HscMain.hs

-------------------------------------------------------------------------------
--
-- | Main API for compiling plain Haskell source code.
--
-- This module implements compilation of a Haskell source. It is
-- /not/ concerned with preprocessing of source files; this is handled
-- in "DriverPipeline".
--
-- There are various entry points depending on what mode we're in:
-- "batch" mode (@--make@), "one-shot" mode (@-c@, @-S@ etc.), and
-- "interactive" mode (GHCi). There are also entry points for
-- individual passes: parsing, typechecking/renaming, desugaring, and
-- simplification.
--
-- All the functions here take an 'HscEnv' as a parameter, but none of
-- them return a new one: 'HscEnv' is treated as an immutable value
-- from here on in (although it has mutable components, for the
-- caches).
--
-- Warning messages are dealt with consistently throughout this API:
-- during compilation warnings are collected, and before any function
-- in @HscMain@ returns, the warnings are either printed, or turned
-- into a real compialtion error if the @-Werror@ flag is enabled.
--
-- (c) The GRASP/AQUA Project, Glasgow University, 1993-2000
--
-------------------------------------------------------------------------------

module HscMain
    (
    -- * Making an HscEnv
      newHscEnv

    -- * Compiling complete source files
    , Compiler
    , HscStatus' (..)
    , InteractiveStatus, HscStatus
    , hscCompileOneShot
    , hscCompileBatch
    , hscCompileNothing
    , hscCompileInteractive
    , hscCompileCmmFile
    , hscCompileCore

    -- * Running passes separately
    , hscParse
    , hscTypecheckRename
    , hscDesugar
    , makeSimpleIface
    , makeSimpleDetails
    , hscSimplify -- ToDo, shouldn't really export this

    -- ** Backends
    , hscOneShotBackendOnly
    , hscBatchBackendOnly
    , hscNothingBackendOnly
    , hscInteractiveBackendOnly

    -- * Support for interactive evaluation
    , hscParseIdentifier
    , hscTcRcLookupName
    , hscTcRnGetInfo
    , hscCheckSafe
    , hscGetSafe
#ifdef GHCI
    , hscIsGHCiMonad
    , hscGetModuleInterface
    , hscRnImportDecls
    , hscTcRnLookupRdrName
    , hscStmt, hscStmtWithLocation
    , hscDecls, hscDeclsWithLocation
    , hscTcExpr, hscImport, hscKcType
    , hscCompileCoreExpr
#endif
    ) where

#ifdef GHCI
import Id
import ByteCodeGen      ( byteCodeGen, coreExprToBCOs )
import Linker
import CoreTidy         ( tidyExpr )
import Type             ( Type )
import PrelNames
import {- Kind parts of -} Type         ( Kind )
import CoreLint         ( lintUnfolding )
import DsMeta           ( templateHaskellNames )
import VarSet
import VarEnv           ( emptyTidyEnv )
import Panic

import GHC.Exts
#endif

import Module
import Packages
import RdrName
import HsSyn
import CoreSyn
import StringBuffer
import Parser
import Lexer
import SrcLoc
import TcRnDriver
import TcIface          ( typecheckIface )
import TcRnMonad
import IfaceEnv         ( initNameCache )
import LoadIface        ( ifaceStats, initExternalPackageState )
import PrelInfo
import MkIface
import Desugar
import SimplCore
import TidyPgm
import CorePrep
import CoreToStg        ( coreToStg )
import qualified StgCmm ( codeGen )
import StgSyn
import CostCentre
import ProfInit
import TyCon
import Name
import SimplStg         ( stg2stg )
import qualified OldCmm as Old
import qualified Cmm as New
import CmmParse         ( parseCmmFile )
import CmmBuildInfoTables
import CmmPipeline
import CmmInfo
import CmmCvt
import CodeOutput
import NameEnv          ( emptyNameEnv )
import NameSet          ( emptyNameSet )
import InstEnv
import FamInstEnv
import Fingerprint      ( Fingerprint )

import DynFlags
import ErrUtils

import Outputable
import HscStats         ( ppSourceStats )
import HscTypes
import MkExternalCore   ( emitExternalCore )
import FastString
import UniqFM           ( emptyUFM )
import UniqSupply
import Bag
import Exception
import qualified Stream
import Stream (Stream)

import Util

import Data.List
import Control.Monad
import Data.Maybe
import Data.IORef
import System.FilePath as FilePath
import System.Directory

#include "HsVersions.h"


{- **********************************************************************
%*                                                                      *
                Initialisation
%*                                                                      *
%********************************************************************* -}

newHscEnv :: DynFlags -> IO HscEnv
newHscEnv dflags = do
    eps_var <- newIORef initExternalPackageState
    us      <- mkSplitUniqSupply 'r'
    nc_var  <- newIORef (initNameCache us knownKeyNames)
    fc_var  <- newIORef emptyUFM
    mlc_var <- newIORef emptyModuleEnv
    return HscEnv {  hsc_dflags       = dflags,
                     hsc_targets      = [],
                     hsc_mod_graph    = [],
                     hsc_IC           = emptyInteractiveContext dflags,
                     hsc_HPT          = emptyHomePackageTable,
                     hsc_EPS          = eps_var,
                     hsc_NC           = nc_var,
                     hsc_FC           = fc_var,
                     hsc_MLC          = mlc_var,
                     hsc_type_env_var = Nothing }


knownKeyNames :: [Name]      -- Put here to avoid loops involving DsMeta,
knownKeyNames =              -- where templateHaskellNames are defined
    map getName wiredInThings
        ++ basicKnownKeyNames
#ifdef GHCI
        ++ templateHaskellNames
#endif

-- -----------------------------------------------------------------------------
-- The Hsc monad: Passing an enviornment and warning state

newtype Hsc a = Hsc (HscEnv -> WarningMessages -> IO (a, WarningMessages))

instance Monad Hsc where
    return a    = Hsc $ \_ w -> return (a, w)
    Hsc m >>= k = Hsc $ \e w -> do (a, w1) <- m e w
                                   case k a of
                                       Hsc k' -> k' e w1

instance MonadIO Hsc where
    liftIO io = Hsc $ \_ w -> do a <- io; return (a, w)

instance Functor Hsc where
    fmap f m = m >>= \a -> return $ f a

runHsc :: HscEnv -> Hsc a -> IO a
runHsc hsc_env (Hsc hsc) = do
    (a, w) <- hsc hsc_env emptyBag
    printOrThrowWarnings (hsc_dflags hsc_env) w
    return a

-- A variant of runHsc that switches in the DynFlags from the
-- InteractiveContext before running the Hsc computation.
--
runInteractiveHsc :: HscEnv -> Hsc a -> IO a
runInteractiveHsc hsc_env =
  runHsc (hsc_env { hsc_dflags = ic_dflags (hsc_IC hsc_env) })

getWarnings :: Hsc WarningMessages
getWarnings = Hsc $ \_ w -> return (w, w)

clearWarnings :: Hsc ()
clearWarnings = Hsc $ \_ _ -> return ((), emptyBag)

logWarnings :: WarningMessages -> Hsc ()
logWarnings w = Hsc $ \_ w0 -> return ((), w0 `unionBags` w)

getHscEnv :: Hsc HscEnv
getHscEnv = Hsc $ \e w -> return (e, w)

instance HasDynFlags Hsc where
    getDynFlags = Hsc $ \e w -> return (hsc_dflags e, w)

handleWarnings :: Hsc ()
handleWarnings = do
    dflags <- getDynFlags
    w <- getWarnings
    liftIO $ printOrThrowWarnings dflags w
    clearWarnings

-- | log warning in the monad, and if there are errors then
-- throw a SourceError exception.
logWarningsReportErrors :: Messages -> Hsc ()
logWarningsReportErrors (warns,errs) = do
    logWarnings warns
    when (not $ isEmptyBag errs) $ throwErrors errs

-- | Throw some errors.
throwErrors :: ErrorMessages -> Hsc a
throwErrors = liftIO . throwIO . mkSrcErr

-- | Deal with errors and warnings returned by a compilation step
--
-- In order to reduce dependencies to other parts of the compiler, functions
-- outside the "main" parts of GHC return warnings and errors as a parameter
-- and signal success via by wrapping the result in a 'Maybe' type. This
-- function logs the returned warnings and propagates errors as exceptions
-- (of type 'SourceError').
--
-- This function assumes the following invariants:
--
--  1. If the second result indicates success (is of the form 'Just x'),
--     there must be no error messages in the first result.
--
--  2. If there are no error messages, but the second result indicates failure
--     there should be warnings in the first result. That is, if the action
--     failed, it must have been due to the warnings (i.e., @-Werror@).
ioMsgMaybe :: IO (Messages, Maybe a) -> Hsc a
ioMsgMaybe ioA = do
    ((warns,errs), mb_r) <- liftIO ioA
    logWarnings warns
    case mb_r of
        Nothing -> throwErrors errs
        Just r  -> ASSERT( isEmptyBag errs ) return r

-- | like ioMsgMaybe, except that we ignore error messages and return
-- 'Nothing' instead.
ioMsgMaybe' :: IO (Messages, Maybe a) -> Hsc (Maybe a)
ioMsgMaybe' ioA = do
    ((warns,_errs), mb_r) <- liftIO $ ioA
    logWarnings warns
    return mb_r

-- -----------------------------------------------------------------------------
-- | Lookup things in the compiler's environment

#ifdef GHCI
hscTcRnLookupRdrName :: HscEnv -> RdrName -> IO [Name]
hscTcRnLookupRdrName hsc_env0 rdr_name = runInteractiveHsc hsc_env0 $ do
   hsc_env <- getHscEnv
   ioMsgMaybe $ tcRnLookupRdrName hsc_env rdr_name
#endif

hscTcRcLookupName :: HscEnv -> Name -> IO (Maybe TyThing)
hscTcRcLookupName hsc_env0 name = runInteractiveHsc hsc_env0 $ do
  hsc_env <- getHscEnv
  ioMsgMaybe' $ tcRnLookupName hsc_env name
      -- ignore errors: the only error we're likely to get is
      -- "name not found", and the Maybe in the return type
      -- is used to indicate that.

hscTcRnGetInfo :: HscEnv -> Name -> IO (Maybe (TyThing, Fixity, [ClsInst]))
hscTcRnGetInfo hsc_env0 name = runInteractiveHsc hsc_env0 $ do
  hsc_env <- getHscEnv
  ioMsgMaybe' $ tcRnGetInfo hsc_env name

#ifdef GHCI
hscIsGHCiMonad :: HscEnv -> String -> IO Name
hscIsGHCiMonad hsc_env name =
    let icntxt   = hsc_IC hsc_env
    in runHsc hsc_env $ ioMsgMaybe $ isGHCiMonad hsc_env icntxt name

hscGetModuleInterface :: HscEnv -> Module -> IO ModIface
hscGetModuleInterface hsc_env0 mod = runInteractiveHsc hsc_env0 $ do
  hsc_env <- getHscEnv
  ioMsgMaybe $ getModuleInterface hsc_env mod

-- -----------------------------------------------------------------------------
-- | Rename some import declarations
hscRnImportDecls :: HscEnv -> [LImportDecl RdrName] -> IO GlobalRdrEnv
hscRnImportDecls hsc_env0 import_decls = runInteractiveHsc hsc_env0 $ do
  hsc_env <- getHscEnv
  ioMsgMaybe $ tcRnImportDecls hsc_env import_decls
#endif

-- -----------------------------------------------------------------------------
-- | parse a file, returning the abstract syntax

hscParse :: HscEnv -> ModSummary -> IO HsParsedModule
hscParse hsc_env mod_summary = runHsc hsc_env $ hscParse' mod_summary

-- internal version, that doesn't fail due to -Werror
hscParse' :: ModSummary -> Hsc HsParsedModule
hscParse' mod_summary = do
    dflags <- getDynFlags
    let src_filename  = ms_hspp_file mod_summary
        maybe_src_buf = ms_hspp_buf  mod_summary

    --------------------------  Parser  ----------------
    liftIO $ showPass dflags "Parser"
    {-# SCC "Parser" #-} do

    -- sometimes we already have the buffer in memory, perhaps
    -- because we needed to parse the imports out of it, or get the
    -- module name.
    buf <- case maybe_src_buf of
               Just b  -> return b
               Nothing -> liftIO $ hGetStringBuffer src_filename

    let loc = mkRealSrcLoc (mkFastString src_filename) 1 1

    case unP parseModule (mkPState dflags buf loc) of
        PFailed span err ->
            liftIO $ throwOneError (mkPlainErrMsg dflags span err)

        POk pst rdr_module -> do
            logWarningsReportErrors (getMessages pst)
            liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed "Parser" $
                                   ppr rdr_module
            liftIO $ dumpIfSet_dyn dflags Opt_D_source_stats "Source Statistics" $
                                   ppSourceStats False rdr_module

            -- To get the list of extra source files, we take the list
            -- that the parser gave us,
            --   - eliminate files beginning with '<'.  gcc likes to use
            --     pseudo-filenames like "<built-in>" and "<command-line>"
            --   - normalise them (elimiante differences between ./f and f)
            --   - filter out the preprocessed source file
            --   - filter out anything beginning with tmpdir
            --   - remove duplicates
            --   - filter out the .hs/.lhs source filename if we have one
            --
            let n_hspp  = FilePath.normalise src_filename
                srcs0 = nub $ filter (not . (tmpDir dflags `isPrefixOf`))
                            $ filter (not . (== n_hspp))
                            $ map FilePath.normalise
                            $ filter (not . (isPrefixOf "<"))
                            $ map unpackFS
                            $ srcfiles pst
                srcs1 = case ml_hs_file (ms_location mod_summary) of
                          Just f  -> filter (/= FilePath.normalise f) srcs0
                          Nothing -> srcs0

            -- sometimes we see source files from earlier
            -- preprocessing stages that cannot be found, so just
            -- filter them out:
            srcs2 <- liftIO $ filterM doesFileExist srcs1

            return HsParsedModule {
                      hpm_module    = rdr_module,
                      hpm_src_files = srcs2
                   }

-- XXX: should this really be a Maybe X?  Check under which circumstances this
-- can become a Nothing and decide whether this should instead throw an
-- exception/signal an error.
type RenamedStuff =
        (Maybe (HsGroup Name, [LImportDecl Name], Maybe [LIE Name],
                Maybe LHsDocString))

-- | Rename and typecheck a module, additionally returning the renamed syntax
hscTypecheckRename :: HscEnv -> ModSummary -> HsParsedModule
                   -> IO (TcGblEnv, RenamedStuff)
hscTypecheckRename hsc_env mod_summary rdr_module = runHsc hsc_env $ do
    tc_result <- tcRnModule' hsc_env mod_summary True rdr_module

        -- This 'do' is in the Maybe monad!
    let rn_info = do decl <- tcg_rn_decls tc_result
                     let imports = tcg_rn_imports tc_result
                         exports = tcg_rn_exports tc_result
                         doc_hdr = tcg_doc_hdr tc_result
                     return (decl,imports,exports,doc_hdr)

    return (tc_result, rn_info)

-- wrapper around tcRnModule to handle safe haskell extras
tcRnModule' :: HscEnv -> ModSummary -> Bool -> HsParsedModule
            -> Hsc TcGblEnv
tcRnModule' hsc_env sum save_rn_syntax mod = do
    tcg_res <- {-# SCC "Typecheck-Rename" #-}
               ioMsgMaybe $
                   tcRnModule hsc_env (ms_hsc_src sum) save_rn_syntax mod

    tcSafeOK <- liftIO $ readIORef (tcg_safeInfer tcg_res)
    dflags   <- getDynFlags

    -- end of the Safe Haskell line, how to respond to user?
    if not (safeHaskellOn dflags) || (safeInferOn dflags && not tcSafeOK)
        -- if safe haskell off or safe infer failed, wipe trust
        then wipeTrust tcg_res emptyBag

        -- module safe, throw warning if needed
        else do
            tcg_res' <- hscCheckSafeImports tcg_res
            safe <- liftIO $ readIORef (tcg_safeInfer tcg_res')
            when (safe && wopt Opt_WarnSafe dflags)
                 (logWarnings $ unitBag $
                     mkPlainWarnMsg dflags (warnSafeOnLoc dflags) $ errSafe tcg_res')
            return tcg_res'
  where
    pprMod t  = ppr $ moduleName $ tcg_mod t
    errSafe t = quotes (pprMod t) <+> text "has been inferred as safe!"

-- | Convert a typechecked module to Core
hscDesugar :: HscEnv -> ModSummary -> TcGblEnv -> IO ModGuts
hscDesugar hsc_env mod_summary tc_result =
    runHsc hsc_env $ hscDesugar' (ms_location mod_summary) tc_result

hscDesugar' :: ModLocation -> TcGblEnv -> Hsc ModGuts
hscDesugar' mod_location tc_result = do
    hsc_env <- getHscEnv
    r <- ioMsgMaybe $
      {-# SCC "deSugar" #-}
      deSugar hsc_env mod_location tc_result

    -- always check -Werror after desugaring, this is the last opportunity for
    -- warnings to arise before the backend.
    handleWarnings
    return r

-- | Make a 'ModIface' from the results of typechecking. Used when
-- not optimising, and the interface doesn't need to contain any
-- unfoldings or other cross-module optimisation info.
-- ToDo: the old interface is only needed to get the version numbers,
-- we should use fingerprint versions instead.
makeSimpleIface :: HscEnv -> Maybe ModIface -> TcGblEnv -> ModDetails
                -> IO (ModIface,Bool)
makeSimpleIface hsc_env maybe_old_iface tc_result details = runHsc hsc_env $ do
    safe_mode <- hscGetSafeMode tc_result
    ioMsgMaybe $ do
        mkIfaceTc hsc_env (fmap mi_iface_hash maybe_old_iface) safe_mode
                  details tc_result

-- | Make a 'ModDetails' from the results of typechecking. Used when
-- typechecking only, as opposed to full compilation.
makeSimpleDetails :: HscEnv -> TcGblEnv -> IO ModDetails
makeSimpleDetails hsc_env tc_result = mkBootModDetailsTc hsc_env tc_result


{- **********************************************************************
%*                                                                      *
                The main compiler pipeline
%*                                                                      *
%********************************************************************* -}

{-
                   --------------------------------
                        The compilation proper
                   --------------------------------

It's the task of the compilation proper to compile Haskell, hs-boot and core
files to either byte-code, hard-code (C, asm, LLVM, ect) or to nothing at all
(the module is still parsed and type-checked. This feature is mostly used by
IDE's and the likes). Compilation can happen in either 'one-shot', 'batch',
'nothing', or 'interactive' mode. 'One-shot' mode targets hard-code, 'batch'
mode targets hard-code, 'nothing' mode targets nothing and 'interactive' mode
targets byte-code.

The modes are kept separate because of their different types and meanings:

 * In 'one-shot' mode, we're only compiling a single file and can therefore
 discard the new ModIface and ModDetails. This is also the reason it only
 targets hard-code; compiling to byte-code or nothing doesn't make sense when
 we discard the result.

 * 'Batch' mode is like 'one-shot' except that we keep the resulting ModIface
 and ModDetails. 'Batch' mode doesn't target byte-code since that require us to
 return the newly compiled byte-code.

 * 'Nothing' mode has exactly the same type as 'batch' mode but they're still
 kept separate. This is because compiling to nothing is fairly special: We
 don't output any interface files, we don't run the simplifier and we don't
 generate any code.

 * 'Interactive' mode is similar to 'batch' mode except that we return the
 compiled byte-code together with the ModIface and ModDetails.

Trying to compile a hs-boot file to byte-code will result in a run-time error.
This is the only thing that isn't caught by the type-system.
-}


-- | Status of a compilation to hard-code or nothing.
data HscStatus' a
    = HscNoRecomp
    | HscRecomp
          (Maybe FilePath) -- Has stub files. This is a hack. We can't compile
                           -- C files here since it's done in DriverPipeline.
                           -- For now we just return True if we want the caller
                           -- to compile them for us.
          a

-- This is a bit ugly. Since we use a typeclass below and would like to avoid
-- functional dependencies, we have to parameterise the typeclass over the
-- result type. Therefore we need to artificially distinguish some types. We do
-- this by adding type tags which will simply be ignored by the caller.
type HscStatus         = HscStatus' ()
type InteractiveStatus = HscStatus' (Maybe (CompiledByteCode, ModBreaks))
    -- INVARIANT: result is @Nothing@ <=> input was a boot file

type OneShotResult     = HscStatus
type BatchResult       = (HscStatus, ModIface, ModDetails)
type NothingResult     = (HscStatus, ModIface, ModDetails)
type InteractiveResult = (InteractiveStatus, ModIface, ModDetails)

-- ToDo: The old interface and module index are only using in 'batch' and
--       'interactive' mode. They should be removed from 'oneshot' mode.
type Compiler result =  HscEnv
                     -> ModSummary
                     -> SourceModified
                     -> Maybe ModIface  -- Old interface, if available
                     -> Maybe (Int,Int) -- Just (i,n) <=> module i of n (for msgs)
                     -> IO result

data HsCompiler a = HsCompiler {
    -- | Called when no recompilation is necessary.
    hscNoRecomp :: ModIface
                -> Hsc a,

    -- | Called to recompile the module.
    hscRecompile :: ModSummary -> Maybe Fingerprint
                 -> Hsc a,

    hscBackend :: TcGblEnv -> ModSummary -> Maybe Fingerprint
               -> Hsc a,

    -- | Code generation for Boot modules.
    hscGenBootOutput :: TcGblEnv -> ModSummary -> Maybe Fingerprint
                     -> Hsc a,

    -- | Code generation for normal modules.
    hscGenOutput :: ModGuts -> ModSummary -> Maybe Fingerprint
                 -> Hsc a
  }

genericHscCompile :: HsCompiler a
                  -> (HscEnv -> Maybe (Int,Int) -> RecompileRequired -> ModSummary -> IO ())
                  -> HscEnv -> ModSummary -> SourceModified
                  -> Maybe ModIface -> Maybe (Int, Int)
                  -> IO a
genericHscCompile compiler hscMessage hsc_env
                  mod_summary source_modified
                  mb_old_iface0 mb_mod_index
  = do
    (recomp_reqd, mb_checked_iface)
        <- {-# SCC "checkOldIface" #-}
           checkOldIface hsc_env mod_summary
                         source_modified mb_old_iface0
    -- save the interface that comes back from checkOldIface.
    -- In one-shot mode we don't have the old iface until this
    -- point, when checkOldIface reads it from the disk.
    let mb_old_hash = fmap mi_iface_hash mb_checked_iface

    let skip iface = do
            hscMessage hsc_env mb_mod_index UpToDate mod_summary
            runHsc hsc_env $ hscNoRecomp compiler iface

        compile reason = do
            hscMessage hsc_env mb_mod_index reason mod_summary
            runHsc hsc_env $ hscRecompile compiler mod_summary mb_old_hash

        stable = case source_modified of
                     SourceUnmodifiedAndStable -> True
                     _                         -> False

        -- If the module used TH splices when it was last compiled,
        -- then the recompilation check is not accurate enough (#481)
        -- and we must ignore it. However, if the module is stable
        -- (none of the modules it depends on, directly or indirectly,
        -- changed), then we *can* skip recompilation. This is why
        -- the SourceModified type contains SourceUnmodifiedAndStable,
        -- and it's pretty important: otherwise ghc --make would
        -- always recompile TH modules, even if nothing at all has
        -- changed. Stability is just the same check that make is
        -- doing for us in one-shot mode.

    case mb_checked_iface of
        Just iface | not (recompileRequired recomp_reqd) ->
            if mi_used_th iface && not stable
                then compile (RecompBecause "TH")
                else skip iface
        _otherwise ->
            compile recomp_reqd

hscCheckRecompBackend :: HsCompiler a -> TcGblEnv -> Compiler a
hscCheckRecompBackend compiler tc_result hsc_env mod_summary
                      source_modified mb_old_iface _m_of_n
  = do
    (recomp_reqd, mb_checked_iface)
        <- {-# SCC "checkOldIface" #-}
           checkOldIface hsc_env mod_summary
                         source_modified mb_old_iface

    let mb_old_hash = fmap mi_iface_hash mb_checked_iface
    case mb_checked_iface of
        Just iface | not (recompileRequired recomp_reqd)
            -> runHsc hsc_env $
                   hscNoRecomp compiler
                       iface{ mi_globals = Just (tcg_rdr_env tc_result) }
        _otherwise
            -> runHsc hsc_env $
                   hscBackend compiler tc_result mod_summary mb_old_hash

genericHscRecompile :: HsCompiler a
                    -> ModSummary -> Maybe Fingerprint
                    -> Hsc a
genericHscRecompile compiler mod_summary mb_old_hash
    | ExtCoreFile <- ms_hsc_src mod_summary =
        panic "GHC does not currently support reading External Core files"
    | otherwise = do
        tc_result <- hscFileFrontEnd mod_summary
        hscBackend compiler tc_result mod_summary mb_old_hash

genericHscBackend :: HsCompiler a
                  -> TcGblEnv -> ModSummary -> Maybe Fingerprint
                  -> Hsc a
genericHscBackend compiler tc_result mod_summary mb_old_hash
    | HsBootFile <- ms_hsc_src mod_summary =
        hscGenBootOutput compiler tc_result mod_summary mb_old_hash
    | otherwise = do
        guts <- hscDesugar' (ms_location mod_summary) tc_result
        hscGenOutput compiler guts mod_summary mb_old_hash

compilerBackend :: HsCompiler a -> TcGblEnv -> Compiler a
compilerBackend comp tcg hsc_env ms' _ _mb_old_iface _ =
    runHsc hsc_env $ hscBackend comp tcg ms' Nothing

--------------------------------------------------------------
-- Compilers
--------------------------------------------------------------

hscOneShotCompiler :: HsCompiler OneShotResult
hscOneShotCompiler = HsCompiler {

    hscNoRecomp = \_old_iface -> do
        hsc_env <- getHscEnv
        liftIO $ dumpIfaceStats hsc_env
        return HscNoRecomp

  , hscRecompile = genericHscRecompile hscOneShotCompiler

  , hscBackend = \tc_result mod_summary mb_old_hash -> do
        dflags <- getDynFlags
        case hscTarget dflags of
            HscNothing -> return (HscRecomp Nothing ())
            _otherw    -> genericHscBackend hscOneShotCompiler
                              tc_result mod_summary mb_old_hash

  , hscGenBootOutput = \tc_result mod_summary mb_old_iface -> do
        (iface, changed, _) <- hscSimpleIface tc_result mb_old_iface
        hscWriteIface iface changed mod_summary
        return (HscRecomp Nothing ())

  , hscGenOutput = \guts0 mod_summary mb_old_iface -> do
        guts <- hscSimplify' guts0
        (iface, changed, _details, cgguts) <- hscNormalIface guts mb_old_iface
        hscWriteIface iface changed mod_summary
        hasStub <- hscGenHardCode cgguts mod_summary
        return (HscRecomp hasStub ())
  }

-- Compile Haskell, boot and extCore in OneShot mode.
hscCompileOneShot :: Compiler OneShotResult
hscCompileOneShot hsc_env mod_summary src_changed mb_old_iface mb_i_of_n
  = do
    -- One-shot mode needs a knot-tying mutable variable for interface
    -- files. See TcRnTypes.TcGblEnv.tcg_type_env_var.
    type_env_var <- newIORef emptyNameEnv
    let mod = ms_mod mod_summary
        hsc_env' = hsc_env{ hsc_type_env_var = Just (mod, type_env_var) }

    genericHscCompile hscOneShotCompiler
                      oneShotMsg hsc_env' mod_summary src_changed
                      mb_old_iface mb_i_of_n

hscOneShotBackendOnly :: TcGblEnv -> Compiler OneShotResult
hscOneShotBackendOnly = compilerBackend hscOneShotCompiler

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

hscBatchCompiler :: HsCompiler BatchResult
hscBatchCompiler = HsCompiler {

    hscNoRecomp = \iface -> do
        details <- genModDetails iface
        return (HscNoRecomp, iface, details)

  , hscRecompile = genericHscRecompile hscBatchCompiler

  , hscBackend = genericHscBackend hscBatchCompiler

  , hscGenBootOutput = \tc_result mod_summary mb_old_iface -> do
        (iface, changed, details) <- hscSimpleIface tc_result mb_old_iface
        hscWriteIface iface changed mod_summary
        return (HscRecomp Nothing (), iface, details)

  , hscGenOutput = \guts0 mod_summary mb_old_iface -> do
        guts <- hscSimplify' guts0
        (iface, changed, details, cgguts) <- hscNormalIface guts mb_old_iface
        hscWriteIface iface changed mod_summary
        hasStub <- hscGenHardCode cgguts mod_summary
        return (HscRecomp hasStub (), iface, details)
  }

-- | Compile Haskell, boot and extCore in batch mode.
hscCompileBatch :: Compiler (HscStatus, ModIface, ModDetails)
hscCompileBatch = genericHscCompile hscBatchCompiler batchMsg

hscBatchBackendOnly :: TcGblEnv -> Compiler BatchResult
hscBatchBackendOnly = hscCheckRecompBackend hscBatchCompiler

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

hscInteractiveCompiler :: HsCompiler InteractiveResult
hscInteractiveCompiler = HsCompiler {
    hscNoRecomp = \iface -> do
        details <- genModDetails iface
        return (HscNoRecomp, iface, details)

  , hscRecompile = genericHscRecompile hscInteractiveCompiler

  , hscBackend = genericHscBackend hscInteractiveCompiler

  , hscGenBootOutput = \tc_result _mod_summary mb_old_iface -> do
        (iface, _changed, details) <- hscSimpleIface tc_result mb_old_iface
        return (HscRecomp Nothing Nothing, iface, details)

  , hscGenOutput = \guts0 mod_summary mb_old_iface -> do
        guts <- hscSimplify' guts0
        (iface, _changed, details, cgguts) <- hscNormalIface guts mb_old_iface
        hscInteractive (iface, details, cgguts) mod_summary
  }

-- Compile Haskell, extCore to bytecode.
hscCompileInteractive :: Compiler (InteractiveStatus, ModIface, ModDetails)
hscCompileInteractive = genericHscCompile hscInteractiveCompiler batchMsg

hscInteractiveBackendOnly :: TcGblEnv -> Compiler InteractiveResult
hscInteractiveBackendOnly = compilerBackend hscInteractiveCompiler

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

hscNothingCompiler :: HsCompiler NothingResult
hscNothingCompiler = HsCompiler {
    hscNoRecomp = \iface -> do
        details <- genModDetails iface
        return (HscNoRecomp, iface, details)

  , hscRecompile = genericHscRecompile hscNothingCompiler

  , hscBackend = \tc_result _mod_summary mb_old_iface -> do
        handleWarnings
        (iface, _changed, details) <- hscSimpleIface tc_result mb_old_iface
        return (HscRecomp Nothing (), iface, details)

  , hscGenBootOutput = \_ _ _ ->
        panic "hscCompileNothing: hscGenBootOutput should not be called"

  , hscGenOutput = \_ _ _ ->
        panic "hscCompileNothing: hscGenOutput should not be called"
  }

-- Type-check Haskell and .hs-boot only (no external core)
hscCompileNothing :: Compiler (HscStatus, ModIface, ModDetails)
hscCompileNothing = genericHscCompile hscNothingCompiler batchMsg

hscNothingBackendOnly :: TcGblEnv -> Compiler NothingResult
hscNothingBackendOnly = compilerBackend hscNothingCompiler

--------------------------------------------------------------
-- NoRecomp handlers
--------------------------------------------------------------

genModDetails :: ModIface -> Hsc ModDetails
genModDetails old_iface
  = do
    hsc_env <- getHscEnv
    new_details <- {-# SCC "tcRnIface" #-}
                   liftIO $ initIfaceCheck hsc_env (typecheckIface old_iface)
    liftIO $ dumpIfaceStats hsc_env
    return new_details

--------------------------------------------------------------
-- Progress displayers.
--------------------------------------------------------------

oneShotMsg :: HscEnv -> Maybe (Int,Int) -> RecompileRequired -> ModSummary
            -> IO ()
oneShotMsg hsc_env _mb_mod_index recomp _mod_summary =
    case recomp of
        UpToDate ->
            compilationProgressMsg (hsc_dflags hsc_env) $
                   "compilation IS NOT required"
        _other ->
            return ()

batchMsg :: HscEnv -> Maybe (Int,Int) -> RecompileRequired -> ModSummary
         -> IO ()
batchMsg hsc_env mb_mod_index recomp mod_summary =
    case recomp of
        MustCompile -> showMsg "Compiling " ""
        UpToDate
            | verbosity (hsc_dflags hsc_env) >= 2 -> showMsg "Skipping  " ""
            | otherwise -> return ()
        RecompBecause reason -> showMsg "Compiling " (" [" ++ reason ++ "]")
    where
        dflags = hsc_dflags hsc_env
        showMsg msg reason =
            compilationProgressMsg dflags $
            (showModuleIndex mb_mod_index ++
            msg ++ showModMsg dflags (hscTarget dflags)
                              (recompileRequired recomp) mod_summary)
                ++ reason

--------------------------------------------------------------
-- FrontEnds
--------------------------------------------------------------

hscFileFrontEnd :: ModSummary -> Hsc TcGblEnv
hscFileFrontEnd mod_summary = do
    hpm <- hscParse' mod_summary
    hsc_env <- getHscEnv
    tcg_env <- tcRnModule' hsc_env mod_summary False hpm
    return tcg_env

--------------------------------------------------------------
-- Safe Haskell
--------------------------------------------------------------

-- Note [Safe Haskell Trust Check]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Safe Haskell checks that an import is trusted according to the following
-- rules for an import of module M that resides in Package P:
--
--   * If M is recorded as Safe and all its trust dependencies are OK
--     then M is considered safe.
--   * If M is recorded as Trustworthy and P is considered trusted and
--     all M's trust dependencies are OK then M is considered safe.
--
-- By trust dependencies we mean that the check is transitive. So if
-- a module M that is Safe relies on a module N that is trustworthy,
-- importing module M will first check (according to the second case)
-- that N is trusted before checking M is trusted.
--
-- This is a minimal description, so please refer to the user guide
-- for more details. The user guide is also considered the authoritative
-- source in this matter, not the comments or code.


-- Note [Safe Haskell Inference]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Safe Haskell does Safe inference on modules that don't have any specific
-- safe haskell mode flag. The basic aproach to this is:
--   * When deciding if we need to do a Safe language check, treat
--     an unmarked module as having -XSafe mode specified.
--   * For checks, don't throw errors but return them to the caller.
--   * Caller checks if there are errors:
--     * For modules explicitly marked -XSafe, we throw the errors.
--     * For unmarked modules (inference mode), we drop the errors
--       and mark the module as being Unsafe.


-- | Check that the safe imports of the module being compiled are valid.
-- If not we either issue a compilation error if the module is explicitly
-- using Safe Haskell, or mark the module as unsafe if we're in safe
-- inference mode.
hscCheckSafeImports :: TcGblEnv -> Hsc TcGblEnv
hscCheckSafeImports tcg_env = do
    dflags   <- getDynFlags
    tcg_env' <- checkSafeImports dflags tcg_env