HscMain.hs 76.3 KB
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{-# LANGUAGE BangPatterns, CPP, MagicHash, NondecreasingIndentation #-}
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{-# OPTIONS_GHC -fprof-auto-top #-}
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-------------------------------------------------------------------------------
--
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-- | Main API for compiling plain Haskell source code.
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--
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-- This module implements compilation of a Haskell source. It is
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-- /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
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-- "interactive" mode (GHCi). There are also entry points for
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-- 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).
--
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-- 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.
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--
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-- (c) The GRASP/AQUA Project, Glasgow University, 1993-2000
--
-------------------------------------------------------------------------------

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module HscMain
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    (
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    -- * Making an HscEnv
      newHscEnv

    -- * Compiling complete source files
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    , Messager, batchMsg
    , HscStatus (..)
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    , hscIncrementalCompile
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    , hscCompileCmmFile

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    , hscGenHardCode
    , hscInteractive

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

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    -- * Safe Haskell
    , hscCheckSafe
    , hscGetSafe

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

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import Data.Data hiding (Fixity, TyCon)
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import Data.Maybe       ( fromJust )
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import Id
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import GHCi             ( addSptEntry )
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import GHCi.RemoteTypes ( ForeignHValue )
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import ByteCodeGen      ( byteCodeGen, coreExprToBCOs )
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import Linker
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import CoreTidy         ( tidyExpr )
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import Type             ( Type )
import {- Kind parts of -} Type         ( Kind )
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import CoreLint         ( lintInteractiveExpr )
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import VarEnv           ( emptyTidyEnv )
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import Panic
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import ConLike
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import Control.Concurrent
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import Module
import Packages
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import RdrName
import HsSyn
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import HsDumpAst
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import CoreSyn
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import StringBuffer
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import Parser
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import Lexer
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import SrcLoc
import TcRnDriver
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import TcIface          ( typecheckIface )
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import TcRnMonad
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import NameCache        ( initNameCache )
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import LoadIface        ( ifaceStats, initExternalPackageState )
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import PrelInfo
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import MkIface
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import Desugar
import SimplCore
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import TidyPgm
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import CorePrep
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import CoreToStg        ( coreToStg )
import qualified StgCmm ( codeGen )
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import StgSyn
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import StgFVs           ( annTopBindingsFreeVars )
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import CostCentre
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import ProfInit
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import TyCon
import Name
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import SimplStg         ( stg2stg )
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import Cmm
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import CmmParse         ( parseCmmFile )
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import CmmBuildInfoTables
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import CmmPipeline
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import CmmInfo
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import CodeOutput
import InstEnv
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import FamInstEnv
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import Fingerprint      ( Fingerprint )
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import Hooks
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import TcEnv
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import PrelNames
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import Plugins
import DynamicLoading   ( initializePlugins )
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import DynFlags
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import ErrUtils
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import Platform ( platformOS, osSubsectionsViaSymbols )
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import Outputable
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import NameEnv
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import HscStats         ( ppSourceStats )
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import HscTypes
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import FastString
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import UniqSupply
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import Bag
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import Exception
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import qualified Stream
import Stream (Stream)

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import Util
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import Data.List
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import Control.Monad
import Data.IORef
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import System.FilePath as FilePath
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import System.Directory
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import System.IO (fixIO)
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import qualified Data.Map as M
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import qualified Data.Set as S
import Data.Set (Set)
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import HieAst           ( mkHieFile )
import HieTypes         ( getAsts, hie_asts )
import HieBin           ( readHieFile, writeHieFile )
import HieDebug         ( diffFile, validateScopes )

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#include "HsVersions.h"
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{- **********************************************************************
%*                                                                      *
                Initialisation
%*                                                                      *
%********************************************************************* -}
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newHscEnv :: DynFlags -> IO HscEnv
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newHscEnv dflags = do
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    eps_var <- newIORef initExternalPackageState
    us      <- mkSplitUniqSupply 'r'
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    nc_var  <- newIORef (initNameCache us knownKeyNames)
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    fc_var  <- newIORef emptyInstalledModuleEnv
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    iserv_mvar <- newMVar Nothing
    return HscEnv {  hsc_dflags       = dflags
                  ,  hsc_targets      = []
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                  ,  hsc_mod_graph    = emptyMG
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                  ,  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
                  }
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-- -----------------------------------------------------------------------------
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getWarnings :: Hsc WarningMessages
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getWarnings = Hsc $ \_ w -> return (w, w)
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clearWarnings :: Hsc ()
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clearWarnings = Hsc $ \_ _ -> return ((), emptyBag)
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logWarnings :: WarningMessages -> Hsc ()
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logWarnings w = Hsc $ \_ w0 -> return ((), w0 `unionBags` w)
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getHscEnv :: Hsc HscEnv
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getHscEnv = Hsc $ \e w -> return (e, w)
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handleWarnings :: Hsc ()
handleWarnings = do
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    dflags <- getDynFlags
    w <- getWarnings
    liftIO $ printOrThrowWarnings dflags w
    clearWarnings
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-- | log warning in the monad, and if there are errors then
-- throw a SourceError exception.
logWarningsReportErrors :: Messages -> Hsc ()
logWarningsReportErrors (warns,errs) = do
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    logWarnings warns
    when (not $ isEmptyBag errs) $ throwErrors errs
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-- | Throw some errors.
throwErrors :: ErrorMessages -> Hsc a
throwErrors = liftIO . throwIO . mkSrcErr
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-- | 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
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-- and signal success via by wrapping the result in a 'Maybe' type. This
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-- 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
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--     there should be warnings in the first result. That is, if the action
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--     failed, it must have been due to the warnings (i.e., @-Werror@).
ioMsgMaybe :: IO (Messages, Maybe a) -> Hsc a
ioMsgMaybe ioA = do
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    ((warns,errs), mb_r) <- liftIO ioA
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    logWarnings warns
    case mb_r of
        Nothing -> throwErrors errs
        Just r  -> ASSERT( isEmptyBag errs ) return r
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-- | like ioMsgMaybe, except that we ignore error messages and return
-- 'Nothing' instead.
ioMsgMaybe' :: IO (Messages, Maybe a) -> Hsc (Maybe a)
ioMsgMaybe' ioA = do
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    ((warns,_errs), mb_r) <- liftIO $ ioA
    logWarnings warns
    return mb_r
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-- -----------------------------------------------------------------------------
-- | Lookup things in the compiler's environment

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hscTcRnLookupRdrName :: HscEnv -> Located RdrName -> IO [Name]
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hscTcRnLookupRdrName hsc_env0 rdr_name
  = runInteractiveHsc hsc_env0 $
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    do { hsc_env <- getHscEnv
       ; ioMsgMaybe $ tcRnLookupRdrName hsc_env rdr_name }
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hscTcRcLookupName :: HscEnv -> Name -> IO (Maybe TyThing)
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hscTcRcLookupName hsc_env0 name = runInteractiveHsc hsc_env0 $ do
  hsc_env <- getHscEnv
  ioMsgMaybe' $ tcRnLookupName hsc_env name
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      -- 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.
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hscTcRnGetInfo :: HscEnv -> Name
               -> IO (Maybe (TyThing, Fixity, [ClsInst], [FamInst], SDoc))
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hscTcRnGetInfo hsc_env0 name
  = runInteractiveHsc hsc_env0 $
    do { hsc_env <- getHscEnv
       ; ioMsgMaybe' $ tcRnGetInfo hsc_env name }
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hscIsGHCiMonad :: HscEnv -> String -> IO Name
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hscIsGHCiMonad hsc_env name
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  = runHsc hsc_env $ ioMsgMaybe $ isGHCiMonad hsc_env name
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hscGetModuleInterface :: HscEnv -> Module -> IO ModIface
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hscGetModuleInterface hsc_env0 mod = runInteractiveHsc hsc_env0 $ do
  hsc_env <- getHscEnv
  ioMsgMaybe $ getModuleInterface hsc_env mod
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-- -----------------------------------------------------------------------------
-- | Rename some import declarations
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hscRnImportDecls :: HscEnv -> [LImportDecl GhcPs] -> IO GlobalRdrEnv
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hscRnImportDecls hsc_env0 import_decls = runInteractiveHsc hsc_env0 $ do
  hsc_env <- getHscEnv
  ioMsgMaybe $ tcRnImportDecls hsc_env import_decls
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-- -----------------------------------------------------------------------------
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-- | parse a file, returning the abstract syntax
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hscParse :: HscEnv -> ModSummary -> IO HsParsedModule
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hscParse hsc_env mod_summary = runHsc hsc_env $ hscParse' mod_summary

-- internal version, that doesn't fail due to -Werror
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hscParse' :: ModSummary -> Hsc HsParsedModule
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hscParse' mod_summary
 | Just r <- ms_parsed_mod mod_summary = return r
 | otherwise = {-# SCC "Parser" #-}
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    withTiming getDynFlags
               (text "Parser"<+>brackets (ppr $ ms_mod mod_summary))
               (const ()) $ do
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    dflags <- getDynFlags
    let src_filename  = ms_hspp_file mod_summary
        maybe_src_buf = ms_hspp_buf  mod_summary
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    --------------------------  Parser  ----------------
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    -- sometimes we already have the buffer in memory, perhaps
    -- because we needed to parse the imports out of it, or get the
    -- module name.
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    buf <- case maybe_src_buf of
               Just b  -> return b
               Nothing -> liftIO $ hGetStringBuffer src_filename
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    let loc = mkRealSrcLoc (mkFastString src_filename) 1 1
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    let parseMod | HsigFile == ms_hsc_src mod_summary
                 = parseSignature
                 | otherwise = parseModule
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    case unP parseMod (mkPState dflags buf loc) of
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        PFailed warnFn span err -> do
            logWarningsReportErrors (warnFn dflags)
            handleWarnings
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            liftIO $ throwOneError (mkPlainErrMsg dflags span err)
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        POk pst rdr_module -> do
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            logWarningsReportErrors (getMessages pst dflags)
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            liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed "Parser" $
                                   ppr rdr_module
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            liftIO $ dumpIfSet_dyn dflags Opt_D_dump_parsed_ast "Parser AST" $
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                                   showAstData NoBlankSrcSpan rdr_module
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            liftIO $ dumpIfSet_dyn dflags Opt_D_source_stats "Source Statistics" $
                                   ppSourceStats False rdr_module
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            -- 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>"
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            --   - normalise them (eliminate differences between ./f and f)
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            --   - 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
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                            $ filter (not . isPrefixOf "<")
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                            $ map unpackFS
                            $ srcfiles pst
                srcs1 = case ml_hs_file (ms_location mod_summary) of
                          Just f  -> filter (/= FilePath.normalise f) srcs0
                          Nothing -> srcs0

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

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            let res = HsParsedModule {
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                      hpm_module    = rdr_module,
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                      hpm_src_files = srcs2,
                      hpm_annotations
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                              = (M.fromListWith (++) $ annotations pst,
                                 M.fromList $ ((noSrcSpan,comment_q pst)
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                                                 :(annotations_comments pst)))
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                   }
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            -- apply parse transformation of plugins
            let applyPluginAction p opts
                  = parsedResultAction p opts mod_summary
            withPlugins dflags applyPluginAction res

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-- -----------------------------------------------------------------------------
-- | If the renamed source has been kept, extract it. Dump it if requested.
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extract_renamed_stuff :: ModSummary -> TcGblEnv -> Hsc RenamedStuff
extract_renamed_stuff mod_summary tc_result = do
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    let rn_info = getRenamedStuff tc_result
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    dflags <- getDynFlags
    liftIO $ dumpIfSet_dyn dflags Opt_D_dump_rn_ast "Renamer" $
                           showAstData NoBlankSrcSpan rn_info

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    -- Create HIE files
    when (gopt Opt_WriteHie dflags) $ do
        hieFile <- mkHieFile mod_summary (tcg_binds 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
              case validateScopes $ 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 file' of
                [] ->
                  putMsg dflags $ text "Got no roundtrip errors"
                xs -> do
                  putMsg dflags $ text "Got roundtrip errors"
                  mapM_ (putMsg dflags) xs
    return rn_info
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-- -----------------------------------------------------------------------------
-- | 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
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    tc_result <- hsc_typecheck True mod_summary (Just rdr_module)
    rn_info <- extract_renamed_stuff mod_summary tc_result
    return (tc_result, rn_info)
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-- | Rename and typecheck a module, but don't return the renamed syntax
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hscTypecheck :: Bool -- ^ Keep renamed source?
             -> ModSummary -> Maybe HsParsedModule
             -> Hsc TcGblEnv
hscTypecheck keep_rn mod_summary mb_rdr_module = do
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    tc_result <- hsc_typecheck keep_rn mod_summary mb_rdr_module
    _ <- extract_renamed_stuff mod_summary tc_result
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    return tc_result

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

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-- wrapper around tcRnModule to handle safe haskell extras
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tcRnModule' :: ModSummary -> Bool -> HsParsedModule
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            -> Hsc TcGblEnv
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tcRnModule' sum save_rn_syntax mod = do
    hsc_env <- getHscEnv
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    dflags   <- getDynFlags

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    tcg_res <- {-# SCC "Typecheck-Rename" #-}
               ioMsgMaybe $
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                   tcRnModule hsc_env sum
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                     save_rn_syntax mod
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    -- 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)
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    let allSafeOK = safeInferred dflags && tcSafeOK
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    -- end of the safe haskell line, how to respond to user?
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    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 -> (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
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    return res
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  where
    pprMod t  = ppr $ moduleName $ tcg_mod t
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    errSafe t = quotes (pprMod t) <+> text "has been inferred as safe!"
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    errTwthySafe t = quotes (pprMod t)
      <+> text "is marked as Trustworthy but has been inferred as safe!"
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-- | Convert a typechecked module to Core
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hscDesugar :: HscEnv -> ModSummary -> TcGblEnv -> IO ModGuts
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hscDesugar hsc_env mod_summary tc_result =
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    runHsc hsc_env $ hscDesugar' (ms_location mod_summary) tc_result
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hscDesugar' :: ModLocation -> TcGblEnv -> Hsc ModGuts
hscDesugar' mod_location tc_result = do
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    hsc_env <- getHscEnv
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    r <- ioMsgMaybe $
      {-# SCC "deSugar" #-}
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      deSugar hsc_env mod_location tc_result
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    -- always check -Werror after desugaring, this is the last opportunity for
    -- warnings to arise before the backend.
    handleWarnings
    return r
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-- | Make a 'ModDetails' from the results of typechecking. Used when
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-- typechecking only, as opposed to full compilation.
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makeSimpleDetails :: HscEnv -> TcGblEnv -> IO ModDetails
makeSimpleDetails hsc_env tc_result = mkBootModDetailsTc hsc_env tc_result
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{- **********************************************************************
%*                                                                      *
                The main compiler pipeline
%*                                                                      *
%********************************************************************* -}

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

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It's the task of the compilation proper to compile Haskell, hs-boot and core
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files to either byte-code, hard-code (C, asm, LLVM, etc.) or to nothing at all
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(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
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targets byte-code.
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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.
-}


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

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-- | 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
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  always_do_basic_recompilation_check m_tc_result
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  mHscMessage mod_summary source_modified mb_old_iface mod_index
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    = do
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    hsc_env <- getHscEnv
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    let msg what = case mHscMessage of
                   Just hscMessage -> hscMessage hsc_env mod_index what mod_summary
                   Nothing -> return ()
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        skip iface = do
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            liftIO $ msg UpToDate
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            return $ Left iface
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        compile mb_old_hash reason = do
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            liftIO $ msg reason
            result <- genericHscFrontend mod_summary
            return $ Right (result, mb_old_hash)
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        stable = case source_modified of
                     SourceUnmodifiedAndStable -> True
                     _                         -> False
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    case m_tc_result of
         Just tc_result
          | not always_do_basic_recompilation_check ->
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             return $ Right (FrontendTypecheck tc_result, Nothing)
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         _ -> do
            (recomp_reqd, mb_checked_iface)
                <- {-# SCC "checkOldIface" #-}
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                   liftIO $ checkOldIface hsc_env mod_summary
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                                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) ->
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                    -- 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.
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                    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 ->
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                        return $ Right (FrontendTypecheck tc_result, mb_old_hash)
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genericHscFrontend :: ModSummary -> Hsc FrontendResult
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genericHscFrontend mod_summary =
  getHooked hscFrontendHook genericHscFrontend' >>= ($ mod_summary)

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

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-- Compile Haskell/boot in OneShot mode.
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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
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  = do
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    dflags <- initializePlugins hsc_env' (hsc_dflags hsc_env')
    let hsc_env'' = hsc_env' { hsc_dflags = dflags }

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    -- One-shot mode needs a knot-tying mutable variable for interface
    -- files. See TcRnTypes.TcGblEnv.tcg_type_env_var.
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    -- See also Note [hsc_type_env_var hack]
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    type_env_var <- newIORef emptyNameEnv
    let mod = ms_mod mod_summary
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        hsc_env | isOneShot (ghcMode (hsc_dflags hsc_env''))
                = hsc_env'' { hsc_type_env_var = Just (mod, type_env_var) }
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                | otherwise
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                = hsc_env''
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    -- 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
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        -- We didn't need to do any typechecking; the old interface
        -- file on disk was good enough.
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        Left iface -> do
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            -- 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.)
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        Right (FrontendTypecheck tc_result, mb_old_hash) ->
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            finish mod_summary tc_result mb_old_hash
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-- 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
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-- in the interface file.
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finish :: ModSummary
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       -> TcGblEnv
       -> Maybe Fingerprint
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       -> Hsc (HscStatus, HomeModInfo)
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finish summary tc_result mb_old_hash = do
  hsc_env <- getHscEnv
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  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 = do
        let hsc_status =
              case (target, hsc_src) of
                (HscNothing, _) -> HscNotGeneratingCode
                (_, HsBootFile) -> HscUpdateBoot
                (_, HsigFile) -> HscUpdateSig
                _ -> panic "finish"
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        (iface, no_change, details) <- liftIO $
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          hscSimpleIface hsc_env tc_result mb_old_hash
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        return (iface, no_change, details, hsc_status)
  (iface, no_change, details, hsc_status) <-
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    -- 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.
    if should_desugar
      then do
        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
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            plugins <- liftIO $ readIORef (tcg_th_coreplugins tc_result)
            desugared_guts <- hscSimplify' plugins desugared_guts0
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            (iface, no_change, details, cgguts) <-
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              liftIO $ hscNormalIface hsc_env desugared_guts mb_old_hash
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            return (iface, no_change, details, HscRecomp cgguts summary)
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      else mk_simple_iface
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  liftIO $ hscMaybeWriteIface dflags iface no_change summary
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  return
    ( hsc_status
    , HomeModInfo
      {hm_details = details, hm_iface = iface, hm_linkable = Nothing})
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hscMaybeWriteIface :: DynFlags -> ModIface -> Bool -> ModSummary -> IO ()
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hscMaybeWriteIface dflags iface no_change summary =
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    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) $
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            hscWriteIface dflags iface no_change summary
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--------------------------------------------------------------
-- NoRecomp handlers
--------------------------------------------------------------

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

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

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batchMsg :: Messager
batchMsg hsc_env mod_index recomp mod_summary =
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    case recomp of
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        MustCompile -> showMsg "Compiling " ""
        UpToDate
            | verbosity (hsc_dflags hsc_env) >= 2 -> showMsg "Skipping  " ""
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            | otherwise -> return ()
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        RecompBecause reason -> showMsg "Compiling " (" [" ++ reason ++ "]")
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    where
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        dflags = hsc_dflags hsc_env
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        showMsg msg reason =
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            compilationProgressMsg dflags $
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            (showModuleIndex mod_index ++
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            msg ++ showModMsg dflags (hscTarget dflags)
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                              (recompileRequired recomp) mod_summary)
                ++ reason
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--------------------------------------------------------------
-- FrontEnds
--------------------------------------------------------------
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-- | Given a 'ModSummary', parses and typechecks it, returning the
-- 'TcGblEnv' resulting from type-checking.
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hscFileFrontEnd :: ModSummary -> Hsc TcGblEnv
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hscFileFrontEnd mod_summary = hscTypecheck False mod_summary Nothing
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--------------------------------------------------------------
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-- Safe Haskell
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--------------------------------------------------------------

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-- 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.


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-- Note [Safe Haskell Inference]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Safe Haskell does Safe inference on modules that don't have any specific
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-- safe haskell mode flag. The basic approach to this is:
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