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
    , hscMaybeWriteIface
    , 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, hscParseStmtWithLocation, hscStmtWithLocation, hscParsedStmt
    , hscDecls, hscParseDeclsWithLocation, hscDeclsWithLocation, hscParsedDecls
    , hscTcExpr, TcRnExprMode(..), hscImport, hscKcType
    , hscParseExpr
    , hscParseType
    , 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', doCodeGen
    , getHscEnv
    , hscSimpleIface'
    , oneShotMsg
    , hscFileFrontEnd, genericHscFrontend, dumpIfaceStats
    , ioMsgMaybe
    , showModuleIndex
    , hscAddSptEntries
    ) where

import GhcPrelude

import Data.Data hiding (Fixity, TyCon)
import Data.Maybe       ( fromJust )
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 GHC.Hs
import GHC.Hs.Dump
import CoreSyn
import StringBuffer
import Parser
import Lexer
import SrcLoc
import TcRnDriver
import TcIface          ( typecheckIface )
import TcRnMonad
import TcHsSyn          ( ZonkFlexi (DefaultFlexi) )
import NameCache        ( initNameCache )
import LoadIface        ( ifaceStats, initExternalPackageState )
import PrelInfo
import MkIface
import Desugar
import SimplCore
import TidyPgm
import GHC.CoreToStg.Prep
import GHC.CoreToStg        ( coreToStg )
import GHC.Stg.Syntax
import GHC.Stg.FVs      ( annTopBindingsFreeVars )
import GHC.Stg.Pipeline ( stg2stg )
import qualified GHC.StgToCmm as StgToCmm ( codeGen )
import CostCentre
import ProfInit
import TyCon
import Name
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 PrelNames
import Plugins
import DynamicLoading   ( initializePlugins )

import DynFlags
import ErrUtils

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 M
import qualified Data.Set as S
import Data.Set (Set)
import Control.DeepSeq (force)

import HieAst           ( mkHieFile )
import HieTypes         ( getAsts, hie_asts, hie_module )
import HieBin           ( readHieFile, writeHieFile , hie_file_result)
import HieDebug         ( diffFile, validateScopes )

#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
    emptyDynLinker <- uninitializedLinker
    return HscEnv {  hsc_dflags       = dflags
                  ,  hsc_targets      = []
                  ,  hsc_mod_graph    = emptyMG
                  ,  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
                  ,  hsc_dynLinker    = emptyDynLinker
                  }

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

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

-- | Log warnings and throw errors, assuming the messages
-- contain at least one error (e.g. coming from PFailed)
handleWarningsThrowErrors :: Messages -> Hsc a
handleWarningsThrowErrors (warns, errs) = do
    logWarnings warns
    dflags <- getDynFlags
    (wWarns, wErrs) <- warningsToMessages dflags <$> getWarnings
    liftIO $ printBagOfErrors dflags wWarns
    throwErrors (unionBags errs wErrs)

-- | 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], SDoc))
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 GhcPs] -> 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" #-}
    withTimingD (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 pst ->
            handleWarningsThrowErrors (getMessages pst dflags)
        POk pst rdr_module -> do
            let (warns, errs) = getMessages pst dflags
            logWarnings warns
            liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed "Parser"
                        FormatHaskell (ppr rdr_module)
            liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed_ast "Parser AST"
                        FormatHaskell (showAstData NoBlankSrcSpan rdr_module)
            liftIO $ dumpIfSet_dyn dflags Opt_D_source_stats "Source Statistics"
                        FormatText (ppSourceStats False rdr_module)
            when (not $ isEmptyBag errs) $ throwErrors errs

            -- 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 (eliminate 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

            let res = HsParsedModule {
                      hpm_module    = rdr_module,
                      hpm_src_files = srcs2,
                      hpm_annotations
                              = (M.fromListWith (++) $ annotations pst,
                                 M.fromList $ ((noSrcSpan,comment_q pst)
                                                 :(annotations_comments pst)))
                   }

            -- apply parse transformation of plugins
            let applyPluginAction p opts
                  = parsedResultAction p opts mod_summary
            withPlugins dflags applyPluginAction res


-- -----------------------------------------------------------------------------
-- | If the renamed source has been kept, extract it. Dump it if requested.
extract_renamed_stuff :: ModSummary -> TcGblEnv -> Hsc RenamedStuff
extract_renamed_stuff mod_summary tc_result = do
    let rn_info = getRenamedStuff tc_result

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

    -- Create HIE files
    when (gopt Opt_WriteHie dflags) $ do
        -- I assume this fromJust is safe because `-fwrite-hie-file`
        -- enables the option which keeps the renamed source.
        hieFile <- mkHieFile mod_summary tc_result (fromJust rn_info)
        let out_file = ml_hie_file $ ms_location mod_summary
        liftIO $ writeHieFile out_file hieFile

        -- Validate HIE files
        when (gopt Opt_ValidateHie dflags) $ do
            hs_env <- Hsc $ \e w -> return (e, w)
            liftIO $ do
              -- Validate Scopes
              let mdl = hie_module hieFile
              case validateScopes mdl $ getAsts $ hie_asts hieFile of
                  [] -> putMsg dflags $ text "Got valid scopes"
                  xs -> do
                    putMsg dflags $ text "Got invalid scopes"
                    mapM_ (putMsg dflags) xs
              -- Roundtrip testing
              nc <- readIORef $ hsc_NC hs_env
              (file', _) <- readHieFile nc out_file
              case diffFile hieFile (hie_file_result file') of
                [] ->
                  putMsg dflags $ text "Got no roundtrip errors"
                xs -> do
                  putMsg dflags $ text "Got roundtrip errors"
                  mapM_ (putMsg dflags) xs
    return 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 <- hsc_typecheck True mod_summary (Just rdr_module)
    rn_info <- extract_renamed_stuff mod_summary tc_result
    return (tc_result, rn_info)

-- | Rename and typecheck a module, but don't return the renamed syntax
hscTypecheck :: Bool -- ^ Keep renamed source?
             -> ModSummary -> Maybe HsParsedModule
             -> Hsc TcGblEnv
hscTypecheck keep_rn mod_summary mb_rdr_module = do
    tc_result <- hsc_typecheck keep_rn mod_summary mb_rdr_module
    _ <- extract_renamed_stuff mod_summary tc_result
    return tc_result

hsc_typecheck :: Bool -- ^ Keep renamed source?
              -> ModSummary -> Maybe HsParsedModule
              -> Hsc TcGblEnv
hsc_typecheck 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
        keep_rn' = gopt Opt_WriteHie dflags || keep_rn
    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' 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' :: ModSummary -> Bool -> HsParsedModule
            -> Hsc TcGblEnv
tcRnModule' sum save_rn_syntax mod = do
    hsc_env <- getHscEnv
    dflags   <- getDynFlags

    -- -Wmissing-safe-haskell-mode
    when (not (safeHaskellModeEnabled dflags)
          && wopt Opt_WarnMissingSafeHaskellMode dflags) $
        logWarnings $ unitBag $
        makeIntoWarning (Reason Opt_WarnMissingSafeHaskellMode) $
        mkPlainWarnMsg dflags (getLoc (hpm_module mod)) $
        warnMissingSafeHaskellMode

    tcg_res <- {-# SCC "Typecheck-Rename" #-}
               ioMsgMaybe $
                   tcRnModule hsc_env 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)
    let allSafeOK = safeInferred dflags && tcSafeOK

    -- end of the safe haskell line, how to respond to user?
    res <- 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
                       | safeHaskell dflags == Sf_Safe -> return ()
                       | otherwise -> (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'

    -- apply plugins to the type checking result


    return 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!"
    warnMissingSafeHaskellMode = ppr (moduleName (ms_mod sum))
      <+> text "is missing Safe Haskell mode"

-- | 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, etc.) 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 . mi_final_exts) 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
--------------------------------------------------------------

-- | Used by both OneShot and batch mode. Runs the pipeline HsSyn and Core parts
-- of the pipeline.
-- We return a interface if we already had an old one around and recompilation
-- was not needed. Otherwise it will be created during later passes when we
-- run the compilation pipeline.
hscIncrementalCompile :: Bool
                      -> Maybe TcGblEnv
                      -> Maybe Messager
                      -> HscEnv
                      -> ModSummary
                      -> SourceModified
                      -> Maybe ModIface
                      -> (Int,Int)
                      -> IO (HscStatus, DynFlags)
hscIncrementalCompile always_do_basic_recompilation_check m_tc_result
    mHscMessage hsc_env' mod_summary source_modified mb_old_iface mod_index
  = do
    dflags <- initializePlugins hsc_env' (hsc_dflags hsc_env')
    let hsc_env'' = hsc_env' { hsc_dflags = dflags }

    -- 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
    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]
            details <- liftIO . fixIO $ \details' -> do
                let hsc_env' =
                        hsc_env {
                            hsc_HPT = addToHpt (hsc_HPT hsc_env)
                                        (ms_mod_name mod_summary) (HomeModInfo iface details' Nothing)
                        }
                -- 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 details
            return (HscUpToDate iface details, dflags)
        -- 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 <- finish mod_summary tc_result mb_old_hash
            return (status, dflags)

-- Runs the post-typechecking frontend (desugar and simplify). We want to
-- generate most of the interface as late as possible. This gets us up-to-date
-- and good unfoldings and other info in the interface file.
--
-- We might create a interface right away, in which case we also return the
-- updated HomeModInfo. But we might also need to run the backend first. In the
-- later case Status will be HscRecomp and we return a function from ModIface ->
-- HomeModInfo.
--
-- HscRecomp in turn will carry the information required to compute a interface
-- when passed the result of the code generator. So all this can and is done at
-- the call site of the backend code gen if it is run.
finish :: ModSummary
       -> TcGblEnv
       -> Maybe Fingerprint
       -> Hsc HscStatus
finish summary tc_result mb_old_hash = do
  hsc_env <- getHscEnv
  let dflags = hsc_dflags hsc_env
      target = hscTarget dflags
      hsc_src = ms_hsc_src summary
      should_desugar =
        ms_mod summary /= gHC_PRIM && hsc_src == HsSrcFile
      mk_simple_iface :: Hsc HscStatus
      mk_simple_iface = do
        (iface, mb_old_iface_hash, details) <- liftIO $
          hscSimpleIface hsc_env tc_result mb_old_hash

        liftIO $ hscMaybeWriteIface dflags iface mb_old_iface_hash (ms_location summary)

        return $ case (target, hsc_src) of
          (HscNothing, _) -> HscNotGeneratingCode iface details
          (_, HsBootFile) -> HscUpdateBoot iface details
          (_, HsigFile) -> HscUpdateSig iface details
          _ -> panic "finish"

  if should_desugar
    then do
      -- We usually desugar even when we are not generating code, otherwise we
      -- would miss errors thrown by the desugaring (see #10600). The only
      -- exceptions are when the Module is Ghc.Prim or when it is not a
      -- HsSrcFile Module.
      desugared_guts0 <- hscDesugar' (ms_location summary) tc_result
      if target == HscNothing
        -- We are not generating code, so we can skip simplification
        -- and generate a simple interface.
        then mk_simple_iface
        else do
          plugins <- liftIO $ readIORef (tcg_th_coreplugins tc_result)
          desugared_guts <- hscSimplify' plugins desugared_guts0

          (cg_guts, details) <- {-# SCC "CoreTidy" #-}
              liftIO $ tidyProgram hsc_env desugared_guts

          let !partial_iface =
                {-# SCC "HscMain.mkPartialIface" #-}
                -- This `force` saves 2M residency in test T10370
                -- See Note [Avoiding space leaks in toIface*] for details.
                force (mkPartialIface hsc_env details desugared_guts)

          return HscRecomp { hscs_guts = cg_guts,
                             hscs_mod_location = ms_location summary,
                             hscs_mod_details = details,
                             hscs_partial_iface = partial_iface,
                             hscs_old_iface_hash = mb_old_hash,
                             hscs_iface_dflags = dflags }
    else mk_simple_iface


{-
Note [Writing interface files]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We write interface files in HscMain.hs and DriverPipeline.hs using
hscMaybeWriteIface, but only once per compilation (twice with dynamic-too).

* If a compilation does NOT require (re)compilation of the hard code we call
  hscMaybeWriteIface inside HscMain:finish.
* If we run in One Shot mode and target bytecode we write it in compileOne'
* Otherwise we must be compiling to regular hard code and require recompilation.
  In this case we create the interface file inside RunPhase using the interface
  generator contained inside the HscRecomp status.
-}
hscMaybeWriteIface :: DynFlags -> ModIface -> Maybe Fingerprint -> ModLocation -> IO ()
hscMaybeWriteIface dflags iface old_iface location = do
    let force_write_interface = gopt Opt_WriteInterface dflags
        write_interface = case hscTarget dflags of
                            HscNothing      -> False
                            HscInterpreted  -> False
                            _               -> True
        no_change = old_iface == Just (mi_iface_hash (mi_final_exts iface))

    when (write_interface || force_write_interface) $
          hscWriteIface dflags iface no_change location

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