     "-include", autogenModulesDir lbi </> cppHeaderName ] ]
           ++ [ "--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 ] ]
           ++ [ "--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
        -- TODO: installedPkgs contains ALL dependencies associated with
        -- the package, but we really only want to look at packages for the
        -- *current* dependency.  We should use PackageIndex.dependencyClosure
        -- on the direct depends of the component.  Can't easily do that,
        -- because the signature of this function is wrong.  Tracked with
        -- #2971 (which has a test case.)
        pkgs = PackageIndex.topologicalOrder (packageHacks (installedPkgs lbi))
        isOSX = case buildOS of OSX -> True; _ -> False
        isELF = case buildOS of OSX -> False; Windows -> False; AIX -> False; _ -> True;
        packageHacks = case compilerFlavor (compiler lbi) of
          GHC   -> hackRtsPackage
          GHCJS -> 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!!"

    ppHsc2hsExtras :: PreProcessorExtras
    ppHsc2hsExtras buildBaseDir = filter ("_hsc.c" `isSuffixOf`) `fmap`
                                  getDirectoryContentsRecursive buildBaseDir

    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 ]
            ++ [ "--cppopts=-include" ++ (autogenModulesDir lbi </> cppHeaderName) ]
            ++ [ "--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)

    ppC2hsExtras :: PreProcessorExtras
    ppC2hsExtras d = filter (\p -> takeExtensions p == ".chs.c") `fmap`
                     getDirectoryContentsRecursive d

    --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
        = platformDefines lbi
       ++ cppOptions bi
       ++ ["-I" ++ dir | dir <- PD.includeDirs bi]
       ++ [opt | opt@('-':c:_) <- PD.ccOptions bi, c `elem` "DIU"]

    platformDefines :: LocalBuildInfo -> [String]
    platformDefines lbi =
      case compilerFlavor comp of
        GHC  ->
          ["-D__GLASGOW_HASKELL__=" ++ versionInt version] ++
          ["-D" ++ os   ++ "_BUILD_OS=1"] ++
          ["-D" ++ arch ++ "_BUILD_ARCH=1"] ++
          map (\os'   -> "-D" ++ os'   ++ "_HOST_OS=1")   osStr ++
          map (\arch' -> "-D" ++ arch' ++ "_HOST_ARCH=1") archStr
        GHCJS ->
          compatGlasgowHaskell ++
          ["-D__GHCJS__=" ++ versionInt version] ++
          ["-D" ++ os   ++ "_BUILD_OS=1"] ++
          ["-D" ++ arch ++ "_BUILD_ARCH=1"] ++
          map (\os'   -> "-D" ++ os'   ++ "_HOST_OS=1")   osStr ++
          map (\arch' -> "-D" ++ arch' ++ "_HOST_ARCH=1") archStr
        JHC  -> ["-D__JHC__=" ++ versionInt version]
        HaskellSuite {} ->
          ["-D__HASKELL_SUITE__"] ++
            map (\os'   -> "-D" ++ os'   ++ "_HOST_OS=1")   osStr ++
            map (\arch' -> "-D" ++ arch' ++ "_HOST_ARCH=1") archStr
        _    -> []
      where
        comp = compiler lbi
        Platform hostArch hostOS = hostPlatform lbi
        version = compilerVersion comp
        compatGlasgowHaskell =
          maybe [] (\v -> ["-D__GLASGOW_HASKELL__=" ++ versionInt v])
                   (compilerCompatVersion GHC 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
        osStr = case hostOS of
          Linux     -> ["linux"]
          Windows   -> ["mingw32"]
          OSX       -> ["darwin"]
          FreeBSD   -> ["freebsd"]
          OpenBSD   -> ["openbsd"]
          NetBSD    -> ["netbsd"]
          DragonFly -> ["dragonfly"]
          Solaris   -> ["solaris2"]
          AIX       -> ["aix"]
          HPUX      -> ["hpux"]
          IRIX      -> ["irix"]
          HaLVM     -> []
          IOS       -> ["ios"]
          Android   -> ["android"]
          Ghcjs     -> ["ghcjs"]
          Hurd      -> ["hurd"]
          OtherOS _ -> []
        archStr = case hostArch of
          I386        -> ["i386"]
          X86_64      -> ["x86_64"]
          PPC         -> ["powerpc"]
          PPC64       -> ["powerpc64"]
          Sparc       -> ["sparc"]
          Arm         -> ["arm"]
          Mips        -> ["mips"]
          SH          -> []
          IA64        -> ["ia64"]
          S390        -> ["s390"]
          Alpha       -> ["alpha"]
          Hppa        -> ["hppa"]
          Rs6000      -> ["rs6000"]
          M68k        -> ["m68k"]
          Vax         -> ["vax"]
          JavaScript  -> ["javascript"]
          OtherArch _ -> []

    ppHappy :: BuildInfo -> LocalBuildInfo -> PreProcessor
    ppHappy _ lbi = pp { platformIndependent = True }
      where pp = standardPP lbi happyProgram (hcFlags hc)
            hc = compilerFlavor (compiler lbi)
            hcFlags GHC = ["-agc"]
            hcFlags GHCJS = ["-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 GHCJS = ["-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)
      ]

    -- |Standard preprocessors with possible extra C sources: c2hs, hsc2hs.
    knownExtrasHandlers :: [ PreProcessorExtras ]
    knownExtrasHandlers = [ ppC2hsExtras, ppHsc2hsExtras ]

    -- | Find any extra C sources generated by preprocessing that need to
    -- be added to the component (addresses issue #238).
    preprocessExtras :: Component
                     -> LocalBuildInfo
                     -> IO [FilePath]
    preprocessExtras comp lbi = case comp of
      CLib _ -> pp $ buildDir lbi
      (CExe Executable { exeName = nm }) ->
        pp $ buildDir lbi </> nm </> nm ++ "-tmp"
      CTest test -> do
        case testInterface test of
          TestSuiteExeV10 _ _ ->
              pp $ buildDir lbi </> testName test </> testName test ++ "-tmp"
          TestSuiteLibV09 _ _ ->
              pp $ buildDir lbi </> stubName test </> stubName test ++ "-tmp"
          TestSuiteUnsupported tt -> die $ "No support for preprocessing test "
                                        ++ "suite type " ++ display tt
      CBench bm -> do
        case benchmarkInterface bm of
          BenchmarkExeV10 _ _ ->
              pp $ buildDir lbi </> benchmarkName bm </> benchmarkName bm ++ "-tmp"
          BenchmarkUnsupported tt -> die $ "No support for preprocessing benchmark "
                                     ++ "type " ++ display tt
      where
        pp dir = (map (dir </>) . concat) `fmap` forM knownExtrasHandlers ($ dir)