path: root/compiler/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))

-- | 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)

        -- 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)

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
    imports' = moduleEnvToList imports -- (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)
            pprTrace "add_spt_entry" (ppr fpr <+> ppr 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