/ghc-7.0.4/compiler/main/HscTypes.lhs

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%
% (c) The University of Glasgow, 2006
%
\section[HscTypes]{Types for the per-module compiler}

\begin{code}
-- | Types for the per-module compiler
module HscTypes ( 
        -- * 'Ghc' monad stuff
        Ghc(..), GhcT(..), liftGhcT,
        GhcMonad(..), WarnLogMonad(..),
        liftIO,
        ioMsgMaybe, ioMsg,
        logWarnings, clearWarnings, hasWarnings,
        SourceError, GhcApiError, mkSrcErr, srcErrorMessages, mkApiErr,
        throwOneError, handleSourceError,
        reflectGhc, reifyGhc,
        handleFlagWarnings,

	-- * Sessions and compilation state
	Session(..), withSession, modifySession, withTempSession,
        HscEnv(..), hscEPS,
	FinderCache, FindResult(..), ModLocationCache,
	Target(..), TargetId(..), pprTarget, pprTargetId,
	ModuleGraph, emptyMG,
        -- ** Callbacks
        GhcApiCallbacks(..), withLocalCallbacks,

        -- * Information about modules
	ModDetails(..),	emptyModDetails,
	ModGuts(..), CoreModule(..), CgGuts(..), ForeignStubs(..),
        ImportedMods,

	ModSummary(..), ms_mod_name, showModMsg, isBootSummary,
	msHsFilePath, msHiFilePath, msObjFilePath,

        -- * Information about the module being compiled
	HscSource(..), isHsBoot, hscSourceString,	-- Re-exported from DriverPhases
	
	-- * State relating to modules in this package
	HomePackageTable, HomeModInfo(..), emptyHomePackageTable,
	hptInstances, hptRules, hptVectInfo,
	
	-- * State relating to known packages
	ExternalPackageState(..), EpsStats(..), addEpsInStats,
	PackageTypeEnv, PackageIfaceTable, emptyPackageIfaceTable,
	lookupIfaceByModule, emptyModIface,
	
	PackageInstEnv, PackageRuleBase,


        -- * Annotations
        prepareAnnotations,

        -- * Interactive context
	InteractiveContext(..), emptyInteractiveContext, 
	icPrintUnqual, extendInteractiveContext,
        substInteractiveContext,
        mkPrintUnqualified, pprModulePrefix,

	-- * Interfaces
	ModIface(..), mkIfaceWarnCache, mkIfaceHashCache, mkIfaceFixCache,
	emptyIfaceWarnCache,

        -- * Fixity
	FixityEnv, FixItem(..), lookupFixity, emptyFixityEnv,

        -- * TyThings and type environments
	TyThing(..),
	tyThingClass, tyThingTyCon, tyThingDataCon, tyThingId,
	implicitTyThings, isImplicitTyThing,
	
	TypeEnv, lookupType, lookupTypeHscEnv, mkTypeEnv, emptyTypeEnv,
	extendTypeEnv, extendTypeEnvList, extendTypeEnvWithIds, lookupTypeEnv,
	typeEnvElts, typeEnvClasses, typeEnvTyCons, typeEnvIds,
	typeEnvDataCons,

        -- * MonadThings
        MonadThings(..),

        -- * Information on imports and exports
	WhetherHasOrphans, IsBootInterface, Usage(..), 
	Dependencies(..), noDependencies,
	NameCache(..), OrigNameCache, OrigIParamCache,
	Avails, availsToNameSet, availsToNameEnv, availName, availNames,
	GenAvailInfo(..), AvailInfo, RdrAvailInfo, 
	IfaceExport,

	-- * Warnings
	Warnings(..), WarningTxt(..), plusWarns,

	-- * Linker stuff
	Linkable(..), isObjectLinkable,
	Unlinked(..), CompiledByteCode,
	isObject, nameOfObject, isInterpretable, byteCodeOfObject,
        
        -- * Program coverage
        HpcInfo(..), emptyHpcInfo, isHpcUsed, AnyHpcUsage,

        -- * Breakpoints
        ModBreaks (..), BreakIndex, emptyModBreaks,

        -- * Vectorisation information
        VectInfo(..), IfaceVectInfo(..), noVectInfo, plusVectInfo, 
        noIfaceVectInfo
    ) where

#include "HsVersions.h"

#ifdef GHCI
import ByteCodeAsm	( CompiledByteCode )
import {-# SOURCE #-}  InteractiveEval ( Resume )
#endif

import HsSyn
import RdrName
import Name
import NameEnv
import NameSet	
import Module
import InstEnv		( InstEnv, Instance )
import FamInstEnv	( FamInstEnv, FamInst )
import Rules		( RuleBase )
import CoreSyn		( CoreBind )
import VarEnv
import Var
import Id
import Type		

import Annotations
import Class		( Class, classAllSelIds, classATs, classTyCon )
import TyCon
import DataCon		( DataCon, dataConImplicitIds, dataConWrapId )
import PrelNames	( gHC_PRIM )
import Packages hiding ( Version(..) )
import DynFlags		( DynFlags(..), isOneShot, HscTarget (..), dopt,
                          DynFlag(..) )
import DriverPhases	( HscSource(..), isHsBoot, hscSourceString, Phase )
import BasicTypes	( IPName, defaultFixity, WarningTxt(..) )
import OptimizationFuel	( OptFuelState )
import IfaceSyn
import CoreSyn		( CoreRule )
import Maybes		( orElse, expectJust, catMaybes )
import Outputable
import BreakArray
import SrcLoc		( SrcSpan, Located(..) )
import UniqFM		( lookupUFM, eltsUFM, emptyUFM )
import UniqSupply	( UniqSupply )
import FastString
import StringBuffer	( StringBuffer )
import Fingerprint
import MonadUtils
import Data.Dynamic     ( Typeable )
import qualified Data.Dynamic as Dyn
import Bag
import ErrUtils

import System.FilePath
import System.Time	( ClockTime )
import Data.IORef
import Data.Array       ( Array, array )
import Data.List
import Data.Map (Map)
import Control.Monad    ( mplus, guard, liftM, when )
import Exception
\end{code}


%************************************************************************
%*									*
\subsection{Compilation environment}
%*									*
%************************************************************************


\begin{code}
-- | The Session is a handle to the complete state of a compilation
-- session.  A compilation session consists of a set of modules
-- constituting the current program or library, the context for
-- interactive evaluation, and various caches.
data Session = Session !(IORef HscEnv) !(IORef WarningMessages)

mkSrcErr :: ErrorMessages -> SourceError
srcErrorMessages :: SourceError -> ErrorMessages
mkApiErr :: SDoc -> GhcApiError

throwOneError :: MonadIO m => ErrMsg -> m ab
throwOneError err = liftIO $ throwIO $ mkSrcErr $ unitBag err

-- | A source error is an error that is caused by one or more errors in the
-- source code.  A 'SourceError' is thrown by many functions in the
-- compilation pipeline.  Inside GHC these errors are merely printed via
-- 'log_action', but API clients may treat them differently, for example,
-- insert them into a list box.  If you want the default behaviour, use the
-- idiom:
--
-- > handleSourceError printExceptionAndWarnings $ do
-- >   ... api calls that may fail ...
--
-- The 'SourceError's error messages can be accessed via 'srcErrorMessages'.
-- This list may be empty if the compiler failed due to @-Werror@
-- ('Opt_WarnIsError').
--
-- See 'printExceptionAndWarnings' for more information on what to take care
-- of when writing a custom error handler.
data SourceError = SourceError ErrorMessages

instance Show SourceError where
  show (SourceError msgs) = unlines . map show . bagToList $ msgs
    -- ToDo: is there some nicer way to print this?

sourceErrorTc :: Dyn.TyCon
sourceErrorTc = Dyn.mkTyCon "SourceError"
{-# NOINLINE sourceErrorTc #-}
instance Typeable SourceError where
  typeOf _ = Dyn.mkTyConApp sourceErrorTc []

instance Exception SourceError

mkSrcErr = SourceError

-- | Perform the given action and call the exception handler if the action
-- throws a 'SourceError'.  See 'SourceError' for more information.
handleSourceError :: (ExceptionMonad m) =>
                     (SourceError -> m a) -- ^ exception handler
                  -> m a -- ^ action to perform
                  -> m a
handleSourceError handler act =
  gcatch act (\(e :: SourceError) -> handler e)

srcErrorMessages (SourceError msgs) = msgs

-- | XXX: what exactly is an API error?
data GhcApiError = GhcApiError SDoc

instance Show GhcApiError where
  show (GhcApiError msg) = showSDoc msg

ghcApiErrorTc :: Dyn.TyCon
ghcApiErrorTc = Dyn.mkTyCon "GhcApiError"
{-# NOINLINE ghcApiErrorTc #-}
instance Typeable GhcApiError where
  typeOf _ = Dyn.mkTyConApp ghcApiErrorTc []

instance Exception GhcApiError

mkApiErr = GhcApiError

-- | A monad that allows logging of warnings.
class Monad m => WarnLogMonad m where
  setWarnings  :: WarningMessages -> m ()
  getWarnings :: m WarningMessages

logWarnings :: WarnLogMonad m => WarningMessages -> m ()
logWarnings warns = do
    warns0 <- getWarnings
    setWarnings (unionBags warns warns0)

-- | Clear the log of 'Warnings'.
clearWarnings :: WarnLogMonad m => m ()
clearWarnings = setWarnings emptyBag

-- | Returns true if there were any warnings.
hasWarnings :: WarnLogMonad m => m Bool
hasWarnings = getWarnings >>= return . not . isEmptyBag

-- | A monad that has all the features needed by GHC API calls.
--
-- In short, a GHC monad
--
--   - allows embedding of IO actions,
--
--   - can log warnings,
--
--   - allows handling of (extensible) exceptions, and
--
--   - maintains a current session.
--
-- If you do not use 'Ghc' or 'GhcT', make sure to call 'GHC.initGhcMonad'
-- before any call to the GHC API functions can occur.
--
class (Functor m, MonadIO m, WarnLogMonad m, ExceptionMonad m)
    => GhcMonad m where
  getSession :: m HscEnv
  setSession :: HscEnv -> m ()

-- | Call the argument with the current session.
withSession :: GhcMonad m => (HscEnv -> m a) -> m a
withSession f = getSession >>= f

-- | Set the current session to the result of applying the current session to
-- the argument.
modifySession :: GhcMonad m => (HscEnv -> HscEnv) -> m ()
modifySession f = do h <- getSession
                     setSession $! f h

withSavedSession :: GhcMonad m => m a -> m a
withSavedSession m = do
  saved_session <- getSession
  m `gfinally` setSession saved_session

-- | Call an action with a temporarily modified Session.
withTempSession :: GhcMonad m => (HscEnv -> HscEnv) -> m a -> m a
withTempSession f m =
  withSavedSession $ modifySession f >> m

-- | A minimal implementation of a 'GhcMonad'.  If you need a custom monad,
-- e.g., to maintain additional state consider wrapping this monad or using
-- 'GhcT'.
newtype Ghc a = Ghc { unGhc :: Session -> IO a }

instance Functor Ghc where
  fmap f m = Ghc $ \s -> f `fmap` unGhc m s

instance Monad Ghc where
  return a = Ghc $ \_ -> return a
  m >>= g  = Ghc $ \s -> do a <- unGhc m s; unGhc (g a) s

instance MonadIO Ghc where
  liftIO ioA = Ghc $ \_ -> ioA

instance ExceptionMonad Ghc where
  gcatch act handle =
      Ghc $ \s -> unGhc act s `gcatch` \e -> unGhc (handle e) s
  gblock (Ghc m)   = Ghc $ \s -> gblock (m s)
  gunblock (Ghc m) = Ghc $ \s -> gunblock (m s)
  gmask f =
      Ghc $ \s -> gmask $ \io_restore ->
                             let
                                g_restore (Ghc m) = Ghc $ \s -> io_restore (m s)
                             in
                                unGhc (f g_restore) s

instance WarnLogMonad Ghc where
  setWarnings warns = Ghc $ \(Session _ wref) -> writeIORef wref warns
  -- | Return 'Warnings' accumulated so far.
  getWarnings       = Ghc $ \(Session _ wref) -> readIORef wref

instance GhcMonad Ghc where
  getSession = Ghc $ \(Session r _) -> readIORef r
  setSession s' = Ghc $ \(Session r _) -> writeIORef r s'

-- | A monad transformer to add GHC specific features to another monad.
--
-- Note that the wrapped monad must support IO and handling of exceptions.
newtype GhcT m a = GhcT { unGhcT :: Session -> m a }
liftGhcT :: Monad m => m a -> GhcT m a
liftGhcT m = GhcT $ \_ -> m

instance Functor m => Functor (GhcT m) where
  fmap f m = GhcT $ \s -> f `fmap` unGhcT m s

instance Monad m => Monad (GhcT m) where
  return x = GhcT $ \_ -> return x
  m >>= k  = GhcT $ \s -> do a <- unGhcT m s; unGhcT (k a) s

instance MonadIO m => MonadIO (GhcT m) where
  liftIO ioA = GhcT $ \_ -> liftIO ioA

instance ExceptionMonad m => ExceptionMonad (GhcT m) where
  gcatch act handle =
      GhcT $ \s -> unGhcT act s `gcatch` \e -> unGhcT (handle e) s
  gblock (GhcT m) = GhcT $ \s -> gblock (m s)
  gunblock (GhcT m) = GhcT $ \s -> gunblock (m s)
  gmask f =
      GhcT $ \s -> gmask $ \io_restore ->
                           let
                              g_restore (GhcT m) = GhcT $ \s -> io_restore (m s)
                           in
                              unGhcT (f g_restore) s

instance MonadIO m => WarnLogMonad (GhcT m) where
  setWarnings warns = GhcT $ \(Session _ wref) -> liftIO $ writeIORef wref warns
  -- | Return 'Warnings' accumulated so far.
  getWarnings       = GhcT $ \(Session _ wref) -> liftIO $ readIORef wref

instance (Functor m, ExceptionMonad m, MonadIO m) => GhcMonad (GhcT m) where
  getSession = GhcT $ \(Session r _) -> liftIO $ readIORef r
  setSession s' = GhcT $ \(Session r _) -> liftIO $ writeIORef r s'

-- | Lift an IO action returning errors messages into a 'GhcMonad'.
--
-- In order to reduce dependencies to other parts of the compiler, functions
-- outside the "main" parts of GHC return warnings and errors as a parameter
-- and signal success via by wrapping the result in a 'Maybe' type.  This
-- function logs the returned warnings and propagates errors as exceptions
-- (of type 'SourceError').
--
-- This function assumes the following invariants:
--
--  1. If the second result indicates success (is of the form 'Just x'),
--     there must be no error messages in the first result.
--
--  2. If there are no error messages, but the second result indicates failure
--     there should be warnings in the first result.  That is, if the action
--     failed, it must have been due to the warnings (i.e., @-Werror@).
ioMsgMaybe :: GhcMonad m =>
              IO (Messages, Maybe a) -> m a
ioMsgMaybe ioA = do
  ((warns,errs), mb_r) <- liftIO ioA
  logWarnings warns
  case mb_r of
    Nothing -> liftIO $ throwIO (mkSrcErr errs)
    Just r  -> ASSERT( isEmptyBag errs ) return r

-- | Lift a non-failing IO action into a 'GhcMonad'.
--
-- Like 'ioMsgMaybe', but assumes that the action will never return any error
-- messages.
ioMsg :: GhcMonad m => IO (Messages, a) -> m a
ioMsg ioA = do
    ((warns,errs), r) <- liftIO ioA
    logWarnings warns
    ASSERT( isEmptyBag errs ) return r

-- | Reflect a computation in the 'Ghc' monad into the 'IO' monad.
--
-- You can use this to call functions returning an action in the 'Ghc' monad
-- inside an 'IO' action.  This is needed for some (too restrictive) callback
-- arguments of some library functions:
--
-- > libFunc :: String -> (Int -> IO a) -> IO a
-- > ghcFunc :: Int -> Ghc a
-- >
-- > ghcFuncUsingLibFunc :: String -> Ghc a -> Ghc a
-- > ghcFuncUsingLibFunc str =
-- >   reifyGhc $ \s ->
-- >     libFunc $ \i -> do
-- >       reflectGhc (ghcFunc i) s
--
reflectGhc :: Ghc a -> Session -> IO a
reflectGhc m = unGhc m

-- > Dual to 'reflectGhc'.  See its documentation.
reifyGhc :: (Session -> IO a) -> Ghc a
reifyGhc act = Ghc $ act

handleFlagWarnings :: GhcMonad m => DynFlags -> [Located String] -> m ()
handleFlagWarnings dflags warns
 = when (dopt Opt_WarnDeprecatedFlags dflags)
        (handleFlagWarnings' dflags warns)

handleFlagWarnings' :: GhcMonad m => DynFlags -> [Located String] -> m ()
handleFlagWarnings' _ [] = return ()
handleFlagWarnings' dflags warns
 = do -- It would be nicer if warns :: [Located Message], but that has circular
      -- import problems.
      logWarnings $ listToBag (map mkFlagWarning warns)
      when (dopt Opt_WarnIsError dflags) $
        liftIO $ throwIO $ mkSrcErr emptyBag

mkFlagWarning :: Located String -> WarnMsg
mkFlagWarning (L loc warn)
 = mkPlainWarnMsg loc (text warn)
\end{code}

\begin{code}
-- | These functions are called in various places of the GHC API.
--
-- API clients can override any of these callbacks to change GHC's default
-- behaviour.
data GhcApiCallbacks
  = GhcApiCallbacks {

    -- | Called by 'load' after the compilating of each module.
    --
    -- The default implementation simply prints all warnings and errors to
    -- @stderr@.  Don't forget to call 'clearWarnings' when implementing your
    -- own call.
    --
    -- The first argument is the module that was compiled.
    --
    -- The second argument is @Nothing@ if no errors occured, but there may
    -- have been warnings.  If it is @Just err@ at least one error has
    -- occured.  If 'srcErrorMessages' is empty, compilation failed due to
    -- @-Werror@.
    reportModuleCompilationResult :: GhcMonad m =>
                                     ModSummary -> Maybe SourceError
                                  -> m ()
  }

-- | Temporarily modify the callbacks.  After the action is executed all
-- callbacks are reset (not, however, any other modifications to the session
-- state.)
withLocalCallbacks :: GhcMonad m =>
                      (GhcApiCallbacks -> GhcApiCallbacks)
                   -> m a -> m a
withLocalCallbacks f m = do
  hsc_env <- getSession
  let cb0 = hsc_callbacks hsc_env
  let cb' = f cb0
  setSession (hsc_env { hsc_callbacks = cb' `seq` cb' })
  r <- m
  hsc_env' <- getSession
  setSession (hsc_env' { hsc_callbacks = cb0 })
  return r

\end{code}

\begin{code}
-- | Hscenv is like 'Session', except that some of the fields are immutable.
-- An HscEnv is used to compile a single module from plain Haskell source
-- code (after preprocessing) to either C, assembly or C--.  Things like
-- the module graph don't change during a single compilation.
--
-- Historical note: \"hsc\" used to be the name of the compiler binary,
-- when there was a separate driver and compiler.  To compile a single
-- module, the driver would invoke hsc on the source code... so nowadays
-- we think of hsc as the layer of the compiler that deals with compiling
-- a single module.
data HscEnv 
  = HscEnv { 
	hsc_dflags :: DynFlags,
		-- ^ The dynamic flag settings

        hsc_callbacks :: GhcApiCallbacks,
                -- ^ Callbacks for the GHC API.

	hsc_targets :: [Target],
		-- ^ The targets (or roots) of the current session

	hsc_mod_graph :: ModuleGraph,
		-- ^ The module graph of the current session

	hsc_IC :: InteractiveContext,
		-- ^ The context for evaluating interactive statements

	hsc_HPT    :: HomePackageTable,
		-- ^ The home package table describes already-compiled
		-- home-package modules, /excluding/ the module we 
		-- are compiling right now.
		-- (In one-shot mode the current module is the only
		--  home-package module, so hsc_HPT is empty.  All other
		--  modules count as \"external-package\" modules.
		--  However, even in GHCi mode, hi-boot interfaces are
		--  demand-loaded into the external-package table.)
		--
		-- 'hsc_HPT' is not mutable because we only demand-load 
		-- external packages; the home package is eagerly 
		-- loaded, module by module, by the compilation manager.
		--	
		-- The HPT may contain modules compiled earlier by @--make@
		-- but not actually below the current module in the dependency
		-- graph.

		-- (This changes a previous invariant: changed Jan 05.)
	
	hsc_EPS	:: {-# UNPACK #-} !(IORef ExternalPackageState),
	        -- ^ Information about the currently loaded external packages.
	        -- This is mutable because packages will be demand-loaded during
	        -- a compilation run as required.
	
	hsc_NC	:: {-# UNPACK #-} !(IORef NameCache),
		-- ^ As with 'hsc_EPS', this is side-effected by compiling to
		-- reflect sucking in interface files.  They cache the state of
		-- external interface files, in effect.

	hsc_FC   :: {-# UNPACK #-} !(IORef FinderCache),
	        -- ^ The cached result of performing finding in the file system
	hsc_MLC  :: {-# UNPACK #-} !(IORef ModLocationCache),
		-- ^ This caches the location of modules, so we don't have to 
		-- search the filesystem multiple times. See also 'hsc_FC'.

        hsc_OptFuel :: OptFuelState,
                -- ^ Settings to control the use of \"optimization fuel\":
                -- by limiting the number of transformations,
                -- we can use binary search to help find compiler bugs.

        hsc_type_env_var :: Maybe (Module, IORef TypeEnv)
                -- ^ Used for one-shot compilation only, to initialise
                -- the 'IfGblEnv'. See 'TcRnTypes.tcg_type_env_var' for 
                -- 'TcRunTypes.TcGblEnv'
 }

hscEPS :: HscEnv -> IO ExternalPackageState
hscEPS hsc_env = readIORef (hsc_EPS hsc_env)

-- | A compilation target.
--
-- A target may be supplied with the actual text of the
-- module.  If so, use this instead of the file contents (this
-- is for use in an IDE where the file hasn't been saved by
-- the user yet).
data Target = Target
      { targetId           :: TargetId  -- ^ module or filename
      , targetAllowObjCode :: Bool      -- ^ object code allowed?
      , targetContents     :: Maybe (StringBuffer,ClockTime)
                                        -- ^ in-memory text buffer?
      }

data TargetId
  = TargetModule ModuleName
	-- ^ A module name: search for the file
  | TargetFile FilePath (Maybe Phase)
	-- ^ A filename: preprocess & parse it to find the module name.
	-- If specified, the Phase indicates how to compile this file
	-- (which phase to start from).  Nothing indicates the starting phase
	-- should be determined from the suffix of the filename.
  deriving Eq

pprTarget :: Target -> SDoc
pprTarget (Target id obj _) = 
   (if obj then char '*' else empty) <> pprTargetId id

instance Outputable Target where
    ppr = pprTarget

pprTargetId :: TargetId -> SDoc
pprTargetId (TargetModule m) = ppr m
pprTargetId (TargetFile f _) = text f

instance Outputable TargetId where
    ppr = pprTargetId

-- | Helps us find information about modules in the home package
type HomePackageTable  = ModuleNameEnv HomeModInfo
	-- Domain = modules in the home package that have been fully compiled
	-- "home" package name cached here for convenience

-- | Helps us find information about modules in the imported packages
type PackageIfaceTable = ModuleEnv ModIface
	-- Domain = modules in the imported packages

emptyHomePackageTable :: HomePackageTable
emptyHomePackageTable  = emptyUFM

emptyPackageIfaceTable :: PackageIfaceTable
emptyPackageIfaceTable = emptyModuleEnv

-- | Information about modules in the package being compiled
data HomeModInfo 
  = HomeModInfo {
      hm_iface    :: !ModIface,
        -- ^ The basic loaded interface file: every loaded module has one of
        -- these, even if it is imported from another package
      hm_details  :: !ModDetails,
        -- ^ Extra information that has been created from the 'ModIface' for
	-- the module, typically during typechecking
      hm_linkable :: !(Maybe Linkable)
        -- ^ The actual artifact we would like to link to access things in
	-- this module.
	--
	-- 'hm_linkable' might be Nothing:
	--
	--   1. If this is an .hs-boot module
	--
	--   2. Temporarily during compilation if we pruned away
	--      the old linkable because it was out of date.
	--
	-- After a complete compilation ('GHC.load'), all 'hm_linkable' fields
	-- in the 'HomePackageTable' will be @Just@.
	--
	-- When re-linking a module ('HscMain.HscNoRecomp'), we construct the
	-- 'HomeModInfo' by building a new 'ModDetails' from the old
	-- 'ModIface' (only).
    }

-- | Find the 'ModIface' for a 'Module', searching in both the loaded home
-- and external package module information
lookupIfaceByModule
	:: DynFlags
	-> HomePackageTable
	-> PackageIfaceTable
	-> Module
	-> Maybe ModIface
lookupIfaceByModule dflags hpt pit mod
  | modulePackageId mod == thisPackage dflags
  = 	-- The module comes from the home package, so look first
	-- in the HPT.  If it's not from the home package it's wrong to look
	-- in the HPT, because the HPT is indexed by *ModuleName* not Module
    fmap hm_iface (lookupUFM hpt (moduleName mod)) 
    `mplus` lookupModuleEnv pit mod

  | otherwise = lookupModuleEnv pit mod		-- Look in PIT only 

-- If the module does come from the home package, why do we look in the PIT as well?
-- (a) In OneShot mode, even home-package modules accumulate in the PIT
-- (b) Even in Batch (--make) mode, there is *one* case where a home-package
--     module is in the PIT, namely GHC.Prim when compiling the base package.
-- We could eliminate (b) if we wanted, by making GHC.Prim belong to a package
-- of its own, but it doesn't seem worth the bother.
\end{code}


\begin{code}
hptInstances :: HscEnv -> (ModuleName -> Bool) -> ([Instance], [FamInst])
-- ^ Find all the instance declarations (of classes and families) that are in
-- modules imported by this one, directly or indirectly, and are in the Home
-- Package Table.  This ensures that we don't see instances from modules @--make@
-- compiled before this one, but which are not below this one.
hptInstances hsc_env want_this_module
  = let (insts, famInsts) = unzip $ flip hptAllThings hsc_env $ \mod_info -> do
                guard (want_this_module (moduleName (mi_module (hm_iface mod_info))))
                let details = hm_details mod_info
                return (md_insts details, md_fam_insts details)
    in (concat insts, concat famInsts)

hptVectInfo :: HscEnv -> VectInfo
-- ^ Get the combined VectInfo of all modules in the home package table.  In
-- contrast to instances and rules, we don't care whether the modules are
-- \"below\" us in the dependency sense.  The VectInfo of those modules not \"below\" 
-- us does not affect the compilation of the current module.
hptVectInfo = concatVectInfo . hptAllThings ((: []) . md_vect_info . hm_details)

hptRules :: HscEnv -> [(ModuleName, IsBootInterface)] -> [CoreRule]
-- ^ Get rules from modules \"below\" this one (in the dependency sense)
hptRules = hptSomeThingsBelowUs (md_rules . hm_details) False


hptAnns :: HscEnv -> Maybe [(ModuleName, IsBootInterface)] -> [Annotation]
-- ^ Get annotations from modules \"below\" this one (in the dependency sense)
hptAnns hsc_env (Just deps) = hptSomeThingsBelowUs (md_anns . hm_details) False hsc_env deps
hptAnns hsc_env Nothing = hptAllThings (md_anns . hm_details) hsc_env

hptAllThings :: (HomeModInfo -> [a]) -> HscEnv -> [a]
hptAllThings extract hsc_env = concatMap extract (eltsUFM (hsc_HPT hsc_env))

hptSomeThingsBelowUs :: (HomeModInfo -> [a]) -> Bool -> HscEnv -> [(ModuleName, IsBootInterface)] -> [a]
-- Get things from modules \"below\" this one (in the dependency sense)
-- C.f Inst.hptInstances
hptSomeThingsBelowUs extract include_hi_boot hsc_env deps
 | isOneShot (ghcMode (hsc_dflags hsc_env)) = []
  | otherwise
  = let 
	hpt = hsc_HPT hsc_env
    in
    [ thing
    |	-- Find each non-hi-boot module below me
      (mod, is_boot_mod) <- deps
    , include_hi_boot || not is_boot_mod

	-- unsavoury: when compiling the base package with --make, we
	-- sometimes try to look up RULES etc for GHC.Prim.  GHC.Prim won't
	-- be in the HPT, because we never compile it; it's in the EPT
	-- instead.  ToDo: clean up, and remove this slightly bogus
	-- filter:
    , mod /= moduleName gHC_PRIM

	-- Look it up in the HPT
    , let things = case lookupUFM hpt mod of
		    Just info -> extract info
		    Nothing -> pprTrace "WARNING in hptSomeThingsBelowUs" msg [] 
	  msg = vcat [ptext (sLit "missing module") <+> ppr mod,
		      ptext (sLit "Probable cause: out-of-date interface files")]
			-- This really shouldn't happen, but see Trac #962

	-- And get its dfuns
    , thing <- things ]
\end{code}

%************************************************************************
%*									*
\subsection{Dealing with Annotations}
%*									*
%************************************************************************

\begin{code}
prepareAnnotations :: HscEnv -> Maybe ModGuts -> IO AnnEnv
-- ^ Deal with gathering annotations in from all possible places 
--   and combining them into a single 'AnnEnv'
prepareAnnotations hsc_env mb_guts
  = do { eps <- hscEPS hsc_env
       ; let -- Extract annotations from the module being compiled if supplied one
            mb_this_module_anns = fmap (mkAnnEnv . mg_anns) mb_guts
        -- Extract dependencies of the module if we are supplied one,
        -- otherwise load annotations from all home package table
        -- entries regardless of dependency ordering.
            home_pkg_anns  = (mkAnnEnv . hptAnns hsc_env) $ fmap (dep_mods . mg_deps) mb_guts
            other_pkg_anns = eps_ann_env eps
            ann_env        = foldl1' plusAnnEnv $ catMaybes [mb_this_module_anns, 
                                                             Just home_pkg_anns, 
                                                             Just other_pkg_anns]

       ; return ann_env }
\end{code}

%************************************************************************
%*									*
\subsection{The Finder cache}
%*									*
%************************************************************************

\begin{code}
-- | The 'FinderCache' maps home module names to the result of
-- searching for that module.  It records the results of searching for
-- modules along the search path.  On @:load@, we flush the entire
-- contents of this cache.
--
-- Although the @FinderCache@ range is 'FindResult' for convenience ,
-- in fact it will only ever contain 'Found' or 'NotFound' entries.
--
type FinderCache = ModuleNameEnv FindResult

-- | The result of searching for an imported module.
data FindResult
  = Found ModLocation Module
	-- ^ The module was found
  | NoPackage PackageId
	-- ^ The requested package was not found
  | FoundMultiple [PackageId]
	-- ^ _Error_: both in multiple packages
  | NotFound [FilePath] (Maybe PackageId) [PackageId] [PackageId]
	-- ^ The module was not found, including either
        --    * the specified places were searched
        --    * the package that this module should have been in
        --    * list of packages in which the module was hidden,
        --    * list of hidden packages containing this module
  | NotFoundInPackage PackageId
	-- ^ The module was not found in this package

-- | Cache that remembers where we found a particular module.  Contains both
-- home modules and package modules.  On @:load@, only home modules are
-- purged from this cache.
type ModLocationCache = ModuleEnv ModLocation
\end{code}

%************************************************************************
%*									*
\subsection{Symbol tables and Module details}
%*									*
%************************************************************************

\begin{code}
-- | A 'ModIface' plus a 'ModDetails' summarises everything we know 
-- about a compiled module.  The 'ModIface' is the stuff *before* linking,
-- and can be written out to an interface file. The 'ModDetails is after 
-- linking and can be completely recovered from just the 'ModIface'.
-- 
-- When we read an interface file, we also construct a 'ModIface' from it,
-- except that we explicitly make the 'mi_decls' and a few other fields empty;
-- as when reading we consolidate the declarations etc. into a number of indexed
-- maps and environments in the 'ExternalPackageState'.
data ModIface 
   = ModIface {
        mi_module   :: !Module,             -- ^ Name of the module we are for
        mi_iface_hash :: !Fingerprint,      -- ^ Hash of the whole interface
        mi_mod_hash :: !Fingerprint,	    -- ^ Hash of the ABI only

        mi_orphan   :: !WhetherHasOrphans,  -- ^ Whether this module has orphans
        mi_finsts   :: !WhetherHasFamInst,  -- ^ Whether this module has family instances
	mi_boot	    :: !IsBootInterface,    -- ^ Read from an hi-boot file?

	mi_deps	    :: Dependencies,
	        -- ^ The dependencies of the module.  This is
		-- consulted for directly-imported modules, but not
		-- for anything else (hence lazy)

        mi_usages   :: [Usage],
                -- ^ Usages; kept sorted so that it's easy to decide
		-- whether to write a new iface file (changing usages
		-- doesn't affect the hash of this module)
        
		-- NOT STRICT!  we read this field lazily from the interface file
		-- It is *only* consulted by the recompilation checker

		-- Exports
		-- Kept sorted by (mod,occ), to make version comparisons easier
        mi_exports  :: ![IfaceExport],
                -- ^ Records the modules that are the declaration points for things
                -- exported by this module, and the 'OccName's of those things
        
        mi_exp_hash :: !Fingerprint,	-- ^ Hash of export list

        mi_fixities :: [(OccName,Fixity)],
                -- ^ Fixities
        
		-- NOT STRICT!  we read this field lazily from the interface file

	mi_warns  :: Warnings,
		-- ^ Warnings
		
		-- NOT STRICT!  we read this field lazily from the interface file

	mi_anns  :: [IfaceAnnotation],
	        -- ^ Annotations
	
		-- NOT STRICT!  we read this field lazily from the interface file

		-- Type, class and variable declarations
		-- The hash of an Id changes if its fixity or deprecations change
		--	(as well as its type of course)
		-- Ditto data constructors, class operations, except that 
		-- the hash of the parent class/tycon changes
	mi_decls :: [(Fingerprint,IfaceDecl)],	-- ^ Sorted type, variable, class etc. declarations

        mi_globals  :: !(Maybe GlobalRdrEnv),
		-- ^ Binds all the things defined at the top level in
		-- the /original source/ code for this module. which
		-- is NOT the same as mi_exports, nor mi_decls (which
		-- may contains declarations for things not actually
		-- defined by the user).  Used for GHCi and for inspecting
		-- the contents of modules via the GHC API only.
		--
		-- (We need the source file to figure out the
		-- top-level environment, if we didn't compile this module
		-- from source then this field contains @Nothing@).
		--
		-- Strictly speaking this field should live in the
		-- 'HomeModInfo', but that leads to more plumbing.

		-- Instance declarations and rules
	mi_insts     :: [IfaceInst],			-- ^ Sorted class instance
	mi_fam_insts :: [IfaceFamInst],			-- ^ Sorted family instances
	mi_rules     :: [IfaceRule],			-- ^ Sorted rules
	mi_orphan_hash :: !Fingerprint,	-- ^ Hash for orphan rules and 
					-- class and family instances
					-- combined

        mi_vect_info :: !IfaceVectInfo, -- ^ Vectorisation information

		-- Cached environments for easy lookup
		-- These are computed (lazily) from other fields
		-- and are not put into the interface file
	mi_warn_fn  :: Name -> Maybe WarningTxt,        -- ^ Cached lookup for 'mi_warns'
	mi_fix_fn  :: OccName -> Fixity,	        -- ^ Cached lookup for 'mi_fixities'
	mi_hash_fn :: OccName -> Maybe (OccName, Fingerprint),
                        -- ^ Cached lookup for 'mi_decls'.
			-- The @Nothing@ in 'mi_hash_fn' means that the thing
			-- isn't in decls. It's useful to know that when
			-- seeing if we are up to date wrt. the old interface.
                        -- The 'OccName' is the parent of the name, if it has one.
	mi_hpc    :: !AnyHpcUsage
	        -- ^ True if this program uses Hpc at any point in the program.
     }

-- | The 'ModDetails' is essentially a cache for information in the 'ModIface'
-- for home modules only. Information relating to packages will be loaded into
-- global environments in 'ExternalPackageState'.
data ModDetails
   = ModDetails {
	-- The next two fields are created by the typechecker
	md_exports   :: [AvailInfo],
        md_types     :: !TypeEnv,       -- ^ Local type environment for this particular module
        md_insts     :: ![Instance],    -- ^ 'DFunId's for the instances in this module
        md_fam_insts :: ![FamInst],
        md_rules     :: ![CoreRule],    -- ^ Domain may include 'Id's from other modules
        md_anns      :: ![Annotation],  -- ^ Annotations present in this module: currently 
                                        -- they only annotate things also declared in this module
        md_vect_info :: !VectInfo       -- ^ Module vectorisation information
     }

emptyModDetails :: ModDetails
emptyModDetails = ModDetails { md_types = emptyTypeEnv,
			       md_exports = [],
			       md_insts     = [],
			       md_rules     = [],
			       md_fam_insts = [],
                               md_anns      = [],
                               md_vect_info = noVectInfo
                             } 

-- | Records the modules directly imported by a module for extracting e.g. usage information
type ImportedMods = ModuleEnv [(ModuleName, Bool, SrcSpan)]
-- TODO: we are not actually using the codomain of this type at all, so it can be
-- replaced with ModuleEnv ()

-- | A ModGuts is carried through the compiler, accumulating stuff as it goes
-- There is only one ModGuts at any time, the one for the module
-- being compiled right now.  Once it is compiled, a 'ModIface' and 
-- 'ModDetails' are extracted and the ModGuts is dicarded.
data ModGuts
  = ModGuts {
        mg_module    :: !Module,         -- ^ Module being compiled
	mg_boot      :: IsBootInterface, -- ^ Whether it's an hs-boot module
	mg_exports   :: ![AvailInfo],	 -- ^ What it exports
	mg_deps	     :: !Dependencies,	 -- ^ What it depends on, directly or
	                                 -- otherwise
	mg_dir_imps  :: !ImportedMods,	 -- ^ Directly-imported modules; used to
					 -- generate initialisation code
	mg_used_names:: !NameSet,	 -- ^ What the module needed (used in 'MkIface.mkIface')

        mg_rdr_env   :: !GlobalRdrEnv,	 -- ^ Top-level lexical environment

	-- These fields all describe the things **declared in this module**
	mg_fix_env   :: !FixityEnv,	 -- ^ Fixities declared in this module
	                                 -- TODO: I'm unconvinced this is actually used anywhere
	mg_types     :: !TypeEnv,        -- ^ Types declared in this module
	mg_insts     :: ![Instance],	 -- ^ Class instances declared in this module
	mg_fam_insts :: ![FamInst],	 -- ^ Family instances declared in this module
        mg_rules     :: ![CoreRule],	 -- ^ Before the core pipeline starts, contains 
		     			 -- See Note [Overall plumbing for rules] in Rules.lhs
	mg_binds     :: ![CoreBind],	 -- ^ Bindings for this module
	mg_foreign   :: !ForeignStubs,   -- ^ Foreign exports declared in this module
	mg_warns     :: !Warnings,	 -- ^ Warnings declared in the module
	mg_anns      :: [Annotation],    -- ^ Annotations declared in this module
	mg_hpc_info  :: !HpcInfo,        -- ^ Coverage tick boxes in the module
        mg_modBreaks :: !ModBreaks,      -- ^ Breakpoints for the module
        mg_vect_info :: !VectInfo,       -- ^ Pool of vectorised declarations in the module

	-- The next two fields are unusual, because they give instance
	-- environments for *all* modules in the home package, including
	-- this module, rather than for *just* this module.  
	-- Reason: when looking up an instance we don't want to have to
	--	  look at each module in the home package in turn
	mg_inst_env     :: InstEnv,
        -- ^ Class instance environment from /home-package/ modules (including
	-- this one); c.f. 'tcg_inst_env'
	mg_fam_inst_env :: FamInstEnv
        -- ^ Type-family instance enviroment for /home-package/ modules
	-- (including this one); c.f. 'tcg_fam_inst_env'
    }

-- The ModGuts takes on several slightly different forms:
--
-- After simplification, the following fields change slightly:
--	mg_rules	Orphan rules only (local ones now attached to binds)
--	mg_binds	With rules attached

-- | 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    :: [CoreBind],
      -- | Imports
      cm_imports  :: ![Module]
    }

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

-- The ModGuts takes on several slightly different forms:
--
-- After simplification, the following fields change slightly:
--	mg_rules	Orphan rules only (local ones now attached to binds)
--	mg_binds	With rules attached


---------------------------------------------------------
-- The Tidy pass forks the information about this module: 
--	* one lot goes to interface file generation (ModIface)
--	  and later compilations (ModDetails)
--	* the other lot goes to code generation (CgGuts)

-- | A restricted form of 'ModGuts' for code generation purposes
data CgGuts 
  = CgGuts {
	cg_module   :: !Module, -- ^ Module being compiled

	cg_tycons   :: [TyCon],
		-- ^ Algebraic data types (including ones that started
		-- life as classes); generate constructors and info
		-- tables. Includes newtypes, just for the benefit of
		-- External Core

	cg_binds    :: [CoreBind],
		-- ^ The tidied main bindings, including
		-- previously-implicit bindings for record and class
		-- selectors, and data construtor wrappers.  But *not*
		-- data constructor workers; reason: we we regard them
		-- as part of the code-gen of tycons

	cg_dir_imps :: ![Module],
		-- ^ Directly-imported modules; used to generate
		-- initialisation code

	cg_foreign  :: !ForeignStubs,	-- ^ Foreign export stubs
	cg_dep_pkgs :: ![PackageId],	-- ^ Dependent packages, used to 
	                                -- generate #includes for C code gen
        cg_hpc_info :: !HpcInfo,        -- ^ Program coverage tick box information
        cg_modBreaks :: !ModBreaks      -- ^ Module breakpoints
    }

-----------------------------------
-- | Foreign export stubs
data ForeignStubs = NoStubs             -- ^ We don't have any stubs
		  | ForeignStubs
			SDoc 		
			SDoc 		
		   -- ^ There are some stubs. Parameters:
		   --
		   --  1) Header file prototypes for
                   --     "foreign exported" functions
                   --
                   --  2) C stubs to use when calling
                   --     "foreign exported" functions
\end{code}

\begin{code}
emptyModIface :: Module -> ModIface
emptyModIface mod
  = ModIface { mi_module   = mod,
	       mi_iface_hash = fingerprint0,
	       mi_mod_hash = fingerprint0,
	       mi_orphan   = False,
	       mi_finsts   = False,
	       mi_boot	   = False,
	       mi_deps     = noDependencies,
	       mi_usages   = [],
	       mi_exports  = [],
	       mi_exp_hash = fingerprint0,
	       mi_fixities = [],
	       mi_warns    = NoWarnings,
	       mi_anns     = [],
	       mi_insts     = [],
	       mi_fam_insts = [],
	       mi_rules     = [],
	       mi_decls     = [],
	       mi_globals   = Nothing,
	       mi_orphan_hash = fingerprint0,
               mi_vect_info = noIfaceVectInfo,
	       mi_warn_fn    = emptyIfaceWarnCache,
	       mi_fix_fn    = emptyIfaceFixCache,
	       mi_hash_fn   = emptyIfaceHashCache,
	       mi_hpc       = False
    }		
\end{code}


%************************************************************************
%*									*
\subsection{The interactive context}
%*									*
%************************************************************************

\begin{code}
-- | Interactive context, recording information relevant to GHCi
data InteractiveContext 
  = InteractiveContext { 
          ic_toplev_scope :: [Module]   -- ^ The context includes the "top-level" scope of
					-- these modules

        , ic_exports :: [(Module, Maybe (ImportDecl RdrName))]    -- ^ The context includes just the exported parts of these
					-- modules

        , ic_rn_gbl_env :: GlobalRdrEnv -- ^ The contexts' cached 'GlobalRdrEnv', built from
					-- 'ic_toplev_scope' and 'ic_exports'

        , ic_tmp_ids :: [Id]   -- ^ Names bound during interaction with the user.
                               -- Later Ids shadow earlier ones with the same OccName
                               -- Expressions are typed with these Ids in the envt
                               -- For runtime-debugging, these Ids may have free
                               -- TcTyVars of RuntimUnkSkol flavour, but no free TyVars
                               -- (because the typechecker doesn't expect that)

#ifdef GHCI
        , ic_resume :: [Resume]         -- ^ The stack of breakpoint contexts
#endif

        , ic_cwd :: Maybe FilePath      -- virtual CWD of the program
    }


emptyInteractiveContext :: InteractiveContext
emptyInteractiveContext
  = InteractiveContext { ic_toplev_scope = [],
			 ic_exports = [],
			 ic_rn_gbl_env = emptyGlobalRdrEnv,
			 ic_tmp_ids = []
#ifdef GHCI
                         , ic_resume = []
#endif
                         , ic_cwd = Nothing
                       }

icPrintUnqual :: DynFlags -> InteractiveContext -> PrintUnqualified
icPrintUnqual dflags ictxt = mkPrintUnqualified dflags (ic_rn_gbl_env ictxt)


extendInteractiveContext
        :: InteractiveContext
        -> [Id]
        -> InteractiveContext
extendInteractiveContext ictxt ids
  = ictxt { ic_tmp_ids =  snub ((ic_tmp_ids ictxt \\ ids) ++ ids)
                          -- NB. must be this way around, because we want
                          -- new ids to shadow existing bindings.
          }
    where snub = map head . group . sort

substInteractiveContext :: InteractiveContext -> TvSubst -> InteractiveContext
substInteractiveContext ictxt subst | isEmptyTvSubst subst = ictxt
substInteractiveContext ictxt@InteractiveContext{ic_tmp_ids=ids} subst 
  = ictxt { ic_tmp_ids = map subst_ty ids }
  where
   subst_ty id = id `setIdType` substTy subst (idType id)
\end{code}

%************************************************************************
%*									*
        Building a PrintUnqualified		
%*									*
%************************************************************************

Note [Printing original names]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Deciding how to print names is pretty tricky.  We are given a name
P:M.T, where P is the package name, M is the defining module, and T is
the occurrence name, and we have to decide in which form to display
the name given a GlobalRdrEnv describing the current scope.

Ideally we want to display the name in the form in which it is in
scope.  However, the name might not be in scope at all, and that's
where it gets tricky.  Here are the cases:

 1. T uniquely maps to  P:M.T      --->  "T"      NameUnqual
 2. There is an X for which X.T 
       uniquely maps to  P:M.T     --->  "X.T"    NameQual X
 3. There is no binding for "M.T"  --->  "M.T"    NameNotInScope1
 4. Otherwise                      --->  "P:M.T"  NameNotInScope2

(3) and (4) apply when the entity P:M.T is not in the GlobalRdrEnv at
all. In these cases we still want to refer to the name as "M.T", *but*
"M.T" might mean something else in the current scope (e.g. if there's
an "import X as M"), so to avoid confusion we avoid using "M.T" if
there's already a binding for it.  Instead we write P:M.T.

There's one further subtlety: in case (3), what if there are two
things around, P1:M.T and P2:M.T?  Then we don't want to print both of
them as M.T!  However only one of the modules P1:M and P2:M can be
exposed (say P2), so we use M.T for that, and P1:M.T for the other one.
This is handled by the qual_mod component of PrintUnqualified, inside
the (ppr mod) of case (3), in Name.pprModulePrefix

\begin{code}
-- | Creates some functions that work out the best ways to format
-- names for the user according to a set of heuristics
mkPrintUnqualified :: DynFlags -> GlobalRdrEnv -> PrintUnqualified
mkPrintUnqualified dflags env = (qual_name, qual_mod)
  where
  qual_name mod occ	-- The (mod,occ) pair is the original name of the thing
        | [gre] <- unqual_gres, right_name gre = NameUnqual
		-- If there's a unique entity that's in scope unqualified with 'occ'
		-- AND that entity is the right one, then we can use the unqualified name

        | [gre] <- qual_gres = NameQual (get_qual_mod (gre_prov gre))

        | null qual_gres = 
              if null (lookupGRE_RdrName (mkRdrQual (moduleName mod) occ) env)
                   then NameNotInScope1
                   else NameNotInScope2

	| otherwise = panic "mkPrintUnqualified"
      where
	right_name gre = nameModule_maybe (gre_name gre) == Just mod

        unqual_gres = lookupGRE_RdrName (mkRdrUnqual occ) env
        qual_gres   = filter right_name (lookupGlobalRdrEnv env occ)

	get_qual_mod LocalDef      = moduleName mod
	get_qual_mod (Imported is) = ASSERT( not (null is) ) is_as (is_decl (head is))

    -- we can mention a module P:M without the P: qualifier iff
    -- "import M" would resolve unambiguously to P:M.  (if P is the
    -- current package we can just assume it is unqualified).

  qual_mod mod
     | modulePackageId mod == thisPackage dflags = False

     | [pkgconfig] <- [pkg | (pkg,exposed_module) <- lookup, 
                             exposed pkg && exposed_module],
       packageConfigId pkgconfig == modulePackageId mod
        -- this says: we are given a module P:M, is there just one exposed package
        -- that exposes a module M, and is it package P?
     = False

     | otherwise = True
     where lookup = lookupModuleInAllPackages dflags (moduleName mod)
\end{code}


%************************************************************************
%*									*
		TyThing
%*									*
%************************************************************************

\begin{code}
-- | Determine the 'TyThing's brought into scope by another 'TyThing'
-- /other/ than itself. For example, Id's don't have any implicit TyThings
-- as they just bring themselves into scope, but classes bring their
-- dictionary datatype, type constructor and some selector functions into
-- scope, just for a start!

-- N.B. the set of TyThings returned here *must* match the set of
-- names returned by LoadIface.ifaceDeclSubBndrs, in the sense that
-- TyThing.getOccName should define a bijection between the two lists.
-- This invariant is used in LoadIface.loadDecl (see note [Tricky iface loop])
-- The order of the list does not matter.
implicitTyThings :: TyThing -> [TyThing]

-- For data and newtype declarations:
implicitTyThings (ATyCon tc)
  =   -- fields (names of selectors)
      -- (possibly) implicit coercion and family coercion
      --   depending on whether it's a newtype or a family instance or both
    implicitCoTyCon tc ++
      -- for each data constructor in order,
      --   the contructor, worker, and (possibly) wrapper
    concatMap (extras_plus . ADataCon) (tyConDataCons tc)
		     
implicitTyThings (AClass cl) 
  = -- dictionary datatype:
    --    [extras_plus:]
    --      type constructor 
    --    [recursive call:]
    --      (possibly) newtype coe…