DriverPipeline.hs

{-# OPTIONS -fno-cse #-}
-- -fno-cse is needed for GLOBAL_VAR's to behave properly

-----------------------------------------------------------------------------
--
-- GHC Driver
--
-- (c) The University of Glasgow 2005
--
-----------------------------------------------------------------------------

module DriverPipeline (
	-- Run a series of compilation steps in a pipeline, for a
	-- collection of source files.
   oneShot, compileFile,

	-- Interfaces for the batch-mode driver
   linkBinary,

	-- Interfaces for the compilation manager (interpreted/batch-mode)
   preprocess, 
   compile, compile',
   link, 

  ) where

#include "HsVersions.h"

import Packages
import HeaderInfo
import DriverPhases
import SysTools
import HscMain
import Finder
import HscTypes
import Outputable
import Module
import LazyUniqFM		( eltsUFM )
import ErrUtils
import DynFlags
import StaticFlags	( v_Ld_inputs, opt_Static, WayName(..) )
import Config
import Panic
import Util
import StringBuffer	( hGetStringBuffer )
import BasicTypes	( SuccessFlag(..) )
import Maybes		( expectJust )
import ParserCoreUtils	( getCoreModuleName )
import SrcLoc
import FastString
import MonadUtils

import Data.Either
import Exception
import Data.IORef	( readIORef )
import GHC.Exts		( Int(..) )
import System.Directory
import System.FilePath
import System.IO
import System.IO.Error as IO
import Control.Monad
import Data.List	( isSuffixOf )
import Data.Maybe
import System.Environment

-- ---------------------------------------------------------------------------
-- Pre-process

-- | Just preprocess a file, put the result in a temp. file (used by the
-- compilation manager during the summary phase).
--
-- We return the augmented DynFlags, because they contain the result
-- of slurping in the OPTIONS pragmas

preprocess :: GhcMonad m =>
              HscEnv
           -> (FilePath, Maybe Phase) -- ^ filename and starting phase
           -> m (DynFlags, FilePath)
preprocess hsc_env (filename, mb_phase) =
  ASSERT2(isJust mb_phase || isHaskellSrcFilename filename, text filename) 
  runPipeline anyHsc hsc_env (filename, mb_phase) 
        Nothing Temporary Nothing{-no ModLocation-}

-- ---------------------------------------------------------------------------

-- | Compile
--
-- Compile a single module, under the control of the compilation manager.
--
-- This is the interface between the compilation manager and the
-- compiler proper (hsc), where we deal with tedious details like
-- reading the OPTIONS pragma from the source file, and passing the
-- output of hsc through the C compiler.
--
-- NB.  No old interface can also mean that the source has changed.

compile :: GhcMonad m =>
           HscEnv
        -> ModSummary      -- ^ summary for module being compiled
        -> Int             -- ^ module N ...
        -> Int             -- ^ ... of M
        -> Maybe ModIface  -- ^ old interface, if we have one
        -> Maybe Linkable  -- ^ old linkable, if we have one
        -> m HomeModInfo   -- ^ the complete HomeModInfo, if successful

compile = compile' (hscCompileNothing, hscCompileInteractive, hscCompileBatch)

type Compiler m a = HscEnv -> ModSummary -> Bool
                  -> Maybe ModIface -> Maybe (Int, Int)
                  -> m a

compile' :: GhcMonad m =>
           (Compiler m (HscStatus, ModIface, ModDetails),
            Compiler m (InteractiveStatus, ModIface, ModDetails),
            Compiler m (HscStatus, ModIface, ModDetails))
        -> HscEnv
        -> ModSummary      -- ^ summary for module being compiled
        -> Int             -- ^ module N ...
        -> Int             -- ^ ... of M
        -> Maybe ModIface  -- ^ old interface, if we have one
        -> Maybe Linkable  -- ^ old linkable, if we have one
        -> m HomeModInfo   -- ^ the complete HomeModInfo, if successful

compile' (nothingCompiler, interactiveCompiler, batchCompiler)
        hsc_env0 summary mod_index nmods mb_old_iface maybe_old_linkable
 = do
   let dflags0     = ms_hspp_opts summary
       this_mod    = ms_mod summary
       src_flavour = ms_hsc_src summary
       location	   = ms_location summary
       input_fn    = expectJust "compile:hs" (ml_hs_file location) 
       input_fnpp  = ms_hspp_file summary

   liftIO $ debugTraceMsg dflags0 2 (text "compile: input file" <+> text input_fnpp)

   let basename = dropExtension input_fn

  -- We add the directory in which the .hs files resides) to the import path.
  -- This is needed when we try to compile the .hc file later, if it
  -- imports a _stub.h file that we created here.
   let current_dir = case takeDirectory basename of
                     "" -> "." -- XXX Hack
                     d -> d
       old_paths   = includePaths dflags0
       dflags      = dflags0 { includePaths = current_dir : old_paths }
       hsc_env     = hsc_env0 {hsc_dflags = dflags}

   -- Figure out what lang we're generating
   let hsc_lang = hscMaybeAdjustTarget dflags StopLn src_flavour (hscTarget dflags)
   -- ... and what the next phase should be
   let next_phase = hscNextPhase dflags src_flavour hsc_lang
   -- ... and what file to generate the output into
   output_fn <- liftIO $ getOutputFilename next_phase
			Temporary basename dflags next_phase (Just location)

   let dflags' = dflags { hscTarget = hsc_lang,
				hscOutName = output_fn,
				extCoreName = basename ++ ".hcr" }
   let hsc_env' = hsc_env { hsc_dflags = dflags' }

   -- -fforce-recomp should also work with --make
   let force_recomp = dopt Opt_ForceRecomp dflags
       source_unchanged = isJust maybe_old_linkable && not force_recomp
       object_filename = ml_obj_file location

   let getStubLinkable False = return []
       getStubLinkable True
           = do stub_o <- compileStub hsc_env' this_mod location
                return [ DotO stub_o ]

       handleBatch HscNoRecomp
           = ASSERT (isJust maybe_old_linkable)
             return maybe_old_linkable

       handleBatch (HscRecomp hasStub _)
           | isHsBoot src_flavour
               = do when (isObjectTarget hsc_lang) $ -- interpreted reaches here too
                       liftIO $ SysTools.touch dflags' "Touching object file"
                                   object_filename
                    return maybe_old_linkable

           | otherwise
               = do stub_unlinked <- getStubLinkable hasStub
                    (hs_unlinked, unlinked_time) <-
                        case hsc_lang of
                          HscNothing
                            -> return ([], ms_hs_date summary)
                          -- We're in --make mode: finish the compilation pipeline.
                          _other
                            -> do runPipeline StopLn hsc_env' (output_fn,Nothing)
                                              (Just basename)
                                              Persistent
                                              (Just location)
                                  -- The object filename comes from the ModLocation
                                  o_time <- liftIO $ getModificationTime object_filename
                                  return ([DotO object_filename], o_time)
                    let linkable = LM unlinked_time this_mod
			           (hs_unlinked ++ stub_unlinked)
                    return (Just linkable)

       handleInterpreted HscNoRecomp
           = ASSERT (isJust maybe_old_linkable)
             return maybe_old_linkable
       handleInterpreted (HscRecomp _hasStub Nothing)
           = ASSERT (isHsBoot src_flavour)
             return maybe_old_linkable
       handleInterpreted (HscRecomp hasStub (Just (comp_bc, modBreaks)))
           = do stub_unlinked <- getStubLinkable hasStub
                let hs_unlinked = [BCOs comp_bc modBreaks]
                    unlinked_time = ms_hs_date summary
                  -- Why do we use the timestamp of the source file here,
                  -- rather than the current time?  This works better in
                  -- the case where the local clock is out of sync
                  -- with the filesystem's clock.  It's just as accurate:
                  -- if the source is modified, then the linkable will
                  -- be out of date.
                let linkable = LM unlinked_time this_mod
                               (hs_unlinked ++ stub_unlinked)
                return (Just linkable)

   let -- runCompiler :: Compiler result -> (result -> Maybe Linkable)
       --            -> m HomeModInfo
       runCompiler compiler handle
           = do (result, iface, details)
                    <- compiler hsc_env' summary source_unchanged mb_old_iface
                                (Just (mod_index, nmods))
                linkable <- handle result
                return (HomeModInfo{ hm_details  = details,
                                     hm_iface    = iface,
                                     hm_linkable = linkable })
   -- run the compiler
   case hsc_lang of
      HscInterpreted ->
                runCompiler interactiveCompiler handleInterpreted
      HscNothing -> 
                runCompiler nothingCompiler handleBatch
      _other -> 
                runCompiler batchCompiler handleBatch


-----------------------------------------------------------------------------
-- stub .h and .c files (for foreign export support)

-- The _stub.c file is derived from the haskell source file, possibly taking
-- into account the -stubdir option.
--
-- Consequently, we derive the _stub.o filename from the haskell object
-- filename.  
--
-- This isn't necessarily the same as the object filename we
-- would get if we just compiled the _stub.c file using the pipeline.
-- For example:
--
--    ghc src/A.hs -odir obj
-- 
-- results in obj/A.o, and src/A_stub.c.  If we compile src/A_stub.c with
-- -odir obj, we would get obj/src/A_stub.o, which is wrong; we want
-- obj/A_stub.o.

compileStub :: GhcMonad m => HscEnv -> Module -> ModLocation
            -> m FilePath
compileStub hsc_env mod location = do
	let (o_base, o_ext) = splitExtension (ml_obj_file location)
	    stub_o = (o_base ++ "_stub") <.> o_ext

	-- compile the _stub.c file w/ gcc
	let (stub_c,_,_) = mkStubPaths (hsc_dflags hsc_env) (moduleName mod) location
	runPipeline StopLn hsc_env (stub_c,Nothing)  Nothing
		(SpecificFile stub_o) Nothing{-no ModLocation-}

	return stub_o


-- ---------------------------------------------------------------------------
-- Link

link :: GhcLink                 -- interactive or batch
     -> DynFlags                -- dynamic flags
     -> Bool                    -- attempt linking in batch mode?
     -> HomePackageTable        -- what to link
     -> IO SuccessFlag

-- For the moment, in the batch linker, we don't bother to tell doLink
-- which packages to link -- it just tries all that are available.
-- batch_attempt_linking should only be *looked at* in batch mode.  It
-- should only be True if the upsweep was successful and someone
-- exports main, i.e., we have good reason to believe that linking
-- will succeed.

#ifdef GHCI
link LinkInMemory _ _ _
    = do -- Not Linking...(demand linker will do the job)
         return Succeeded
#endif

link NoLink _ _ _
   = return Succeeded

link LinkBinary dflags batch_attempt_linking hpt
   | batch_attempt_linking
   = do
        let
            home_mod_infos = eltsUFM hpt

            -- the packages we depend on
            pkg_deps  = concatMap (dep_pkgs . mi_deps . hm_iface) home_mod_infos

            -- the linkables to link
            linkables = map (expectJust "link".hm_linkable) home_mod_infos

        debugTraceMsg dflags 3 (text "link: linkables are ..." $$ vcat (map ppr linkables))

        -- check for the -no-link flag
        if isNoLink (ghcLink dflags)
          then do debugTraceMsg dflags 3 (text "link(batch): linking omitted (-c flag given).")
                  return Succeeded
          else do

        let getOfiles (LM _ _ us) = map nameOfObject (filter isObject us)
            obj_files = concatMap getOfiles linkables

            exe_file = exeFileName dflags

        linking_needed <- linkingNeeded dflags linkables pkg_deps

        if not (dopt Opt_ForceRecomp dflags) && not linking_needed
           then do debugTraceMsg dflags 2 (text exe_file <+> ptext (sLit "is up to date, linking not required."))
                   return Succeeded
           else do

        debugTraceMsg dflags 1 (ptext (sLit "Linking") <+> text exe_file
                                 <+> text "...")

        -- Don't showPass in Batch mode; doLink will do that for us.
        let link = case ghcLink dflags of
                LinkBinary  -> linkBinary
                LinkDynLib  -> linkDynLib
                other       -> panicBadLink other
        link dflags obj_files pkg_deps

        debugTraceMsg dflags 3 (text "link: done")

        -- linkBinary only returns if it succeeds
        return Succeeded

   | otherwise
   = do debugTraceMsg dflags 3 (text "link(batch): upsweep (partially) failed OR" $$
                                text "   Main.main not exported; not linking.")
        return Succeeded

-- warning suppression
link other _ _ _ = panicBadLink other

panicBadLink :: GhcLink -> a
panicBadLink other = panic ("link: GHC not built to link this way: " ++
                            show other)


linkingNeeded :: DynFlags -> [Linkable] -> [PackageId] -> IO Bool
linkingNeeded dflags linkables pkg_deps = do
        -- if the modification time on the executable is later than the
        -- modification times on all of the objects and libraries, then omit
        -- linking (unless the -fforce-recomp flag was given).
  let exe_file = exeFileName dflags
  e_exe_time <- IO.try $ getModificationTime exe_file
  case e_exe_time of
    Left _  -> return True
    Right t -> do
        -- first check object files and extra_ld_inputs
        extra_ld_inputs <- readIORef v_Ld_inputs
        e_extra_times <- mapM (IO.try . getModificationTime) extra_ld_inputs
        let (errs,extra_times) = splitEithers e_extra_times
        let obj_times =  map linkableTime linkables ++ extra_times
        if not (null errs) || any (t <) obj_times
            then return True 
            else do

        -- next, check libraries. XXX this only checks Haskell libraries,
        -- not extra_libraries or -l things from the command line.
        let pkg_map = pkgIdMap (pkgState dflags)
            pkg_hslibs  = [ (libraryDirs c, lib)
                          | Just c <- map (lookupPackage pkg_map) pkg_deps,
                            lib <- packageHsLibs dflags c ]

        pkg_libfiles <- mapM (uncurry findHSLib) pkg_hslibs
        if any isNothing pkg_libfiles then return True else do
        e_lib_times <- mapM (IO.try . getModificationTime)
                          (catMaybes pkg_libfiles)
        let (lib_errs,lib_times) = splitEithers e_lib_times
        if not (null lib_errs) || any (t <) lib_times
           then return True
           else return False

findHSLib :: [String] -> String -> IO (Maybe FilePath)
findHSLib dirs lib = do
  let batch_lib_file = "lib" ++ lib <.> "a"
  found <- filterM doesFileExist (map (</> batch_lib_file) dirs)
  case found of
    [] -> return Nothing
    (x:_) -> return (Just x)

-- -----------------------------------------------------------------------------
-- Compile files in one-shot mode.

oneShot :: GhcMonad m =>
           HscEnv -> Phase -> [(String, Maybe Phase)] -> m ()
oneShot hsc_env stop_phase srcs = do
  o_files <- mapM (compileFile hsc_env stop_phase) srcs
  liftIO $ doLink (hsc_dflags hsc_env) stop_phase o_files

compileFile :: GhcMonad m =>
               HscEnv -> Phase -> (FilePath, Maybe Phase) -> m FilePath
compileFile hsc_env stop_phase (src, mb_phase) = do
   exists <- liftIO $ doesFileExist src
   when (not exists) $ 
   	ghcError (CmdLineError ("does not exist: " ++ src))
   
   let
        dflags = hsc_dflags hsc_env
	split     = dopt Opt_SplitObjs dflags
	mb_o_file = outputFile dflags
	ghc_link  = ghcLink dflags	-- Set by -c or -no-link

	-- When linking, the -o argument refers to the linker's output.	
	-- otherwise, we use it as the name for the pipeline's output.
        output
	 | StopLn <- stop_phase, not (isNoLink ghc_link) = Persistent
		-- -o foo applies to linker
	 | Just o_file <- mb_o_file = SpecificFile o_file
		-- -o foo applies to the file we are compiling now
	 | otherwise = Persistent

        stop_phase' = case stop_phase of 
			As | split -> SplitAs
                        _          -> stop_phase

   ( _, out_file) <- runPipeline stop_phase' hsc_env
                            (src, mb_phase) Nothing output
                            Nothing{-no ModLocation-}
   return out_file


doLink :: DynFlags -> Phase -> [FilePath] -> IO ()
doLink dflags stop_phase o_files
  | not (isStopLn stop_phase)
  = return ()		-- We stopped before the linking phase

  | otherwise
  = case ghcLink dflags of
	NoLink     -> return ()
	LinkBinary -> linkBinary dflags o_files link_pkgs
	LinkDynLib -> linkDynLib dflags o_files []
        other      -> panicBadLink other
  where
   -- Always link in the haskell98 package for static linking.  Other
   -- packages have to be specified via the -package flag.
    link_pkgs
     | dopt Opt_AutoLinkPackages dflags = [haskell98PackageId]
     | otherwise                        = []


-- ---------------------------------------------------------------------------

data PipelineOutput 
  = Temporary
	-- ^ Output should be to a temporary file: we're going to
	-- run more compilation steps on this output later.
  | Persistent
	-- ^ We want a persistent file, i.e. a file in the current directory
	-- derived from the input filename, but with the appropriate extension.
	-- eg. in "ghc -c Foo.hs" the output goes into ./Foo.o.
  | SpecificFile FilePath
	-- ^ The output must go into the specified file.

-- | Run a compilation pipeline, consisting of multiple phases.
--
-- This is the interface to the compilation pipeline, which runs
-- a series of compilation steps on a single source file, specifying
-- at which stage to stop.
--
-- The DynFlags can be modified by phases in the pipeline (eg. by
-- GHC_OPTIONS pragmas), and the changes affect later phases in the
-- pipeline.
runPipeline
  :: GhcMonad m =>
     Phase		        -- ^ When to stop
  -> HscEnv                     -- ^ Compilation environment
  -> (FilePath,Maybe Phase)     -- ^ Input filename (and maybe -x suffix)
  -> Maybe FilePath             -- ^ original basename (if different from ^^^)
  -> PipelineOutput	        -- ^ Output filename
  -> Maybe ModLocation          -- ^ A ModLocation, if this is a Haskell module
  -> m (DynFlags, FilePath)	-- ^ (final flags, output filename)

runPipeline stop_phase hsc_env0 (input_fn, mb_phase) mb_basename output maybe_loc
  = do
  let dflags0 = hsc_dflags hsc_env0
      (input_basename, suffix) = splitExtension input_fn
      suffix' = drop 1 suffix -- strip off the .
      basename | Just b <- mb_basename = b
               | otherwise             = input_basename

      -- Decide where dump files should go based on the pipeline output
      dflags = dflags0 { dumpPrefix = Just (basename ++ ".") }
      hsc_env = hsc_env0 {hsc_dflags = dflags}

	-- If we were given a -x flag, then use that phase to start from
      start_phase = fromMaybe (startPhase suffix') mb_phase

  -- We want to catch cases of "you can't get there from here" before
  -- we start the pipeline, because otherwise it will just run off the
  -- end.
  --
  -- There is a partial ordering on phases, where A < B iff A occurs
  -- before B in a normal compilation pipeline.

  when (not (start_phase `happensBefore` stop_phase)) $
	ghcError (UsageError 
		    ("cannot compile this file to desired target: "
		       ++ input_fn))

  -- this is a function which will be used to calculate output file names
  -- as we go along (we partially apply it to some of its inputs here)
  let get_output_fn = getOutputFilename stop_phase output basename

  -- Execute the pipeline...
  (dflags', output_fn, maybe_loc) <- 
	pipeLoop hsc_env start_phase stop_phase input_fn 
	  	 basename suffix' get_output_fn maybe_loc

  -- Sometimes, a compilation phase doesn't actually generate any output
  -- (eg. the CPP phase when -fcpp is not turned on).  If we end on this
  -- stage, but we wanted to keep the output, then we have to explicitly
  -- copy the file, remembering to prepend a {-# LINE #-} pragma so that
  -- further compilation stages can tell what the original filename was.
  case output of
    Temporary -> 
	return (dflags', output_fn)
    _other -> liftIO $
	do final_fn <- get_output_fn dflags' stop_phase maybe_loc
	   when (final_fn /= output_fn) $ do
              let msg = ("Copying `" ++ output_fn ++"' to `" ++ final_fn ++ "'")
                  line_prag = Just ("{-# LINE 1 \"" ++ input_fn ++ "\" #-}\n")
	      copyWithHeader dflags msg line_prag output_fn final_fn
	   return (dflags', final_fn)



pipeLoop :: GhcMonad m =>
            HscEnv -> Phase -> Phase
	 -> FilePath  -> String -> Suffix
	 -> (DynFlags -> Phase -> Maybe ModLocation -> IO FilePath)
	 -> Maybe ModLocation
	 -> m (DynFlags, FilePath, Maybe ModLocation)

pipeLoop hsc_env phase stop_phase 
	 input_fn orig_basename orig_suff 
	 orig_get_output_fn maybe_loc

  | phase `eqPhase` stop_phase		  -- All done
  = return (hsc_dflags hsc_env, input_fn, maybe_loc)

  | not (phase `happensBefore` stop_phase)
	-- Something has gone wrong.  We'll try to cover all the cases when
	-- this could happen, so if we reach here it is a panic.
	-- eg. it might happen if the -C flag is used on a source file that
	-- has {-# OPTIONS -fasm #-}.
  = panic ("pipeLoop: at phase " ++ show phase ++ 
	   " but I wanted to stop at phase " ++ show stop_phase)

  | otherwise 
  = do (next_phase, dflags', maybe_loc, output_fn)
          <- runPhase phase stop_phase hsc_env orig_basename 
                      orig_suff input_fn orig_get_output_fn maybe_loc
       let hsc_env' = hsc_env {hsc_dflags = dflags'}
       pipeLoop hsc_env' next_phase stop_phase output_fn
                orig_basename orig_suff orig_get_output_fn maybe_loc

getOutputFilename
  :: Phase -> PipelineOutput -> String
  -> DynFlags -> Phase{-next phase-} -> Maybe ModLocation -> IO FilePath
getOutputFilename stop_phase output basename
 = func
 where
	func dflags next_phase maybe_location
	   | is_last_phase, Persistent <- output     = persistent_fn
	   | is_last_phase, SpecificFile f <- output = return f
	   | keep_this_output	   		     = persistent_fn
     	   | otherwise        	   		     = newTempName dflags suffix
	   where
		hcsuf      = hcSuf dflags
		odir       = objectDir dflags
		osuf       = objectSuf dflags
		keep_hc    = dopt Opt_KeepHcFiles dflags
		keep_raw_s = dopt Opt_KeepRawSFiles dflags
		keep_s     = dopt Opt_KeepSFiles dflags

		myPhaseInputExt HCc    = hcsuf
		myPhaseInputExt StopLn = osuf
		myPhaseInputExt other  = phaseInputExt other

		is_last_phase = next_phase `eqPhase` stop_phase

		-- sometimes, we keep output from intermediate stages
		keep_this_output = 
     		     case next_phase of
     			     StopLn              -> True
     			     Mangle | keep_raw_s -> True
     			     As     | keep_s     -> True
     			     HCc    | keep_hc    -> True
     			     _other              -> False

		suffix = myPhaseInputExt next_phase

		-- persistent object files get put in odir
	        persistent_fn 
		   | StopLn <- next_phase = return odir_persistent
		   | otherwise            = return persistent

		persistent = basename <.> suffix

		odir_persistent
		   | Just loc <- maybe_location = ml_obj_file loc
		   | Just d <- odir = d </> persistent
		   | otherwise      = persistent


-- -----------------------------------------------------------------------------
-- | Each phase in the pipeline returns the next phase to execute, and the
-- name of the file in which the output was placed.
--
-- We must do things dynamically this way, because we often don't know
-- what the rest of the phases will be until part-way through the
-- compilation: for example, an {-# OPTIONS -fasm #-} at the beginning
-- of a source file can change the latter stages of the pipeline from
-- taking the via-C route to using the native code generator.
--
runPhase :: GhcMonad m =>
            Phase	-- ^ Do this phase first
	 -> Phase	-- ^ Stop just before this phase
	 -> HscEnv
	 -> String	-- ^ basename of original input source
	 -> String	-- ^ its extension
	 -> FilePath	-- ^ name of file which contains the input to this phase.
	 -> (DynFlags -> Phase -> Maybe ModLocation -> IO FilePath)
			-- ^ how to calculate the output filename
	 -> Maybe ModLocation		-- ^ the ModLocation, if we have one
	 -> m (Phase,	  		-- next phase
               DynFlags,		-- new dynamic flags
	       Maybe ModLocation,	-- the ModLocation, if we have one
	       FilePath)		-- output filename

	-- Invariant: the output filename always contains the output
	-- Interesting case: Hsc when there is no recompilation to do
	--		     Then the output filename is still a .o file 

-------------------------------------------------------------------------------
-- Unlit phase 

runPhase (Unlit sf) _stop hsc_env _basename _suff input_fn get_output_fn maybe_loc
  = do
       let dflags = hsc_dflags hsc_env
       output_fn <- liftIO $ get_output_fn dflags (Cpp sf) maybe_loc

       let unlit_flags = getOpts dflags opt_L
           flags = map SysTools.Option unlit_flags ++
                   [ -- The -h option passes the file name for unlit to
                     -- put in a #line directive
                     SysTools.Option     "-h"
                     -- cpp interprets \b etc as escape sequences,
                     -- so we use / for filenames in pragmas
                   , SysTools.Option $ reslash Forwards $ normalise input_fn
                   , SysTools.FileOption "" input_fn
                   , SysTools.FileOption "" output_fn
                   ]

       liftIO $ SysTools.runUnlit dflags flags

       return (Cpp sf, dflags, maybe_loc, output_fn)

-------------------------------------------------------------------------------
-- Cpp phase : (a) gets OPTIONS out of file
--	       (b) runs cpp if necessary

runPhase (Cpp sf) _stop hsc_env _basename _suff input_fn get_output_fn maybe_loc
  = do let dflags0 = hsc_dflags hsc_env
       src_opts <- liftIO $ getOptionsFromFile dflags0 input_fn
       (dflags, unhandled_flags, warns)
           <- liftIO $ parseDynamicNoPackageFlags dflags0 src_opts
       handleFlagWarnings dflags warns
       checkProcessArgsResult unhandled_flags

       if not (dopt Opt_Cpp dflags) then
           -- no need to preprocess CPP, just pass input file along
	   -- to the next phase of the pipeline.
          return (HsPp sf, dflags, maybe_loc, input_fn)
	else do
	    output_fn <- liftIO $ get_output_fn dflags (HsPp sf) maybe_loc
	    liftIO $ doCpp dflags True{-raw-} False{-no CC opts-} input_fn output_fn
	    return (HsPp sf, dflags, maybe_loc, output_fn)

-------------------------------------------------------------------------------
-- HsPp phase 

runPhase (HsPp sf) _stop hsc_env basename suff input_fn get_output_fn maybe_loc
  = do let dflags = hsc_dflags hsc_env
       if not (dopt Opt_Pp dflags) then
           -- no need to preprocess, just pass input file along
	   -- to the next phase of the pipeline.
          return (Hsc sf, dflags, maybe_loc, input_fn)
	else do
	    let hspp_opts = getOpts dflags opt_F
	    let orig_fn = basename <.> suff
	    output_fn <- liftIO $ get_output_fn dflags (Hsc sf) maybe_loc
	    liftIO $ SysTools.runPp dflags
			   ( [ SysTools.Option     orig_fn
			     , SysTools.Option     input_fn
			     , SysTools.FileOption "" output_fn
			     ] ++
			     map SysTools.Option hspp_opts
			   )
	    return (Hsc sf, dflags, maybe_loc, output_fn)

-----------------------------------------------------------------------------
-- Hsc phase

-- Compilation of a single module, in "legacy" mode (_not_ under
-- the direction of the compilation manager).
runPhase (Hsc src_flavour) stop hsc_env basename suff input_fn get_output_fn _maybe_loc 
 = do	-- normal Hsc mode, not mkdependHS
        let dflags0 = hsc_dflags hsc_env

  -- we add the current directory (i.e. the directory in which
  -- the .hs files resides) to the include path, since this is
  -- what gcc does, and it's probably what you want.
	let current_dir = case takeDirectory basename of
                      "" -> "." -- XXX Hack
                      d -> d
	
	    paths = includePaths dflags0
	    dflags = dflags0 { includePaths = current_dir : paths }
	
  -- gather the imports and module name
        (hspp_buf,mod_name,imps,src_imps) <- 
            case src_flavour of
                ExtCoreFile -> do  -- no explicit imports in ExtCore input.
                    m <- liftIO $ getCoreModuleName input_fn
                    return (Nothing, mkModuleName m, [], [])

                _           -> do
                    buf <- liftIO $ hGetStringBuffer input_fn
                    (src_imps,imps,L _ mod_name) <- getImports dflags buf input_fn (basename <.> suff)
                    return (Just buf, mod_name, imps, src_imps)

  -- Build a ModLocation to pass to hscMain.
  -- The source filename is rather irrelevant by now, but it's used
  -- by hscMain for messages.  hscMain also needs 
  -- the .hi and .o filenames, and this is as good a way
  -- as any to generate them, and better than most. (e.g. takes 
  -- into accout the -osuf flags)
	location1 <- liftIO $ mkHomeModLocation2 dflags mod_name basename suff

  -- Boot-ify it if necessary
	let location2 | isHsBoot src_flavour = addBootSuffixLocn location1
		      | otherwise	     = location1 
					

  -- Take -ohi into account if present
  -- This can't be done in mkHomeModuleLocation because
  -- it only applies to the module being compiles
	let ohi = outputHi dflags
	    location3 | Just fn <- ohi = location2{ ml_hi_file = fn }
		      | otherwise      = location2

  -- Take -o into account if present
  -- Very like -ohi, but we must *only* do this if we aren't linking
  -- (If we're linking then the -o applies to the linked thing, not to
  -- the object file for one module.)
  -- Note the nasty duplication with the same computation in compileFile above
	let expl_o_file = outputFile dflags
	    location4 | Just ofile <- expl_o_file
		      , isNoLink (ghcLink dflags)
		      = location3 { ml_obj_file = ofile }
		      | otherwise = location3

	    o_file = ml_obj_file location4 	-- The real object file


  -- Figure out if the source has changed, for recompilation avoidance.
  --
  -- Setting source_unchanged to True means that M.o seems
  -- to be up to date wrt M.hs; so no need to recompile unless imports have
  -- changed (which the compiler itself figures out).
  -- Setting source_unchanged to False tells the compiler that M.o is out of
  -- date wrt M.hs (or M.o doesn't exist) so we must recompile regardless.
	src_timestamp <- liftIO $ getModificationTime (basename <.> suff)

	let force_recomp = dopt Opt_ForceRecomp dflags
	source_unchanged <-
          if force_recomp || not (isStopLn stop)
		-- Set source_unchanged to False unconditionally if
		--	(a) recompilation checker is off, or
		-- 	(b) we aren't going all the way to .o file (e.g. ghc -S)
	     then return False	
		-- Otherwise look at file modification dates
	     else do o_file_exists <- liftIO $ doesFileExist o_file