module RnNames (
        rnImports, getLocalNonValBinders,
        rnExports, extendGlobalRdrEnvRn,
        gresFromAvails,
        reportUnusedNames, finishWarnings,
    ) where

#include "HsVersions.h"

import DynFlags
import HsSyn
import TcEnv            ( isBrackStage )
import RnEnv
import RnHsDoc          ( rnHsDoc )
import LoadIface        ( loadSrcInterface )
import TcRnMonad

import HeaderInfo       ( mkPrelImports )
import PrelNames
import Module
import Name
import NameEnv
import NameSet
import HscTypes
import RdrName
import Outputable
import Maybes
import SrcLoc
import ErrUtils
import Util
import FastString
import ListSetOps
import Data.List        ( partition, (\\), find )
import qualified Data.Set as Set
import System.IO
import Control.Monad
import Data.Map         ( Map )
import qualified Data.Map as Map

rnImports :: [LImportDecl RdrName]
           -> RnM ([LImportDecl Name], GlobalRdrEnv, ImportAvails, AnyHpcUsage)

rnImports imports
         -- PROCESS IMPORT DECLS
         -- Do the non {- SOURCE -} ones first, so that we get a helpful
         -- warning for {- SOURCE -} ones that are unnecessary
    = do this_mod <- getModule
         implicit_prelude <- xoptM Opt_ImplicitPrelude
         let prel_imports = mkPrelImports (moduleName this_mod)
                                implicit_prelude imports
             (source, ordinary) = partition is_source_import imports
             is_source_import (L _ (ImportDecl _ _ is_boot _ _ _ _)) = is_boot

         ifWOptM Opt_WarnImplicitPrelude $
             when (notNull prel_imports) $ addWarn (implicitPreludeWarn)

         stuff1 <- mapM (rnImportDecl this_mod True)  prel_imports
         stuff2 <- mapM (rnImportDecl this_mod False) ordinary
         stuff3 <- mapM (rnImportDecl this_mod False) source
         -- Safe Haskell: See Note [Tracking Trust Transitively]
         let (decls, rdr_env, imp_avails, hpc_usage) = 
                        combine (stuff1 ++ stuff2 ++ stuff3)
         return (decls, rdr_env, imp_avails, hpc_usage)

    where
      combine :: [(LImportDecl Name,  GlobalRdrEnv, ImportAvails, AnyHpcUsage)]
              -> ([LImportDecl Name], GlobalRdrEnv, ImportAvails, AnyHpcUsage)
      combine = foldr plus ([], emptyGlobalRdrEnv, emptyImportAvails, False)
        where
          plus (decl,  gbl_env1, imp_avails1,hpc_usage1)
               (decls, gbl_env2, imp_avails2,hpc_usage2)
            = ( decl:decls,
                gbl_env1 `plusGlobalRdrEnv` gbl_env2,
                imp_avails1 `plusImportAvails` imp_avails2,
                hpc_usage1 || hpc_usage2 )

rnImportDecl  :: Module -> Bool
              -> LImportDecl RdrName
              -> RnM (LImportDecl Name, GlobalRdrEnv, ImportAvails, AnyHpcUsage)

rnImportDecl this_mod implicit_prelude
             (L loc (ImportDecl { ideclName = loc_imp_mod_name, ideclPkgQual = mb_pkg
                                , ideclSource = want_boot, ideclSafe = mod_safe
                                , ideclQualified = qual_only
                                , ideclAs = as_mod, ideclHiding = imp_details }))
  = setSrcSpan loc $ do

    when (isJust mb_pkg) $ do
        pkg_imports <- xoptM Opt_PackageImports
        when (not pkg_imports) $ addErr packageImportErr

        -- If there's an error in loadInterface, (e.g. interface
        -- file not found) we get lots of spurious errors from 'filterImports'
    let
        imp_mod_name = unLoc loc_imp_mod_name
        doc = ppr imp_mod_name <+> ptext (sLit "is directly imported")

        -- Check for a missing import list
        -- (Opt_WarnMissingImportList also checks for T(..) items
        --  but that is done in checkDodgyImport below)
    case imp_details of
        Just (False, _)       -> return () -- Explicit import list
        _  | implicit_prelude -> return ()
           | qual_only        -> return ()
           | otherwise        -> ifWOptM Opt_WarnMissingImportList $
                                 addWarn (missingImportListWarn imp_mod_name)

    iface <- loadSrcInterface doc imp_mod_name want_boot mb_pkg

        -- Compiler sanity check: if the import didn't say
        -- {-# SOURCE #-} we should not get a hi-boot file
    WARN( not want_boot && mi_boot iface, ppr imp_mod_name ) (do

        -- Issue a user warning for a redundant {- SOURCE -} import
        -- NB that we arrange to read all the ordinary imports before
        -- any of the {- SOURCE -} imports.
        --
        -- in --make and GHCi, the compilation manager checks for this,
        -- and indeed we shouldn't do it here because the existence of
        -- the non-boot module depends on the compilation order, which
        -- is not deterministic.  The hs-boot test can show this up.
    dflags <- getDOpts
    warnIf (want_boot && not (mi_boot iface) && isOneShot (ghcMode dflags))
           (warnRedundantSourceImport imp_mod_name)

    let
        imp_mod    = mi_module iface
        warns      = mi_warns iface
        orph_iface = mi_orphan iface
        has_finsts = mi_finsts iface
        deps       = mi_deps iface
        trust      = getSafeMode $ mi_trust iface
        trust_pkg  = mi_trust_pkg iface

        qual_mod_name = case as_mod of
                          Nothing           -> imp_mod_name
                          Just another_name -> another_name
        imp_spec  = ImpDeclSpec { is_mod = imp_mod_name, is_qual = qual_only,
                                  is_dloc = loc, is_as = qual_mod_name }

    -- filter the imports according to the import declaration
    (new_imp_details, gres) <- filterImports iface imp_spec imp_details

    let gbl_env = mkGlobalRdrEnv (filterOut from_this_mod gres)
        from_this_mod gre = nameModule (gre_name gre) == this_mod
        -- If the module exports anything defined in this module, just
        -- ignore it.  Reason: otherwise it looks as if there are two
        -- local definition sites for the thing, and an error gets
        -- reported.  Easiest thing is just to filter them out up
        -- front. This situation only arises if a module imports
        -- itself, or another module that imported it.  (Necessarily,
        -- this invoves a loop.)
        --
        -- We do this *after* filterImports, so that if you say
        --      module A where
        --         import B( AType )
        --         type AType = ...
        --
        --      module B( AType ) where
        --         import {-# SOURCE #-} A( AType )
        --
        -- then you won't get a 'B does not export AType' message.


        -- Compute new transitive dependencies

        orphans | orph_iface = ASSERT( not (imp_mod `elem` dep_orphs deps) )
                               imp_mod : dep_orphs deps
                | otherwise  = dep_orphs deps

        finsts | has_finsts = ASSERT( not (imp_mod `elem` dep_finsts deps) )
                              imp_mod : dep_finsts deps
               | otherwise  = dep_finsts deps

        pkg = modulePackageId (mi_module iface)

        -- Does this import mean we now require our own pkg
        -- to be trusted? See Note [Trust Own Package]
        ptrust = trust == Sf_Trustworthy || trust_pkg

        (dependent_mods, dependent_pkgs, pkg_trust_req)
           | pkg == thisPackage dflags =
                -- Imported module is from the home package
                -- Take its dependent modules and add imp_mod itself
                -- Take its dependent packages unchanged
                --
                -- NB: (dep_mods deps) might include a hi-boot file
                -- for the module being compiled, CM. Do *not* filter
                -- this out (as we used to), because when we've
                -- finished dealing with the direct imports we want to
                -- know if any of them depended on CM.hi-boot, in
                -- which case we should do the hi-boot consistency
                -- check.  See LoadIface.loadHiBootInterface
                ((imp_mod_name, want_boot) : dep_mods deps, dep_pkgs deps, ptrust)

           | otherwise =
                -- Imported module is from another package
                -- Dump the dependent modules
                -- Add the package imp_mod comes from to the dependent packages
                ASSERT2( not (pkg `elem` (map fst $ dep_pkgs deps))
                       , ppr pkg <+> ppr (dep_pkgs deps) )
                ([], (pkg, False) : dep_pkgs deps, False)

        -- True <=> import M ()
        import_all = case imp_details of
                        Just (is_hiding, ls) -> not is_hiding && null ls
                        _                    -> False

        -- should the import be safe?
        mod_safe' = mod_safe
                    || (not implicit_prelude && safeDirectImpsReq dflags)
                    || (implicit_prelude && safeImplicitImpsReq dflags)

        imports   = ImportAvails {
                        imp_mods       = unitModuleEnv imp_mod
                                        [(qual_mod_name, import_all, loc, mod_safe')],
                        imp_orphs      = orphans,
                        imp_finsts     = finsts,
                        imp_dep_mods   = mkModDeps dependent_mods,
                        imp_dep_pkgs   = map fst $ dependent_pkgs,
                        -- Add in the imported modules trusted package
                        -- requirements. ONLY do this though if we import the
                        -- module as a safe import.
                        -- See Note [Tracking Trust Transitively]
                        -- and Note [Trust Transitive Property]
                        imp_trust_pkgs = if mod_safe' 
                                            then map fst $ filter snd dependent_pkgs
                                            else [],
                        -- Do we require our own pkg to be trusted?
                        -- See Note [Trust Own Package]
                        imp_trust_own_pkg = pkg_trust_req
                   }

    -- Complain if we import a deprecated module
    ifWOptM Opt_WarnWarningsDeprecations        (
       case warns of
          WarnAll txt -> addWarn (moduleWarn imp_mod_name txt)
          _           -> return ()
     )

    let new_imp_decl = L loc (ImportDecl loc_imp_mod_name mb_pkg want_boot mod_safe'
                                         qual_only as_mod new_imp_details)

    return (new_imp_decl, gbl_env, imports, mi_hpc iface)
    )

warnRedundantSourceImport :: ModuleName -> SDoc
warnRedundantSourceImport mod_name
  = ptext (sLit "Unnecessary {-# SOURCE #-} in the import of module")
          <+> quotes (ppr mod_name)

extendGlobalRdrEnvRn :: [AvailInfo]
                     -> MiniFixityEnv
                     -> RnM (TcGblEnv, TcLclEnv)
-- Updates both the GlobalRdrEnv and the FixityEnv
-- We return a new TcLclEnv only because we might have to
-- delete some bindings from it;
-- see Note [Top-level Names in Template Haskell decl quotes]

extendGlobalRdrEnvRn avails new_fixities
  = do  { (gbl_env, lcl_env) <- getEnvs
        ; stage <- getStage
        ; let rdr_env = tcg_rdr_env gbl_env
              fix_env = tcg_fix_env gbl_env

              -- Delete new_occs from global and local envs
              -- If we are in a TemplateHaskell decl bracket,
              --    we are going to shadow them
              -- See Note [Top-level Names in Template Haskell decl quotes]
              shadowP  = isBrackStage stage
              new_occs = map (nameOccName . gre_name) gres
              rdr_env1 = transformGREs qual_gre new_occs rdr_env
              lcl_env1 = lcl_env { tcl_rdr = delListFromOccEnv (tcl_rdr lcl_env) new_occs }
              (rdr_env2, lcl_env2) | shadowP   = (rdr_env1, lcl_env1)
                                   | otherwise = (rdr_env,  lcl_env)

              rdr_env3 = foldl extendGlobalRdrEnv rdr_env2 gres
              fix_env' = foldl extend_fix_env     fix_env  gres
              (rdr_env', dups) = findLocalDupsRdrEnv rdr_env3 new_occs

              gbl_env' = gbl_env { tcg_rdr_env = rdr_env', tcg_fix_env = fix_env' }

        ; mapM_ addDupDeclErr dups

        ; traceRn (text "extendGlobalRdrEnvRn" <+> (ppr new_fixities $$ ppr fix_env $$ ppr fix_env'))
        ; return (gbl_env', lcl_env2) }
  where
    gres = gresFromAvails LocalDef avails

    -- If there is a fixity decl for the gre, add it to the fixity env
    extend_fix_env fix_env gre
      | Just (L _ fi) <- lookupFsEnv new_fixities (occNameFS occ)
      = extendNameEnv fix_env name (FixItem occ fi)
      | otherwise
      = fix_env
      where
        name = gre_name gre
        occ  = nameOccName name

    qual_gre :: GlobalRdrElt -> GlobalRdrElt
    -- Transform top-level GREs from the module being compiled
    -- so that they are out of the way of new definitions in a Template
    -- Haskell bracket
    -- See Note [Top-level Names in Template Haskell decl quotes]
    -- Seems like 5 times as much work as it deserves!
    --
    -- For a LocalDef we make a (fake) qualified imported GRE for a
    -- local GRE so that the original *qualified* name is still in scope
    -- but the *unqualified* one no longer is.  What a hack!

    qual_gre gre@(GRE { gre_prov = LocalDef, gre_name = name })
        | isExternalName name = gre { gre_prov = Imported [imp_spec] }
        | otherwise           = gre
          -- Do not shadow Internal (ie Template Haskell) Names
          -- See Note [Top-level Names in Template Haskell decl quotes]
        where
          mod = ASSERT2( isExternalName name, ppr name) moduleName (nameModule name)
          imp_spec = ImpSpec { is_item = ImpAll, is_decl = decl_spec }
          decl_spec = ImpDeclSpec { is_mod = mod, is_as = mod,
                                    is_qual = True,  -- Qualified only!
                                    is_dloc = srcLocSpan (nameSrcLoc name) }

    qual_gre gre@(GRE { gre_prov = Imported specs })
        = gre { gre_prov = Imported (map qual_spec specs) }

    qual_spec spec@(ImpSpec { is_decl = decl_spec })
        = spec { is_decl = decl_spec { is_qual = True } }

getLocalNonValBinders :: HsGroup RdrName -> RnM [AvailInfo]
-- Get all the top-level binders bound the group *except*
-- for value bindings, which are treated separately
-- Specificaly we return AvailInfo for
--      type decls (incl constructors and record selectors)
--      class decls (including class ops)
--      associated types
--      foreign imports
--      (in hs-boot files) value signatures

getLocalNonValBinders group
  = do { gbl_env <- getGblEnv
       ; get_local_binders gbl_env group }

get_local_binders :: TcGblEnv -> HsGroup RdrName -> RnM [AvailInfo]
get_local_binders gbl_env (HsGroup {hs_valds  = ValBindsIn _ val_sigs,
                                    hs_tyclds = tycl_decls,
                                    hs_instds = inst_decls,
                                    hs_fords  = foreign_decls })
  = do  { -- separate out the family instance declarations
          let (tyinst_decls1, tycl_decls_noinsts)
                           = partition (isFamInstDecl . unLoc) (concat tycl_decls)
              tyinst_decls = tyinst_decls1 ++ instDeclATs inst_decls

          -- process all type/class decls except family instances
        ; tc_avails  <- mapM new_tc tycl_decls_noinsts

          -- Create a temporary env of the type binders
	  -- See Note [Looking up family names in family instances]
	  -- NB: associated types may be a sub-bndr of a class
	  -- 		AvailTC C [C,T,op]
	  -- Hence availNames, not availName
        ; let local_tc_env :: OccEnv Name
              local_tc_env = mkOccEnv [ (occ, n) 
                                      | a <- tc_avails
                                      , n <- availNames a
				      , let occ = nameOccName n
                                      , isTcOcc occ  ]

          -- Process all family instances
        ; ti_avails <- mapM (new_ti local_tc_env) tyinst_decls

          -- finish off with value binder in case of a hs-boot file
        ; val_avails <- mapM new_simple val_bndrs
        ; return (val_avails ++ tc_avails ++ ti_avails) }
  where
    is_hs_boot = isHsBoot (tcg_src gbl_env) ;

    for_hs_bndrs :: [Located RdrName]
    for_hs_bndrs = [nm | L _ (ForeignImport nm _ _) <- foreign_decls]

    -- In a hs-boot file, the value binders come from the
    --  *signatures*, and there should be no foreign binders
    val_bndrs :: [Located RdrName]
    val_bndrs | is_hs_boot = [n | L _ (TypeSig ns _) <- val_sigs, n <- ns]
              | otherwise  = for_hs_bndrs

    new_simple :: Located RdrName -> RnM AvailInfo
    new_simple rdr_name = do{ nm <- newTopSrcBinder rdr_name
                            ; return (Avail nm) }

    new_tc tc_decl              -- NOT for type/data instances
        = do { names@(main_name : _) <- mapM newTopSrcBinder (hsTyClDeclBinders tc_decl)
             ; return (AvailTC main_name names) }

    new_ti local_tc_env ti_decl  -- ONLY for type/data instances
        = do { let L loc tc_rdr = tcdLName (unLoc ti_decl)
             ; main_name <- setSrcSpan loc $
                            case lookupOccEnv local_tc_env (rdrNameOcc tc_rdr) of
                              Nothing -> lookupGlobalOccRn tc_rdr
                              Just n  -> return n
		    -- See Note [Looking up family names in family instances]

             ; sub_names <- mapM newTopSrcBinder (hsTyClDeclBinders ti_decl)
             ; return (AvailTC main_name sub_names) }
                        -- main_name is not bound here!

get_local_binders _ g = pprPanic "get_local_binders" (ppr g)

filterImports :: ModIface
              -> ImpDeclSpec                    -- The span for the entire import decl
              -> Maybe (Bool, [LIE RdrName])    -- Import spec; True => hiding
              -> RnM (Maybe (Bool, [LIE Name]), -- Import spec w/ Names
                      [GlobalRdrElt])           -- Same again, but in GRE form
filterImports iface decl_spec Nothing
  = return (Nothing, gresFromAvails prov (mi_exports iface))
  where
    prov = Imported [ImpSpec { is_decl = decl_spec, is_item = ImpAll }]


filterImports iface decl_spec (Just (want_hiding, import_items))
  = do  -- check for errors, convert RdrNames to Names
        opt_typeFamilies <- xoptM Opt_TypeFamilies
        items1 <- mapM (lookup_lie opt_typeFamilies) import_items

        let items2 :: [(LIE Name, AvailInfo)]
            items2 = concat items1
                -- NB the AvailInfo may have duplicates, and several items
                --    for the same parent; e.g N(x) and N(y)

            names  = availsToNameSet (map snd items2)
            keep n = not (n `elemNameSet` names)
            pruned_avails = filterAvails keep all_avails
            hiding_prov = Imported [ImpSpec { is_decl = decl_spec, is_item = ImpAll }]

            gres | want_hiding = gresFromAvails hiding_prov pruned_avails
                 | otherwise   = concatMap (gresFromIE decl_spec) items2

        return (Just (want_hiding, map fst items2), gres)
  where
    all_avails = mi_exports iface

        -- This environment is how we map names mentioned in the import
        -- list to the actual Name they correspond to, and the name family
        -- that the Name belongs to (the AvailInfo).  The situation is
        -- complicated by associated families, which introduce a three-level
        -- hierachy, where class = grand parent, assoc family = parent, and
        -- data constructors = children.  The occ_env entries for associated
        -- families needs to capture all this information; hence, we have the
        -- third component of the environment that gives the class name (=
        -- grand parent) in case of associated families.
        --
        -- This env will have entries for data constructors too,
        -- they won't make any difference because naked entities like T
        -- in an import list map to TcOccs, not VarOccs.
    occ_env :: OccEnv (Name,        -- the name
                       AvailInfo,   -- the export item providing the name
                       Maybe Name)  -- the parent of associated types
    occ_env = mkOccEnv_C combine [ (nameOccName n, (n, a, Nothing))
                                 | a <- all_avails, n <- availNames a]
      where
        -- we know that (1) there are at most entries for one name, (2) their
        -- first component is identical, (3) they are for tys/cls, and (4) one
        -- entry has the name in its parent position (the other doesn't)
        combine (name, AvailTC p1 subs1, Nothing)
                (_   , AvailTC p2 subs2, Nothing)
          = let
              (parent, subs) = if p1 == name then (p2, subs1) else (p1, subs2)
            in
            (name, AvailTC name subs, Just parent)
        combine x y = pprPanic "filterImports/combine" (ppr x $$ ppr y)

    lookup_lie :: Bool -> LIE RdrName -> TcRn [(LIE Name, AvailInfo)]
    lookup_lie opt_typeFamilies (L loc ieRdr)
        = do
             stuff <- setSrcSpan loc $
                      case lookup_ie opt_typeFamilies ieRdr of
                            Failed err  -> addErr err >> return []
                            Succeeded a -> return a
             checkDodgyImport stuff
             return [ (L loc ie, avail) | (ie,avail) <- stuff ]
        where
            -- Warn when importing T(..) if T was exported abstractly
            checkDodgyImport stuff
                | IEThingAll n <- ieRdr, (_, AvailTC _ [_]):_ <- stuff
                = ifWOptM Opt_WarnDodgyImports (addWarn (dodgyImportWarn n))
                    -- NB. use the RdrName for reporting the warning
                | IEThingAll {} <- ieRdr
                , not (is_qual decl_spec)
                = ifWOptM Opt_WarnMissingImportList $
                  addWarn (missingImportListItem ieRdr)
            checkDodgyImport _
                = return ()

        -- For each import item, we convert its RdrNames to Names,
        -- and at the same time construct an AvailInfo corresponding
        -- to what is actually imported by this item.
        -- Returns Nothing on error.
        -- We return a list here, because in the case of an import
        -- item like C, if we are hiding, then C refers to *both* a
        -- type/class and a data constructor.  Moreover, when we import
        -- data constructors of an associated family, we need separate
        -- AvailInfos for the data constructors and the family (as they have
        -- different parents).  See the discussion at occ_env.
    lookup_ie :: Bool -> IE RdrName -> MaybeErr Message [(IE Name,AvailInfo)]
    lookup_ie opt_typeFamilies ie
      = let bad_ie :: MaybeErr Message a
            bad_ie = Failed (badImportItemErr iface decl_spec ie all_avails)

            lookup_name rdr
              | isQual rdr = Failed (qualImportItemErr rdr)
              | Just nm <- lookupOccEnv occ_env (rdrNameOcc rdr) = return nm
              | otherwise                                        = bad_ie
        in
        case ie of
         IEVar n -> do
             (name, avail, _) <- lookup_name n
             return [(IEVar name, trimAvail avail name)]

         IEThingAll tc -> do
             (name, avail@(AvailTC name2 subs), mb_parent) <- lookup_name tc
             case mb_parent of
               -- non-associated ty/cls
               Nothing     -> return [(IEThingAll name, avail)]
               -- associated ty
               Just parent -> return [(IEThingAll name,
                                       AvailTC name2 (subs \\ [name])),
                                      (IEThingAll name, AvailTC parent [name])]

         IEThingAbs tc
             | want_hiding   -- hiding ( C )
                        -- Here the 'C' can be a data constructor
                        --  *or* a type/class, or even both
             -> let tc_name = lookup_name tc
                    dc_name = lookup_name (setRdrNameSpace tc srcDataName)
                in
                case catMaybeErr [ tc_name, dc_name ] of
                  []    -> bad_ie
                  names -> return [mkIEThingAbs name | name <- names]
             | otherwise
             -> do nameAvail <- lookup_name tc
                   return [mkIEThingAbs nameAvail]

         IEThingWith tc ns -> do
            (name, AvailTC _ subnames, mb_parent) <- lookup_name tc
            let
              env         = mkOccEnv [(nameOccName s, s) | s <- subnames]
              mb_children = map (lookupOccEnv env . rdrNameOcc) ns
            children <- if any isNothing mb_children
                        then bad_ie
                        else return (catMaybes mb_children)
            -- check for proper import of type families
            when (not opt_typeFamilies && any isTyConName children) $
              Failed (typeItemErr (head . filter isTyConName $ children)
                                  (text "in import list"))
            case mb_parent of
              -- non-associated ty/cls
              Nothing     -> return [(IEThingWith name children,
                                      AvailTC name (name:children))]
              -- associated ty
              Just parent -> return [(IEThingWith name children,
                                      AvailTC name children),
                                     (IEThingWith name children,
                                      AvailTC parent [name])]

         _other -> Failed illegalImportItemErr
         -- could be IEModuleContents, IEGroup, IEDoc, IEDocNamed
         -- all errors.

      where
        mkIEThingAbs (n, av, Nothing    ) = (IEThingAbs n, trimAvail av n)
        mkIEThingAbs (n, _,  Just parent) = (IEThingAbs n, AvailTC parent [n])


catMaybeErr :: [MaybeErr err a] -> [a]
catMaybeErr ms =  [ a | Succeeded a <- ms ]

-- | make a 'GlobalRdrEnv' where all the elements point to the same
-- import declaration (useful for "hiding" imports, or imports with
-- no details).
gresFromAvails :: Provenance -> [AvailInfo] -> [GlobalRdrElt]
gresFromAvails prov avails
  = concatMap (gresFromAvail (const prov)) avails

gresFromAvail :: (Name -> Provenance) -> AvailInfo -> [GlobalRdrElt]
gresFromAvail prov_fn avail
  = [ GRE {gre_name = n,
           gre_par = availParent n avail,
           gre_prov = prov_fn n}
    | n <- availNames avail ]

greExportAvail :: Bool -> GlobalRdrElt -> AvailInfo
-- For 'include_parent' see Note [Exports of data families]
greExportAvail include_parent gre 
  = case gre_par gre of
      ParentIs p | include_parent -> AvailTC p  [p,me]
                 | otherwise      -> AvailTC p  [me]
      NoParent   | isTyConName me -> AvailTC me [me]
                 | otherwise      -> Avail   me
  where
    me = gre_name gre

plusAvail :: AvailInfo -> AvailInfo -> AvailInfo
plusAvail a1 a2
  | debugIsOn && availName a1 /= availName a2 
  = pprPanic "RnEnv.plusAvail names differ" (hsep [ppr a1,ppr a2])
plusAvail a1@(Avail {})         (Avail {})      = a1
plusAvail (AvailTC _ [])        a2@(AvailTC {}) = a2
plusAvail a1@(AvailTC {})       (AvailTC _ [])  = a1
plusAvail (AvailTC n1 (s1:ss1)) (AvailTC n2 (s2:ss2))
  = case (n1==s1, n2==s2) of  -- Maintain invariant the parent is first
       (True,True)   -> AvailTC n1 (s1 : (ss1 `unionLists` ss2))
       (True,False)  -> AvailTC n1 (s1 : (ss1 `unionLists` (s2:ss2)))
       (False,True)  -> AvailTC n1 (s2 : ((s1:ss1) `unionLists` ss2))
       (False,False) -> AvailTC n1 ((s1:ss1) `unionLists` (s2:ss2))
plusAvail a1 a2 = pprPanic "RnEnv.plusAvail" (hsep [ppr a1,ppr a2])

availParent :: Name -> AvailInfo -> Parent
availParent _ (Avail _)                 = NoParent
availParent n (AvailTC m _) | n == m    = NoParent
                            | otherwise = ParentIs m

trimAvail :: AvailInfo -> Name -> AvailInfo
trimAvail (Avail n)      _ = Avail n
trimAvail (AvailTC n ns) m = ASSERT( m `elem` ns) AvailTC n [m]

-- | filters 'AvailInfo's by the given predicate
filterAvails  :: (Name -> Bool) -> [AvailInfo] -> [AvailInfo]
filterAvails keep avails = foldr (filterAvail keep) [] avails

-- | filters an 'AvailInfo' by the given predicate
filterAvail :: (Name -> Bool) -> AvailInfo -> [AvailInfo] -> [AvailInfo]
filterAvail keep ie rest =
  case ie of
    Avail n | keep n    -> ie : rest
            | otherwise -> rest
    AvailTC tc ns ->
        let left = filter keep ns in
        if null left then rest else AvailTC tc left : rest

-- | Given an import\/export spec, construct the appropriate 'GlobalRdrElt's.
gresFromIE :: ImpDeclSpec -> (LIE Name, AvailInfo) -> [GlobalRdrElt]
gresFromIE decl_spec (L loc ie, avail)
  = gresFromAvail prov_fn avail
  where
    is_explicit = case ie of
                    IEThingAll name -> \n -> n == name
                    _               -> \_ -> True
    prov_fn name = Imported [imp_spec]
        where
          imp_spec  = ImpSpec { is_decl = decl_spec, is_item = item_spec }
          item_spec = ImpSome { is_explicit = is_explicit name, is_iloc = loc }

mkChildEnv :: [GlobalRdrElt] -> NameEnv [Name]
mkChildEnv gres = foldr add emptyNameEnv gres
    where
        add (GRE { gre_name = n, gre_par = ParentIs p }) env = extendNameEnv_Acc (:) singleton env p n
        add _                                            env = env

findChildren :: NameEnv [Name] -> Name -> [Name]
findChildren env n = lookupNameEnv env n `orElse` []

-- | Combines 'AvailInfo's from the same family
-- 'avails' may have several items with the same availName
-- E.g  import Ix( Ix(..), index )
-- will give Ix(Ix,index,range) and Ix(index)
-- We want to combine these; addAvail does that
nubAvails :: [AvailInfo] -> [AvailInfo]
nubAvails avails = nameEnvElts (foldl add emptyNameEnv avails)
  where
    add env avail = extendNameEnv_C plusAvail env (availName avail) avail

type ExportAccum        -- The type of the accumulating parameter of
                        -- the main worker function in rnExports
     = ([LIE Name],             -- Export items with Names
        ExportOccMap,           -- Tracks exported occurrence names
        [AvailInfo])            -- The accumulated exported stuff
                                --   Not nub'd!

emptyExportAccum :: ExportAccum
emptyExportAccum = ([], emptyOccEnv, [])

type ExportOccMap = OccEnv (Name, IE RdrName)
        -- Tracks what a particular exported OccName
        --   in an export list refers to, and which item
        --   it came from.  It's illegal to export two distinct things
        --   that have the same occurrence name

rnExports :: Bool       -- False => no 'module M(..) where' header at all
          -> Maybe [LIE RdrName]        -- Nothing => no explicit export list
          -> TcGblEnv
          -> RnM TcGblEnv

        -- Complains if two distinct exports have same OccName
        -- Warns about identical exports.
        -- Complains about exports items not in scope

rnExports explicit_mod exports
          tcg_env@(TcGblEnv { tcg_mod     = this_mod,
                              tcg_rdr_env = rdr_env,
                              tcg_imports = imports })
 = do   {
        -- If the module header is omitted altogether, then behave
        -- as if the user had written "module Main(main) where..."
        -- EXCEPT in interactive mode, when we behave as if he had
        -- written "module Main where ..."
        -- Reason: don't want to complain about 'main' not in scope
        --         in interactive mode
        ; dflags <- getDOpts
        ; let real_exports
                 | explicit_mod = exports
                 | ghcLink dflags == LinkInMemory = Nothing
                 | otherwise = Just ([noLoc (IEVar main_RDR_Unqual)])
                        -- ToDo: the 'noLoc' here is unhelpful if 'main'
                        --       turns out to be out of scope

        ; (rn_exports, avails) <- exports_from_avail real_exports rdr_env imports this_mod
        ; let final_avails = nubAvails avails    -- Combine families

        ; return (tcg_env { tcg_exports    = final_avails,
                            tcg_rn_exports = case tcg_rn_exports tcg_env of
                                                Nothing -> Nothing
                                                Just _  -> rn_exports,
                            tcg_dus = tcg_dus tcg_env `plusDU`
                                      usesOnly (availsToNameSet final_avails) }) }

exports_from_avail :: Maybe [LIE RdrName]
                         -- Nothing => no explicit export list
                   -> GlobalRdrEnv
                   -> ImportAvails
                   -> Module
                   -> RnM (Maybe [LIE Name], [AvailInfo])

exports_from_avail Nothing rdr_env _imports _this_mod
 = -- The same as (module M) where M is the current module name,
   -- so that's how we handle it.
   let
       avails = [ greExportAvail True gre 
                | gre <- globalRdrEnvElts rdr_env
                , isLocalGRE gre ]
   in
   return (Nothing, avails)

exports_from_avail (Just rdr_items) rdr_env imports this_mod
  = do (ie_names, _, exports) <- foldlM do_litem emptyExportAccum rdr_items

       return (Just ie_names, exports)
  where
    do_litem :: ExportAccum -> LIE RdrName -> RnM ExportAccum
    do_litem acc lie = setSrcSpan (getLoc lie) (exports_from_item acc lie)

    kids_env :: NameEnv [Name]  -- Maps a parent to its in-scope children
    kids_env = mkChildEnv (globalRdrEnvElts rdr_env)

    imported_modules = [ qual_name
                       | xs <- moduleEnvElts $ imp_mods imports,
                         (qual_name, _, _, _) <- xs ]

    exports_from_item :: ExportAccum -> LIE RdrName -> RnM ExportAccum
    exports_from_item acc@(ie_names, occs, exports)
                      (L loc (IEModuleContents mod))
        | let earlier_mods = [ mod | (L _ (IEModuleContents mod)) <- ie_names ]
        , mod `elem` earlier_mods    -- Duplicate export of M
        = do { warn_dup_exports <- woptM Opt_WarnDuplicateExports ;
               warnIf warn_dup_exports (dupModuleExport mod) ;
               return acc }

        | otherwise
        = do { implicit_prelude <- xoptM Opt_ImplicitPrelude
             ; warnDodgyExports <- woptM Opt_WarnDodgyExports
             ; let { exportValid = (mod `elem` imported_modules)
                            || (moduleName this_mod == mod)
                   ; gres = filter (isModuleExported implicit_prelude mod)
                                   (globalRdrEnvElts rdr_env)
                   ; names = map gre_name gres
                   }

             ; checkErr exportValid (moduleNotImported mod)
             ; warnIf (warnDodgyExports && exportValid && null gres) (nullModuleExport mod)

             ; addUsedRdrNames (concat [ [mkRdrQual mod occ, mkRdrUnqual occ]
                                       | occ <- map nameOccName names ])
                        -- The qualified and unqualified version of all of
                        -- these names are, in effect, used by this export

             ; occs' <- check_occs (IEModuleContents mod) occs names
                      -- This check_occs not only finds conflicts
                      -- between this item and others, but also
                      -- internally within this item.  That is, if
                      -- 'M.x' is in scope in several ways, we'll have
                      -- several members of mod_avails with the same
                      -- OccName.
             ; return (L loc (IEModuleContents mod) : ie_names,
                       occs', map (greExportAvail True) gres ++ exports) }

    exports_from_item acc@(lie_names, occs, exports) (L loc ie)
        | isDoc ie
        = do new_ie <- lookup_doc_ie ie
             return (L loc new_ie : lie_names, occs, exports)

        | otherwise
        = do (new_ie, avail) <- lookup_ie ie
             if isUnboundName (ieName new_ie)
                  then return acc    -- Avoid error cascade
                  else do

             occs' <- check_occs ie occs (availNames avail)

             return (L loc new_ie : lie_names, occs', avail : exports)

    -------------
    lookup_ie :: IE RdrName -> RnM (IE Name, AvailInfo)
    lookup_ie (IEVar rdr)
        = do gre <- lookupGreRn rdr
             return (IEVar (gre_name gre), greExportAvail False gre)

    lookup_ie (IEThingAbs rdr)
        = do gre <- lookupGreRn rdr
             let name = gre_name gre
             case gre_par gre of
                NoParent   -> return (IEThingAbs name,
                                      AvailTC name [name])
                ParentIs p -> return (IEThingAbs name,
                                      AvailTC p [name])

    lookup_ie ie@(IEThingAll rdr)
        = do name <- lookupGlobalOccRn rdr
             let kids = findChildren kids_env name
                 mkKidRdrName = case isQual_maybe rdr of
                                Nothing -> mkRdrUnqual
                                Just (modName, _) -> mkRdrQual modName
             addUsedRdrNames $ map (mkKidRdrName . nameOccName) kids
             warnDodgyExports <- woptM Opt_WarnDodgyExports
             when (null kids) $
                  if isTyConName name
                  then when warnDodgyExports $ addWarn (dodgyExportWarn name)
                  else -- This occurs when you export T(..), but
                       -- only import T abstractly, or T is a synonym.
                       addErr (exportItemErr ie)

             return (IEThingAll name, AvailTC name (name:kids))

    lookup_ie ie@(IEThingWith rdr sub_rdrs)
        = do name <- lookupGlobalOccRn rdr
             if isUnboundName name
                then return (IEThingWith name [], AvailTC name [name])
                else do
             let env = mkOccEnv [ (nameOccName s, s)
                                | s <- findChildren kids_env name ]
                 mb_names = map (lookupOccEnv env . rdrNameOcc) sub_rdrs
             if any isNothing mb_names
                then do addErr (exportItemErr ie)
                        return (IEThingWith name [], AvailTC name [name])
                else do let names = catMaybes mb_names
                        optTyFam <- xoptM Opt_TypeFamilies
                        when (not optTyFam && any isTyConName names) $
                          addErr (typeItemErr ( head
                                              . filter isTyConName
                                              $ names )
                                              (text "in export list"))
                        return (IEThingWith name names, AvailTC name (name:names))

    lookup_ie _ = panic "lookup_ie"    -- Other cases covered earlier

    -------------
    lookup_doc_ie :: IE RdrName -> RnM (IE Name)
    lookup_doc_ie (IEGroup lev doc) = do rn_doc <- rnHsDoc doc
                                         return (IEGroup lev rn_doc)
    lookup_doc_ie (IEDoc doc)       = do rn_doc <- rnHsDoc doc
                                         return (IEDoc rn_doc)
    lookup_doc_ie (IEDocNamed str)  = return (IEDocNamed str)
    lookup_doc_ie _ = panic "lookup_doc_ie"    -- Other cases covered earlier


isDoc :: IE RdrName -> Bool
isDoc (IEDoc _)      = True
isDoc (IEDocNamed _) = True
isDoc (IEGroup _ _)  = True
isDoc _ = False

-------------------------------
isModuleExported :: Bool -> ModuleName -> GlobalRdrElt -> Bool
-- True if the thing is in scope *both* unqualified, *and* with qualifier M
isModuleExported implicit_prelude mod (GRE { gre_name = name, gre_prov = prov })
  | implicit_prelude && isBuiltInSyntax name = False
        -- Optimisation: filter out names for built-in syntax
        -- They just clutter up the environment (esp tuples), and the parser
        -- will generate Exact RdrNames for them, so the cluttered
        -- envt is no use.  To avoid doing this filter all the time,
        -- we use -XNoImplicitPrelude as a clue that the filter is
        -- worth while.  Really, it's only useful for GHC.Base and GHC.Tuple.
        --
        -- It's worth doing because it makes the environment smaller for
        -- every module that imports the Prelude
  | otherwise
  = case prov of
        LocalDef | Just name_mod <- nameModule_maybe name
                 -> moduleName name_mod == mod
                 | otherwise -> False
        Imported is -> any unQualSpecOK is && any (qualSpecOK mod) is

-------------------------------
check_occs :: IE RdrName -> ExportOccMap -> [Name] -> RnM ExportOccMap
check_occs ie occs names  -- 'names' are the entities specifed by 'ie'
  = foldlM check occs names
  where
    check occs name
      = case lookupOccEnv occs name_occ of
          Nothing -> return (extendOccEnv occs name_occ (name, ie))

          Just (name', ie')
            | name == name'   -- Duplicate export
            -- But we don't want to warn if the same thing is exported
            -- by two different module exports. See ticket #4478.
            -> do unless (dupExport_ok name ie ie') $ do
                      warn_dup_exports <- woptM Opt_WarnDuplicateExports
                      warnIf warn_dup_exports (dupExportWarn name_occ ie ie')
                  return occs

            | otherwise    -- Same occ name but different names: an error
            ->  do { global_env <- getGlobalRdrEnv ;
                     addErr (exportClashErr global_env name' name ie' ie) ;
                     return occs }
      where
        name_occ = nameOccName name


dupExport_ok :: Name -> IE RdrName -> IE RdrName -> Bool
-- The Name is exported by both IEs. Is that ok?
-- "No"  iff the name is mentioned explicitly in both IEs
--        or one of the IEs mentions the name *alone*
-- "Yes" otherwise
-- 
-- Examples of "no":  module M( f, f )
--                    module M( fmap, Functor(..) )
--                    module M( module Data.List, head )
--
-- Example of "yes"
--    module M( module A, module B ) where
--        import A( f )
--        import B( f )
--
-- Example of "yes" (Trac #2436)
--    module M( C(..), T(..) ) where
--         class C a where { data T a }
--         instace C Int where { data T Int = TInt }
-- 
-- Example of "yes" (Trac #2436)
--    module Foo ( T ) where
--      data family T a
--    module Bar ( T(..), module Foo ) where
--        import Foo
--        data instance T Int = TInt

dupExport_ok n ie1 ie2 
  = not (  single ie1 || single ie2
        || (explicit_in ie1 && explicit_in ie2) )
  where
    explicit_in (IEModuleContents _) = False                -- module M
    explicit_in (IEThingAll r) = nameOccName n == rdrNameOcc r  -- T(..)
    explicit_in _              = True
  
    single (IEVar {})      = True
    single (IEThingAbs {}) = True
    single _               = False

finishWarnings :: DynFlags -> Maybe WarningTxt
               -> TcGblEnv -> RnM TcGblEnv
-- (a) Report usage of imports that are deprecated or have other warnings
-- (b) If the whole module is warned about or deprecated, update tcg_warns
--     All this happens only once per module
finishWarnings dflags mod_warn tcg_env
  = do  { (eps,hpt) <- getEpsAndHpt
        ; ifWOptM Opt_WarnWarningsDeprecations $
          mapM_ (check hpt (eps_PIT eps)) all_gres
                -- By this time, typechecking is complete,
                -- so the PIT is fully populated

        -- Deal with a module deprecation; it overrides all existing warns
        ; let new_warns = case mod_warn of
                                Just txt -> WarnAll txt
                                Nothing  -> tcg_warns tcg_env
        ; return (tcg_env { tcg_warns = new_warns }) }
  where
    used_names = allUses (tcg_dus tcg_env)
        -- Report on all deprecated uses; hence allUses
    all_gres   = globalRdrEnvElts (tcg_rdr_env tcg_env)

    check hpt pit gre@(GRE {gre_name = name, gre_prov = Imported (imp_spec:_)})
      | name `elemNameSet` used_names
      , Just deprec_txt <- lookupImpDeprec dflags hpt pit gre
      = addWarnAt (importSpecLoc imp_spec)
                  (sep [ptext (sLit "In the use of") <+>
                        pprNonVarNameSpace (occNameSpace (nameOccName name)) <+>
                        quotes (ppr name),
                      (parens imp_msg) <> colon,
                      (ppr deprec_txt) ])
        where
          name_mod = ASSERT2( isExternalName name, ppr name ) nameModule name
          imp_mod  = importSpecModule imp_spec
          imp_msg  = ptext (sLit "imported from") <+> ppr imp_mod <> extra
          extra | imp_mod == moduleName name_mod = empty
                | otherwise = ptext (sLit ", but defined in") <+> ppr name_mod

    check _ _ _ = return ()        -- Local, or not used, or not deprectated
            -- The Imported pattern-match: don't deprecate locally defined names
            -- For a start, we may be exporting a deprecated thing
            -- Also we may use a deprecated thing in the defn of another
            -- deprecated things.  We may even use a deprecated thing in
            -- the defn of a non-deprecated thing, when changing a module's
            -- interface

lookupImpDeprec :: DynFlags -> HomePackageTable -> PackageIfaceTable
                -> GlobalRdrElt -> Maybe WarningTxt
-- The name is definitely imported, so look in HPT, PIT
lookupImpDeprec dflags hpt pit gre
  = case lookupIfaceByModule dflags hpt pit mod of
        Just iface -> mi_warn_fn iface name `mplus`    -- Bleat if the thing, *or
                      case gre_par gre of
                        ParentIs p -> mi_warn_fn iface p    -- its parent*, is warn'd
                        NoParent   -> Nothing

        Nothing -> Nothing    -- See Note [Used names with interface not loaded]
  where
    name = gre_name gre
    mod = ASSERT2( isExternalName name, ppr name ) nameModule name

reportUnusedNames :: Maybe [LIE RdrName]    -- Export list
                  -> TcGblEnv -> RnM ()
reportUnusedNames _export_decls gbl_env
  = do  { traceRn ((text "RUN") <+> (ppr (tcg_dus gbl_env)))
        ; warnUnusedImportDecls gbl_env
        ; warnUnusedTopBinds   unused_locals }
  where
    used_names :: NameSet
    used_names = findUses (tcg_dus gbl_env) emptyNameSet
    -- NB: currently, if f x = g, we only treat 'g' as used if 'f' is used
    -- Hence findUses

    -- Collect the defined names from the in-scope environment
    defined_names :: [GlobalRdrElt]
    defined_names = globalRdrEnvElts (tcg_rdr_env gbl_env)

    -- Note that defined_and_used, defined_but_not_used
    -- are both [GRE]; that's why we need defined_and_used
    -- rather than just used_names
    _defined_and_used, defined_but_not_used :: [GlobalRdrElt]
    (_defined_and_used, defined_but_not_used)
        = partition (gre_is_used used_names) defined_names

    kids_env = mkChildEnv defined_names
    -- This is done in mkExports too; duplicated work

    gre_is_used :: NameSet -> GlobalRdrElt -> Bool
    gre_is_used used_names (GRE {gre_name = name})
        = name `elemNameSet` used_names
          || any (`elemNameSet` used_names) (findChildren kids_env name)
                -- A use of C implies a use of T,
                -- if C was brought into scope by T(..) or T(C)

    -- Filter out the ones that are
    --  (a) defined in this module, and
    --  (b) not defined by a 'deriving' clause
    -- The latter have an Internal Name, so we can filter them out easily
    unused_locals :: [GlobalRdrElt]
    unused_locals = filter is_unused_local defined_but_not_used
    is_unused_local :: GlobalRdrElt -> Bool
    is_unused_local gre = isLocalGRE gre && isExternalName (gre_name gre)

type ImportDeclUsage
   = ( LImportDecl Name   -- The import declaration
     , [AvailInfo]        -- What *is* used (normalised)
     , [Name] )           -- What is imported but *not* used

warnUnusedImportDecls :: TcGblEnv -> RnM ()
warnUnusedImportDecls gbl_env
  = do { uses <- readMutVar (tcg_used_rdrnames gbl_env)
       ; let imports = filter explicit_import (tcg_rn_imports gbl_env)
             rdr_env = tcg_rdr_env gbl_env

       ; let usage :: [ImportDeclUsage]
             usage = findImportUsage imports rdr_env (Set.elems uses)

       ; traceRn (ptext (sLit "Import usage") <+> ppr usage)
       ; ifWOptM Opt_WarnUnusedImports $
         mapM_ warnUnusedImport usage

       ; ifDOptM Opt_D_dump_minimal_imports $
         printMinimalImports usage }
  where
    explicit_import (L loc _) = case loc of
                                UnhelpfulSpan _ -> False
                                RealSrcSpan _ -> True
        -- Filter out the implicit Prelude import
        -- which we do not want to bleat about

findImportUsage :: [LImportDecl Name]
                -> GlobalRdrEnv
                -> [RdrName]
                -> [ImportDeclUsage]

type ImportMap = Map SrcLoc [AvailInfo]
-- The intermediate data struture records, for each import
-- declaration, what stuff brought into scope by that
-- declaration is actually used in the module.
--
-- The SrcLoc is the location of the start
-- of a particular 'import' declaration
--
-- The AvailInfos are the things imported from that decl
-- (just a list, not normalised)

findImportUsage imports rdr_env rdrs
  = map unused_decl imports
  where
    import_usage :: ImportMap
    import_usage = foldr (addUsedRdrName rdr_env) Map.empty rdrs

    unused_decl decl@(L loc (ImportDecl { ideclHiding = imps }))
      = (decl, nubAvails used_avails, unused_imps)
      where
        used_avails = Map.lookup (srcSpanStart loc) import_usage `orElse` []
        dont_report_as_unused = foldr add emptyNameSet used_avails
        add (Avail n) s = s `addOneToNameSet` n
        add (AvailTC n ns) s = s `addListToNameSet` (n:ns)
       -- If you use 'signum' from Num, then the user may well have
       -- imported Num(signum).  We don't want to complain that
       -- Num is not itself mentioned.  Hence adding 'n' as
       -- well to the list of of "don't report if unused" names

        unused_imps = case imps of
                        Just (False, imp_ies) -> nameSetToList unused_imps
                          where
                            imp_names = mkNameSet (concatMap (ieNames . unLoc) imp_ies)
                            unused_imps = imp_names `minusNameSet` dont_report_as_unused

                        _other -> []    -- No explicit import list => no unused-name list

addUsedRdrName :: GlobalRdrEnv -> RdrName -> ImportMap -> ImportMap
-- For a used RdrName, find all the import decls that brought
-- it into scope; choose one of them (bestImport), and record
-- the RdrName in that import decl's entry in the ImportMap
addUsedRdrName rdr_env rdr imp_map
  | [gre] <- lookupGRE_RdrName rdr rdr_env
  , Imported imps <- gre_prov gre
  = add_imp gre (bestImport imps) imp_map
  | otherwise
  = imp_map
  where
    add_imp :: GlobalRdrElt -> ImportSpec -> ImportMap -> ImportMap
    add_imp gre (ImpSpec { is_decl = imp_decl_spec }) imp_map
      = Map.insertWith add decl_loc [avail] imp_map
      where
        add _ avails = avail : avails -- add is really just a specialised (++)
        decl_loc = srcSpanStart (is_dloc imp_decl_spec)
        name     = gre_name gre
        avail    = case gre_par gre of
                      ParentIs p                  -> AvailTC p [name]
                      NoParent | isTyConName name -> AvailTC name [name]
                               | otherwise        -> Avail name

    bestImport :: [ImportSpec] -> ImportSpec
    bestImport iss
      = case partition isImpAll iss of
          ([], imp_somes) -> textuallyFirst imp_somes
          (imp_alls, _)   -> textuallyFirst imp_alls

    textuallyFirst :: [ImportSpec] -> ImportSpec
    textuallyFirst iss = case sortWith (is_dloc . is_decl) iss of
                           []     -> pprPanic "textuallyFirst" (ppr iss)
                           (is:_) -> is

    isImpAll :: ImportSpec -> Bool
    isImpAll (ImpSpec { is_item = ImpAll }) = True
    isImpAll _other                         = False

warnUnusedImport :: ImportDeclUsage -> RnM ()
warnUnusedImport (L loc decl, used, unused)
  | Just (False,[]) <- ideclHiding decl
                = return ()            -- Do not warn for 'import M()'
  | null used   = addWarnAt loc msg1   -- Nothing used; drop entire decl
  | null unused = return ()            -- Everything imported is used; nop
  | otherwise   = addWarnAt loc msg2   -- Some imports are unused
  where
    msg1 = vcat [pp_herald <+> quotes pp_mod <+> pp_not_used,
                 nest 2 (ptext (sLit "except perhaps to import instances from")
                                   <+> quotes pp_mod),
                 ptext (sLit "To import instances alone, use:")
                                   <+> ptext (sLit "import") <+> pp_mod <> parens empty ]
    msg2 = sep [pp_herald <+> quotes (pprWithCommas ppr unused),
                    text "from module" <+> quotes pp_mod <+> pp_not_used]
    pp_herald   = text "The import of"
    pp_mod      = ppr (unLoc (ideclName decl))
    pp_not_used = text "is redundant"

printMinimalImports :: [ImportDeclUsage] -> RnM ()
printMinimalImports imports_w_usage
  = do { imports' <- mapM mk_minimal imports_w_usage
       ; this_mod <- getModule
       ; liftIO $
         do { h <- openFile (mkFilename this_mod) WriteMode
            ; printForUser h neverQualify (vcat (map ppr imports')) }
              -- The neverQualify is important.  We are printing Names
              -- but they are in the context of an 'import' decl, and
              -- we never qualify things inside there
              -- E.g.   import Blag( f, b )
              -- not    import Blag( Blag.f, Blag.g )!
       }
  where
    mkFilename this_mod = moduleNameString (moduleName this_mod) ++ ".imports"

    mk_minimal (L l decl, used, unused)
      | null unused
      , Just (False, _) <- ideclHiding decl
      = return (L l decl)
      | otherwise
      = do { let ImportDecl { ideclName    = L _ mod_name
                            , ideclSource  = is_boot
                            , ideclPkgQual = mb_pkg } = decl
           ; iface <- loadSrcInterface doc mod_name is_boot mb_pkg
           ; let lies = map (L l) (concatMap (to_ie iface) used)
           ; return (L l (decl { ideclHiding = Just (False, lies) })) }
      where
        doc = text "Compute minimal imports for" <+> ppr decl

    to_ie :: ModIface -> AvailInfo -> [IE Name]
    -- The main trick here is that if we're importing all the constructors
    -- we want to say "T(..)", but if we're importing only a subset we want
    -- to say "T(A,B,C)".  So we have to find out what the module exports.
    to_ie _ (Avail n)
       = [IEVar n]
    to_ie _ (AvailTC n [m])
       | n==m = [IEThingAbs n]
    to_ie iface (AvailTC n ns)
      = case [xs | AvailTC x xs <- mi_exports iface
                 , x == n
                 , x `elem` xs    -- Note [Partial export]
                 ] of
           [xs] | all_used xs -> [IEThingAll n]
                | otherwise   -> [IEThingWith n (filter (/= n) ns)]
           _other             -> map IEVar ns
        where
          all_used avail_occs = all (`elem` ns) avail_occs

qualImportItemErr :: RdrName -> SDoc
qualImportItemErr rdr
  = hang (ptext (sLit "Illegal qualified name in import item:"))
       2 (ppr rdr)

badImportItemErrStd :: ModIface -> ImpDeclSpec -> IE RdrName -> SDoc
badImportItemErrStd iface decl_spec ie
  = sep [ptext (sLit "Module"), quotes (ppr (is_mod decl_spec)), source_import,
         ptext (sLit "does not export"), quotes (ppr ie)]
  where
    source_import | mi_boot iface = ptext (sLit "(hi-boot interface)")
                  | otherwise     = empty

badImportItemErrDataCon :: OccName -> ModIface -> ImpDeclSpec -> IE RdrName -> SDoc
badImportItemErrDataCon dataType iface decl_spec ie
  = vcat [ ptext (sLit "In module")
             <+> quotes (ppr (is_mod decl_spec))
             <+> source_import <> colon
         , nest 2 $ quotes datacon
             <+> ptext (sLit "is a data constructor of")
             <+> quotes (ppr dataType)
         , ptext (sLit "To import it use")
         , nest 2 $ quotes (ptext (sLit "import")
             <+> ppr (is_mod decl_spec)
             <+> parens (ppr dataType <+> parens datacon))
         , ptext (sLit "or")
         , nest 2 $ quotes (ptext (sLit "import")
             <+> ppr (is_mod decl_spec)
             <+> parens (ppr dataType <+> parens (ptext $ sLit "..")))
         ]
  where
    datacon = ppr . rdrNameOcc $ ieName ie
    source_import | mi_boot iface = ptext (sLit "(hi-boot interface)")
                  | otherwise     = empty

badImportItemErr :: ModIface -> ImpDeclSpec -> IE RdrName -> [AvailInfo] -> SDoc
badImportItemErr iface decl_spec ie avails
  = case find checkIfDataCon avails of
      Just con -> badImportItemErrDataCon (availOccName con) iface decl_spec ie
      Nothing  -> badImportItemErrStd iface decl_spec ie
  where
    checkIfDataCon (AvailTC _ ns) =
      case find (\n -> importedFS == nameOccNameFS n) ns of
        Just n  -> isDataConName n
        Nothing -> False
    checkIfDataCon _ = False
    availOccName = nameOccName . availName
    nameOccNameFS = occNameFS . nameOccName
    importedFS = occNameFS . rdrNameOcc $ ieName ie

illegalImportItemErr :: SDoc
illegalImportItemErr = ptext (sLit "Illegal import item")

dodgyImportWarn :: RdrName -> SDoc
dodgyImportWarn item = dodgyMsg (ptext (sLit "import")) item
dodgyExportWarn :: Name -> SDoc
dodgyExportWarn item = dodgyMsg (ptext (sLit "export")) item

dodgyMsg :: OutputableBndr n => SDoc -> n -> SDoc
dodgyMsg kind tc
  = sep [ ptext (sLit "The") <+> kind <+> ptext (sLit "item") <+> quotes (ppr (IEThingAll tc))
                <+> ptext (sLit "suggests that"),
          quotes (ppr tc) <+> ptext (sLit "has (in-scope) constructors or class methods,"),
          ptext (sLit "but it has none") ]

exportItemErr :: IE RdrName -> SDoc
exportItemErr export_item
  = sep [ ptext (sLit "The export item") <+> quotes (ppr export_item),
          ptext (sLit "attempts to export constructors or class methods that are not visible here") ]

typeItemErr :: Name -> SDoc -> SDoc
typeItemErr name wherestr
  = sep [ ptext (sLit "Using 'type' tag on") <+> quotes (ppr name) <+> wherestr,
          ptext (sLit "Use -XTypeFamilies to enable this extension") ]

exportClashErr :: GlobalRdrEnv -> Name -> Name -> IE RdrName -> IE RdrName
               -> Message
exportClashErr global_env name1 name2 ie1 ie2
  = vcat [ ptext (sLit "Conflicting exports for") <+> quotes (ppr occ) <> colon
         , ppr_export ie1' name1'
         , ppr_export ie2' name2' ]
  where
    occ = nameOccName name1
    ppr_export ie name = nest 2 (quotes (ppr ie) <+> ptext (sLit "exports") <+>
                                 quotes (ppr name) <+> pprNameProvenance (get_gre name))

    -- get_gre finds a GRE for the Name, so that we can show its provenance
    get_gre name
        = case lookupGRE_Name global_env name of
             (gre:_) -> gre
             []      -> pprPanic "exportClashErr" (ppr name)
    get_loc name = greSrcSpan (get_gre name)
    (name1', ie1', name2', ie2') = if get_loc name1 < get_loc name2
                                   then (name1, ie1, name2, ie2)
                                   else (name2, ie2, name1, ie1)

-- the SrcSpan that pprNameProvenance prints out depends on whether
-- the Name is defined locally or not: for a local definition the
-- definition site is used, otherwise the location of the import
-- declaration.  We want to sort the export locations in
-- exportClashErr by this SrcSpan, we need to extract it:
greSrcSpan :: GlobalRdrElt -> SrcSpan
greSrcSpan gre
  | Imported (is:_) <- gre_prov gre = is_dloc (is_decl is)
  | otherwise                       = name_span
  where
    name_span = nameSrcSpan (gre_name gre)

addDupDeclErr :: [Name] -> TcRn ()
addDupDeclErr []
  = panic "addDupDeclErr: empty list"
addDupDeclErr names@(name : _)
  = addErrAt (getSrcSpan (last sorted_names)) $
    -- Report the error at the later location
    vcat [ptext (sLit "Multiple declarations of") <+> quotes (ppr name),
          ptext (sLit "Declared at:") <+> vcat (map (ppr . nameSrcLoc) sorted_names)]
  where
    sorted_names = sortWith nameSrcLoc names

dupExportWarn :: OccName -> IE RdrName -> IE RdrName -> SDoc
dupExportWarn occ_name ie1 ie2
  = hsep [quotes (ppr occ_name),
          ptext (sLit "is exported by"), quotes (ppr ie1),
          ptext (sLit "and"),            quotes (ppr ie2)]

dupModuleExport :: ModuleName -> SDoc
dupModuleExport mod
  = hsep [ptext (sLit "Duplicate"),
          quotes (ptext (sLit "Module") <+> ppr mod),
          ptext (sLit "in export list")]

moduleNotImported :: ModuleName -> SDoc
moduleNotImported mod
  = ptext (sLit "The export item `module") <+> ppr mod <>
    ptext (sLit "' is not imported")

nullModuleExport :: ModuleName -> SDoc
nullModuleExport mod
  = ptext (sLit "The export item `module") <+> ppr mod <> ptext (sLit "' exports nothing")

missingImportListWarn :: ModuleName -> SDoc
missingImportListWarn mod
  = ptext (sLit "The module") <+> quotes (ppr mod) <+> ptext (sLit "does not have an explicit import list")

missingImportListItem :: IE RdrName -> SDoc
missingImportListItem ie
  = ptext (sLit "The import item") <+> quotes (ppr ie) <+> ptext (sLit "does not have an explicit import list")

moduleWarn :: ModuleName -> WarningTxt -> SDoc
moduleWarn mod (WarningTxt txt)
  = sep [ ptext (sLit "Module") <+> quotes (ppr mod) <> ptext (sLit ":"),
          nest 2 (vcat (map ppr txt)) ]
moduleWarn mod (DeprecatedTxt txt)
  = sep [ ptext (sLit "Module") <+> quotes (ppr mod)
                                <+> ptext (sLit "is deprecated:"),
          nest 2 (vcat (map ppr txt)) ]

implicitPreludeWarn :: SDoc
implicitPreludeWarn
  = ptext (sLit "Module `Prelude' implicitly imported")

packageImportErr :: SDoc
packageImportErr
  = ptext (sLit "Package-qualified imports are not enabled; use -XPackageImports")