GHC.hs

-- -----------------------------------------------------------------------------
--
-- (c) The University of Glasgow, 2005
--
-- The GHC API
--
-- -----------------------------------------------------------------------------

module GHC (
	-- * Initialisation
	Session,
	defaultErrorHandler,
	defaultCleanupHandler,
	init, initFromArgs,
	newSession,

	-- * Flags and settings
	DynFlags(..), DynFlag(..), Severity(..), GhcMode(..), HscTarget(..), dopt,
	parseDynamicFlags,
	initPackages,
	getSessionDynFlags,
	setSessionDynFlags,

	-- * Targets
	Target(..), TargetId(..), Phase,
	setTargets,
	getTargets,
	addTarget,
	removeTarget,
	guessTarget,
	
        -- * Extending the program scope 
        extendGlobalRdrScope,  -- :: Session -> [GlobalRdrElt] -> IO ()
        setGlobalRdrScope,     -- :: Session -> [GlobalRdrElt] -> IO ()
        extendGlobalTypeScope, -- :: Session -> [Id] -> IO ()
        setGlobalTypeScope,    -- :: Session -> [Id] -> IO ()

	-- * Loading\/compiling the program
	depanal,
	load, LoadHowMuch(..), SuccessFlag(..),	-- also does depanal
	workingDirectoryChanged,
	checkModule, CheckedModule(..),
	TypecheckedSource, ParsedSource, RenamedSource,

	-- * Inspecting the module structure of the program
	ModuleGraph, ModSummary(..), ms_mod_name, ModLocation(..),
	getModuleGraph,
	isLoaded,
	topSortModuleGraph,

	-- * Inspecting modules
	ModuleInfo,
	getModuleInfo,
	modInfoTyThings,
	modInfoTopLevelScope,
	modInfoPrintUnqualified,
	modInfoExports,
	modInfoInstances,
	modInfoIsExportedName,
	modInfoLookupName,
	lookupGlobalName,

	-- * Printing
	PrintUnqualified, alwaysQualify,

	-- * Interactive evaluation
	getBindings, getPrintUnqual,
        findModule,
#ifdef GHCI
	setContext, getContext,	
	getNamesInScope,
	getRdrNamesInScope,
	moduleIsInterpreted,
	getInfo,
	exprType,
	typeKind,
	parseName,
	RunResult(..),
	runStmt,
	showModule,
	compileExpr, HValue,
	lookupName,
#endif

	-- * Abstract syntax elements

        -- ** Packages
        PackageId,

	-- ** Modules
	Module, mkModule, pprModule, moduleName, modulePackageId,
        ModuleName, mkModuleName, moduleNameString,

	-- ** Names
	Name, 
	nameModule, nameParent_maybe, pprParenSymName, nameSrcLoc,
	NamedThing(..),
	RdrName(Qual,Unqual),
	
	-- ** Identifiers
	Id, idType,
	isImplicitId, isDeadBinder,
	isExportedId, isLocalId, isGlobalId,
	isRecordSelector,
	isPrimOpId, isFCallId, isClassOpId_maybe,
	isDataConWorkId, idDataCon,
	isBottomingId, isDictonaryId,
	recordSelectorFieldLabel,

	-- ** Type constructors
	TyCon, 
	tyConTyVars, tyConDataCons, tyConArity,
	isClassTyCon, isSynTyCon, isNewTyCon, isPrimTyCon, isFunTyCon,
	synTyConDefn, synTyConRhs,

	-- ** Type variables
	TyVar,
	alphaTyVars,

	-- ** Data constructors
	DataCon,
	dataConSig, dataConType, dataConTyCon, dataConFieldLabels,
	dataConIsInfix, isVanillaDataCon,
	dataConStrictMarks,  
	StrictnessMark(..), isMarkedStrict,

	-- ** Classes
	Class, 
	classMethods, classSCTheta, classTvsFds,
	pprFundeps,

	-- ** Instances
	Instance, 
	instanceDFunId, pprInstance, pprInstanceHdr,

	-- ** Types and Kinds
	Type, dropForAlls, splitForAllTys, funResultTy, pprParendType,
	Kind,
	PredType,
	ThetaType, pprThetaArrow,

	-- ** Entities
	TyThing(..), 

	-- ** Syntax
	module HsSyn, -- ToDo: remove extraneous bits

	-- ** Fixities
	FixityDirection(..), 
	defaultFixity, maxPrecedence, 
	negateFixity,
	compareFixity,

	-- ** Source locations
	SrcLoc, pprDefnLoc,

	-- * Exceptions
	GhcException(..), showGhcException,

	-- * Miscellaneous
	sessionHscEnv,
	cyclicModuleErr,
  ) where

{-
 ToDo:

  * inline bits of HscMain here to simplify layering: hscTcExpr, hscStmt.
  * we need to expose DynFlags, so should parseDynamicFlags really be
    part of this interface?
  * what StaticFlags should we expose, if any?
-}

#include "HsVersions.h"

#ifdef GHCI
import qualified Linker
import Linker		( HValue, extendLinkEnv )
import TcRnDriver	( tcRnLookupRdrName, tcRnGetInfo,
			  tcRnLookupName, getModuleExports )
import RdrName		( plusGlobalRdrEnv, Provenance(..), 
			  ImportSpec(..), ImpDeclSpec(..), ImpItemSpec(..),
			  mkGlobalRdrEnv )
import HscMain		( hscParseIdentifier, hscStmt, hscTcExpr, hscKcType )
import Name		( nameOccName )
import Type		( tidyType )
import VarEnv		( emptyTidyEnv )
import GHC.Exts		( unsafeCoerce# )
#endif

import Packages		( initPackages )
import NameSet		( NameSet, nameSetToList, elemNameSet )
import RdrName		( GlobalRdrEnv, GlobalRdrElt(..), RdrName(..), 
			  globalRdrEnvElts, extendGlobalRdrEnv,
                          emptyGlobalRdrEnv )
import HsSyn
import Type		( Kind, Type, dropForAlls, PredType, ThetaType,
			  pprThetaArrow, pprParendType, splitForAllTys,
			  funResultTy )
import Id		( Id, idType, isImplicitId, isDeadBinder,
                          isExportedId, isLocalId, isGlobalId,
                          isRecordSelector, recordSelectorFieldLabel,
                          isPrimOpId, isFCallId, isClassOpId_maybe,
                          isDataConWorkId, idDataCon,
                          isBottomingId )
import Var		( TyVar )
import TysPrim		( alphaTyVars )
import TyCon		( TyCon, isClassTyCon, isSynTyCon, isNewTyCon,
			  isPrimTyCon, isFunTyCon, tyConArity,
			  tyConTyVars, tyConDataCons, synTyConDefn, synTyConRhs )
import Class		( Class, classSCTheta, classTvsFds, classMethods )
import FunDeps		( pprFundeps )
import DataCon		( DataCon, dataConWrapId, dataConSig, dataConTyCon,
			  dataConFieldLabels, dataConStrictMarks, 
			  dataConIsInfix, isVanillaDataCon )
import Name		( Name, nameModule, NamedThing(..), nameParent_maybe,
			  nameSrcLoc )
import OccName		( parenSymOcc )
import NameEnv		( nameEnvElts )
import InstEnv		( Instance, instanceDFunId, pprInstance, pprInstanceHdr )
import SrcLoc
import DriverPipeline
import DriverPhases	( Phase(..), isHaskellSrcFilename, startPhase )
import HeaderInfo	( getImports, getOptions )
import Finder
import HscMain		( newHscEnv, hscFileCheck, HscChecked(..) )
import HscTypes
import DynFlags
import SysTools		( initSysTools, cleanTempFiles )
import Module
import UniqFM
import PackageConfig    ( PackageId )
import FiniteMap
import Panic
import Digraph
import Bag		( unitBag )
import ErrUtils		( Severity(..), showPass, fatalErrorMsg, debugTraceMsg,
			  mkPlainErrMsg, printBagOfErrors )
import qualified ErrUtils
import Util
import StringBuffer	( StringBuffer, hGetStringBuffer )
import Outputable
import SysTools		( cleanTempFilesExcept )
import BasicTypes
import TcType           ( tcSplitSigmaTy, isDictTy )
import Maybes		( expectJust, mapCatMaybes )

import Control.Concurrent
import System.Directory ( getModificationTime, doesFileExist )
import Data.Maybe	( isJust, isNothing )
import Data.List	( partition, nub )
import qualified Data.List as List
import Control.Monad	( unless, when )
import System.Exit	( exitWith, ExitCode(..) )
import System.Time	( ClockTime )
import Control.Exception as Exception hiding (handle)
import Data.IORef
import System.IO
import System.IO.Error	( isDoesNotExistError )
import Prelude hiding (init)

#if __GLASGOW_HASKELL__ < 600
import System.IO as System.IO.Error ( try )
#else
import System.IO.Error	( try )
#endif

-- -----------------------------------------------------------------------------
-- Exception handlers

-- | Install some default exception handlers and run the inner computation.
-- Unless you want to handle exceptions yourself, you should wrap this around
-- the top level of your program.  The default handlers output the error
-- message(s) to stderr and exit cleanly.
defaultErrorHandler :: DynFlags -> IO a -> IO a
defaultErrorHandler dflags inner = 
  -- top-level exception handler: any unrecognised exception is a compiler bug.
  handle (\exception -> do
  	   hFlush stdout
	   case exception of
		-- an IO exception probably isn't our fault, so don't panic
		IOException _ ->
		  fatalErrorMsg dflags (text (show exception))
		AsyncException StackOverflow ->
		  fatalErrorMsg dflags (text "stack overflow: use +RTS -K<size> to increase it")
		_other ->
		  fatalErrorMsg dflags (text (show (Panic (show exception))))
	   exitWith (ExitFailure 1)
         ) $

  -- program errors: messages with locations attached.  Sometimes it is
  -- convenient to just throw these as exceptions.
  handleDyn (\dyn -> do printBagOfErrors dflags (unitBag dyn)
			exitWith (ExitFailure 1)) $

  -- error messages propagated as exceptions
  handleDyn (\dyn -> do
  		hFlush stdout
  		case dyn of
		     PhaseFailed _ code -> exitWith code
		     Interrupted -> exitWith (ExitFailure 1)
		     _ -> do fatalErrorMsg dflags (text (show (dyn :: GhcException)))
			     exitWith (ExitFailure 1)
	    ) $
  inner

-- | Install a default cleanup handler to remove temporary files
-- deposited by a GHC run.  This is seperate from
-- 'defaultErrorHandler', because you might want to override the error
-- handling, but still get the ordinary cleanup behaviour.
defaultCleanupHandler :: DynFlags -> IO a -> IO a
defaultCleanupHandler dflags inner = 
   -- make sure we clean up after ourselves
   later (unless (dopt Opt_KeepTmpFiles dflags) $ 
	    cleanTempFiles dflags) 
	-- exceptions will be blocked while we clean the temporary files,
	-- so there shouldn't be any difficulty if we receive further
	-- signals.
   inner


-- | Initialises GHC.  This must be done /once/ only.  Takes the
-- TopDir path without the '-B' prefix.

init :: Maybe String -> IO ()
init mbMinusB = do
   -- catch ^C
   main_thread <- myThreadId
   putMVar interruptTargetThread [main_thread]
   installSignalHandlers

   dflags0 <- initSysTools mbMinusB defaultDynFlags
   writeIORef v_initDynFlags dflags0

-- | Initialises GHC. This must be done /once/ only. Takes the
-- command-line arguments.  All command-line arguments which aren't
-- understood by GHC will be returned.

initFromArgs :: [String] -> IO [String]
initFromArgs args
    = do init mbMinusB
         return argv1
    where -- Grab the -B option if there is one
          (minusB_args, argv1) = partition (prefixMatch "-B") args
          mbMinusB | null minusB_args
                       = Nothing
                   | otherwise
                       = Just (drop 2 (last minusB_args))

GLOBAL_VAR(v_initDynFlags, error "initDynFlags", DynFlags)
	-- stores the DynFlags between the call to init and subsequent
	-- calls to newSession.

-- | Starts a new session.  A session consists of a set of loaded
-- modules, a set of options (DynFlags), and an interactive context.
-- ToDo: GhcMode should say "keep typechecked code" and\/or "keep renamed
-- code".
newSession :: GhcMode -> IO Session
newSession mode = do
  dflags0 <- readIORef v_initDynFlags
  dflags <- initDynFlags dflags0
  env <- newHscEnv dflags{ ghcMode=mode }
  ref <- newIORef env
  return (Session ref)

-- tmp: this breaks the abstraction, but required because DriverMkDepend
-- needs to call the Finder.  ToDo: untangle this.
sessionHscEnv :: Session -> IO HscEnv
sessionHscEnv (Session ref) = readIORef ref

withSession :: Session -> (HscEnv -> IO a) -> IO a
withSession (Session ref) f = do h <- readIORef ref; f h

modifySession :: Session -> (HscEnv -> HscEnv) -> IO ()
modifySession (Session ref) f = do h <- readIORef ref; writeIORef ref $! f h

-- -----------------------------------------------------------------------------
-- Flags & settings

-- | Grabs the DynFlags from the Session
getSessionDynFlags :: Session -> IO DynFlags
getSessionDynFlags s = withSession s (return . hsc_dflags)

-- | Updates the DynFlags in a Session
setSessionDynFlags :: Session -> DynFlags -> IO ()
setSessionDynFlags s dflags = modifySession s (\h -> h{ hsc_dflags = dflags })

-- | If there is no -o option, guess the name of target executable
-- by using top-level source file name as a base.
guessOutputFile :: Session -> IO ()
guessOutputFile s = modifySession s $ \env ->
    let dflags = hsc_dflags env
        mod_graph = hsc_mod_graph env
        mainModuleSrcPath, guessedName :: Maybe String
        mainModuleSrcPath = do
            let isMain = (== mainModIs dflags) . ms_mod
            [ms] <- return (filter isMain mod_graph)
            ml_hs_file (ms_location ms)
        guessedName = fmap basenameOf mainModuleSrcPath
    in
    case outputFile dflags of
        Just _ -> env
        Nothing -> env { hsc_dflags = dflags { outputFile = guessedName } }

-- -----------------------------------------------------------------------------
-- Targets

-- ToDo: think about relative vs. absolute file paths. And what
-- happens when the current directory changes.

-- | Sets the targets for this session.  Each target may be a module name
-- or a filename.  The targets correspond to the set of root modules for
-- the program\/library.  Unloading the current program is achieved by
-- setting the current set of targets to be empty, followed by load.
setTargets :: Session -> [Target] -> IO ()
setTargets s targets = modifySession s (\h -> h{ hsc_targets = targets })

-- | returns the current set of targets
getTargets :: Session -> IO [Target]
getTargets s = withSession s (return . hsc_targets)

-- | Add another target
addTarget :: Session -> Target -> IO ()
addTarget s target
  = modifySession s (\h -> h{ hsc_targets = target : hsc_targets h })

-- | Remove a target
removeTarget :: Session -> TargetId -> IO ()
removeTarget s target_id
  = modifySession s (\h -> h{ hsc_targets = filter (hsc_targets h) })
  where
   filter targets = [ t | t@(Target id _) <- targets, id /= target_id ]

-- Attempts to guess what Target a string refers to.  This function implements
-- the --make/GHCi command-line syntax for filenames: 
--
-- 	- if the string looks like a Haskell source filename, then interpret
--	  it as such
--	- if adding a .hs or .lhs suffix yields the name of an existing file,
--	  then use that
-- 	- otherwise interpret the string as a module name
--
guessTarget :: String -> Maybe Phase -> IO Target
guessTarget file (Just phase)
   = return (Target (TargetFile file (Just phase)) Nothing)
guessTarget file Nothing
   | isHaskellSrcFilename file
   = return (Target (TargetFile file Nothing) Nothing)
   | otherwise
   = do exists <- doesFileExist hs_file
	if exists
	   then return (Target (TargetFile hs_file Nothing) Nothing)
	   else do
	exists <- doesFileExist lhs_file
	if exists
	   then return (Target (TargetFile lhs_file Nothing) Nothing)
	   else do
	return (Target (TargetModule (mkModuleName file)) Nothing)
     where 
	 hs_file  = file `joinFileExt` "hs"
	 lhs_file = file `joinFileExt` "lhs"

-- -----------------------------------------------------------------------------
-- Extending the program scope

extendGlobalRdrScope :: Session -> [GlobalRdrElt] -> IO ()
extendGlobalRdrScope session rdrElts
    = modifySession session $ \hscEnv ->
      let global_rdr = hsc_global_rdr_env hscEnv
      in hscEnv{ hsc_global_rdr_env = foldl extendGlobalRdrEnv global_rdr rdrElts }

setGlobalRdrScope :: Session -> [GlobalRdrElt] -> IO ()
setGlobalRdrScope session rdrElts
    = modifySession session $ \hscEnv ->
      hscEnv{ hsc_global_rdr_env = foldl extendGlobalRdrEnv emptyGlobalRdrEnv rdrElts }

extendGlobalTypeScope :: Session -> [Id] -> IO ()
extendGlobalTypeScope session ids
    = modifySession session $ \hscEnv ->
      let global_type = hsc_global_type_env hscEnv
      in hscEnv{ hsc_global_type_env = extendTypeEnvWithIds global_type ids }

setGlobalTypeScope :: Session -> [Id] -> IO ()
setGlobalTypeScope session ids
    = modifySession session $ \hscEnv ->
      hscEnv{ hsc_global_type_env = extendTypeEnvWithIds emptyTypeEnv ids }

-- -----------------------------------------------------------------------------
-- Loading the program

-- Perform a dependency analysis starting from the current targets
-- and update the session with the new module graph.
depanal :: Session -> [ModuleName] -> Bool -> IO (Maybe ModuleGraph)
depanal (Session ref) excluded_mods allow_dup_roots = do
  hsc_env <- readIORef ref
  let
	 dflags  = hsc_dflags hsc_env
	 gmode   = ghcMode (hsc_dflags hsc_env)
	 targets = hsc_targets hsc_env
	 old_graph = hsc_mod_graph hsc_env
	
  showPass dflags "Chasing dependencies"
  when (gmode == BatchCompile) $
	debugTraceMsg dflags 2 (hcat [
		     text "Chasing modules from: ",
	     		hcat (punctuate comma (map pprTarget targets))])

  r <- downsweep hsc_env old_graph excluded_mods allow_dup_roots
  case r of
    Just mod_graph -> writeIORef ref hsc_env{ hsc_mod_graph = mod_graph }
    _ -> return ()
  return r

{-
-- | The result of load.
data LoadResult
  = LoadOk	Errors	-- ^ all specified targets were loaded successfully.
  | LoadFailed  Errors	-- ^ not all modules were loaded.

type Errors = [String]

data ErrMsg = ErrMsg { 
	errMsgSeverity  :: Severity,  -- warning, error, etc.
	errMsgSpans     :: [SrcSpan],
	errMsgShortDoc  :: Doc,
	errMsgExtraInfo :: Doc
	}
-}

data LoadHowMuch
   = LoadAllTargets
   | LoadUpTo ModuleName
   | LoadDependenciesOf ModuleName

-- | Try to load the program.  If a Module is supplied, then just
-- attempt to load up to this target.  If no Module is supplied,
-- then try to load all targets.
load :: Session -> LoadHowMuch -> IO SuccessFlag
load s@(Session ref) how_much
   = do 
	-- Dependency analysis first.  Note that this fixes the module graph:
	-- even if we don't get a fully successful upsweep, the full module
	-- graph is still retained in the Session.  We can tell which modules
	-- were successfully loaded by inspecting the Session's HPT.
	mb_graph <- depanal s [] False
	case mb_graph of	   
	   Just mod_graph -> load2 s how_much mod_graph 
	   Nothing        -> return Failed

load2 s@(Session ref) how_much mod_graph = do
        guessOutputFile s
	hsc_env <- readIORef ref

        let hpt1      = hsc_HPT hsc_env
        let dflags    = hsc_dflags hsc_env
        let ghci_mode = ghcMode dflags -- this never changes

	-- The "bad" boot modules are the ones for which we have
	-- B.hs-boot in the module graph, but no B.hs
	-- The downsweep should have ensured this does not happen
	-- (see msDeps)
        let all_home_mods = [ms_mod_name s 
			    | s <- mod_graph, not (isBootSummary s)]
#ifdef DEBUG
	    bad_boot_mods = [s 	      | s <- mod_graph, isBootSummary s,
					not (ms_mod_name s `elem` all_home_mods)]
#endif
	ASSERT( null bad_boot_mods ) return ()

        -- mg2_with_srcimps drops the hi-boot nodes, returning a 
	-- graph with cycles.  Among other things, it is used for
        -- backing out partially complete cycles following a failed
        -- upsweep, and for removing from hpt all the modules
        -- not in strict downwards closure, during calls to compile.
        let mg2_with_srcimps :: [SCC ModSummary]
	    mg2_with_srcimps = topSortModuleGraph True mod_graph Nothing

	    -- check the stability property for each module.
	    stable_mods@(stable_obj,stable_bco)
		| BatchCompile <- ghci_mode = ([],[])
	        | otherwise = checkStability hpt1 mg2_with_srcimps all_home_mods

	    -- prune bits of the HPT which are definitely redundant now,
	    -- to save space.
	    pruned_hpt = pruneHomePackageTable hpt1 
				(flattenSCCs mg2_with_srcimps)
				stable_mods

	evaluate pruned_hpt

	debugTraceMsg dflags 2 (text "Stable obj:" <+> ppr stable_obj $$
				text "Stable BCO:" <+> ppr stable_bco)

	-- Unload any modules which are going to be re-linked this time around.
	let stable_linkables = [ linkable
			       | m <- stable_obj++stable_bco,
				 Just hmi <- [lookupUFM pruned_hpt m],
				 Just linkable <- [hm_linkable hmi] ]
	unload hsc_env stable_linkables

        -- We could at this point detect cycles which aren't broken by
        -- a source-import, and complain immediately, but it seems better
        -- to let upsweep_mods do this, so at least some useful work gets
        -- done before the upsweep is abandoned.
        --hPutStrLn stderr "after tsort:\n"
        --hPutStrLn stderr (showSDoc (vcat (map ppr mg2)))

        -- Now do the upsweep, calling compile for each module in
        -- turn.  Final result is version 3 of everything.

        -- Topologically sort the module graph, this time including hi-boot
	-- nodes, and possibly just including the portion of the graph
	-- reachable from the module specified in the 2nd argument to load.
	-- This graph should be cycle-free.
	-- If we're restricting the upsweep to a portion of the graph, we
	-- also want to retain everything that is still stable.
        let full_mg :: [SCC ModSummary]
	    full_mg    = topSortModuleGraph False mod_graph Nothing

	    maybe_top_mod = case how_much of
				LoadUpTo m           -> Just m
			  	LoadDependenciesOf m -> Just m
			  	_		     -> Nothing

	    partial_mg0 :: [SCC ModSummary]
	    partial_mg0 = topSortModuleGraph False mod_graph maybe_top_mod

	    -- LoadDependenciesOf m: we want the upsweep to stop just
	    -- short of the specified module (unless the specified module
	    -- is stable).
	    partial_mg
		| LoadDependenciesOf mod <- how_much
		= ASSERT( case last partial_mg0 of 
			    AcyclicSCC ms -> ms_mod_name ms == mod; _ -> False )
		  List.init partial_mg0
		| otherwise
		= partial_mg0
  
	    stable_mg = 
		[ AcyclicSCC ms
	        | AcyclicSCC ms <- full_mg,
		  ms_mod_name ms `elem` stable_obj++stable_bco,
		  ms_mod_name ms `notElem` [ ms_mod_name ms' | 
						AcyclicSCC ms' <- partial_mg ] ]

	    mg = stable_mg ++ partial_mg

	-- clean up between compilations
	let cleanup = cleanTempFilesExcept dflags
			  (ppFilesFromSummaries (flattenSCCs mg2_with_srcimps))

        (upsweep_ok, hsc_env1, modsUpswept)
           <- upsweep (hsc_env { hsc_HPT = emptyHomePackageTable })
			   pruned_hpt stable_mods cleanup mg

	-- Make modsDone be the summaries for each home module now
	-- available; this should equal the domain of hpt3.
        -- Get in in a roughly top .. bottom order (hence reverse).

        let modsDone = reverse modsUpswept

        -- Try and do linking in some form, depending on whether the
        -- upsweep was completely or only partially successful.

        if succeeded upsweep_ok

         then 
           -- Easy; just relink it all.
           do debugTraceMsg dflags 2 (text "Upsweep completely successful.")

	      -- Clean up after ourselves
	      cleanTempFilesExcept dflags (ppFilesFromSummaries modsDone)

	      -- Issue a warning for the confusing case where the user
	      -- said '-o foo' but we're not going to do any linking.
	      -- We attempt linking if either (a) one of the modules is
	      -- called Main, or (b) the user said -no-hs-main, indicating
	      -- that main() is going to come from somewhere else.
	      --
	      let ofile = outputFile dflags
	      let no_hs_main = dopt Opt_NoHsMain dflags
	      let 
	 	main_mod = mainModIs dflags
		a_root_is_Main = any ((==main_mod).ms_mod) mod_graph
		do_linking = a_root_is_Main || no_hs_main

	      when (ghci_mode == BatchCompile && isJust ofile && not do_linking) $
	        debugTraceMsg dflags 1 (text ("Warning: output was redirected with -o, " ++
				              "but no output will be generated\n" ++
				              "because there is no " ++ moduleNameString (moduleName main_mod) ++ " module."))

	      -- link everything together
              linkresult <- link ghci_mode dflags do_linking (hsc_HPT hsc_env1)

	      loadFinish Succeeded linkresult ref hsc_env1

         else 
           -- Tricky.  We need to back out the effects of compiling any
           -- half-done cycles, both so as to clean up the top level envs
           -- and to avoid telling the interactive linker to link them.
           do debugTraceMsg dflags 2 (text "Upsweep partially successful.")

              let modsDone_names
                     = map ms_mod modsDone
              let mods_to_zap_names 
                     = findPartiallyCompletedCycles modsDone_names 
			  mg2_with_srcimps
              let mods_to_keep
                     = filter ((`notElem` mods_to_zap_names).ms_mod) 
			  modsDone

              let hpt4 = retainInTopLevelEnvs (map ms_mod_name mods_to_keep) 
					      (hsc_HPT hsc_env1)

	      -- Clean up after ourselves
	      cleanTempFilesExcept dflags (ppFilesFromSummaries mods_to_keep)

	      -- there should be no Nothings where linkables should be, now
	      ASSERT(all (isJust.hm_linkable) 
			(eltsUFM (hsc_HPT hsc_env))) do
	
	      -- Link everything together
              linkresult <- link ghci_mode dflags False hpt4

	      let hsc_env4 = hsc_env1{ hsc_HPT = hpt4 }
	      loadFinish Failed linkresult ref hsc_env4

-- Finish up after a load.

-- If the link failed, unload everything and return.
loadFinish all_ok Failed ref hsc_env
  = do unload hsc_env []
       writeIORef ref $! discardProg hsc_env
       return Failed

-- Empty the interactive context and set the module context to the topmost
-- newly loaded module, or the Prelude if none were loaded.
loadFinish all_ok Succeeded ref hsc_env
  = do writeIORef ref $! hsc_env{ hsc_IC = emptyInteractiveContext }
       return all_ok


-- Forget the current program, but retain the persistent info in HscEnv
discardProg :: HscEnv -> HscEnv
discardProg hsc_env
  = hsc_env { hsc_mod_graph = emptyMG, 
	      hsc_IC = emptyInteractiveContext,
	      hsc_HPT = emptyHomePackageTable }

-- used to fish out the preprocess output files for the purposes of
-- cleaning up.  The preprocessed file *might* be the same as the
-- source file, but that doesn't do any harm.
ppFilesFromSummaries summaries = map ms_hspp_file summaries

-- -----------------------------------------------------------------------------
-- Check module

data CheckedModule = 
  CheckedModule { parsedSource      :: ParsedSource,
		  renamedSource     :: Maybe RenamedSource,
		  typecheckedSource :: Maybe TypecheckedSource,
		  checkedModuleInfo :: Maybe ModuleInfo
	        }
	-- ToDo: improvements that could be made here:
	--  if the module succeeded renaming but not typechecking,
	--  we can still get back the GlobalRdrEnv and exports, so
	--  perhaps the ModuleInfo should be split up into separate
	--  fields within CheckedModule.

type ParsedSource      = Located (HsModule RdrName)
type RenamedSource     = (HsGroup Name, [LImportDecl Name], Maybe [LIE Name])
type TypecheckedSource = LHsBinds Id

-- NOTE:
--   - things that aren't in the output of the typechecker right now:
--     - the export list
--     - the imports
--     - type signatures
--     - type/data/newtype declarations
--     - class declarations
--     - instances
--   - extra things in the typechecker's output:
--     - default methods are turned into top-level decls.
--     - dictionary bindings


-- | This is the way to get access to parsed and typechecked source code
-- for a module.  'checkModule' loads all the dependencies of the specified
-- module in the Session, and then attempts to typecheck the module.  If
-- successful, it returns the abstract syntax for the module.
checkModule :: Session -> ModuleName -> IO (Maybe CheckedModule)
checkModule session@(Session ref) mod = do
	-- load up the dependencies first
   r <- load session (LoadDependenciesOf mod)
   if (failed r) then return Nothing else do

	-- now parse & typecheck the module
   hsc_env <- readIORef ref   
   let mg  = hsc_mod_graph hsc_env
   case [ ms | ms <- mg, ms_mod_name ms == mod ] of
	[] -> return Nothing
	(ms:_) -> do 
	   mbChecked <- hscFileCheck hsc_env{hsc_dflags=ms_hspp_opts ms} ms
	   case mbChecked of
             Nothing -> return Nothing
             Just (HscChecked parsed renamed Nothing) ->
		   return (Just (CheckedModule {
					parsedSource = parsed,
					renamedSource = renamed,
					typecheckedSource = Nothing,
					checkedModuleInfo = Nothing }))
             Just (HscChecked parsed renamed
			   (Just (tc_binds, rdr_env, details))) -> do
		   let minf = ModuleInfo {
				minf_type_env  = md_types details,
				minf_exports   = md_exports details,
				minf_rdr_env   = Just rdr_env,
				minf_instances = md_insts details
			      }
		   return (Just (CheckedModule {
					parsedSource = parsed,
					renamedSource = renamed,
					typecheckedSource = Just tc_binds,
					checkedModuleInfo = Just minf }))

-- ---------------------------------------------------------------------------
-- Unloading

unload :: HscEnv -> [Linkable] -> IO ()
unload hsc_env stable_linkables	-- Unload everthing *except* 'stable_linkables'
  = case ghcMode (hsc_dflags hsc_env) of
	BatchCompile  -> return ()
	JustTypecheck -> return ()
#ifdef GHCI
	Interactive -> Linker.unload (hsc_dflags hsc_env) stable_linkables
#else
	Interactive -> panic "unload: no interpreter"
#endif
	other -> panic "unload: strange mode"

-- -----------------------------------------------------------------------------
-- checkStability

{-
  Stability tells us which modules definitely do not need to be recompiled.
  There are two main reasons for having stability:
  
   - avoid doing a complete upsweep of the module graph in GHCi when
     modules near the bottom of the tree have not changed.

   - to tell GHCi when it can load object code: we can only load object code
     for a module when we also load object code fo  all of the imports of the
     module.  So we need to know that we will definitely not be recompiling
     any of these modules, and we can use the object code.

  NB. stability is of no importance to BatchCompile at all, only Interactive.
  (ToDo: what about JustTypecheck?)

  The stability check is as follows.  Both stableObject and
  stableBCO are used during the upsweep phase later.

  -------------------
  stable m = stableObject m || stableBCO m

  stableObject m = 
	all stableObject (imports m)
	&& old linkable does not exist, or is == on-disk .o
	&& date(on-disk .o) > date(.hs)

  stableBCO m =
	all stable (imports m)
	&& date(BCO) > date(.hs)
  -------------------    

  These properties embody the following ideas:

    - if a module is stable:
	- if it has been compiled in a previous pass (present in HPT)
	  then it does not need to be compiled or re-linked.
        - if it has not been compiled in a previous pass,
	  then we only need to read its .hi file from disk and
	  link it to produce a ModDetails.

    - if a modules is not stable, we will definitely be at least
      re-linking, and possibly re-compiling it during the upsweep.
      All non-stable modules can (and should) therefore be unlinked
      before the upsweep.

    - Note that objects are only considered stable if they only depend
      on other objects.  We can't link object code against byte code.
-}

checkStability
	:: HomePackageTable		-- HPT from last compilation
	-> [SCC ModSummary]		-- current module graph (cyclic)
	-> [ModuleName]			-- all home modules
	-> ([ModuleName],		-- stableObject
	    [ModuleName])		-- stableBCO

checkStability hpt sccs all_home_mods = foldl checkSCC ([],[]) sccs
  where
   checkSCC (stable_obj, stable_bco) scc0
     | stableObjects = (scc_mods ++ stable_obj, stable_bco)
     | stableBCOs    = (stable_obj, scc_mods ++ stable_bco)
     | otherwise     = (stable_obj, stable_bco)
     where
	scc = flattenSCC scc0
	scc_mods = map ms_mod_name scc
	home_module m   = m `elem` all_home_mods && m `notElem` scc_mods

        scc_allimps = nub (filter home_module (concatMap ms_allimps scc))
	    -- all imports outside the current SCC, but in the home pkg
	
	stable_obj_imps = map (`elem` stable_obj) scc_allimps
	stable_bco_imps = map (`elem` stable_bco) scc_allimps

	stableObjects = 
	   and stable_obj_imps
	   && all object_ok scc

	stableBCOs = 
	   and (zipWith (||) stable_obj_imps stable_bco_imps)
	   && all bco_ok scc

	object_ok ms
	  | Just t <- ms_obj_date ms  =  t >= ms_hs_date ms 
					 && same_as_prev t
	  | otherwise = False
	  where
	     same_as_prev t = case lookupUFM hpt (ms_mod_name ms) of
				Just hmi  | Just l <- hm_linkable hmi
				 -> isObjectLinkable l && t == linkableTime l
				_other  -> True
		-- why '>=' rather than '>' above?  If the filesystem stores
		-- times to the nearset second, we may occasionally find that
		-- the object & source have the same modification time, 
		-- especially if the source was automatically generated
		-- and compiled.  Using >= is slightly unsafe, but it matches
		-- make's behaviour.

	bco_ok ms
	  = case lookupUFM hpt (ms_mod_name ms) of
		Just hmi  | Just l <- hm_linkable hmi ->
			not (isObjectLinkable l) && 
			linkableTime l >= ms_hs_date ms
		_other  -> False

ms_allimps :: ModSummary -> [ModuleName]
ms_allimps ms = map unLoc (ms_srcimps ms ++ ms_imps ms)

-- -----------------------------------------------------------------------------
-- Prune the HomePackageTable

-- Before doing an upsweep, we can throw away:
--
--   - For non-stable modules:
--	- all ModDetails, all linked code
--   - all unlinked code that is out of date with respect to
--     the source file
--
-- This is VERY IMPORTANT otherwise we'll end up requiring 2x the
-- space at the end of the upsweep, because the topmost ModDetails of the
-- old HPT holds on to the entire type environment from the previous
-- compilation.

pruneHomePackageTable
   :: HomePackageTable
   -> [ModSummary]
   -> ([ModuleName],[ModuleName])
   -> HomePackageTable

pruneHomePackageTable hpt summ (stable_obj, stable_bco)
  = mapUFM prune hpt
  where prune hmi
	  | is_stable modl = hmi'
	  | otherwise      = hmi'{ hm_details = emptyModDetails }
	  where
	   modl = moduleName (mi_module (hm_iface hmi))
	   hmi' | Just l <- hm_linkable hmi, linkableTime l < ms_hs_date ms
		= hmi{ hm_linkable = Nothing }
		| otherwise
		= hmi
		where ms = expectJust "prune" (lookupUFM ms_map modl)

        ms_map = listToUFM [(ms_mod_name ms, ms) | ms <- summ]

	is_stable m = m `elem` stable_obj || m `elem` stable_bco

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

-- Return (names of) all those in modsDone who are part of a cycle
-- as defined by theGraph.
findPartiallyCompletedCycles :: [Module] -> [SCC ModSummary] -> [Module]
findPartiallyCompletedCycles modsDone theGraph
   = chew theGraph
     where
        chew [] = []
        chew ((AcyclicSCC v):rest) = chew rest    -- acyclic?  not interesting.
        chew ((CyclicSCC vs):rest)
           = let names_in_this_cycle = nub (map ms_mod vs)
                 mods_in_this_cycle  
                    = nub ([done | done <- modsDone, 
                                   done `elem` names_in_this_cycle])
                 chewed_rest = chew rest
             in 
             if   notNull mods_in_this_cycle
                  && length mods_in_this_cycle < length names_in_this_cycle
             then mods_in_this_cycle ++ chewed_rest
             else chewed_rest

-- -----------------------------------------------------------------------------
-- The upsweep

-- This is where we compile each module in the module graph, in a pass
-- from the bottom to the top of the graph.

-- There better had not be any cyclic groups here -- we check for them.

upsweep
    :: HscEnv			-- Includes initially-empty HPT
    -> HomePackageTable		-- HPT from last time round (pruned)
    -> ([ModuleName],[ModuleName]) -- stable modules (see checkStability)
    -> IO ()			-- How to clean up unwanted tmp files
    -> [SCC ModSummary]		-- Mods to do (the worklist)
    -> IO (SuccessFlag,
           HscEnv,		-- With an updated HPT
           [ModSummary])	-- Mods which succeeded

upsweep hsc_env old_hpt stable_mods cleanup mods
   = upsweep' hsc_env old_hpt stable_mods cleanup mods 1 (length mods)

upsweep' hsc_env old_hpt stable_mods cleanup
     [] _ _
   = return (Succeeded, hsc_env, [])

upsweep' hsc_env old_hpt stable_mods cleanup
     (CyclicSCC ms:_) _ _
   = do fatalErrorMsg (hsc_dflags hsc_env) (cyclicModuleErr ms)
        return (Failed, hsc_env, [])

upsweep' hsc_env old_hpt stable_mods cleanup
     (AcyclicSCC mod:mods) mod_index nmods
   = do -- putStrLn ("UPSWEEP_MOD: hpt = " ++ 
	--	     show (map (moduleUserString.moduleName.mi_module.hm_iface) 
	--		       (moduleEnvElts (hsc_HPT hsc_env)))

        mb_mod_info <- upsweep_mod hsc_env old_hpt stable_mods mod 
                       mod_index nmods

	cleanup		-- Remove unwanted tmp files between compilations

        case mb_mod_info of
	    Nothing -> return (Failed, hsc_env, [])
	    Just mod_info -> do 
		{ let this_mod = ms_mod_name mod

			-- Add new info to hsc_env
		      hpt1     = addToUFM (hsc_HPT hsc_env) this_mod mod_info
		      hsc_env1 = hsc_env { hsc_HPT = hpt1 }

			-- Space-saving: delete the old HPT entry
			-- for mod BUT if mod is a hs-boot
			-- node, don't delete it.  For the
			-- interface, the HPT entry is probaby for the
			-- main Haskell source file.  Deleting it
			-- would force .. (what?? --SDM)
		      old_hpt1 | isBootSummary mod = old_hpt
			       | otherwise = delFromUFM old_hpt this_mod

		; (restOK, hsc_env2, modOKs) 
			<- upsweep' hsc_env1 old_hpt1 stable_mods cleanup 
				mods (mod_index+1) nmods
		; return (restOK, hsc_env2, mod:modOKs)
		}


-- Compile a single module.  Always produce a Linkable for it if 
-- successful.  If no compilation happened, return the old Linkable.
upsweep_mod :: HscEnv
            -> HomePackageTable
	    -> ([ModuleName],[ModuleName])
            -> ModSummary
            -> Int  -- index of module
            -> Int  -- total number of modules
            -> IO (Maybe HomeModInfo)	-- Nothing => Failed

upsweep_mod hsc_env old_hpt (stable_obj, stable_bco) summary mod_index nmods
   = do 
        let 
	    this_mod_name = ms_mod_name summary
	    this_mod    = ms_mod summary
	    mb_obj_date = ms_obj_date summary
	    obj_fn	= ml_obj_file (ms_location summary)
	    hs_date     = ms_hs_date summary

	    compile_it :: Maybe Linkable -> IO (Maybe HomeModInfo)
	    compile_it  = upsweep_compile hsc_env old_hpt this_mod_name 
				summary mod_index nmods

	case ghcMode (hsc_dflags hsc_env) of
	    BatchCompile ->
		case () of
		   -- Batch-compilating is easy: just check whether we have
		   -- an up-to-date object file.  If we do, then the compiler
		   -- needs to do a recompilation check.
		   _ | Just obj_date <- mb_obj_date, obj_date >= hs_date -> do
		           linkable <- 
				findObjectLinkable this_mod obj_fn obj_date
			   compile_it (Just linkable)

		     | otherwise ->
		           compile_it Nothing

	    interactive ->
		case () of
		    _ | is_stable_obj, isJust old_hmi ->
			   return old_hmi
			-- object is stable, and we have an entry in the
			-- old HPT: nothing to do

		      | is_stable_obj, isNothing old_hmi -> do
		           linkable <-
				findObjectLinkable this_mod obj_fn 
					(expectJust "upseep1" mb_obj_date)
			   compile_it (Just linkable)
			-- object is stable, but we need to load the interface
			-- off disk to make a HMI.

		      | is_stable_bco -> 
			   ASSERT(isJust old_hmi) -- must be in the old_hpt
			   return old_hmi
			-- BCO is stable: nothing to do

		      | Just hmi <- old_hmi,
			Just l <- hm_linkable hmi, not (isObjectLinkable l),
			linkableTime l >= ms_hs_date summary ->
			   compile_it (Just l)
			-- we have an old BCO that is up to date with respect
			-- to the source: do a recompilation check as normal.

		      | otherwise ->
			  compile_it Nothing
			-- no existing code at all: we must recompile.
		   where
		    is_stable_obj = this_mod_name `elem` stable_obj
		    is_stable_bco = this_mod_name `elem` stable_bco

		    old_hmi = lookupUFM old_hpt this_mod_name

-- Run hsc to compile a module
upsweep_compile hsc_env old_hpt this_mod summary
                mod_index nmods
                mb_old_linkable = do
  let
	-- The old interface is ok if it's in the old HPT 
	--	a) we're compiling a source file, and the old HPT
	--	   entry is for a source file
	--	b) we're compiling a hs-boot file
	-- Case (b) allows an hs-boot file to get the interface of its
	-- real source file on the second iteration of the compilation
	-- manager, but that does no harm.  Otherwise the hs-boot file
	-- will always be recompiled

        mb_old_iface 
		= case lookupUFM old_hpt this_mod of
		     Nothing	 			  -> Nothing
		     Just hm_info | isBootSummary summary -> Just iface
				  | not (mi_boot iface)   -> Just iface
				  | otherwise		  -> Nothing
				   where 
				     iface = hm_iface hm_info

  compresult <- compile hsc_env summary mb_old_linkable mb_old_iface
                        mod_index nmods