main/HscMain.hs

    {-# LANGUAGE BangPatterns, CPP, MagicHash, NondecreasingIndentation #-}
    {-# OPTIONS_GHC -fprof-auto-top #-}

    -------------------------------------------------------------------------------
    --
    -- | 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).
    --
    -- We use the Hsc monad to deal with warning messages consistently:
    -- specifically, while executing within an Hsc monad, warnings are
    -- collected. When a Hsc monad returns to an IO monad, the
    -- warnings are printed, or compilation aborts 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
        , Messager, batchMsg
        , HscStatus (..)
        , hscIncrementalCompile
        , hscCompileCmmFile

        , hscGenHardCode
        , hscInteractive

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

        -- * Safe Haskell
        , hscCheckSafe
        , hscGetSafe

        -- * Support for interactive evaluation
        , hscParseIdentifier
        , hscTcRcLookupName
        , hscTcRnGetInfo
        , hscIsGHCiMonad
        , hscGetModuleInterface
        , hscRnImportDecls
        , hscTcRnLookupRdrName
        , hscStmt, hscStmtWithLocation, hscParsedStmt
        , hscDecls, hscDeclsWithLocation
        , hscTcExpr, TcRnExprMode(..), hscImport, hscKcType
        , hscParseExpr
        , hscCompileCoreExpr
        -- * Low-level exports for hooks
        , hscCompileCoreExpr'
          -- We want to make sure that we export enough to be able to redefine
          -- hscFileFrontEnd in client code
        , hscParse', hscSimplify', hscDesugar', tcRnModule'
        , getHscEnv
        , hscSimpleIface', hscNormalIface'
        , oneShotMsg
        , hscFileFrontEnd, genericHscFrontend, dumpIfaceStats
        , ioMsgMaybe
        , showModuleIndex
        , hscAddSptEntries
        ) where

    import Data.Data hiding (Fixity, TyCon)
    import Id
    import GHCi             ( addSptEntry )
    import GHCi.RemoteTypes ( ForeignHValue )
    import ByteCodeGen      ( byteCodeGen, coreExprToBCOs )
    import Linker
    import CoreTidy         ( tidyExpr )
    import Type             ( Type )
    import {- Kind parts of -} Type         ( Kind )
    import CoreLint         ( lintInteractiveExpr )
    import VarEnv           ( emptyTidyEnv )
    import Panic
    import ConLike
    import Control.Concurrent

    import Module
    import Packages
    import RdrName
    import HsSyn
    import HsDumpAst
    import CoreSyn
    import StringBuffer
    import Parser
    import Lexer
    import SrcLoc
    import TcRnDriver
    import TcIface          ( typecheckIface )
    import TcRnMonad
    import NameCache        ( 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 Cmm
    import CmmParse         ( parseCmmFile )
    import CmmBuildInfoTables
    import CmmPipeline
    import CmmInfo
    import CodeOutput
    import InstEnv
    import FamInstEnv
    import Fingerprint      ( Fingerprint )
    import Hooks
    import TcEnv

    import DynFlags
    import ErrUtils
    import Platform ( platformOS, osSubsectionsViaSymbols )

    import Outputable
    import NameEnv
    import HscStats         ( ppSourceStats )
    import HscTypes
    import FastString
    import UniqSupply
    import Bag
    import Exception
    import qualified Stream
    import Stream (Stream)

    import Util

    import Data.List
    import Control.Monad
    import Data.IORef
    import System.FilePath as FilePath
    import System.Directory
    import System.IO (fixIO)
    import qualified Data.Map as Map
    import qualified Data.Set as S
    import Data.Set (Set)

    #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 emptyInstalledModuleEnv
        iserv_mvar <- newMVar Nothing
        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_type_env_var = Nothing
                      , hsc_iserv        = iserv_mvar
                      }

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

    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)

    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

    hscTcRnLookupRdrName :: HscEnv -> Located RdrName -> IO [Name]
    hscTcRnLookupRdrName hsc_env0 rdr_name
      = runInteractiveHsc hsc_env0 $
        do { hsc_env <- getHscEnv
           ; ioMsgMaybe $ tcRnLookupRdrName hsc_env rdr_name }

    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], [FamInst]))
    hscTcRnGetInfo hsc_env0 name
      = runInteractiveHsc hsc_env0 $
        do { hsc_env <- getHscEnv
           ; ioMsgMaybe' $ tcRnGetInfo hsc_env name }

    hscIsGHCiMonad :: HscEnv -> String -> IO Name
    hscIsGHCiMonad hsc_env name
      = runHsc hsc_env $ ioMsgMaybe $ isGHCiMonad hsc_env 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

    -- -----------------------------------------------------------------------------
    -- | 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
     | Just r <- ms_parsed_mod mod_summary = return r
     | otherwise = {-# SCC "Parser" #-}
        withTiming getDynFlags
                   (text "Parser"<+>brackets (ppr $ ms_mod mod_summary))
                   (const ()) $ do
        dflags <- getDynFlags
        let src_filename  = ms_hspp_file mod_summary
            maybe_src_buf = ms_hspp_buf  mod_summary

        --------------------------  Parser  ----------------
        -- 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
        let parseMod | HsigFile == ms_hsc_src mod_summary
                     = parseSignature
                     | otherwise = parseModule

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

            POk pst rdr_module -> do
                logWarningsReportErrors (getMessages pst dflags)
                liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed "Parser" $
                                       ppr rdr_module
                liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed_ast "Parser AST" $
                                       text (showAstData NoBlankSrcSpan 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,
                          hpm_annotations
                                  = (Map.fromListWith (++) $ annotations pst,
                                     Map.fromList $ ((noSrcSpan,comment_q pst)
                                                     :(annotations_comments pst)))
                       }

    -- 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))

    -- -----------------------------------------------------------------------------
    -- | If the renamed source has been kept, extract it. Dump it if requested.
    extract_renamed_stuff :: TcGblEnv -> Hsc (TcGblEnv, RenamedStuff)
    extract_renamed_stuff tc_result = do

        -- 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)

        dflags <- getDynFlags
        liftIO $ dumpIfSet_dyn dflags Opt_D_dump_rn_ast "Renamer" $
                               text (showAstData NoBlankSrcSpan rn_info)

        return (tc_result, rn_info)

    -- -----------------------------------------------------------------------------
    -- | 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 <- hscTypecheck True mod_summary (Just rdr_module)
        extract_renamed_stuff tc_result

    hscTypecheck :: Bool -- ^ Keep renamed source?
                 -> ModSummary -> Maybe HsParsedModule
                 -> Hsc TcGblEnv
    hscTypecheck keep_rn mod_summary mb_rdr_module = do
        tc_result <- hscTypecheck' keep_rn mod_summary mb_rdr_module
        _ <- extract_renamed_stuff tc_result
        return tc_result

    hscTypecheck' :: Bool -- ^ Keep renamed source?
                  -> ModSummary -> Maybe HsParsedModule
                  -> Hsc TcGblEnv
    hscTypecheck' keep_rn mod_summary mb_rdr_module = do
        hsc_env <- getHscEnv
        let hsc_src = ms_hsc_src mod_summary
            dflags = hsc_dflags hsc_env
            outer_mod = ms_mod mod_summary
            mod_name = moduleName outer_mod
            outer_mod' = mkModule (thisPackage dflags) mod_name
            inner_mod = canonicalizeHomeModule dflags mod_name
            src_filename  = ms_hspp_file mod_summary
            real_loc = realSrcLocSpan $ mkRealSrcLoc (mkFastString src_filename) 1 1
        MASSERT( moduleUnitId outer_mod == thisPackage dflags )
        if hsc_src == HsigFile && not (isHoleModule inner_mod)
            then ioMsgMaybe $ tcRnInstantiateSignature hsc_env outer_mod' real_loc
            else
             do hpm <- case mb_rdr_module of
                        Just hpm -> return hpm
                        Nothing -> hscParse' mod_summary
                tc_result0 <- tcRnModule' hsc_env mod_summary keep_rn hpm
                if hsc_src == HsigFile
                    then do (iface, _, _) <- liftIO $ hscSimpleIface hsc_env tc_result0 Nothing
                            ioMsgMaybe $
                                tcRnMergeSignatures hsc_env hpm tc_result0 iface
                    else return tc_result0

    -- 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

        -- See Note [Safe Haskell Overlapping Instances Implementation]
        -- although this is used for more than just that failure case.
        (tcSafeOK, whyUnsafe) <- liftIO $ readIORef (tcg_safeInfer tcg_res)
        dflags   <- getDynFlags
        let allSafeOK = safeInferred dflags && tcSafeOK

        -- end of the safe haskell line, how to respond to user?
        if not (safeHaskellOn dflags) || (safeInferOn dflags && not allSafeOK)
            -- if safe Haskell off or safe infer failed, mark unsafe
            then markUnsafeInfer tcg_res whyUnsafe

            -- module (could be) safe, throw warning if needed
            else do
                tcg_res' <- hscCheckSafeImports tcg_res
                safe <- liftIO $ fst <$> readIORef (tcg_safeInfer tcg_res')
                when safe $ do
                  case wopt Opt_WarnSafe dflags of
                    True -> (logWarnings $ unitBag $
                             makeIntoWarning (Reason Opt_WarnSafe) $
                             mkPlainWarnMsg dflags (warnSafeOnLoc dflags) $
                             errSafe tcg_res')
                    False | safeHaskell dflags == Sf_Trustworthy &&
                            wopt Opt_WarnTrustworthySafe dflags ->
                            (logWarnings $ unitBag $
                             makeIntoWarning (Reason Opt_WarnTrustworthySafe) $
                             mkPlainWarnMsg dflags (trustworthyOnLoc dflags) $
                             errTwthySafe tcg_res')
                    False -> return ()
                return tcg_res'
      where
        pprMod t  = ppr $ moduleName $ tcg_mod t
        errSafe t = quotes (pprMod t) <+> text "has been inferred as safe!"
        errTwthySafe t = quotes (pprMod t)
          <+> text "is marked as Trustworthy but 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 '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.
    -}

    type Messager = HscEnv -> (Int,Int) -> RecompileRequired -> ModSummary -> IO ()

    -- | This function runs GHC's frontend with recompilation
    -- avoidance. Specifically, it checks if recompilation is needed,
    -- and if it is, it parses and typechecks the input module.
    -- It does not write out the results of typechecking (See
    -- compileOne and hscIncrementalCompile).
    hscIncrementalFrontend :: Bool -- always do basic recompilation check?
                           -> Maybe TcGblEnv
                           -> Maybe Messager
                           -> ModSummary
                           -> SourceModified
                           -> Maybe ModIface  -- Old interface, if available
                           -> (Int,Int)       -- (i,n) = module i of n (for msgs)
                           -> Hsc (Either ModIface (FrontendResult, Maybe Fingerprint))

    hscIncrementalFrontend
      always_do_basic_recompilation_check m_tc_result
      mHscMessage mod_summary source_modified mb_old_iface mod_index
        = do
        hsc_env <- getHscEnv

        let msg what = case mHscMessage of
                       Just hscMessage -> hscMessage hsc_env mod_index what mod_summary
                       Nothing -> return ()

            skip iface = do
                liftIO $ msg UpToDate
                return $ Left iface

            compile mb_old_hash reason = do
                liftIO $ msg reason
                result <- genericHscFrontend mod_summary
                return $ Right (result, mb_old_hash)

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

        case m_tc_result of
             Just tc_result
              | not always_do_basic_recompilation_check ->
                 return $ Right (FrontendTypecheck tc_result, Nothing)
             _ -> do
                (recomp_reqd, mb_checked_iface)
                    <- {-# SCC "checkOldIface" #-}
                       liftIO $ checkOldIface hsc_env mod_summary
                                    source_modified mb_old_iface
                -- 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

                case mb_checked_iface of
                    Just iface | not (recompileRequired recomp_reqd) ->
                        -- 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 m_tc_result of
                        Nothing
                         | mi_used_th iface && not stable ->
                            compile mb_old_hash (RecompBecause "TH")
                        _ ->
                            skip iface
                    _ ->
                        case m_tc_result of
                        Nothing -> compile mb_old_hash recomp_reqd
                        Just tc_result ->
                            return $ Right (FrontendTypecheck tc_result, mb_old_hash)

    genericHscFrontend :: ModSummary -> Hsc FrontendResult
    genericHscFrontend mod_summary =
      getHooked hscFrontendHook genericHscFrontend' >>= ($ mod_summary)

    genericHscFrontend' :: ModSummary -> Hsc FrontendResult
    genericHscFrontend' mod_summary
        = FrontendTypecheck `fmap` hscFileFrontEnd mod_summary

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

    -- Compile Haskell/boot in OneShot mode.
    hscIncrementalCompile :: Bool
                          -> Maybe TcGblEnv
                          -> Maybe Messager
                          -> HscEnv
                          -> ModSummary
                          -> SourceModified
                          -> Maybe ModIface
                          -> (Int,Int)
                          -- HomeModInfo does not contain linkable, since we haven't
                          -- code-genned yet
                          -> IO (HscStatus, HomeModInfo)
    hscIncrementalCompile always_do_basic_recompilation_check m_tc_result
        mHscMessage hsc_env' mod_summary source_modified mb_old_iface mod_index
      = do
        -- One-shot mode needs a knot-tying mutable variable for interface
        -- files. See TcRnTypes.TcGblEnv.tcg_type_env_var.
        -- See also Note [hsc_type_env_var hack]
        type_env_var <- newIORef emptyNameEnv
        let mod = ms_mod mod_summary
            hsc_env | isOneShot (ghcMode (hsc_dflags hsc_env'))
                    = hsc_env' { hsc_type_env_var = Just (mod, type_env_var) }
                    | otherwise
                    = hsc_env'

        -- NB: enter Hsc monad here so that we don't bail out early with
        -- -Werror on typechecker warnings; we also want to run the desugarer
        -- to get those warnings too. (But we'll always exit at that point
        -- because the desugarer runs ioMsgMaybe.)
        runHsc hsc_env $ do
        let dflags = hsc_dflags hsc_env

        e <- hscIncrementalFrontend always_do_basic_recompilation_check m_tc_result mHscMessage
                mod_summary source_modified mb_old_iface mod_index
        case e of
            -- We didn't need to do any typechecking; the old interface
            -- file on disk was good enough.
            Left iface -> do
                -- Knot tying!  See Note [Knot-tying typecheckIface]
                hmi <- liftIO . fixIO $ \hmi' -> do
                    let hsc_env' =
                            hsc_env {
                                hsc_HPT = addToHpt (hsc_HPT hsc_env)
                                            (ms_mod_name mod_summary) hmi'
                            }
                    -- NB: This result is actually not that useful
                    -- in one-shot mode, since we're not going to do
                    -- any further typechecking.  It's much more useful
                    -- in make mode, since this HMI will go into the HPT.
                    details <- genModDetails hsc_env' iface
                    return HomeModInfo{
                        hm_details = details,
                        hm_iface = iface,
                        hm_linkable = Nothing }
                return (HscUpToDate, hmi)
            -- We finished type checking.  (mb_old_hash is the hash of
            -- the interface that existed on disk; it's possible we had
            -- to retypecheck but the resulting interface is exactly
            -- the same.)
            Right (FrontendTypecheck tc_result, mb_old_hash) -> do
                (status, hmi, no_change)
                    <- case ms_hsc_src mod_summary of
                            HsSrcFile | hscTarget dflags /= HscNothing ->
                                finish              hsc_env mod_summary tc_result mb_old_hash
                            _ ->
                                finishTypecheckOnly hsc_env mod_summary tc_result mb_old_hash
                liftIO $ hscMaybeWriteIface dflags (hm_iface hmi) no_change mod_summary
                return (status, hmi)

    -- Generates and writes out the final interface for a typecheck.
    finishTypecheckOnly :: HscEnv
                  -> ModSummary
                  -> TcGblEnv
                  -> Maybe Fingerprint
                  -> Hsc (HscStatus, HomeModInfo, Bool)
    finishTypecheckOnly hsc_env summary tc_result mb_old_hash = do
        let dflags = hsc_dflags hsc_env
        (iface, changed, details) <- liftIO $ hscSimpleIface hsc_env tc_result mb_old_hash
        let hsc_status =
              case (hscTarget dflags, ms_hsc_src summary) of
                (HscNothing, _) -> HscNotGeneratingCode
                (_, HsBootFile) -> HscUpdateBoot
                (_, HsigFile) -> HscUpdateSig
                _ -> panic "finishTypecheckOnly"
        return (hsc_status,
                HomeModInfo{ hm_details  = details,
                             hm_iface    = iface,
                             hm_linkable = Nothing },
                changed)

    -- Runs the post-typechecking frontend (desugar and simplify),
    -- and then generates and writes out the final interface. We want
    -- to write the interface AFTER simplification so we can get
    -- as up-to-date and good unfoldings and other info as possible
    -- in the interface file.  This is only ever run for HsSrcFile,
    -- and NOT for HscNothing.
    finish :: HscEnv
           -> ModSummary
           -> TcGblEnv
           -> Maybe Fingerprint
           -> Hsc (HscStatus, HomeModInfo, Bool)
    finish hsc_env summary tc_result mb_old_hash = do
        let dflags = hsc_dflags hsc_env
        MASSERT( ms_hsc_src summary == HsSrcFile )
        MASSERT( hscTarget dflags /= HscNothing )
        guts0 <- hscDesugar' (ms_location summary) tc_result
        guts <- hscSimplify' guts0
        (iface, changed, details, cgguts) <- liftIO $ hscNormalIface hsc_env guts mb_old_hash

        return (HscRecomp cgguts summary,
                HomeModInfo{ hm_details  = details,
                             hm_iface    = iface,
                             hm_linkable = Nothing },
                changed)

    hscMaybeWriteIface :: DynFlags -> ModIface -> Bool -> ModSummary -> IO ()
    hscMaybeWriteIface dflags iface changed summary =
        let force_write_interface = gopt Opt_WriteInterface dflags
            write_interface = case hscTarget dflags of
                                HscNothing      -> False
                                HscInterpreted  -> False
                                _               -> True
        in when (write_interface || force_write_interface) $
                hscWriteIface dflags iface changed summary

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

    -- NB: this must be knot-tied appropriately, see hscIncrementalCompile
    genModDetails :: HscEnv -> ModIface -> IO ModDetails
    genModDetails hsc_env old_iface
      = do
        new_details <- {-# SCC "tcRnIface" #-}
                       initIfaceLoad hsc_env (typecheckIface old_iface)
        dumpIfaceStats hsc_env
        return new_details

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

    oneShotMsg :: HscEnv -> RecompileRequired -> IO ()
    oneShotMsg hsc_env recomp =
        case recomp of
            UpToDate ->
                compilationProgressMsg (hsc_dflags hsc_env) $
                       "compilation IS NOT required"
            _ ->
                return ()

    batchMsg :: Messager
    batchMsg hsc_env 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 mod_index ++
                msg ++ showModMsg dflags (hscTarget dflags)
                                  (recompileRequired recomp) mod_summary)
                    ++ reason

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

    -- | Given a 'ModSummary', parses and typechecks it, returning the
    -- 'TcGblEnv' resulting from type-checking.
    hscFileFrontEnd :: ModSummary -> Hsc TcGblEnv
    hscFileFrontEnd mod_summary = hscTypecheck False mod_summary Nothing

    --------------------------------------------------------------
    -- 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 approach 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.
    --
    -- It used to be that we only did safe inference on modules that had no Safe
    -- Haskell flags, but now we perform safe inference on all modules as we want
    -- to allow users to set the `-Wsafe`, `-Wunsafe` and
    -- `-Wtrustworthy-safe` flags on Trustworthy and Unsafe modules so that a
    -- user can ensure their assumptions are correct and see reasons for why a
    -- module is safe or unsafe.
    --
    -- This is tricky as we must be careful when we should throw an error compared
    -- to just warnings. For checking safe imports we manage it as two steps. First
    -- we check any imports that are required to be safe, then we check all other
    -- imports to see if we can infer them to be safe.

    -- | 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
        checkRULES dflags tcg_env'

      where
        checkRULES dflags tcg_env' = do
          case safeLanguageOn dflags of
              True -> do
                  -- XSafe: we nuke user written RULES
                  logWarnings $ warns dflags (tcg_rules tcg_env')
                  return tcg_env' { tcg_rules = [] }
              False
                    -- SafeInferred: user defined RULES, so not safe
                  | safeInferOn dflags && not (null $ tcg_rules tcg_env')
                  -> markUnsafeInfer tcg_env' $ warns dflags (tcg_rules tcg_env')

                    -- Trustworthy OR SafeInferred: with no RULES
                  | otherwise
                  -> return tcg_env'

        warns dflags rules = listToBag $ map (warnRules dflags) rules
        warnRules dflags (L loc (HsRule n _ _ _ _ _ _)) =
            mkPlainWarnMsg dflags loc $
                text "Rule \"" <> ftext (snd $ unLoc n) <> text "\" ignored" $+$
                text "User defined rules are disabled under Safe Haskell"

    -- | Validate that safe imported modules are actually safe.  For modules in the
    -- HomePackage (the package the module we are compiling in resides) this just
    -- involves checking its trust type is 'Safe' or 'Trustworthy'. For modules
    -- that reside in another package we also must check that the external pacakge
    -- is trusted. See the Note [Safe Haskell Trust Check] above for more
    -- information.
    --
    -- The code for this is quite tricky as the whole algorithm is done in a few
    -- distinct phases in different parts of the code base. See
    -- RnNames.rnImportDecl for where package trust dependencies for a module are
    -- collected and unioned.  Specifically see the Note [RnNames . Tracking Trust
    -- Transitively] and the Note [RnNames . Trust Own Package].
    checkSafeImports :: DynFlags -> TcGblEnv -> Hsc TcGblEnv
    checkSafeImports dflags tcg_env
        = do
            imps <- mapM condense imports'
            let (safeImps, regImps) = partition (\(_,_,s) -> s) imps

            -- We want to use the warning state specifically for detecting if safe
            -- inference has failed, so store and clear any existing warnings.
            oldErrs <- getWarnings
            clearWarnings

            -- Check safe imports are correct
            safePkgs <- S.fromList <$> mapMaybeM checkSafe safeImps
            safeErrs <- getWarnings
            clearWarnings

            -- Check non-safe imports are correct if inferring safety
            -- See the Note [Safe Haskell Inference]
            (infErrs, infPkgs) <- case (safeInferOn dflags) of
              False -> return (emptyBag, S.empty)
              True -> do infPkgs <- S.fromList <$> mapMaybeM checkSafe regImps
                         infErrs <- getWarnings
                         clearWarnings
                         return (infErrs, infPkgs)

            -- restore old errors
            logWarnings oldErrs

            case (isEmptyBag safeErrs) of
              -- Failed safe check
              False -> liftIO . throwIO . mkSrcErr $ safeErrs

              -- Passed safe check
              True -> do
                let infPassed = isEmptyBag infErrs
                tcg_env' <- case (not infPassed) of
                  True  -> markUnsafeInfer tcg_env infErrs
                  False -> return tcg_env
                when (packageTrustOn dflags) $ checkPkgTrust dflags pkgReqs
                let newTrust = pkgTrustReqs safePkgs infPkgs infPassed
                return tcg_env' { tcg_imports = impInfo `plusImportAvails` newTrust }

      where
        impInfo  = tcg_imports tcg_env     -- ImportAvails
        imports  = imp_mods impInfo        -- ImportedMods
        imports1 = moduleEnvToList imports -- (Module, [ImportedBy])
        imports' = map (fmap importedByUser) imports1 -- (Module, [ImportedModsVal])
        pkgReqs  = imp_trust_pkgs impInfo  -- [UnitId]

        condense :: (Module, [ImportedModsVal]) -> Hsc (Module, SrcSpan, IsSafeImport)
        condense (_, [])   = panic "HscMain.condense: Pattern match failure!"
        condense (m, x:xs) = do imv <- foldlM cond' x xs
                                return (m, imv_span imv, imv_is_safe imv)

        -- ImportedModsVal = (ModuleName, Bool, SrcSpan, IsSafeImport)
        cond' :: ImportedModsVal -> ImportedModsVal -> Hsc ImportedModsVal
        cond' v1 v2
            | imv_is_safe v1 /= imv_is_safe v2
            = throwErrors $ unitBag $ mkPlainErrMsg dflags (imv_span v1)
                  (text "Module" <+> ppr (imv_name v1) <+>
                  (text $ "is imported both as a safe and unsafe import!"))
            | otherwise
            = return v1

        -- easier interface to work with
        checkSafe :: (Module, SrcSpan, a) -> Hsc (Maybe InstalledUnitId)
        checkSafe (m, l, _) = fst `fmap` hscCheckSafe' dflags m l

        -- what pkg's to add to our trust requirements
        pkgTrustReqs :: Set InstalledUnitId -> Set InstalledUnitId -> Bool -> ImportAvails
        pkgTrustReqs req inf infPassed | safeInferOn dflags
                                      && safeHaskell dflags == Sf_None && infPassed
                                       = emptyImportAvails {
                                           imp_trust_pkgs = req `S.union` inf
                                       }
        pkgTrustReqs _   _ _ | safeHaskell dflags == Sf_Unsafe
                             = emptyImportAvails
        pkgTrustReqs req _ _ = emptyImportAvails { imp_trust_pkgs = req }

    -- | Check that a module is safe to import.
    --
    -- We return True to indicate the import is safe and False otherwise
    -- although in the False case an exception may be thrown first.
    hscCheckSafe :: HscEnv -> Module -> SrcSpan -> IO Bool
    hscCheckSafe hsc_env m l = runHsc hsc_env $ do
        dflags <- getDynFlags
        pkgs <- snd `fmap` hscCheckSafe' dflags m l
        when (packageTrustOn dflags) $ checkPkgTrust dflags pkgs
        errs <- getWarnings
        return $ isEmptyBag errs

    -- | Return if a module is trusted and the pkgs it depends on to be trusted.
    hscGetSafe :: HscEnv -> Module -> SrcSpan -> IO (Bool, Set InstalledUnitId)
    hscGetSafe hsc_env m l = runHsc hsc_env $ do
        dflags       <- getDynFlags
        (self, pkgs) <- hscCheckSafe' dflags m l
        good         <- isEmptyBag `fmap` getWarnings
        clearWarnings -- don't want them printed...
        let pkgs' | Just p <- self = S.insert p pkgs
                  | otherwise      = pkgs
        return (good, pkgs')

    -- | Is a module trusted? If not, throw or log errors depending on the type.
    -- Return (regardless of trusted or not) if the trust type requires the modules
    -- own package be trusted and a list of other packages required to be trusted
    -- (these later ones haven't been checked) but the own package trust has been.
    hscCheckSafe' :: DynFlags -> Module -> SrcSpan -> Hsc (Maybe InstalledUnitId, Set InstalledUnitId)
    hscCheckSafe' dflags m l = do
        (tw, pkgs) <- isModSafe m l
        case tw of
            False              -> return (Nothing, pkgs)
            True | isHomePkg m -> return (Nothing, pkgs)
                 -- TODO: do we also have to check the trust of the instantiation?
                 -- Not necessary if that is reflected in dependencies
                 | otherwise   -> return (Just $ toInstalledUnitId (moduleUnitId m), pkgs)
      where
        isModSafe :: Module -> SrcSpan -> Hsc (Bool, Set InstalledUnitId)
        isModSafe m l = do
            iface <- lookup' m
            case iface of
                -- can't load iface to check trust!
                Nothing -> throwErrors $ unitBag $ mkPlainErrMsg dflags l
                             $ text "Can't load the interface file for" <+> ppr m
                               <> text ", to check that it can be safely imported"

                -- got iface, check trust
                Just iface' ->
                    let trust = getSafeMode $ mi_trust iface'
                        trust_own_pkg = mi_trust_pkg iface'
                        -- check module is trusted
                        safeM = trust `elem` [Sf_Safe, Sf_Trustworthy]
                        -- check package is trusted
                        safeP = packageTrusted trust trust_own_pkg m
                        -- pkg trust reqs
                        pkgRs = S.fromList . map fst $ filter snd $ dep_pkgs $ mi_deps iface'
                        -- General errors we throw but Safe errors we log
                        errs = case (safeM, safeP) of
                            (True, True ) -> emptyBag
                            (True, False) -> pkgTrustErr
                            (False, _   ) -> modTrustErr
                    in do
                        logWarnings errs
                        return (trust == Sf_Trustworthy, pkgRs)

                    where
                        pkgTrustErr = unitBag $ mkErrMsg dflags l (pkgQual dflags) $
                            sep [ ppr (moduleName m)
                                    <> text ": Can't be safely imported!"
                                , text "The package (" <> ppr (moduleUnitId m)
                                    <> text ") the module resides in isn't trusted."
                                ]
                        modTrustErr = unitBag $ mkErrMsg dflags l (pkgQual dflags) $
                            sep [ ppr (moduleName m)
                                    <> text ": Can't be safely imported!"
                                , text "The module itself isn't safe." ]

        -- | Check the package a module resides in is trusted. Safe compiled
        -- modules are trusted without requiring that their package is trusted. For
        -- trustworthy modules, modules in the home package are trusted but
        -- otherwise we check the package trust flag.
        packageTrusted :: SafeHaskellMode -> Bool -> Module -> Bool
        packageTrusted Sf_None             _ _ = False -- shouldn't hit these cases
        packageTrusted Sf_Unsafe           _ _ = False -- prefer for completeness.
        packageTrusted _ _ _
            | not (packageTrustOn dflags)      = True
        packageTrusted Sf_Safe         False _ = True
        packageTrusted _ _ m
            | isHomePkg m = True
            | otherwise   = trusted $ getPackageDetails dflags (moduleUnitId m)

        lookup' :: Module -> Hsc (Maybe ModIface)
        lookup' m = do
            hsc_env <- getHscEnv
            hsc_eps <- liftIO $ hscEPS hsc_env
            let pkgIfaceT = eps_PIT hsc_eps
                homePkgT  = hsc_HPT hsc_env
                iface     = lookupIfaceByModule dflags homePkgT pkgIfaceT m
            -- the 'lookupIfaceByModule' method will always fail when calling from GHCi
            -- as the compiler hasn't filled in the various module tables
            -- so we need to call 'getModuleInterface' to load from disk
            iface' <- case iface of
                Just _  -> return iface
                Nothing -> snd `fmap` (liftIO $ getModuleInterface hsc_env m)
            return iface'

        isHomePkg :: Module -> Bool
        isHomePkg m
            | thisPackage dflags == moduleUnitId m = True
            | otherwise                               = False

    -- | Check the list of packages are trusted.
    checkPkgTrust :: DynFlags -> Set InstalledUnitId -> Hsc ()
    checkPkgTrust dflags pkgs =
        case errors of
            [] -> return ()
            _  -> (liftIO . throwIO . mkSrcErr . listToBag) errors
        where
            errors = S.foldr go [] pkgs
            go pkg acc
                | trusted $ getInstalledPackageDetails dflags pkg
                = acc
                | otherwise
                = (:acc) $ mkErrMsg dflags noSrcSpan (pkgQual dflags)
                         $ text "The package (" <> ppr pkg <> text ") is required" <>
                           text " to be trusted but it isn't!"

    -- | Set module to unsafe and (potentially) wipe trust information.
    --
    -- Make sure to call this method to set a module to inferred unsafe, it should
    -- be a central and single failure method. We only wipe the trust information
    -- when we aren't in a specific Safe Haskell mode.
    --
    -- While we only use this for recording that a module was inferred unsafe, we
    -- may call it on modules using Trustworthy or Unsafe flags so as to allow
    -- warning flags for safety to function correctly. See Note [Safe Haskell
    -- Inference].
    markUnsafeInfer :: TcGblEnv -> WarningMessages -> Hsc TcGblEnv
    markUnsafeInfer tcg_env whyUnsafe = do
        dflags <- getDynFlags

        when (wopt Opt_WarnUnsafe dflags)
             (logWarnings $ unitBag $ makeIntoWarning (Reason Opt_WarnUnsafe) $
                 mkPlainWarnMsg dflags (warnUnsafeOnLoc dflags) (whyUnsafe' dflags))

        liftIO $ writeIORef (tcg_safeInfer tcg_env) (False, whyUnsafe)
        -- NOTE: Only wipe trust when not in an explicity safe haskell mode. Other
        -- times inference may be on but we are in Trustworthy mode -- so we want
        -- to record safe-inference failed but not wipe the trust dependencies.
        case safeHaskell dflags == Sf_None of
          True  -> return $ tcg_env { tcg_imports = wiped_trust }
          False -> return tcg_env

      where
        wiped_trust   = (tcg_imports tcg_env) { imp_trust_pkgs = S.empty }
        pprMod        = ppr $ moduleName $ tcg_mod tcg_env
        whyUnsafe' df = vcat [ quotes pprMod <+> text "has been inferred as unsafe!"
                             , text "Reason:"
                             , nest 4 $ (vcat $ badFlags df) $+$
                                        (vcat $ pprErrMsgBagWithLoc whyUnsafe) $+$
                                        (vcat $ badInsts $ tcg_insts tcg_env)
                             ]
        badFlags df   = concat $ map (badFlag df) unsafeFlagsForInfer
        badFlag df (str,loc,on,_)
            | on df     = [mkLocMessage SevOutput (loc df) $
                                text str <+> text "is not allowed in Safe Haskell"]
            | otherwise = []
        badInsts insts = concat $ map badInst insts

        checkOverlap (NoOverlap _) = False
        checkOverlap _             = True

        badInst ins | checkOverlap (overlapMode (is_flag ins))
                    = [mkLocMessage SevOutput (nameSrcSpan $ getName $ is_dfun ins) $
                          ppr (overlapMode $ is_flag ins) <+>
                          text "overlap mode isn't allowed in Safe Haskell"]
                    | otherwise = []

    -- | Figure out the final correct safe haskell mode
    hscGetSafeMode :: TcGblEnv -> Hsc SafeHaskellMode
    hscGetSafeMode tcg_env = do
        dflags  <- getDynFlags
        liftIO $ finalSafeMode dflags tcg_env

    --------------------------------------------------------------
    -- Simplifiers
    --------------------------------------------------------------

    hscSimplify :: HscEnv -> ModGuts -> IO ModGuts
    hscSimplify hsc_env modguts = runHsc hsc_env $ hscSimplify' modguts

    hscSimplify' :: ModGuts -> Hsc ModGuts
    hscSimplify' ds_result = do
        hsc_env <- getHscEnv
        {-# SCC "Core2Core" #-}
          liftIO $ core2core hsc_env ds_result

    --------------------------------------------------------------
    -- Interface generators
    --------------------------------------------------------------

    hscSimpleIface :: HscEnv
                   -> TcGblEnv
                   -> Maybe Fingerprint
                   -> IO (ModIface, Bool, ModDetails)
    hscSimpleIface hsc_env tc_result mb_old_iface
        = runHsc hsc_env $ hscSimpleIface' tc_result mb_old_iface

    hscSimpleIface' :: TcGblEnv
                    -> Maybe Fingerprint
                    -> Hsc (ModIface, Bool, ModDetails)
    hscSimpleIface' tc_result mb_old_iface = do
        hsc_env   <- getHscEnv
        details   <- liftIO $ mkBootModDetailsTc hsc_env tc_result
        safe_mode <- hscGetSafeMode tc_result
        (new_iface, no_change)
            <- {-# SCC "MkFinalIface" #-}
               liftIO $
                   mkIfaceTc hsc_env mb_old_iface safe_mode details tc_result
        -- And the answer is ...
        liftIO $ dumpIfaceStats hsc_env
        return (new_iface, no_change, details)

    hscNormalIface :: HscEnv
                   -> ModGuts
                   -> Maybe Fingerprint
                   -> IO (ModIface, Bool, ModDetails, CgGuts)
    hscNormalIface hsc_env simpl_result mb_old_iface =
        runHsc hsc_env $ hscNormalIface' simpl_result mb_old_iface

    hscNormalIface' :: ModGuts
                    -> Maybe Fingerprint
                    -> Hsc (ModIface, Bool, ModDetails, CgGuts)
    hscNormalIface' simpl_result mb_old_iface = do
        hsc_env <- getHscEnv
        (cg_guts, details) <- {-# SCC "CoreTidy" #-}
                              liftIO $ tidyProgram hsc_env simpl_result

        -- BUILD THE NEW ModIface and ModDetails
        --  and emit external core if necessary
        -- This has to happen *after* code gen so that the back-end
        -- info has been set. Not yet clear if it matters waiting
        -- until after code output
        (new_iface, no_change)
            <- {-# SCC "MkFinalIface" #-}
               liftIO $
                   mkIface hsc_env mb_old_iface details simpl_result

        liftIO $ dumpIfaceStats hsc_env

        -- Return the prepared code.
        return (new_iface, no_change, details, cg_guts)

    --------------------------------------------------------------
    -- BackEnd combinators
    --------------------------------------------------------------

    hscWriteIface :: DynFlags -> ModIface -> Bool -> ModSummary -> IO ()
    hscWriteIface dflags iface no_change mod_summary = do
        let ifaceFile = ml_hi_file (ms_location mod_summary)
        unless no_change $
            {-# SCC "writeIface" #-}
            writeIfaceFile dflags ifaceFile iface
        whenGeneratingDynamicToo dflags $ do
            -- TODO: We should do a no_change check for the dynamic
            --       interface file too
            -- TODO: Should handle the dynamic hi filename properly
            let dynIfaceFile = replaceExtension ifaceFile (dynHiSuf dflags)
                dynIfaceFile' = addBootSuffix_maybe (mi_boot iface) dynIfaceFile
                dynDflags = dynamicTooMkDynamicDynFlags dflags
            writeIfaceFile dynDflags dynIfaceFile' iface

    -- | Compile to hard-code.
    hscGenHardCode :: HscEnv -> CgGuts -> ModSummary -> FilePath
                   -> IO (FilePath, Maybe FilePath, [(ForeignSrcLang, FilePath)])
                   -- ^ @Just f@ <=> _stub.c is f
    hscGenHardCode hsc_env cgguts mod_summary output_filename = do
            let CgGuts{ -- This is the last use of the ModGuts in a compilation.
                        -- From now on, we just use the bits we need.
                        cg_module   = this_mod,
                        cg_binds    = core_binds,
                        cg_tycons   = tycons,
                        cg_foreign  = foreign_stubs0,
                        cg_foreign_files = foreign_files,
                        cg_dep_pkgs = dependencies,
                        cg_hpc_info = hpc_info } = cgguts
                dflags = hsc_dflags hsc_env
                location = ms_location mod_summary
                data_tycons = filter isDataTyCon tycons
                -- cg_tycons includes newtypes, for the benefit of External Core,
                -- but we don't generate any code for newtypes

            -------------------
            -- PREPARE FOR CODE GENERATION
            -- Do saturation and convert to A-normal form
            prepd_binds <- {-# SCC "CorePrep" #-}
                           corePrepPgm hsc_env this_mod location
                                       core_binds data_tycons
            -----------------  Convert to STG ------------------
            (stg_binds, cost_centre_info)
                <- {-# SCC "CoreToStg" #-}
                   myCoreToStg dflags this_mod prepd_binds

            let prof_init = profilingInitCode this_mod cost_centre_info
                foreign_stubs = foreign_stubs0 `appendStubC` prof_init

            ------------------  Code generation ------------------

            -- The back-end is streamed: each top-level function goes
            -- from Stg all the way to asm before dealing with the next
            -- top-level function, so showPass isn't very useful here.
            -- Hence we have one showPass for the whole backend, the
            -- next showPass after this will be "Assembler".
            withTiming (pure dflags)
                       (text "CodeGen"<+>brackets (ppr this_mod))
                       (const ()) $ do
                cmms <- {-# SCC "StgCmm" #-}
                                doCodeGen hsc_env this_mod data_tycons
                                    cost_centre_info
                                    stg_binds hpc_info

                ------------------  Code output -----------------------
                rawcmms0 <- {-# SCC "cmmToRawCmm" #-}
                          cmmToRawCmm dflags cmms

                let dump a = do dumpIfSet_dyn dflags Opt_D_dump_cmm_raw "Raw Cmm"
                                  (ppr a)
                                return a
                    rawcmms1 = Stream.mapM dump rawcmms0

                (output_filename, (_stub_h_exists, stub_c_exists), foreign_fps)
                    <- {-# SCC "codeOutput" #-}
                      codeOutput dflags this_mod output_filename location
                      foreign_stubs foreign_files dependencies rawcmms1
                return (output_filename, stub_c_exists, foreign_fps)

    hscInteractive :: HscEnv
                   -> CgGuts
                   -> ModSummary
                   -> IO (Maybe FilePath, CompiledByteCode, [SptEntry])
    hscInteractive hsc_env cgguts mod_summary = do
        let dflags = hsc_dflags hsc_env
        let CgGuts{ -- This is the last use of the ModGuts in a compilation.
                    -- From now on, we just use the bits we need.
                   cg_module   = this_mod,
                   cg_binds    = core_binds,
                   cg_tycons   = tycons,
                   cg_foreign  = foreign_stubs,
                   cg_modBreaks = mod_breaks,
                   cg_spt_entries = spt_entries } = cgguts

            location = ms_location mod_summary
            data_tycons = filter isDataTyCon tycons
            -- cg_tycons includes newtypes, for the benefit of External Core,
            -- but we don't generate any code for newtypes

        -------------------
        -- PREPARE FOR CODE GENERATION
        -- Do saturation and convert to A-normal form
        prepd_binds <- {-# SCC "CorePrep" #-}
                       corePrepPgm hsc_env this_mod location core_binds data_tycons
        -----------------  Generate byte code ------------------
        comp_bc <- byteCodeGen hsc_env this_mod prepd_binds data_tycons mod_breaks
        ------------------ Create f-x-dynamic C-side stuff -----
        (_istub_h_exists, istub_c_exists)
            <- outputForeignStubs dflags this_mod location foreign_stubs
        return (istub_c_exists, comp_bc, spt_entries)

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

    hscCompileCmmFile :: HscEnv -> FilePath -> FilePath -> IO ()
    hscCompileCmmFile hsc_env filename output_filename = runHsc hsc_env $ do
        let dflags = hsc_dflags hsc_env
        cmm <- ioMsgMaybe $ parseCmmFile dflags filename
        liftIO $ do
            us <- mkSplitUniqSupply 'S'
            let initTopSRT = initUs_ us emptySRT
            dumpIfSet_dyn dflags Opt_D_dump_cmm_verbose "Parsed Cmm" (ppr cmm)
            (_, cmmgroup) <- cmmPipeline hsc_env initTopSRT cmm
            rawCmms <- cmmToRawCmm dflags (Stream.yield cmmgroup)
            let -- Make up a module name to give the NCG. We can't pass bottom here
                -- lest we reproduce #11784.
                mod_name = mkModuleName $ "Cmm$" ++ FilePath.takeFileName filename
                cmm_mod = mkModule (thisPackage dflags) mod_name
            _ <- codeOutput dflags cmm_mod output_filename no_loc NoStubs [] []
                 rawCmms
            return ()
      where
        no_loc = ModLocation{ ml_hs_file  = Just filename,
                              ml_hi_file  = panic "hscCompileCmmFile: no hi file",
                              ml_obj_file = panic "hscCompileCmmFile: no obj file" }

    -------------------- Stuff for new code gen ---------------------

    doCodeGen   :: HscEnv -> Module -> [TyCon]
                -> CollectedCCs
                -> [StgTopBinding]
                -> HpcInfo
                -> IO (Stream IO CmmGroup ())
             -- Note we produce a 'Stream' of CmmGroups, so that the
             -- backend can be run incrementally.  Otherwise it generates all
             -- the C-- up front, which has a significant space cost.
    doCodeGen hsc_env this_mod data_tycons
                  cost_centre_info stg_binds hpc_info = do
        let dflags = hsc_dflags hsc_env

        let cmm_stream :: Stream IO CmmGroup ()
            cmm_stream = {-# SCC "StgCmm" #-}
                StgCmm.codeGen dflags this_mod data_tycons
                               cost_centre_info stg_binds hpc_info

            -- codegen consumes a stream of CmmGroup, and produces a new
            -- stream of CmmGroup (not necessarily synchronised: one
            -- CmmGroup on input may produce many CmmGroups on output due
            -- to proc-point splitting).

        let dump1 a = do dumpIfSet_dyn dflags Opt_D_dump_cmm_from_stg
                           "Cmm produced by codegen" (ppr a)
                         return a

            ppr_stream1 = Stream.mapM dump1 cmm_stream

        -- We are building a single SRT for the entire module, so
        -- we must thread it through all the procedures as we cps-convert them.
        us <- mkSplitUniqSupply 'S'

        -- When splitting, we generate one SRT per split chunk, otherwise
        -- we generate one SRT for the whole module.
        let
         pipeline_stream
          | gopt Opt_SplitObjs dflags || gopt Opt_SplitSections dflags ||
            osSubsectionsViaSymbols (platformOS (targetPlatform dflags))
            = {-# SCC "cmmPipeline" #-}
              let run_pipeline us cmmgroup = do
                    let (topSRT', us') = initUs us emptySRT
                    (topSRT, cmmgroup) <- cmmPipeline hsc_env topSRT' cmmgroup
                    let srt | isEmptySRT topSRT = []
                            | otherwise         = srtToData topSRT
                    return (us', srt ++ cmmgroup)

              in do _ <- Stream.mapAccumL run_pipeline us ppr_stream1
                    return ()

          | otherwise
            = {-# SCC "cmmPipeline" #-}
              let initTopSRT = initUs_ us emptySRT
                  run_pipeline = cmmPipeline hsc_env
              in do topSRT <- Stream.mapAccumL run_pipeline initTopSRT ppr_stream1
                    Stream.yield (srtToData topSRT)

        let
            dump2 a = do dumpIfSet_dyn dflags Opt_D_dump_cmm
                            "Output Cmm" (ppr a)
                         return a

            ppr_stream2 = Stream.mapM dump2 pipeline_stream

        return ppr_stream2

    myCoreToStg :: DynFlags -> Module -> CoreProgram
                -> IO ( [StgTopBinding] -- output program
                      , CollectedCCs) -- cost centre info (declared and used)
    myCoreToStg dflags this_mod prepd_binds = do
        let stg_binds
             = {-# SCC "Core2Stg" #-}
               coreToStg dflags this_mod prepd_binds

        (stg_binds2, cost_centre_info)
            <- {-# SCC "Stg2Stg" #-}
               stg2stg dflags this_mod stg_binds

        return (stg_binds2, cost_centre_info)

    {- **********************************************************************
    %*                                                                      *
    \subsection{Compiling a do-statement}
    %*                                                                      *
    %********************************************************************* -}

    {-
    When the UnlinkedBCOExpr is linked you get an HValue of type *IO [HValue]* When
    you run it you get a list of HValues that should be the same length as the list
    of names; add them to the ClosureEnv.

    A naked expression returns a singleton Name [it]. The stmt is lifted into the
    IO monad as explained in Note [Interactively-bound Ids in GHCi] in HscTypes
    -}

    -- | Compile a stmt all the way to an HValue, but don't run it
    --
    -- We return Nothing to indicate an empty statement (or comment only), not a
    -- parse error.
    hscStmt :: HscEnv -> String -> IO (Maybe ([Id], ForeignHValue, FixityEnv))
    hscStmt hsc_env stmt = hscStmtWithLocation hsc_env stmt "<interactive>" 1

    -- | Compile a stmt all the way to an HValue, but don't run it
    --
    -- We return Nothing to indicate an empty statement (or comment only), not a
    -- parse error.
    hscStmtWithLocation :: HscEnv
                        -> String -- ^ The statement
                        -> String -- ^ The source
                        -> Int    -- ^ Starting line
                        -> IO ( Maybe ([Id]
                              , ForeignHValue {- IO [HValue] -}
                              , FixityEnv))
    hscStmtWithLocation hsc_env0 stmt source linenumber =
      runInteractiveHsc hsc_env0 $ do
        maybe_stmt <- hscParseStmtWithLocation source linenumber stmt
        case maybe_stmt of
          Nothing -> return Nothing

          Just parsed_stmt -> do
            hsc_env <- getHscEnv
            liftIO $ hscParsedStmt hsc_env parsed_stmt

    hscParsedStmt :: HscEnv
                  -> GhciLStmt RdrName  -- ^ The parsed statement
                  -> IO ( Maybe ([Id]
                        , ForeignHValue {- IO [HValue] -}
                        , FixityEnv))
    hscParsedStmt hsc_env stmt = runInteractiveHsc hsc_env $ do
      -- Rename and typecheck it
      (ids, tc_expr, fix_env) <- ioMsgMaybe $ tcRnStmt hsc_env stmt

      -- Desugar it
      ds_expr <- ioMsgMaybe $ deSugarExpr hsc_env tc_expr
      liftIO (lintInteractiveExpr "desugar expression" hsc_env ds_expr)
      handleWarnings

      -- Then code-gen, and link it
      -- It's important NOT to have package 'interactive' as thisUnitId
      -- for linking, else we try to link 'main' and can't find it.
      -- Whereas the linker already knows to ignore 'interactive'
      let src_span = srcLocSpan interactiveSrcLoc
      hval <- liftIO $ hscCompileCoreExpr hsc_env src_span ds_expr

      return $ Just (ids, hval, fix_env)

    -- | Compile a decls
    hscDecls :: HscEnv
             -> String -- ^ The statement
             -> IO ([TyThing], InteractiveContext)
    hscDecls hsc_env str = hscDeclsWithLocation hsc_env str "<interactive>" 1

    -- | Compile a decls
    hscDeclsWithLocation :: HscEnv
                         -> String -- ^ The statement
                         -> String -- ^ The source
                         -> Int    -- ^ Starting line
                         -> IO ([TyThing], InteractiveContext)
    hscDeclsWithLocation hsc_env0 str source linenumber =
     runInteractiveHsc hsc_env0 $ do
        L _ (HsModule{ hsmodDecls = decls }) <-
            hscParseThingWithLocation source linenumber parseModule str

        {- Rename and typecheck it -}
        hsc_env <- getHscEnv
        tc_gblenv <- ioMsgMaybe $ tcRnDeclsi hsc_env decls

        {- Grab the new instances -}
        -- We grab the whole environment because of the overlapping that may have
        -- been done. See the notes at the definition of InteractiveContext
        -- (ic_instances) for more details.
        let defaults = tcg_default tc_gblenv

        {- Desugar it -}
        -- We use a basically null location for iNTERACTIVE
        let iNTERACTIVELoc = ModLocation{ ml_hs_file   = Nothing,
                                          ml_hi_file   = panic "hsDeclsWithLocation:ml_hi_file",
                                          ml_obj_file  = panic "hsDeclsWithLocation:ml_hi_file"}
        ds_result <- hscDesugar' iNTERACTIVELoc tc_gblenv

        {- Simplify -}
        simpl_mg <- liftIO $ hscSimplify hsc_env ds_result

        {- Tidy -}
        (tidy_cg, mod_details) <- liftIO $ tidyProgram hsc_env simpl_mg

        let !CgGuts{ cg_module    = this_mod,
                     cg_binds     = core_binds,
                     cg_tycons    = tycons,
                     cg_modBreaks = mod_breaks } = tidy_cg

            !ModDetails { md_insts     = cls_insts
                        , md_fam_insts = fam_insts } = mod_details
                -- Get the *tidied* cls_insts and fam_insts

            data_tycons = filter isDataTyCon tycons

        {- Prepare For Code Generation -}
        -- Do saturation and convert to A-normal form
        prepd_binds <- {-# SCC "CorePrep" #-}
          liftIO $ corePrepPgm hsc_env this_mod iNTERACTIVELoc core_binds data_tycons

        {- Generate byte code -}
        cbc <- liftIO $ byteCodeGen hsc_env this_mod
                                    prepd_binds data_tycons mod_breaks

        let src_span = srcLocSpan interactiveSrcLoc
        liftIO $ linkDecls hsc_env src_span cbc

        {- Load static pointer table entries -}
        liftIO $ hscAddSptEntries hsc_env (cg_spt_entries tidy_cg)

        let tcs = filterOut isImplicitTyCon (mg_tcs simpl_mg)
            patsyns = mg_patsyns simpl_mg

            ext_ids = [ id | id <- bindersOfBinds core_binds
                           , isExternalName (idName id)
                           , not (isDFunId id || isImplicitId id) ]
                -- We only need to keep around the external bindings
                -- (as decided by TidyPgm), since those are the only ones
                -- that might later be looked up by name.  But we can exclude
                --    - DFunIds, which are in 'cls_insts' (see Note [ic_tythings] in HscTypes
                --    - Implicit Ids, which are implicit in tcs
                -- c.f. TcRnDriver.runTcInteractive, which reconstructs the TypeEnv

            new_tythings = map AnId ext_ids ++ map ATyCon tcs ++ map (AConLike . PatSynCon) patsyns
            ictxt        = hsc_IC hsc_env
            -- See Note [Fixity declarations in GHCi]
            fix_env      = tcg_fix_env tc_gblenv
            new_ictxt    = extendInteractiveContext ictxt new_tythings cls_insts
                                                    fam_insts defaults fix_env
        return (new_tythings, new_ictxt)

    -- | Load the given static-pointer table entries into the interpreter.
    -- See Note [Grand plan for static forms] in StaticPtrTable.
    hscAddSptEntries :: HscEnv -> [SptEntry] -> IO ()
    hscAddSptEntries hsc_env entries = do
        let add_spt_entry :: SptEntry -> IO ()
            add_spt_entry (SptEntry i fpr) = do
                val <- getHValue hsc_env (idName i)
                addSptEntry hsc_env fpr val
        mapM_ add_spt_entry entries

    {-
      Note [Fixity declarations in GHCi]
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

      To support fixity declarations on types defined within GHCi (as requested
      in #10018) we record the fixity environment in InteractiveContext.
      When we want to evaluate something TcRnDriver.runTcInteractive pulls out this
      fixity environment and uses it to initialize the global typechecker environment.
      After the typechecker has finished its business, an updated fixity environment
      (reflecting whatever fixity declarations were present in the statements we
      passed it) will be returned from hscParsedStmt. This is passed to
      updateFixityEnv, which will stuff it back into InteractiveContext, to be
      used in evaluating the next statement.

    -}

    hscImport :: HscEnv -> String -> IO (ImportDecl RdrName)
    hscImport hsc_env str = runInteractiveHsc hsc_env $ do
        (L _ (HsModule{hsmodImports=is})) <-
           hscParseThing parseModule str
        case is of
            [L _ i] -> return i
            _ -> liftIO $ throwOneError $
                     mkPlainErrMsg (hsc_dflags hsc_env) noSrcSpan $
                         text "parse error in import declaration"

    -- | Typecheck an expression (but don't run it)
    hscTcExpr :: HscEnv
              -> TcRnExprMode
              -> String -- ^ The expression
              -> IO Type
    hscTcExpr hsc_env0 mode expr = runInteractiveHsc hsc_env0 $ do
      hsc_env <- getHscEnv
      parsed_expr <- hscParseExpr expr
      ioMsgMaybe $ tcRnExpr hsc_env mode parsed_expr

    -- | Find the kind of a type
    -- Currently this does *not* generalise the kinds of the type
    hscKcType
      :: HscEnv
      -> Bool            -- ^ Normalise the type
      -> String          -- ^ The type as a string
      -> IO (Type, Kind) -- ^ Resulting type (possibly normalised) and kind
    hscKcType hsc_env0 normalise str = runInteractiveHsc hsc_env0 $ do
        hsc_env <- getHscEnv
        ty <- hscParseType str
        ioMsgMaybe $ tcRnType hsc_env normalise ty

    hscParseExpr :: String -> Hsc (LHsExpr RdrName)
    hscParseExpr expr = do
      hsc_env <- getHscEnv
      maybe_stmt <- hscParseStmt expr
      case maybe_stmt of
        Just (L _ (BodyStmt expr _ _ _)) -> return expr
        _ -> throwErrors $ unitBag $ mkPlainErrMsg (hsc_dflags hsc_env) noSrcSpan
          (text "not an expression:" <+> quotes (text expr))

    hscParseStmt :: String -> Hsc (Maybe (GhciLStmt RdrName))
    hscParseStmt = hscParseThing parseStmt

    hscParseStmtWithLocation :: String -> Int -> String
                             -> Hsc (Maybe (GhciLStmt RdrName))
    hscParseStmtWithLocation source linenumber stmt =
        hscParseThingWithLocation source linenumber parseStmt stmt

    hscParseType :: String -> Hsc (LHsType RdrName)
    hscParseType = hscParseThing parseType

    hscParseIdentifier :: HscEnv -> String -> IO (Located RdrName)
    hscParseIdentifier hsc_env str =
        runInteractiveHsc hsc_env $ hscParseThing parseIdentifier str

    hscParseThing :: (Outputable thing, Data thing)
                  => Lexer.P thing -> String -> Hsc thing
    hscParseThing = hscParseThingWithLocation "<interactive>" 1

    hscParseThingWithLocation :: (Outputable thing, Data thing) => String -> Int
                              -> Lexer.P thing -> String -> Hsc thing
    hscParseThingWithLocation source linenumber parser str
      = withTiming getDynFlags
                   (text "Parser [source]")
                   (const ()) $ {-# SCC "Parser" #-} do
        dflags <- getDynFlags

        let buf = stringToStringBuffer str
            loc = mkRealSrcLoc (fsLit source) linenumber 1

        case unP parser (mkPState dflags buf loc) of
            PFailed span err -> do
                let msg = mkPlainErrMsg dflags span err
                throwErrors $ unitBag msg

            POk pst thing -> do
                logWarningsReportErrors (getMessages pst dflags)
                liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed "Parser" (ppr thing)
                liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed_ast "Parser AST" $
                                       text $ showAstData NoBlankSrcSpan thing
                return thing

    {- **********************************************************************
    %*                                                                      *
            Desugar, simplify, convert to bytecode, and link an expression
    %*                                                                      *
    %********************************************************************* -}

    hscCompileCoreExpr :: HscEnv -> SrcSpan -> CoreExpr -> IO ForeignHValue
    hscCompileCoreExpr hsc_env =
      lookupHook hscCompileCoreExprHook hscCompileCoreExpr' (hsc_dflags hsc_env) hsc_env

    hscCompileCoreExpr' :: HscEnv -> SrcSpan -> CoreExpr -> IO ForeignHValue
    hscCompileCoreExpr' hsc_env srcspan ds_expr
        = do { let dflags = hsc_dflags hsc_env

               {- Simplify it -}
             ; simpl_expr <- simplifyExpr dflags ds_expr

               {- Tidy it (temporary, until coreSat does cloning) -}
             ; let tidy_expr = tidyExpr emptyTidyEnv simpl_expr

               {- Prepare for codegen -}
             ; prepd_expr <- corePrepExpr dflags hsc_env tidy_expr

               {- Lint if necessary -}
             ; lintInteractiveExpr "hscCompileExpr" hsc_env prepd_expr

               {- Convert to BCOs -}
             ; bcos <- coreExprToBCOs hsc_env
                         (icInteractiveModule (hsc_IC hsc_env)) prepd_expr

               {- link it -}
             ; hval <- linkExpr hsc_env srcspan bcos

             ; return hval }

    {- **********************************************************************
    %*                                                                      *
            Statistics on reading interfaces
    %*                                                                      *
    %********************************************************************* -}

    dumpIfaceStats :: HscEnv -> IO ()
    dumpIfaceStats hsc_env = do
        eps <- readIORef (hsc_EPS hsc_env)
        dumpIfSet dflags (dump_if_trace || dump_rn_stats)
                  "Interface statistics"
                  (ifaceStats eps)
      where
        dflags = hsc_dflags hsc_env
        dump_rn_stats = dopt Opt_D_dump_rn_stats dflags
        dump_if_trace = dopt Opt_D_dump_if_trace dflags

    {- **********************************************************************
    %*                                                                      *
            Progress Messages: Module i of n
    %*                                                                      *
    %********************************************************************* -}

    showModuleIndex :: (Int, Int) -> String
    showModuleIndex (i,n) = "[" ++ padded ++ " of " ++ n_str ++ "] "
      where
        n_str = show n
        i_str = show i
        padded = replicate (length n_str - length i_str) ' ' ++ i_str