{-# LANGUAGE CPP, NondecreasingIndentation, ScopedTypeVariables #-}
{-# LANGUAGE TupleSections, NamedFieldPuns #-}

-- -----------------------------------------------------------------------------
--
-- (c) The University of Glasgow, 2005-2012
--
-- The GHC API
--
-- -----------------------------------------------------------------------------

module GHC (
        -- * Initialisation
        defaultErrorHandler,
        defaultCleanupHandler,
        prettyPrintGhcErrors,
        withSignalHandlers,
        withCleanupSession,

        -- * GHC Monad
        Ghc, GhcT, GhcMonad(..), HscEnv,
        runGhc, runGhcT, initGhcMonad,
        gcatch, gbracket, gfinally,
        printException,
        handleSourceError,
        needsTemplateHaskellOrQQ,

        -- * Flags and settings
        DynFlags(..), GeneralFlag(..), Severity(..), HscTarget(..), gopt,
        GhcMode(..), GhcLink(..), defaultObjectTarget,
        parseDynamicFlags,
        getSessionDynFlags, setSessionDynFlags,
        getProgramDynFlags, setProgramDynFlags, setLogAction,
        getInteractiveDynFlags, setInteractiveDynFlags,

        -- * Targets
        Target(..), TargetId(..), Phase,
        setTargets,
        getTargets,
        addTarget,
        removeTarget,
        guessTarget,

        -- * Loading\/compiling the program
        depanal,
        load, LoadHowMuch(..), InteractiveImport(..),
        SuccessFlag(..), succeeded, failed,
        defaultWarnErrLogger, WarnErrLogger,
        workingDirectoryChanged,
        parseModule, typecheckModule, desugarModule, loadModule,
        ParsedModule(..), TypecheckedModule(..), DesugaredModule(..),
        TypecheckedSource, ParsedSource, RenamedSource,   -- ditto
        TypecheckedMod, ParsedMod,
        moduleInfo, renamedSource, typecheckedSource,
        parsedSource, coreModule,

        -- ** Compiling to Core
        CoreModule(..),
        compileToCoreModule, compileToCoreSimplified,

        -- * Inspecting the module structure of the program
        ModuleGraph, emptyMG, mapMG, mkModuleGraph, mgModSummaries,
        mgLookupModule,
        ModSummary(..), ms_mod_name, ModLocation(..),
        getModSummary,
        getModuleGraph,
        isLoaded,
        topSortModuleGraph,

        -- * Inspecting modules
        ModuleInfo,
        getModuleInfo,
        modInfoTyThings,
        modInfoTopLevelScope,
        modInfoExports,
        modInfoExportsWithSelectors,
        modInfoInstances,
        modInfoIsExportedName,
        modInfoLookupName,
        modInfoIface,
        modInfoSafe,
        lookupGlobalName,
        findGlobalAnns,
        mkPrintUnqualifiedForModule,
        ModIface(..),
        SafeHaskellMode(..),

        -- * Querying the environment
        -- packageDbModules,

        -- * Printing
        PrintUnqualified, alwaysQualify,

        -- * Interactive evaluation

        -- ** Executing statements
        execStmt, ExecOptions(..), execOptions, ExecResult(..),
        resumeExec,

        -- ** Adding new declarations
        runDecls, runDeclsWithLocation,

        -- ** Get/set the current context
        parseImportDecl,
        setContext, getContext,
        setGHCiMonad, getGHCiMonad,

        -- ** Inspecting the current context
        getBindings, getInsts, getPrintUnqual,
        findModule, lookupModule,
        isModuleTrusted, moduleTrustReqs,
        getNamesInScope,
        getRdrNamesInScope,
        getGRE,
        moduleIsInterpreted,
        getInfo,
        showModule,
        moduleIsBootOrNotObjectLinkable,
        getNameToInstancesIndex,

        -- ** Inspecting types and kinds
        exprType, TcRnExprMode(..),
        typeKind,

        -- ** Looking up a Name
        parseName,
        lookupName,

        -- ** Compiling expressions
        HValue, parseExpr, compileParsedExpr,
        InteractiveEval.compileExpr, dynCompileExpr,
        ForeignHValue,
        compileExprRemote, compileParsedExprRemote,

        -- ** Other
        runTcInteractive,   -- Desired by some clients (Trac #8878)
        isStmt, hasImport, isImport, isDecl,

        -- ** The debugger
        SingleStep(..),
        Resume(..),
        History(historyBreakInfo, historyEnclosingDecls),
        GHC.getHistorySpan, getHistoryModule,
        abandon, abandonAll,
        getResumeContext,
        GHC.obtainTermFromId, GHC.obtainTermFromVal, reconstructType,
        modInfoModBreaks,
        ModBreaks(..), BreakIndex,
        BreakInfo(breakInfo_number, breakInfo_module),
        InteractiveEval.back,
        InteractiveEval.forward,

        -- * Abstract syntax elements

        -- ** Packages
        UnitId,

        -- ** Modules
        Module, mkModule, pprModule, moduleName, moduleUnitId,
        ModuleName, mkModuleName, moduleNameString,

        -- ** Names
        Name,
        isExternalName, nameModule, pprParenSymName, nameSrcSpan,
        NamedThing(..),
        RdrName(Qual,Unqual),

        -- ** Identifiers
        Id, idType,
        isImplicitId, isDeadBinder,
        isExportedId, isLocalId, isGlobalId,
        isRecordSelector,
        isPrimOpId, isFCallId, isClassOpId_maybe,
        isDataConWorkId, idDataCon,
        isBottomingId, isDictonaryId,
        recordSelectorTyCon,

        -- ** Type constructors
        TyCon,
        tyConTyVars, tyConDataCons, tyConArity,
        isClassTyCon, isTypeSynonymTyCon, isTypeFamilyTyCon, isNewTyCon,
        isPrimTyCon, isFunTyCon,
        isFamilyTyCon, isOpenFamilyTyCon, isOpenTypeFamilyTyCon,
        tyConClass_maybe,
        synTyConRhs_maybe, synTyConDefn_maybe, tyConKind,

        -- ** Type variables
        TyVar,
        alphaTyVars,

        -- ** Data constructors
        DataCon,
        dataConSig, dataConType, dataConTyCon, dataConFieldLabels,
        dataConIsInfix, isVanillaDataCon, dataConUserType,
        dataConSrcBangs,
        StrictnessMark(..), isMarkedStrict,

        -- ** Classes
        Class,
        classMethods, classSCTheta, classTvsFds, classATs,
        pprFundeps,

        -- ** Instances
        ClsInst,
        instanceDFunId,
        pprInstance, pprInstanceHdr,
        pprFamInst,

        FamInst,

        -- ** Types and Kinds
        Type, splitForAllTys, funResultTy,
        pprParendType, pprTypeApp,
        Kind,
        PredType,
        ThetaType, pprForAll, pprThetaArrowTy,

        -- ** Entities
        TyThing(..),

        -- ** Syntax
        module HsSyn, -- ToDo: remove extraneous bits

        -- ** Fixities
        FixityDirection(..),
        defaultFixity, maxPrecedence,
        negateFixity,
        compareFixity,
        LexicalFixity(..),

        -- ** Source locations
        SrcLoc(..), RealSrcLoc,
        mkSrcLoc, noSrcLoc,
        srcLocFile, srcLocLine, srcLocCol,
        SrcSpan(..), RealSrcSpan,
        mkSrcSpan, srcLocSpan, isGoodSrcSpan, noSrcSpan,
        srcSpanStart, srcSpanEnd,
        srcSpanFile,
        srcSpanStartLine, srcSpanEndLine,
        srcSpanStartCol, srcSpanEndCol,

        -- ** Located
        GenLocated(..), Located,

        -- *** Constructing Located
        noLoc, mkGeneralLocated,

        -- *** Deconstructing Located
        getLoc, unLoc,

        -- *** Combining and comparing Located values
        eqLocated, cmpLocated, combineLocs, addCLoc,
        leftmost_smallest, leftmost_largest, rightmost,
        spans, isSubspanOf,

        -- * Exceptions
        GhcException(..), showGhcException,

        -- * Token stream manipulations
        Token,
        getTokenStream, getRichTokenStream,
        showRichTokenStream, addSourceToTokens,

        -- * Pure interface to the parser
        parser,

        -- * API Annotations
        ApiAnns,AnnKeywordId(..),AnnotationComment(..),
        getAnnotation, getAndRemoveAnnotation,
        getAnnotationComments, getAndRemoveAnnotationComments,
        unicodeAnn,

        -- * Miscellaneous
        --sessionHscEnv,
        cyclicModuleErr,
  ) where

{-
 ToDo:

  * inline bits of HscMain here to simplify layering: hscTcExpr, hscStmt.
-}

#include "HsVersions.h"

import GhcPrelude hiding (init)

import ByteCodeTypes
import InteractiveEval
import InteractiveEvalTypes
import TcRnDriver       ( runTcInteractive )
import GHCi
import GHCi.RemoteTypes

import PprTyThing       ( pprFamInst )
import HscMain
import GhcMake
import DriverPipeline   ( compileOne' )
import GhcMonad
import TcRnMonad        ( finalSafeMode, fixSafeInstances )
import TcRnTypes
import Packages
import NameSet
import RdrName
import HsSyn
import Type     hiding( typeKind )
import TcType           hiding( typeKind )
import Id
import TysPrim          ( alphaTyVars )
import TyCon
import Class
import DataCon
import Name             hiding ( varName )
import Avail
import InstEnv
import FamInstEnv ( FamInst )
import SrcLoc
import CoreSyn
import TidyPgm
import DriverPhases     ( Phase(..), isHaskellSrcFilename )
import Finder
import HscTypes
import CmdLineParser
import DynFlags hiding (WarnReason(..))
import SysTools
import Annotations
import Module
import Panic
import Platform
import Bag              ( listToBag, unitBag )
import ErrUtils
import MonadUtils
import Util
import StringBuffer
import Outputable
import BasicTypes
import Maybes           ( expectJust )
import FastString
import qualified Parser
import Lexer
import ApiAnnotation
import qualified GHC.LanguageExtensions as LangExt
import NameEnv
import CoreFVs          ( orphNamesOfFamInst )
import FamInstEnv       ( famInstEnvElts )
import TcRnDriver
import Inst
import FamInst
import FileCleanup

import Data.Foldable
import qualified Data.Map.Strict as Map
import Data.Set (Set)
import qualified Data.Sequence as Seq
import System.Directory ( doesFileExist )
import Data.Maybe
import Data.List        ( find )
import Data.Time
import Data.Typeable    ( Typeable )
import Data.Word        ( Word8 )
import Control.Monad
import System.Exit      ( exitWith, ExitCode(..) )
import Exception
import Data.IORef
import System.FilePath


-- %************************************************************************
-- %*                                                                      *
--             Initialisation: exception handlers
-- %*                                                                      *
-- %************************************************************************


-- | Install some default exception handlers and run the inner computation.
-- Unless you want to handle exceptions yourself, you should wrap this around
-- the top level of your program.  The default handlers output the error
-- message(s) to stderr and exit cleanly.
defaultErrorHandler :: (ExceptionMonad m)
                    => FatalMessager -> FlushOut -> m a -> m a
defaultErrorHandler fm (FlushOut flushOut) inner =
  -- top-level exception handler: any unrecognised exception is a compiler bug.
  ghandle (\exception -> liftIO $ do
           flushOut
           case fromException exception of
                -- an IO exception probably isn't our fault, so don't panic
                Just (ioe :: IOException) ->
                  fatalErrorMsg'' fm (show ioe)
                _ -> case fromException exception of
                     Just UserInterrupt ->
                         -- Important to let this one propagate out so our
                         -- calling process knows we were interrupted by ^C
                         liftIO $ throwIO UserInterrupt
                     Just StackOverflow ->
                         fatalErrorMsg'' fm "stack overflow: use +RTS -K<size> to increase it"
                     _ -> case fromException exception of
                          Just (ex :: ExitCode) -> liftIO $ throwIO ex
                          _ ->
                              fatalErrorMsg'' fm
                                  (show (Panic (show exception)))
           exitWith (ExitFailure 1)
         ) $

  -- error messages propagated as exceptions
  handleGhcException
            (\ge -> liftIO $ do
                flushOut
                case ge of
                     Signal _ -> exitWith (ExitFailure 1)
                     _ -> do fatalErrorMsg'' fm (show ge)
                             exitWith (ExitFailure 1)
            ) $
  inner

-- | This function is no longer necessary, cleanup is now done by
-- runGhc/runGhcT.
{-# DEPRECATED defaultCleanupHandler "Cleanup is now done by runGhc/runGhcT" #-}
defaultCleanupHandler :: (ExceptionMonad m) => DynFlags -> m a -> m a
defaultCleanupHandler _ m = m
 where _warning_suppression = m `gonException` undefined


-- %************************************************************************
-- %*                                                                      *
--             The Ghc Monad
-- %*                                                                      *
-- %************************************************************************

-- | Run function for the 'Ghc' monad.
--
-- It initialises the GHC session and warnings via 'initGhcMonad'.  Each call
-- to this function will create a new session which should not be shared among
-- several threads.
--
-- Any errors not handled inside the 'Ghc' action are propagated as IO
-- exceptions.

runGhc :: Maybe FilePath  -- ^ See argument to 'initGhcMonad'.
       -> Ghc a           -- ^ The action to perform.
       -> IO a
runGhc mb_top_dir ghc = do
  ref <- newIORef (panic "empty session")
  let session = Session ref
  flip unGhc session $ withSignalHandlers $ do -- catch ^C
    initGhcMonad mb_top_dir
    withCleanupSession ghc

-- | Run function for 'GhcT' monad transformer.
--
-- It initialises the GHC session and warnings via 'initGhcMonad'.  Each call
-- to this function will create a new session which should not be shared among
-- several threads.

runGhcT :: ExceptionMonad m =>
           Maybe FilePath  -- ^ See argument to 'initGhcMonad'.
        -> GhcT m a        -- ^ The action to perform.
        -> m a
runGhcT mb_top_dir ghct = do
  ref <- liftIO $ newIORef (panic "empty session")
  let session = Session ref
  flip unGhcT session $ withSignalHandlers $ do -- catch ^C
    initGhcMonad mb_top_dir
    withCleanupSession ghct

withCleanupSession :: GhcMonad m => m a -> m a
withCleanupSession ghc = ghc `gfinally` cleanup
  where
   cleanup = do
      hsc_env <- getSession
      let dflags = hsc_dflags hsc_env
      liftIO $ do
          cleanTempFiles dflags
          cleanTempDirs dflags
          stopIServ hsc_env -- shut down the IServ
          log_finaliser dflags dflags
          --  exceptions will be blocked while we clean the temporary files,
          -- so there shouldn't be any difficulty if we receive further
          -- signals.

-- | Initialise a GHC session.
--
-- If you implement a custom 'GhcMonad' you must call this function in the
-- monad run function.  It will initialise the session variable and clear all
-- warnings.
--
-- The first argument should point to the directory where GHC's library files
-- reside.  More precisely, this should be the output of @ghc --print-libdir@
-- of the version of GHC the module using this API is compiled with.  For
-- portability, you should use the @ghc-paths@ package, available at
-- <http://hackage.haskell.org/package/ghc-paths>.

initGhcMonad :: GhcMonad m => Maybe FilePath -> m ()
initGhcMonad mb_top_dir
  = do { env <- liftIO $
                do { mySettings <- initSysTools mb_top_dir
                   ; myLlvmTargets <- initLlvmTargets mb_top_dir
                   ; dflags <- initDynFlags (defaultDynFlags mySettings myLlvmTargets)
                   ; checkBrokenTablesNextToCode dflags
                   ; setUnsafeGlobalDynFlags dflags
                      -- c.f. DynFlags.parseDynamicFlagsFull, which
                      -- creates DynFlags and sets the UnsafeGlobalDynFlags
                   ; newHscEnv dflags }
       ; setSession env }

-- | The binutils linker on ARM emits unnecessary R_ARM_COPY relocations which
-- breaks tables-next-to-code in dynamically linked modules. This
-- check should be more selective but there is currently no released
-- version where this bug is fixed.
-- See https://sourceware.org/bugzilla/show_bug.cgi?id=16177 and
-- https://ghc.haskell.org/trac/ghc/ticket/4210#comment:29
checkBrokenTablesNextToCode :: MonadIO m => DynFlags -> m ()
checkBrokenTablesNextToCode dflags
  = do { broken <- checkBrokenTablesNextToCode' dflags
       ; when broken
         $ do { _ <- liftIO $ throwIO $ mkApiErr dflags invalidLdErr
              ; fail "unsupported linker"
              }
       }
  where
    invalidLdErr = text "Tables-next-to-code not supported on ARM" <+>
                   text "when using binutils ld (please see:" <+>
                   text "https://sourceware.org/bugzilla/show_bug.cgi?id=16177)"

checkBrokenTablesNextToCode' :: MonadIO m => DynFlags -> m Bool
checkBrokenTablesNextToCode' dflags
  | not (isARM arch)              = return False
  | WayDyn `notElem` ways dflags  = return False
  | not (tablesNextToCode dflags) = return False
  | otherwise                     = do
    linkerInfo <- liftIO $ getLinkerInfo dflags
    case linkerInfo of
      GnuLD _  -> return True
      _        -> return False
  where platform = targetPlatform dflags
        arch = platformArch platform


-- %************************************************************************
-- %*                                                                      *
--             Flags & settings
-- %*                                                                      *
-- %************************************************************************

-- $DynFlags
--
-- The GHC session maintains two sets of 'DynFlags':
--
--   * The "interactive" @DynFlags@, which are used for everything
--     related to interactive evaluation, including 'runStmt',
--     'runDecls', 'exprType', 'lookupName' and so on (everything
--     under \"Interactive evaluation\" in this module).
--
--   * The "program" @DynFlags@, which are used when loading
--     whole modules with 'load'
--
-- 'setInteractiveDynFlags', 'getInteractiveDynFlags' work with the
-- interactive @DynFlags@.
--
-- 'setProgramDynFlags', 'getProgramDynFlags' work with the
-- program @DynFlags@.
--
-- 'setSessionDynFlags' sets both @DynFlags@, and 'getSessionDynFlags'
-- retrieves the program @DynFlags@ (for backwards compatibility).


-- | Updates both the interactive and program DynFlags in a Session.
-- This also reads the package database (unless it has already been
-- read), and prepares the compilers knowledge about packages.  It can
-- be called again to load new packages: just add new package flags to
-- (packageFlags dflags).
--
-- Returns a list of new packages that may need to be linked in using
-- the dynamic linker (see 'linkPackages') as a result of new package
-- flags.  If you are not doing linking or doing static linking, you
-- can ignore the list of packages returned.
--
setSessionDynFlags :: GhcMonad m => DynFlags -> m [InstalledUnitId]
setSessionDynFlags dflags = do
  dflags' <- checkNewDynFlags dflags
  (dflags'', preload) <- liftIO $ initPackages dflags'
  modifySession $ \h -> h{ hsc_dflags = dflags''
                         , hsc_IC = (hsc_IC h){ ic_dflags = dflags'' } }
  invalidateModSummaryCache
  return preload

-- | Sets the program 'DynFlags'.  Note: this invalidates the internal
-- cached module graph, causing more work to be done the next time
-- 'load' is called.
setProgramDynFlags :: GhcMonad m => DynFlags -> m [InstalledUnitId]
setProgramDynFlags dflags = setProgramDynFlags_ True dflags

-- | Set the action taken when the compiler produces a message.  This
-- can also be accomplished using 'setProgramDynFlags', but using
-- 'setLogAction' avoids invalidating the cached module graph.
setLogAction :: GhcMonad m => LogAction -> LogFinaliser -> m ()
setLogAction action finaliser = do
  dflags' <- getProgramDynFlags
  void $ setProgramDynFlags_ False $
    dflags' { log_action = action
            , log_finaliser = finaliser }

setProgramDynFlags_ :: GhcMonad m => Bool -> DynFlags -> m [InstalledUnitId]
setProgramDynFlags_ invalidate_needed dflags = do
  dflags' <- checkNewDynFlags dflags
  dflags_prev <- getProgramDynFlags
  (dflags'', preload) <-
    if (packageFlagsChanged dflags_prev dflags')
       then liftIO $ initPackages dflags'
       else return (dflags', [])
  modifySession $ \h -> h{ hsc_dflags = dflags'' }
  when invalidate_needed $ invalidateModSummaryCache
  return preload


-- When changing the DynFlags, we want the changes to apply to future
-- loads, but without completely discarding the program.  But the
-- DynFlags are cached in each ModSummary in the hsc_mod_graph, so
-- after a change to DynFlags, the changes would apply to new modules
-- but not existing modules; this seems undesirable.
--
-- Furthermore, the GHC API client might expect that changing
-- log_action would affect future compilation messages, but for those
-- modules we have cached ModSummaries for, we'll continue to use the
-- old log_action.  This is definitely wrong (#7478).
--
-- Hence, we invalidate the ModSummary cache after changing the
-- DynFlags.  We do this by tweaking the date on each ModSummary, so
-- that the next downsweep will think that all the files have changed
-- and preprocess them again.  This won't necessarily cause everything
-- to be recompiled, because by the time we check whether we need to
-- recopmile a module, we'll have re-summarised the module and have a
-- correct ModSummary.
--
invalidateModSummaryCache :: GhcMonad m => m ()
invalidateModSummaryCache =
  modifySession $ \h -> h { hsc_mod_graph = mapMG inval (hsc_mod_graph h) }
 where
  inval ms = ms { ms_hs_date = addUTCTime (-1) (ms_hs_date ms) }

-- | Returns the program 'DynFlags'.
getProgramDynFlags :: GhcMonad m => m DynFlags
getProgramDynFlags = getSessionDynFlags

-- | Set the 'DynFlags' used to evaluate interactive expressions.
-- Note: this cannot be used for changes to packages.  Use
-- 'setSessionDynFlags', or 'setProgramDynFlags' and then copy the
-- 'pkgState' into the interactive @DynFlags@.
setInteractiveDynFlags :: GhcMonad m => DynFlags -> m ()
setInteractiveDynFlags dflags = do
  dflags' <- checkNewDynFlags dflags
  dflags'' <- checkNewInteractiveDynFlags dflags'
  modifySession $ \h -> h{ hsc_IC = (hsc_IC h) { ic_dflags = dflags'' }}

-- | Get the 'DynFlags' used to evaluate interactive expressions.
getInteractiveDynFlags :: GhcMonad m => m DynFlags
getInteractiveDynFlags = withSession $ \h -> return (ic_dflags (hsc_IC h))


parseDynamicFlags :: MonadIO m =>
                     DynFlags -> [Located String]
                  -> m (DynFlags, [Located String], [Warn])
parseDynamicFlags = parseDynamicFlagsCmdLine

-- | Checks the set of new DynFlags for possibly erroneous option
-- combinations when invoking 'setSessionDynFlags' and friends, and if
-- found, returns a fixed copy (if possible).
checkNewDynFlags :: MonadIO m => DynFlags -> m DynFlags
checkNewDynFlags dflags = do
  -- See Note [DynFlags consistency]
  let (dflags', warnings) = makeDynFlagsConsistent dflags
  liftIO $ handleFlagWarnings dflags (map (Warn NoReason) warnings)
  return dflags'

checkNewInteractiveDynFlags :: MonadIO m => DynFlags -> m DynFlags
checkNewInteractiveDynFlags dflags0 = do
  dflags1 <-
      if xopt LangExt.StaticPointers dflags0
      then do liftIO $ printOrThrowWarnings dflags0 $ listToBag
                [mkPlainWarnMsg dflags0 interactiveSrcSpan
                 $ text "StaticPointers is not supported in GHCi interactive expressions."]
              return $ xopt_unset dflags0 LangExt.StaticPointers
      else return dflags0
  return dflags1


-- %************************************************************************
-- %*                                                                      *
--             Setting, getting, and modifying the targets
-- %*                                                                      *
-- %************************************************************************

-- ToDo: think about relative vs. absolute file paths. And what
-- happens when the current directory changes.

-- | Sets the targets for this session.  Each target may be a module name
-- or a filename.  The targets correspond to the set of root modules for
-- the program\/library.  Unloading the current program is achieved by
-- setting the current set of targets to be empty, followed by 'load'.
setTargets :: GhcMonad m => [Target] -> m ()
setTargets targets = modifySession (\h -> h{ hsc_targets = targets })

-- | Returns the current set of targets
getTargets :: GhcMonad m => m [Target]
getTargets = withSession (return . hsc_targets)

-- | Add another target.
addTarget :: GhcMonad m => Target -> m ()
addTarget target
  = modifySession (\h -> h{ hsc_targets = target : hsc_targets h })

-- | Remove a target
removeTarget :: GhcMonad m => TargetId -> m ()
removeTarget target_id
  = modifySession (\h -> h{ hsc_targets = filter (hsc_targets h) })
  where
   filter targets = [ t | t@(Target id _ _) <- targets, id /= target_id ]

-- | Attempts to guess what Target a string refers to.  This function
-- implements the @--make@/GHCi command-line syntax for filenames:
--
--   - if the string looks like a Haskell source filename, then interpret it
--     as such
--
--   - if adding a .hs or .lhs suffix yields the name of an existing file,
--     then use that
--
--   - otherwise interpret the string as a module name
--
guessTarget :: GhcMonad m => String -> Maybe Phase -> m Target
guessTarget str (Just phase)
   = return (Target (TargetFile str (Just phase)) True Nothing)
guessTarget str Nothing
   | isHaskellSrcFilename file
   = return (target (TargetFile file Nothing))
   | otherwise
   = do exists <- liftIO $ doesFileExist hs_file
        if exists
           then return (target (TargetFile hs_file Nothing))
           else do
        exists <- liftIO $ doesFileExist lhs_file
        if exists
           then return (target (TargetFile lhs_file Nothing))
           else do
        if looksLikeModuleName file
           then return (target (TargetModule (mkModuleName file)))
           else do
        dflags <- getDynFlags
        liftIO $ throwGhcExceptionIO
                 (ProgramError (showSDoc dflags $
                 text "target" <+> quotes (text file) <+>
                 text "is not a module name or a source file"))
     where
         (file,obj_allowed)
                | '*':rest <- str = (rest, False)
                | otherwise       = (str,  True)

         hs_file  = file <.> "hs"
         lhs_file = file <.> "lhs"

         target tid = Target tid obj_allowed Nothing


-- | Inform GHC that the working directory has changed.  GHC will flush
-- its cache of module locations, since it may no longer be valid.
--
-- Note: Before changing the working directory make sure all threads running
-- in the same session have stopped.  If you change the working directory,
-- you should also unload the current program (set targets to empty,
-- followed by load).
workingDirectoryChanged :: GhcMonad m => m ()
workingDirectoryChanged = withSession $ (liftIO . flushFinderCaches)


-- %************************************************************************
-- %*                                                                      *
--             Running phases one at a time
-- %*                                                                      *
-- %************************************************************************

class ParsedMod m where
  modSummary   :: m -> ModSummary
  parsedSource :: m -> ParsedSource

class ParsedMod m => TypecheckedMod m where
  renamedSource     :: m -> Maybe RenamedSource
  typecheckedSource :: m -> TypecheckedSource
  moduleInfo        :: m -> ModuleInfo
  tm_internals      :: m -> (TcGblEnv, ModDetails)
        -- ToDo: improvements that could be made here:
        --  if the module succeeded renaming but not typechecking,
        --  we can still get back the GlobalRdrEnv and exports, so
        --  perhaps the ModuleInfo should be split up into separate
        --  fields.

class TypecheckedMod m => DesugaredMod m where
  coreModule :: m -> ModGuts

-- | The result of successful parsing.
data ParsedModule =
  ParsedModule { pm_mod_summary   :: ModSummary
               , pm_parsed_source :: ParsedSource
               , pm_extra_src_files :: [FilePath]
               , pm_annotations :: ApiAnns }
               -- See Note [Api annotations] in ApiAnnotation.hs

instance ParsedMod ParsedModule where
  modSummary m    = pm_mod_summary m
  parsedSource m = pm_parsed_source m

-- | The result of successful typechecking.  It also contains the parser
--   result.
data TypecheckedModule =
  TypecheckedModule { tm_parsed_module       :: ParsedModule
                    , tm_renamed_source      :: Maybe RenamedSource
                    , tm_typechecked_source  :: TypecheckedSource
                    , tm_checked_module_info :: ModuleInfo
                    , tm_internals_          :: (TcGblEnv, ModDetails)
                    }

instance ParsedMod TypecheckedModule where
  modSummary m   = modSummary (tm_parsed_module m)
  parsedSource m = parsedSource (tm_parsed_module m)

instance TypecheckedMod TypecheckedModule where
  renamedSource m     = tm_renamed_source m
  typecheckedSource m = tm_typechecked_source m
  moduleInfo m        = tm_checked_module_info m
  tm_internals m      = tm_internals_ m

-- | The result of successful desugaring (i.e., translation to core).  Also
--  contains all the information of a typechecked module.
data DesugaredModule =
  DesugaredModule { dm_typechecked_module :: TypecheckedModule
                  , dm_core_module        :: ModGuts
             }

instance ParsedMod DesugaredModule where
  modSummary m   = modSummary (dm_typechecked_module m)
  parsedSource m = parsedSource (dm_typechecked_module m)

instance TypecheckedMod DesugaredModule where
  renamedSource m     = renamedSource (dm_typechecked_module m)
  typecheckedSource m = typecheckedSource (dm_typechecked_module m)
  moduleInfo m        = moduleInfo (dm_typechecked_module m)
  tm_internals m      = tm_internals_ (dm_typechecked_module m)

instance DesugaredMod DesugaredModule where
  coreModule m = dm_core_module m

type ParsedSource      = Located (HsModule GhcPs)
type RenamedSource     = (HsGroup GhcRn, [LImportDecl GhcRn], Maybe [(LIE GhcRn, Avails)],
                          Maybe LHsDocString)
type TypecheckedSource = LHsBinds GhcTc

-- NOTE:
--   - things that aren't in the output of the typechecker right now:
--     - the export list
--     - the imports
--     - type signatures
--     - type/data/newtype declarations
--     - class declarations
--     - instances
--   - extra things in the typechecker's output:
--     - default methods are turned into top-level decls.
--     - dictionary bindings

-- | Return the 'ModSummary' of a module with the given name.
--
-- The module must be part of the module graph (see 'hsc_mod_graph' and
-- 'ModuleGraph').  If this is not the case, this function will throw a
-- 'GhcApiError'.
--
-- This function ignores boot modules and requires that there is only one
-- non-boot module with the given name.
getModSummary :: GhcMonad m => ModuleName -> m ModSummary
getModSummary mod = do
   mg <- liftM hsc_mod_graph getSession
   let mods_by_name = [ ms | ms <- mgModSummaries mg
                      , ms_mod_name ms == mod
                      , not (isBootSummary ms) ]
   case mods_by_name of
     [] -> do dflags <- getDynFlags
              liftIO $ throwIO $ mkApiErr dflags (text "Module not part of module graph")
     [ms] -> return ms
     multiple -> do dflags <- getDynFlags
                    liftIO $ throwIO $ mkApiErr dflags (text "getModSummary is ambiguous: " <+> ppr multiple)

-- | Parse a module.
--
-- Throws a 'SourceError' on parse error.
parseModule :: GhcMonad m => ModSummary -> m ParsedModule
parseModule ms = do
   hsc_env <- getSession
   let hsc_env_tmp = hsc_env { hsc_dflags = ms_hspp_opts ms }
   hpm <- liftIO $ hscParse hsc_env_tmp ms
   return (ParsedModule ms (hpm_module hpm) (hpm_src_files hpm)
                           (hpm_annotations hpm))
               -- See Note [Api annotations] in ApiAnnotation.hs

-- | Typecheck and rename a parsed module.
--
-- Throws a 'SourceError' if either fails.
typecheckModule :: GhcMonad m => ParsedModule -> m TypecheckedModule
typecheckModule pmod = do
 let ms = modSummary pmod
 hsc_env <- getSession
 let hsc_env_tmp = hsc_env { hsc_dflags = ms_hspp_opts ms }
 (tc_gbl_env, rn_info)
       <- liftIO $ hscTypecheckRename hsc_env_tmp ms $
                      HsParsedModule { hpm_module = parsedSource pmod,
                                       hpm_src_files = pm_extra_src_files pmod,
                                       hpm_annotations = pm_annotations pmod }
 details <- liftIO $ makeSimpleDetails hsc_env_tmp tc_gbl_env
 safe    <- liftIO $ finalSafeMode (ms_hspp_opts ms) tc_gbl_env

 return $
     TypecheckedModule {
       tm_internals_          = (tc_gbl_env, details),
       tm_parsed_module       = pmod,
       tm_renamed_source      = rn_info,
       tm_typechecked_source  = tcg_binds tc_gbl_env,
       tm_checked_module_info =
         ModuleInfo {
           minf_type_env  = md_types details,
           minf_exports   = md_exports details,
           minf_rdr_env   = Just (tcg_rdr_env tc_gbl_env),
           minf_instances = fixSafeInstances safe $ md_insts details,
           minf_iface     = Nothing,
           minf_safe      = safe,
           minf_modBreaks = emptyModBreaks
         }}

-- | Desugar a typechecked module.
desugarModule :: GhcMonad m => TypecheckedModule -> m DesugaredModule
desugarModule tcm = do
 let ms = modSummary tcm
 let (tcg, _) = tm_internals tcm
 hsc_env <- getSession
 let hsc_env_tmp = hsc_env { hsc_dflags = ms_hspp_opts ms }
 guts <- liftIO $ hscDesugar hsc_env_tmp ms tcg
 return $
     DesugaredModule {
       dm_typechecked_module = tcm,
       dm_core_module        = guts
     }

-- | Load a module.  Input doesn't need to be desugared.
--
-- A module must be loaded before dependent modules can be typechecked.  This
-- always includes generating a 'ModIface' and, depending on the
-- 'DynFlags.hscTarget', may also include code generation.
--
-- This function will always cause recompilation and will always overwrite
-- previous compilation results (potentially files on disk).
--
loadModule :: (TypecheckedMod mod, GhcMonad m) => mod -> m mod
loadModule tcm = do
   let ms = modSummary tcm
   let mod = ms_mod_name ms
   let loc = ms_location ms
   let (tcg, _details) = tm_internals tcm

   mb_linkable <- case ms_obj_date ms of
                     Just t | t > ms_hs_date ms  -> do
                         l <- liftIO $ findObjectLinkable (ms_mod ms)
                                                  (ml_obj_file loc) t
                         return (Just l)
                     _otherwise -> return Nothing

   let source_modified | isNothing mb_linkable = SourceModified
                       | otherwise             = SourceUnmodified
                       -- we can't determine stability here

   -- compile doesn't change the session
   hsc_env <- getSession
   mod_info <- liftIO $ compileOne' (Just tcg) Nothing
                                    hsc_env ms 1 1 Nothing mb_linkable
                                    source_modified

   modifySession $ \e -> e{ hsc_HPT = addToHpt (hsc_HPT e) mod mod_info }
   return tcm


-- %************************************************************************
-- %*                                                                      *
--             Dealing with Core
-- %*                                                                      *
-- %************************************************************************

-- | A CoreModule consists of just the fields of a 'ModGuts' that are needed for
-- the 'GHC.compileToCoreModule' interface.
data CoreModule
  = CoreModule {
      -- | Module name
      cm_module   :: !Module,
      -- | Type environment for types declared in this module
      cm_types    :: !TypeEnv,
      -- | Declarations
      cm_binds    :: CoreProgram,
      -- | Safe Haskell mode
      cm_safe     :: SafeHaskellMode
    }

instance Outputable CoreModule where
   ppr (CoreModule {cm_module = mn, cm_types = te, cm_binds = cb,
                    cm_safe = sf})
    = text "%module" <+> ppr mn <+> parens (ppr sf) <+> ppr te
      $$ vcat (map ppr cb)

-- | This is the way to get access to the Core bindings corresponding
-- to a module. 'compileToCore' parses, typechecks, and
-- desugars the module, then returns the resulting Core module (consisting of
-- the module name, type declarations, and function declarations) if
-- successful.
compileToCoreModule :: GhcMonad m => FilePath -> m CoreModule
compileToCoreModule = compileCore False

-- | Like compileToCoreModule, but invokes the simplifier, so
-- as to return simplified and tidied Core.
compileToCoreSimplified :: GhcMonad m => FilePath -> m CoreModule
compileToCoreSimplified = compileCore True

compileCore :: GhcMonad m => Bool -> FilePath -> m CoreModule
compileCore simplify fn = do
   -- First, set the target to the desired filename
   target <- guessTarget fn Nothing
   addTarget target
   _ <- load LoadAllTargets
   -- Then find dependencies
   modGraph <- depanal [] True
   case find ((== fn) . msHsFilePath) (mgModSummaries modGraph) of
     Just modSummary -> do
       -- Now we have the module name;
       -- parse, typecheck and desugar the module
       (tcg, mod_guts) <- -- TODO: space leaky: call hsc* directly?
         do tm <- typecheckModule =<< parseModule modSummary
            let tcg = fst (tm_internals tm)
            (,) tcg . coreModule <$> desugarModule tm
       liftM (gutsToCoreModule (mg_safe_haskell mod_guts)) $
         if simplify
          then do
             -- If simplify is true: simplify (hscSimplify), then tidy
             -- (tidyProgram).
             hsc_env <- getSession
             simpl_guts <- liftIO $ do
               plugins <- readIORef (tcg_th_coreplugins tcg)
               hscSimplify hsc_env plugins mod_guts
             tidy_guts <- liftIO $ tidyProgram hsc_env simpl_guts
             return $ Left tidy_guts
          else
             return $ Right mod_guts

     Nothing -> panic "compileToCoreModule: target FilePath not found in\
                           module dependency graph"
  where -- two versions, based on whether we simplify (thus run tidyProgram,
        -- which returns a (CgGuts, ModDetails) pair, or not (in which case
        -- we just have a ModGuts.
        gutsToCoreModule :: SafeHaskellMode
                         -> Either (CgGuts, ModDetails) ModGuts
                         -> CoreModule
        gutsToCoreModule safe_mode (Left (cg, md)) = CoreModule {
          cm_module = cg_module cg,
          cm_types  = md_types md,
          cm_binds  = cg_binds cg,
          cm_safe   = safe_mode
        }
        gutsToCoreModule safe_mode (Right mg) = CoreModule {
          cm_module  = mg_module mg,
          cm_types   = typeEnvFromEntities (bindersOfBinds (mg_binds mg))
                                           (mg_tcs mg)
                                           (mg_fam_insts mg),
          cm_binds   = mg_binds mg,
          cm_safe    = safe_mode
         }

-- %************************************************************************
-- %*                                                                      *
--             Inspecting the session
-- %*                                                                      *
-- %************************************************************************

-- | Get the module dependency graph.
getModuleGraph :: GhcMonad m => m ModuleGraph -- ToDo: DiGraph ModSummary
getModuleGraph = liftM hsc_mod_graph getSession

-- | Return @True@ <==> module is loaded.
isLoaded :: GhcMonad m => ModuleName -> m Bool
isLoaded m = withSession $ \hsc_env ->
  return $! isJust (lookupHpt (hsc_HPT hsc_env) m)

-- | Return the bindings for the current interactive session.
getBindings :: GhcMonad m => m [TyThing]
getBindings = withSession $ \hsc_env ->
    return $ icInScopeTTs $ hsc_IC hsc_env

-- | Return the instances for the current interactive session.
getInsts :: GhcMonad m => m ([ClsInst], [FamInst])
getInsts = withSession $ \hsc_env ->
    return $ ic_instances (hsc_IC hsc_env)

getPrintUnqual :: GhcMonad m => m PrintUnqualified
getPrintUnqual = withSession $ \hsc_env ->
  return (icPrintUnqual (hsc_dflags hsc_env) (hsc_IC hsc_env))

-- | Container for information about a 'Module'.
data ModuleInfo = ModuleInfo {
        minf_type_env  :: TypeEnv,
        minf_exports   :: [AvailInfo],
        minf_rdr_env   :: Maybe GlobalRdrEnv,   -- Nothing for a compiled/package mod
        minf_instances :: [ClsInst],
        minf_iface     :: Maybe ModIface,
        minf_safe      :: SafeHaskellMode,
        minf_modBreaks :: ModBreaks
  }
        -- We don't want HomeModInfo here, because a ModuleInfo applies
        -- to package modules too.

-- | Request information about a loaded 'Module'
getModuleInfo :: GhcMonad m => Module -> m (Maybe ModuleInfo)  -- XXX: Maybe X
getModuleInfo mdl = withSession $ \hsc_env -> do
  let mg = hsc_mod_graph hsc_env
  if mgElemModule mg mdl
        then liftIO $ getHomeModuleInfo hsc_env mdl
        else do
  {- if isHomeModule (hsc_dflags hsc_env) mdl
        then return Nothing
        else -} liftIO $ getPackageModuleInfo hsc_env mdl
   -- ToDo: we don't understand what the following comment means.
   --    (SDM, 19/7/2011)
   -- getPackageModuleInfo will attempt to find the interface, so
   -- we don't want to call it for a home module, just in case there
   -- was a problem loading the module and the interface doesn't
   -- exist... hence the isHomeModule test here.  (ToDo: reinstate)

getPackageModuleInfo :: HscEnv -> Module -> IO (Maybe ModuleInfo)
getPackageModuleInfo hsc_env mdl
  = do  eps <- hscEPS hsc_env
        iface <- hscGetModuleInterface hsc_env mdl
        let
            avails = mi_exports iface
            pte    = eps_PTE eps
            tys    = [ ty | name <- concatMap availNames avails,
                            Just ty <- [lookupTypeEnv pte name] ]
        --
        return (Just (ModuleInfo {
                        minf_type_env  = mkTypeEnv tys,
                        minf_exports   = avails,
                        minf_rdr_env   = Just $! availsToGlobalRdrEnv (moduleName mdl) avails,
                        minf_instances = error "getModuleInfo: instances for package module unimplemented",
                        minf_iface     = Just iface,
                        minf_safe      = getSafeMode $ mi_trust iface,
                        minf_modBreaks = emptyModBreaks
                }))

getHomeModuleInfo :: HscEnv -> Module -> IO (Maybe ModuleInfo)
getHomeModuleInfo hsc_env mdl =
  case lookupHpt (hsc_HPT hsc_env) (moduleName mdl) of
    Nothing  -> return Nothing
    Just hmi -> do
      let details = hm_details hmi
          iface   = hm_iface hmi
      return (Just (ModuleInfo {
                        minf_type_env  = md_types details,
                        minf_exports   = md_exports details,
                        minf_rdr_env   = mi_globals $! hm_iface hmi,
                        minf_instances = md_insts details,
                        minf_iface     = Just iface,
                        minf_safe      = getSafeMode $ mi_trust iface
                       ,minf_modBreaks = getModBreaks hmi
                        }))

-- | The list of top-level entities defined in a module
modInfoTyThings :: ModuleInfo -> [TyThing]
modInfoTyThings minf = typeEnvElts (minf_type_env minf)

modInfoTopLevelScope :: ModuleInfo -> Maybe [Name]
modInfoTopLevelScope minf
  = fmap (map gre_name . globalRdrEnvElts) (minf_rdr_env minf)

modInfoExports :: ModuleInfo -> [Name]
modInfoExports minf = concatMap availNames $! minf_exports minf

modInfoExportsWithSelectors :: ModuleInfo -> [Name]
modInfoExportsWithSelectors minf = concatMap availNamesWithSelectors $! minf_exports minf

-- | Returns the instances defined by the specified module.
-- Warning: currently unimplemented for package modules.
modInfoInstances :: ModuleInfo -> [ClsInst]
modInfoInstances = minf_instances

modInfoIsExportedName :: ModuleInfo -> Name -> Bool
modInfoIsExportedName minf name = elemNameSet name (availsToNameSet (minf_exports minf))

mkPrintUnqualifiedForModule :: GhcMonad m =>
                               ModuleInfo
                            -> m (Maybe PrintUnqualified) -- XXX: returns a Maybe X
mkPrintUnqualifiedForModule minf = withSession $ \hsc_env -> do
  return (fmap (mkPrintUnqualified (hsc_dflags hsc_env)) (minf_rdr_env minf))

modInfoLookupName :: GhcMonad m =>
                     ModuleInfo -> Name
                  -> m (Maybe TyThing) -- XXX: returns a Maybe X
modInfoLookupName minf name = withSession $ \hsc_env -> do
   case lookupTypeEnv (minf_type_env minf) name of
     Just tyThing -> return (Just tyThing)
     Nothing      -> do
       eps <- liftIO $ readIORef (hsc_EPS hsc_env)
       return $! lookupType (hsc_dflags hsc_env)
                            (hsc_HPT hsc_env) (eps_PTE eps) name

modInfoIface :: ModuleInfo -> Maybe ModIface
modInfoIface = minf_iface

-- | Retrieve module safe haskell mode
modInfoSafe :: ModuleInfo -> SafeHaskellMode
modInfoSafe = minf_safe

modInfoModBreaks :: ModuleInfo -> ModBreaks
modInfoModBreaks = minf_modBreaks

isDictonaryId :: Id -> Bool
isDictonaryId id
  = case tcSplitSigmaTy (idType id) of {
      (_tvs, _theta, tau) -> isDictTy tau }

-- | Looks up a global name: that is, any top-level name in any
-- visible module.  Unlike 'lookupName', lookupGlobalName does not use
-- the interactive context, and therefore does not require a preceding
-- 'setContext'.
lookupGlobalName :: GhcMonad m => Name -> m (Maybe TyThing)
lookupGlobalName name = withSession $ \hsc_env -> do
   liftIO $ lookupTypeHscEnv hsc_env name

findGlobalAnns :: (GhcMonad m, Typeable a) => ([Word8] -> a) -> AnnTarget Name -> m [a]
findGlobalAnns deserialize target = withSession $ \hsc_env -> do
    ann_env <- liftIO $ prepareAnnotations hsc_env Nothing
    return (findAnns deserialize ann_env target)

-- | get the GlobalRdrEnv for a session
getGRE :: GhcMonad m => m GlobalRdrEnv
getGRE = withSession $ \hsc_env-> return $ ic_rn_gbl_env (hsc_IC hsc_env)

-- | Retrieve all type and family instances in the environment, indexed
-- by 'Name'. Each name's lists will contain every instance in which that name
-- is mentioned in the instance head.
getNameToInstancesIndex :: GhcMonad m
  => m (Messages, Maybe (NameEnv ([ClsInst], [FamInst])))
getNameToInstancesIndex = do
  hsc_env <- getSession
  liftIO $ runTcInteractive hsc_env $
    do { loadUnqualIfaces hsc_env (hsc_IC hsc_env)
       ; InstEnvs {ie_global, ie_local, ie_visible} <- tcGetInstEnvs
       ; (pkg_fie, home_fie) <- tcGetFamInstEnvs
       -- We use Data.Sequence.Seq because we are creating left associated
       -- mappends.
       -- cls_index and fam_index below are adapted from TcRnDriver.lookupInsts
       ; let cls_index = Map.fromListWith mappend
                 [ (n, Seq.singleton ispec)
                 | ispec <- instEnvElts ie_local ++ instEnvElts ie_global
                 , instIsVisible ie_visible ispec
                 , n <- nameSetElemsStable $ orphNamesOfClsInst ispec
                 ]
       ; let fam_index = Map.fromListWith mappend
                 [ (n, Seq.singleton fispec)
                 | fispec <- famInstEnvElts home_fie ++ famInstEnvElts pkg_fie
                 , n <- nameSetElemsStable $ orphNamesOfFamInst fispec
                 ]
       ; return $ mkNameEnv $
           [ (nm, (toList clss, toList fams))
           | (nm, (clss, fams)) <- Map.toList $ Map.unionWith mappend
               (fmap (,Seq.empty) cls_index)
               (fmap (Seq.empty,) fam_index)
           ] }

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

{- ToDo: Move the primary logic here to compiler/main/Packages.hs
-- | Return all /external/ modules available in the package database.
-- Modules from the current session (i.e., from the 'HomePackageTable') are
-- not included.  This includes module names which are reexported by packages.
packageDbModules :: GhcMonad m =>
                    Bool  -- ^ Only consider exposed packages.
                 -> m [Module]
packageDbModules only_exposed = do
   dflags <- getSessionDynFlags
   let pkgs = eltsUFM (pkgIdMap (pkgState dflags))
   return $
     [ mkModule pid modname
     | p <- pkgs
     , not only_exposed || exposed p
     , let pid = packageConfigId p
     , modname <- exposedModules p
               ++ map exportName (reexportedModules p) ]
               -}

-- -----------------------------------------------------------------------------
-- Misc exported utils

dataConType :: DataCon -> Type
dataConType dc = idType (dataConWrapId dc)

-- | print a 'NamedThing', adding parentheses if the name is an operator.
pprParenSymName :: NamedThing a => a -> SDoc
pprParenSymName a = parenSymOcc (getOccName a) (ppr (getName a))

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


-- ToDo:
--   - Data and Typeable instances for HsSyn.

-- ToDo: check for small transformations that happen to the syntax in
-- the typechecker (eg. -e ==> negate e, perhaps for fromIntegral)

-- ToDo: maybe use TH syntax instead of IfaceSyn?  There's already a way
-- to get from TyCons, Ids etc. to TH syntax (reify).

-- :browse will use either lm_toplev or inspect lm_interface, depending
-- on whether the module is interpreted or not.


-- Extract the filename, stringbuffer content and dynflags associed to a module
--
-- XXX: Explain pre-conditions
getModuleSourceAndFlags :: GhcMonad m => Module -> m (String, StringBuffer, DynFlags)
getModuleSourceAndFlags mod = do
  m <- getModSummary (moduleName mod)
  case ml_hs_file $ ms_location m of
    Nothing -> do dflags <- getDynFlags
                  liftIO $ throwIO $ mkApiErr dflags (text "No source available for module " <+> ppr mod)
    Just sourceFile -> do
        source <- liftIO $ hGetStringBuffer sourceFile
        return (sourceFile, source, ms_hspp_opts m)


-- | Return module source as token stream, including comments.
--
-- The module must be in the module graph and its source must be available.
-- Throws a 'HscTypes.SourceError' on parse error.
getTokenStream :: GhcMonad m => Module -> m [Located Token]
getTokenStream mod = do
  (sourceFile, source, flags) <- getModuleSourceAndFlags mod
  let startLoc = mkRealSrcLoc (mkFastString sourceFile) 1 1
  case lexTokenStream source startLoc flags of
    POk _ ts  -> return ts
    PFailed _ span err ->
        do dflags <- getDynFlags
           liftIO $ throwIO $ mkSrcErr (unitBag $ mkPlainErrMsg dflags span err)

-- | Give even more information on the source than 'getTokenStream'
-- This function allows reconstructing the source completely with
-- 'showRichTokenStream'.
getRichTokenStream :: GhcMonad m => Module -> m [(Located Token, String)]
getRichTokenStream mod = do
  (sourceFile, source, flags) <- getModuleSourceAndFlags mod
  let startLoc = mkRealSrcLoc (mkFastString sourceFile) 1 1
  case lexTokenStream source startLoc flags of
    POk _ ts -> return $ addSourceToTokens startLoc source ts
    PFailed _ span err ->
        do dflags <- getDynFlags
           liftIO $ throwIO $ mkSrcErr (unitBag $ mkPlainErrMsg dflags span err)

-- | Given a source location and a StringBuffer corresponding to this
-- location, return a rich token stream with the source associated to the
-- tokens.
addSourceToTokens :: RealSrcLoc -> StringBuffer -> [Located Token]
                  -> [(Located Token, String)]
addSourceToTokens _ _ [] = []
addSourceToTokens loc buf (t@(L span _) : ts)
    = case span of
      UnhelpfulSpan _ -> (t,"") : addSourceToTokens loc buf ts
      RealSrcSpan s   -> (t,str) : addSourceToTokens newLoc newBuf ts
        where
          (newLoc, newBuf, str) = go "" loc buf
          start = realSrcSpanStart s
          end = realSrcSpanEnd s
          go acc loc buf | loc < start = go acc nLoc nBuf
                         | start <= loc && loc < end = go (ch:acc) nLoc nBuf
                         | otherwise = (loc, buf, reverse acc)
              where (ch, nBuf) = nextChar buf
                    nLoc = advanceSrcLoc loc ch


-- | Take a rich token stream such as produced from 'getRichTokenStream' and
-- return source code almost identical to the original code (except for
-- insignificant whitespace.)
showRichTokenStream :: [(Located Token, String)] -> String
showRichTokenStream ts = go startLoc ts ""
    where sourceFile = getFile $ map (getLoc . fst) ts
          getFile [] = panic "showRichTokenStream: No source file found"
          getFile (UnhelpfulSpan _ : xs) = getFile xs
          getFile (RealSrcSpan s : _) = srcSpanFile s
          startLoc = mkRealSrcLoc sourceFile 1 1
          go _ [] = id
          go loc ((L span _, str):ts)
              = case span of
                UnhelpfulSpan _ -> go loc ts
                RealSrcSpan s
                 | locLine == tokLine -> ((replicate (tokCol - locCol) ' ') ++)
                                       . (str ++)
                                       . go tokEnd ts
                 | otherwise -> ((replicate (tokLine - locLine) '\n') ++)
                               . ((replicate (tokCol - 1) ' ') ++)
                              . (str ++)
                              . go tokEnd ts
                  where (locLine, locCol) = (srcLocLine loc, srcLocCol loc)
                        (tokLine, tokCol) = (srcSpanStartLine s, srcSpanStartCol s)
                        tokEnd = realSrcSpanEnd s

-- -----------------------------------------------------------------------------
-- Interactive evaluation

-- | Takes a 'ModuleName' and possibly a 'UnitId', and consults the
-- filesystem and package database to find the corresponding 'Module',
-- using the algorithm that is used for an @import@ declaration.
findModule :: GhcMonad m => ModuleName -> Maybe FastString -> m Module
findModule mod_name maybe_pkg = withSession $ \hsc_env -> do
  let
    dflags   = hsc_dflags hsc_env
    this_pkg = thisPackage dflags
  --
  case maybe_pkg of
    Just pkg | fsToUnitId pkg /= this_pkg && pkg /= fsLit "this" -> liftIO $ do
      res <- findImportedModule hsc_env mod_name maybe_pkg
      case res of
        Found _ m -> return m
        err       -> throwOneError $ noModError dflags noSrcSpan mod_name err
    _otherwise -> do
      home <- lookupLoadedHomeModule mod_name
      case home of
        Just m  -> return m
        Nothing -> liftIO $ do
           res <- findImportedModule hsc_env mod_name maybe_pkg
           case res of
             Found loc m | moduleUnitId m /= this_pkg -> return m
                         | otherwise -> modNotLoadedError dflags m loc
             err -> throwOneError $ noModError dflags noSrcSpan mod_name err

modNotLoadedError :: DynFlags -> Module -> ModLocation -> IO a
modNotLoadedError dflags m loc = throwGhcExceptionIO $ CmdLineError $ showSDoc dflags $
   text "module is not loaded:" <+>
   quotes (ppr (moduleName m)) <+>
   parens (text (expectJust "modNotLoadedError" (ml_hs_file loc)))

-- | Like 'findModule', but differs slightly when the module refers to
-- a source file, and the file has not been loaded via 'load'.  In
-- this case, 'findModule' will throw an error (module not loaded),
-- but 'lookupModule' will check to see whether the module can also be
-- found in a package, and if so, that package 'Module' will be
-- returned.  If not, the usual module-not-found error will be thrown.
--
lookupModule :: GhcMonad m => ModuleName -> Maybe FastString -> m Module
lookupModule mod_name (Just pkg) = findModule mod_name (Just pkg)
lookupModule mod_name Nothing = withSession $ \hsc_env -> do
  home <- lookupLoadedHomeModule mod_name
  case home of
    Just m  -> return m
    Nothing -> liftIO $ do
      res <- findExposedPackageModule hsc_env mod_name Nothing
      case res of
        Found _ m -> return m
        err       -> throwOneError $ noModError (hsc_dflags hsc_env) noSrcSpan mod_name err

lookupLoadedHomeModule :: GhcMonad m => ModuleName -> m (Maybe Module)
lookupLoadedHomeModule mod_name = withSession $ \hsc_env ->
  case lookupHpt (hsc_HPT hsc_env) mod_name of
    Just mod_info      -> return (Just (mi_module (hm_iface mod_info)))
    _not_a_home_module -> return Nothing

-- | Check that a module is safe to import (according to Safe Haskell).
--
-- We return True to indicate the import is safe and False otherwise
-- although in the False case an error may be thrown first.
isModuleTrusted :: GhcMonad m => Module -> m Bool
isModuleTrusted m = withSession $ \hsc_env ->
    liftIO $ hscCheckSafe hsc_env m noSrcSpan

-- | Return if a module is trusted and the pkgs it depends on to be trusted.
moduleTrustReqs :: GhcMonad m => Module -> m (Bool, Set InstalledUnitId)
moduleTrustReqs m = withSession $ \hsc_env ->
    liftIO $ hscGetSafe hsc_env m noSrcSpan

-- | Set the monad GHCi lifts user statements into.
--
-- Checks that a type (in string form) is an instance of the
-- @GHC.GHCi.GHCiSandboxIO@ type class. Sets it to be the GHCi monad if it is,
-- throws an error otherwise.
setGHCiMonad :: GhcMonad m => String -> m ()
setGHCiMonad name = withSession $ \hsc_env -> do
    ty <- liftIO $ hscIsGHCiMonad hsc_env name
    modifySession $ \s ->
        let ic = (hsc_IC s) { ic_monad = ty }
        in s { hsc_IC = ic }

-- | Get the monad GHCi lifts user statements into.
getGHCiMonad :: GhcMonad m => m Name
getGHCiMonad = fmap (ic_monad . hsc_IC) getSession

getHistorySpan :: GhcMonad m => History -> m SrcSpan
getHistorySpan h = withSession $ \hsc_env ->
    return $ InteractiveEval.getHistorySpan hsc_env h

obtainTermFromVal :: GhcMonad m => Int ->  Bool -> Type -> a -> m Term
obtainTermFromVal bound force ty a = withSession $ \hsc_env ->
    liftIO $ InteractiveEval.obtainTermFromVal hsc_env bound force ty a

obtainTermFromId :: GhcMonad m => Int -> Bool -> Id -> m Term
obtainTermFromId bound force id = withSession $ \hsc_env ->
    liftIO $ InteractiveEval.obtainTermFromId hsc_env bound force id


-- | Returns the 'TyThing' for a 'Name'.  The 'Name' may refer to any
-- entity known to GHC, including 'Name's defined using 'runStmt'.
lookupName :: GhcMonad m => Name -> m (Maybe TyThing)
lookupName name =
     withSession $ \hsc_env ->
       liftIO $ hscTcRcLookupName hsc_env name

-- -----------------------------------------------------------------------------
-- Pure API

-- | A pure interface to the module parser.
--
parser :: String         -- ^ Haskell module source text (full Unicode is supported)
       -> DynFlags       -- ^ the flags
       -> FilePath       -- ^ the filename (for source locations)
       -> (WarningMessages, Either ErrorMessages (Located (HsModule GhcPs)))

parser str dflags filename =
   let
       loc  = mkRealSrcLoc (mkFastString filename) 1 1
       buf  = stringToStringBuffer str
   in
   case unP Parser.parseModule (mkPState dflags buf loc) of

     PFailed warnFn span err   ->
         let (warns,_) = warnFn dflags in
         (warns, Left $ unitBag (mkPlainErrMsg dflags span err))

     POk pst rdr_module ->
         let (warns,_) = getMessages pst dflags in
         (warns, Right rdr_module)
