rename/RnNames.hs

    {-
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    \section[RnNames]{Extracting imported and top-level names in scope}
    -}

    {-# LANGUAGE CPP, NondecreasingIndentation, MultiWayIf, NamedFieldPuns #-}

    module RnNames (
            rnImports, getLocalNonValBinders, newRecordSelector,
            extendGlobalRdrEnvRn,
            gresFromAvails,
            calculateAvails,
            reportUnusedNames,
            checkConName,
            mkChildEnv,
            findChildren,
            dodgyMsg
        ) where

    #include "HsVersions.h"

    import DynFlags
    import HsSyn
    import TcEnv
    import RnEnv
    import LoadIface        ( loadSrcInterface )
    import TcRnMonad
    import PrelNames
    import Module
    import Name
    import NameEnv
    import NameSet
    import Avail
    import FieldLabel
    import HscTypes
    import RdrName
    import RdrHsSyn        ( setRdrNameSpace )
    import Outputable
    import Maybes
    import SrcLoc
    import BasicTypes      ( TopLevelFlag(..), StringLiteral(..) )
    import Util
    import FastString
    import FastStringEnv
    import Id
    import Type
    import PatSyn
    import qualified GHC.LanguageExtensions as LangExt

    import Control.Monad
    import Data.Either      ( partitionEithers, isRight, rights )
    -- import qualified Data.Foldable as Foldable
    import Data.Map         ( Map )
    import qualified Data.Map as Map
    import Data.Ord         ( comparing )
    import Data.List        ( partition, (\\), find, sortBy )
    import qualified Data.Set as S
    -- import qualified Data.Set as Set
    import System.FilePath  ((</>))

    import System.IO

    {-
    ************************************************************************
    *                                                                      *
    \subsection{rnImports}
    *                                                                      *
    ************************************************************************

    Note [Tracking Trust Transitively]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we import a package as well as checking that the direct imports are safe
    according to the rules outlined in the Note [HscMain . Safe Haskell Trust Check]
    we must also check that these rules hold transitively for all dependent modules
    and packages. Doing this without caching any trust information would be very
    slow as we would need to touch all packages and interface files a module depends
    on. To avoid this we make use of the property that if a modules Safe Haskell
    mode changes, this triggers a recompilation from that module in the dependcy
    graph. So we can just worry mostly about direct imports.

    There is one trust property that can change for a package though without
    recompliation being triggered: package trust. So we must check that all
    packages a module tranitively depends on to be trusted are still trusted when
    we are compiling this module (as due to recompilation avoidance some modules
    below may not be considered trusted any more without recompilation being
    triggered).

    We handle this by augmenting the existing transitive list of packages a module M
    depends on with a bool for each package that says if it must be trusted when the
    module M is being checked for trust. This list of trust required packages for a
    single import is gathered in the rnImportDecl function and stored in an
    ImportAvails data structure. The union of these trust required packages for all
    imports is done by the rnImports function using the combine function which calls
    the plusImportAvails function that is a union operation for the ImportAvails
    type. This gives us in an ImportAvails structure all packages required to be
    trusted for the module we are currently compiling. Checking that these packages
    are still trusted (and that direct imports are trusted) is done in
    HscMain.checkSafeImports.

    See the note below, [Trust Own Package] for a corner case in this method and
    how its handled.

    Note [Trust Own Package]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    There is a corner case of package trust checking that the usual transitive check
    doesn't cover. (For how the usual check operates see the Note [Tracking Trust
    Transitively] below). The case is when you import a -XSafe module M and M
    imports a -XTrustworthy module N. If N resides in a different package than M,
    then the usual check works as M will record a package dependency on N's package
    and mark it as required to be trusted. If N resides in the same package as M
    though, then importing M should require its own package be trusted due to N
    (since M is -XSafe so doesn't create this requirement by itself). The usual
    check fails as a module doesn't record a package dependency of its own package.
    So instead we now have a bool field in a modules interface file that simply
    states if the module requires its own package to be trusted. This field avoids
    us having to load all interface files that the module depends on to see if one
    is trustworthy.

    Note [Trust Transitive Property]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    So there is an interesting design question in regards to transitive trust
    checking. Say I have a module B compiled with -XSafe. B is dependent on a bunch
    of modules and packages, some packages it requires to be trusted as its using
    -XTrustworthy modules from them. Now if I have a module A that doesn't use safe
    haskell at all and simply imports B, should A inherit all the the trust
    requirements from B? Should A now also require that a package p is trusted since
    B required it?

    We currently say no but saying yes also makes sense. The difference is, if a
    module M that doesn't use Safe Haskell imports a module N that does, should all
    the trusted package requirements be dropped since M didn't declare that it cares
    about Safe Haskell (so -XSafe is more strongly associated with the module doing
    the importing) or should it be done still since the author of the module N that
    uses Safe Haskell said they cared (so -XSafe is more strongly associated with
    the module that was compiled that used it).

    Going with yes is a simpler semantics we think and harder for the user to stuff
    up but it does mean that Safe Haskell will affect users who don't care about
    Safe Haskell as they might grab a package from Cabal which uses safe haskell (say
    network) and that packages imports -XTrustworthy modules from another package
    (say bytestring), so requires that package is trusted. The user may now get
    compilation errors in code that doesn't do anything with Safe Haskell simply
    because they are using the network package. They will have to call 'ghc-pkg
    trust network' to get everything working. Due to this invasive nature of going
    with yes we have gone with no for now.
    -}

    -- | Process Import Decls.  See 'rnImportDecl' for a description of what
    -- the return types represent.
    -- Note: Do the non SOURCE ones first, so that we get a helpful warning
    -- for SOURCE ones that are unnecessary
    rnImports :: [LImportDecl RdrName]
              -> RnM ([LImportDecl Name], GlobalRdrEnv, ImportAvails, AnyHpcUsage)
    rnImports imports = do
        tcg_env <- getGblEnv
        -- NB: want an identity module here, because it's OK for a signature
        -- module to import from its implementor
        let this_mod = tcg_mod tcg_env
        let (source, ordinary) = partition is_source_import imports
            is_source_import d = ideclSource (unLoc d)
        stuff1 <- mapAndReportM (rnImportDecl this_mod) ordinary
        stuff2 <- mapAndReportM (rnImportDecl this_mod) source
        -- Safe Haskell: See Note [Tracking Trust Transitively]
        let (decls, rdr_env, imp_avails, hpc_usage) = combine (stuff1 ++ stuff2)
        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)

        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 )

    -- | Given a located import declaration @decl@ from @this_mod@,
    -- calculate the following pieces of information:
    --
    --  1. An updated 'LImportDecl', where all unresolved 'RdrName' in
    --     the entity lists have been resolved into 'Name's,
    --
    --  2. A 'GlobalRdrEnv' representing the new identifiers that were
    --     brought into scope (taking into account module qualification
    --     and hiding),
    --
    --  3. 'ImportAvails' summarizing the identifiers that were imported
    --     by this declaration, and
    --
    --  4. A boolean 'AnyHpcUsage' which is true if the imported module
    --     used HPC.
    rnImportDecl  :: Module -> LImportDecl RdrName
                  -> RnM (LImportDecl Name, GlobalRdrEnv, ImportAvails, AnyHpcUsage)
    rnImportDecl this_mod
                 (L loc decl@(ImportDecl { ideclName = loc_imp_mod_name, ideclPkgQual = mb_pkg
                                         , ideclSource = want_boot, ideclSafe = mod_safe
                                         , ideclQualified = qual_only, ideclImplicit = implicit
                                         , ideclAs = as_mod, ideclHiding = imp_details }))
      = setSrcSpan loc $ do

        when (isJust mb_pkg) $ do
            pkg_imports <- xoptM LangExt.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 <+> text "is directly imported"

        -- Check for self-import, which confuses the typechecker (Trac #9032)
        -- ghc --make rejects self-import cycles already, but batch-mode may not
        -- at least not until TcIface.tcHiBootIface, which is too late to avoid
        -- typechecker crashes.  (Indirect self imports are not caught until
        -- TcIface, see #10337 tracking how to make this error better.)
        --
        -- Originally, we also allowed 'import {-# SOURCE #-} M', but this
        -- caused bug #10182: in one-shot mode, we should never load an hs-boot
        -- file for the module we are compiling into the EPS.  In principle,
        -- it should be possible to support this mode of use, but we would have to
        -- extend Provenance to support a local definition in a qualified location.
        -- For now, we don't support it, but see #10336
        when (imp_mod_name == moduleName this_mod &&
              (case mb_pkg of  -- If we have import "<pkg>" M, then we should
                               -- check that "<pkg>" is "this" (which is magic)
                               -- or the name of this_mod's package.  Yurgh!
                               -- c.f. GHC.findModule, and Trac #9997
                 Nothing         -> True
                 Just (StringLiteral _ pkg_fs) -> pkg_fs == fsLit "this" ||
                                fsToUnitId pkg_fs == moduleUnitId this_mod))
             (addErr (text "A module cannot import itself:" <+> ppr imp_mod_name))

        -- 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   -> return () -- Do not bleat for implicit imports
               | qual_only  -> return ()
               | otherwise  -> whenWOptM Opt_WarnMissingImportList $
                               addWarn (Reason Opt_WarnMissingImportList)
                                       (missingImportListWarn imp_mod_name)

        iface <- loadSrcInterface doc imp_mod_name want_boot (fmap sl_fs 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 <- getDynFlags
        warnIf NoReason
               (want_boot && not (mi_boot iface) && isOneShot (ghcMode dflags))
               (warnRedundantSourceImport imp_mod_name)
        when (mod_safe && not (safeImportsOn dflags)) $
            addErr (text "safe import can't be used as Safe Haskell isn't on!"
                    $+$ ptext (sLit $ "please enable Safe Haskell through either "
                                       ++ "Safe, Trustworthy or Unsafe"))

        let
            qual_mod_name = fmap unLoc as_mod `orElse` imp_mod_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

        -- for certain error messages, we’d like to know what could be imported
        -- here, if everything were imported
        potential_gres <- mkGlobalRdrEnv . snd <$> filterImports iface imp_spec Nothing

        let gbl_env = mkGlobalRdrEnv gres

            is_hiding | Just (True,_) <- imp_details = True
                      | otherwise                    = False

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

        let imv = ImportedModsVal
                { imv_name        = qual_mod_name
                , imv_span        = loc
                , imv_is_safe     = mod_safe'
                , imv_is_hiding   = is_hiding
                , imv_all_exports = potential_gres
                , imv_qualified   = qual_only
                }
            imports = calculateAvails dflags iface mod_safe' want_boot (ImportedByUser imv)

        -- Complain if we import a deprecated module
        whenWOptM Opt_WarnWarningsDeprecations (
           case (mi_warns iface) of
              WarnAll txt -> addWarn (Reason Opt_WarnWarningsDeprecations)
                                    (moduleWarn imp_mod_name txt)
              _           -> return ()
         )

        let new_imp_decl = L loc (decl { ideclSafe = mod_safe'
                                       , ideclHiding = new_imp_details })

        return (new_imp_decl, gbl_env, imports, mi_hpc iface)

    -- | Calculate the 'ImportAvails' induced by an import of a particular
    -- interface, but without 'imp_mods'.
    calculateAvails :: DynFlags
                    -> ModIface
                    -> IsSafeImport
                    -> IsBootInterface
                    -> ImportedBy
                    -> ImportAvails
    calculateAvails dflags iface mod_safe' want_boot imported_by =
      let imp_mod    = mi_module iface
          imp_sem_mod= mi_semantic_module 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

          -- 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
          --
          -- 'dep_orphs' and 'dep_finsts' do NOT include the imported module
          -- itself, but we DO need to include this module in 'imp_orphs' and
          -- 'imp_finsts' if it defines an orphan or instance family; thus the
          -- orph_iface/has_iface tests.

          orphans | orph_iface = ASSERT2( not (imp_sem_mod `elem` dep_orphs deps), ppr imp_sem_mod <+> ppr (dep_orphs deps) )
                                 imp_sem_mod : dep_orphs deps
                  | otherwise  = dep_orphs deps

          finsts | has_finsts = ASSERT2( not (imp_sem_mod `elem` dep_finsts deps), ppr imp_sem_mod <+> ppr (dep_orphs deps) )
                                imp_sem_mod : dep_finsts deps
                 | otherwise  = dep_finsts deps

          pkg = moduleUnitId (mi_module iface)
          ipkg = toInstalledUnitId pkg

          -- 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
                ((moduleName imp_mod,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 (ipkg `elem` (map fst $ dep_pkgs deps))
                       , ppr ipkg <+> ppr (dep_pkgs deps) )
                ([], (ipkg, False) : dep_pkgs deps, False)

      in ImportAvails {
              imp_mods       = unitModuleEnv (mi_module iface) [imported_by],
              imp_orphs      = orphans,
              imp_finsts     = finsts,
              imp_dep_mods   = mkModDeps dependent_mods,
              imp_dep_pkgs   = S.fromList . 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 S.fromList . map fst $ filter snd dependent_pkgs
                                   else S.empty,
              -- Do we require our own pkg to be trusted?
              -- See Note [Trust Own Package]
              imp_trust_own_pkg = pkg_trust_req
         }

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

    {-
    ************************************************************************
    *                                                                      *
    \subsection{importsFromLocalDecls}
    *                                                                      *
    ************************************************************************

    From the top-level declarations of this module produce
            * the lexical environment
            * the ImportAvails
    created by its bindings.

    Note [Top-level Names in Template Haskell decl quotes]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    See also: Note [Interactively-bound Ids in GHCi] in HscTypes
              Note [Looking up Exact RdrNames] in RnEnv

    Consider a Template Haskell declaration quotation like this:
          module M where
            f x = h [d| f = 3 |]
    When renaming the declarations inside [d| ...|], we treat the
    top level binders specially in two ways

    1.  We give them an Internal Name, not (as usual) an External one.
        This is done by RnEnv.newTopSrcBinder.

    2.  We make them *shadow* the outer bindings.
        See Note [GlobalRdrEnv shadowing]

    3. We find out whether we are inside a [d| ... |] by testing the TH
       stage. This is a slight hack, because the stage field was really
       meant for the type checker, and here we are not interested in the
       fields of Brack, hence the error thunks in thRnBrack.
    -}

    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
            ; isGHCi <- getIsGHCi
            ; let rdr_env  = tcg_rdr_env gbl_env
                  fix_env  = tcg_fix_env gbl_env
                  th_bndrs = tcl_th_bndrs lcl_env
                  th_lvl   = thLevel stage

                  -- Delete new_occs from global and local envs
                  -- If we are in a TemplateHaskell decl bracket,
                  --    we are going to shadow them
                  -- See Note [GlobalRdrEnv shadowing]
                  inBracket = isBrackStage stage

                  lcl_env_TH = lcl_env { tcl_rdr = delLocalRdrEnvList (tcl_rdr lcl_env) new_occs }
                               -- See Note [GlobalRdrEnv shadowing]

                  lcl_env2 | inBracket = lcl_env_TH
                           | otherwise = lcl_env

                  -- Deal with shadowing: see Note [GlobalRdrEnv shadowing]
                  want_shadowing = isGHCi || inBracket
                  rdr_env1 | want_shadowing = shadowNames rdr_env new_names
                           | otherwise      = rdr_env

                  lcl_env3 = lcl_env2 { tcl_th_bndrs = extendNameEnvList th_bndrs
                                                           [ (n, (TopLevel, th_lvl))
                                                           | n <- new_names ] }

            ; rdr_env2 <- foldlM add_gre rdr_env1 new_gres

            ; let fix_env' = foldl extend_fix_env fix_env new_gres
                  gbl_env' = gbl_env { tcg_rdr_env = rdr_env2, tcg_fix_env = fix_env' }

            ; traceRn "extendGlobalRdrEnvRn 2" (pprGlobalRdrEnv True rdr_env2)
            ; return (gbl_env', lcl_env3) }
      where
        new_names = concatMap availNames avails
        new_occs  = map nameOccName new_names

        -- 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  = greOccName gre

        new_gres :: [GlobalRdrElt]  -- New LocalDef GREs, derived from avails
        new_gres = concatMap localGREsFromAvail avails

        add_gre :: GlobalRdrEnv -> GlobalRdrElt -> RnM GlobalRdrEnv
        -- Extend the GlobalRdrEnv with a LocalDef GRE
        -- If there is already a LocalDef GRE with the same OccName,
        --    report an error and discard the new GRE
        -- This establishes INVARIANT 1 of GlobalRdrEnvs
        add_gre env gre
          | not (null dups)    -- Same OccName defined twice
          = do { addDupDeclErr (gre : dups); return env }

          | otherwise
          = return (extendGlobalRdrEnv env gre)
          where
            name = gre_name gre
            occ  = nameOccName name
            dups = filter isLocalGRE (lookupGlobalRdrEnv env occ)

    {- *********************************************************************
    *                                                                      *
        getLocalDeclBindersd@ returns the names for an HsDecl
                 It's used for source code.

            *** See Note [The Naming story] in HsDecls ****
    *                                                                      *
    ********************************************************************* -}

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

    getLocalNonValBinders fixity_env
         (HsGroup { hs_valds  = binds,
                    hs_tyclds = tycl_decls,
                    hs_fords  = foreign_decls })
      = do  { -- Process all type/class decls *except* family instances
            ; let inst_decls = tycl_decls >>= group_instds
            ; overload_ok <- xoptM LangExt.DuplicateRecordFields
            ; (tc_avails, tc_fldss)
                <- fmap unzip $ mapM (new_tc overload_ok)
                                     (tyClGroupTyClDecls tycl_decls)
            ; traceRn "getLocalNonValBinders 1" (ppr tc_avails)
            ; envs <- extendGlobalRdrEnvRn tc_avails fixity_env
            ; setEnvs envs $ do {
                -- Bring these things into scope first
                -- See Note [Looking up family names in family instances]

              -- Process all family instances
              -- to bring new data constructors into scope
            ; (nti_availss, nti_fldss) <- mapAndUnzipM (new_assoc overload_ok)
                                                       inst_decls

              -- Finish off with value binders:
              --    foreign decls and pattern synonyms for an ordinary module
              --    type sigs in case of a hs-boot file only
            ; is_boot <- tcIsHsBootOrSig
            ; let val_bndrs | is_boot   = hs_boot_sig_bndrs
                            | otherwise = for_hs_bndrs
            ; val_avails <- mapM new_simple val_bndrs

            ; let avails    = concat nti_availss ++ val_avails
                  new_bndrs = availsToNameSetWithSelectors avails `unionNameSet`
                              availsToNameSetWithSelectors tc_avails
                  flds      = concat nti_fldss ++ concat tc_fldss
            ; traceRn "getLocalNonValBinders 2" (ppr avails)
            ; (tcg_env, tcl_env) <- extendGlobalRdrEnvRn avails fixity_env

            -- Extend tcg_field_env with new fields (this used to be the
            -- work of extendRecordFieldEnv)
            ; let field_env = extendNameEnvList (tcg_field_env tcg_env) flds
                  envs      = (tcg_env { tcg_field_env = field_env }, tcl_env)

            ; traceRn "getLocalNonValBinders 3" (vcat [ppr flds, ppr field_env])
            ; return (envs, new_bndrs) } }
      where
        ValBindsIn _val_binds val_sigs = binds

        for_hs_bndrs :: [Located RdrName]
        for_hs_bndrs = hsForeignDeclsBinders foreign_decls

        -- In a hs-boot file, the value binders come from the
        --  *signatures*, and there should be no foreign binders
        hs_boot_sig_bndrs = [ L decl_loc (unLoc n)
                            | L decl_loc (TypeSig ns _) <- val_sigs, n <- ns]

          -- the SrcSpan attached to the input should be the span of the
          -- declaration, not just the name
        new_simple :: Located RdrName -> RnM AvailInfo
        new_simple rdr_name = do{ nm <- newTopSrcBinder rdr_name
                                ; return (avail nm) }

        new_tc :: Bool -> LTyClDecl RdrName
               -> RnM (AvailInfo, [(Name, [FieldLabel])])
        new_tc overload_ok tc_decl -- NOT for type/data instances
            = do { let (bndrs, flds) = hsLTyClDeclBinders tc_decl
                 ; names@(main_name : sub_names) <- mapM newTopSrcBinder bndrs
                 ; flds' <- mapM (newRecordSelector overload_ok sub_names) flds
                 ; let fld_env = case unLoc tc_decl of
                         DataDecl { tcdDataDefn = d } -> mk_fld_env d names flds'
                         _                            -> []
                 ; return (AvailTC main_name names flds', fld_env) }

        -- Calculate the mapping from constructor names to fields, which
        -- will go in tcg_field_env. It's convenient to do this here where
        -- we are working with a single datatype definition.
        mk_fld_env :: HsDataDefn RdrName -> [Name] -> [FieldLabel] -> [(Name, [FieldLabel])]
        mk_fld_env d names flds = concatMap find_con_flds (dd_cons d)
          where
            find_con_flds (L _ (ConDeclH98 { con_name    = L _ rdr
                                           , con_details = RecCon cdflds }))
                = [( find_con_name rdr
                   , concatMap find_con_decl_flds (unLoc cdflds) )]
            find_con_flds (L _ (ConDeclGADT
                                  { con_names = rdrs
                                  , con_type = (HsIB { hsib_body = res_ty})}))
                = map (\ (L _ rdr) -> ( find_con_name rdr
                                      , concatMap find_con_decl_flds cdflds))
                      rdrs
                where
                  (_tvs, _cxt, tau) = splitLHsSigmaTy res_ty
                  cdflds = case tau of
                     L _ (HsFunTy
                          (L _ (HsAppsTy
                            [L _ (HsAppPrefix (L _ (HsRecTy flds)))])) _) -> flds
                     L _ (HsFunTy (L _ (HsRecTy flds)) _) -> flds
                     _                                    -> []
            find_con_flds _ = []

            find_con_name rdr
              = expectJust "getLocalNonValBinders/find_con_name" $
                  find (\ n -> nameOccName n == rdrNameOcc rdr) names
            find_con_decl_flds (L _ x)
              = map find_con_decl_fld (cd_fld_names x)
            find_con_decl_fld  (L _ (FieldOcc (L _ rdr) _))
              = expectJust "getLocalNonValBinders/find_con_decl_fld" $
                  find (\ fl -> flLabel fl == lbl) flds
              where lbl = occNameFS (rdrNameOcc rdr)

        new_assoc :: Bool -> LInstDecl RdrName
                  -> RnM ([AvailInfo], [(Name, [FieldLabel])])
        new_assoc _ (L _ (TyFamInstD {})) = return ([], [])
          -- type instances don't bind new names

        new_assoc overload_ok (L _ (DataFamInstD d))
          = do { (avail, flds) <- new_di overload_ok Nothing d
               ; return ([avail], flds) }
        new_assoc overload_ok (L _ (ClsInstD (ClsInstDecl { cid_poly_ty = inst_ty
                                                          , cid_datafam_insts = adts })))
          | Just (L loc cls_rdr) <- getLHsInstDeclClass_maybe inst_ty
          = do { cls_nm <- setSrcSpan loc $ lookupGlobalOccRn cls_rdr
               ; (avails, fldss)
                        <- mapAndUnzipM (new_loc_di overload_ok (Just cls_nm)) adts
               ; return (avails, concat fldss) }
          | otherwise
          = return ([], [])    -- Do not crash on ill-formed instances
                               -- Eg   instance !Show Int   Trac #3811c

        new_di :: Bool -> Maybe Name -> DataFamInstDecl RdrName
                       -> RnM (AvailInfo, [(Name, [FieldLabel])])
        new_di overload_ok mb_cls ti_decl
            = do { main_name <- lookupFamInstName mb_cls (dfid_tycon ti_decl)
                 ; let (bndrs, flds) = hsDataFamInstBinders ti_decl
                 ; sub_names <- mapM newTopSrcBinder bndrs
                 ; flds' <- mapM (newRecordSelector overload_ok sub_names) flds
                 ; let avail    = AvailTC (unLoc main_name) sub_names flds'
                                      -- main_name is not bound here!
                       fld_env  = mk_fld_env (dfid_defn ti_decl) sub_names flds'
                 ; return (avail, fld_env) }

        new_loc_di :: Bool -> Maybe Name -> LDataFamInstDecl RdrName
                       -> RnM (AvailInfo, [(Name, [FieldLabel])])
        new_loc_di overload_ok mb_cls (L _ d) = new_di overload_ok mb_cls d

    newRecordSelector :: Bool -> [Name] -> LFieldOcc RdrName -> RnM FieldLabel
    newRecordSelector _ [] _ = error "newRecordSelector: datatype has no constructors!"
    newRecordSelector overload_ok (dc:_) (L loc (FieldOcc (L _ fld) _))
      = do { selName <- newTopSrcBinder $ L loc $ field
           ; return $ qualFieldLbl { flSelector = selName } }
      where
        fieldOccName = occNameFS $ rdrNameOcc fld
        qualFieldLbl = mkFieldLabelOccs fieldOccName (nameOccName dc) overload_ok
        field | isExact fld = fld
                  -- use an Exact RdrName as is to preserve the bindings
                  -- of an already renamer-resolved field and its use
                  -- sites. This is needed to correctly support record
                  -- selectors in Template Haskell. See Note [Binders in
                  -- Template Haskell] in Convert.hs and Note [Looking up
                  -- Exact RdrNames] in RnEnv.hs.
              | otherwise   = mkRdrUnqual (flSelector qualFieldLbl)

    {-
    Note [Looking up family names in family instances]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider

      module M where
        type family T a :: *
        type instance M.T Int = Bool

    We might think that we can simply use 'lookupOccRn' when processing the type
    instance to look up 'M.T'.  Alas, we can't!  The type family declaration is in
    the *same* HsGroup as the type instance declaration.  Hence, as we are
    currently collecting the binders declared in that HsGroup, these binders will
    not have been added to the global environment yet.

    Solution is simple: process the type family declarations first, extend
    the environment, and then process the type instances.

    ************************************************************************
    *                                                                      *
    \subsection{Filtering imports}
    *                                                                      *
    ************************************************************************

    @filterImports@ takes the @ExportEnv@ telling what the imported module makes
    available, and filters it through the import spec (if any).

    Note [Dealing with imports]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    For import M( ies ), we take the mi_exports of M, and make
       imp_occ_env :: OccEnv (Name, AvailInfo, Maybe Name)
    One entry for each Name that M exports; the AvailInfo is the
    AvailInfo exported from M that exports that Name.

    The situation is made more complicated by associated types. E.g.
       module M where
         class    C a    where { data T a }
         instance C Int  where { data T Int = T1 | T2 }
         instance C Bool where { data T Int = T3 }
    Then M's export_avails are (recall the AvailTC invariant from Avails.hs)
      C(C,T), T(T,T1,T2,T3)
    Notice that T appears *twice*, once as a child and once as a parent. From
    this list we construt a raw list including
       T -> (T, T( T1, T2, T3 ), Nothing)
       T -> (C, C( C, T ),       Nothing)
    and we combine these (in function 'combine' in 'imp_occ_env' in
    'filterImports') to get
       T  -> (T,  T(T,T1,T2,T3), Just C)

    So the overall imp_occ_env is
       C  -> (C,  C(C,T),        Nothing)
       T  -> (T,  T(T,T1,T2,T3), Just C)
       T1 -> (T1, T(T,T1,T2,T3), Nothing)   -- similarly T2,T3

    If we say
       import M( T(T1,T2) )
    then we get *two* Avails:  C(T), T(T1,T2)

    Note that the imp_occ_env will have entries for data constructors too,
    although we never look up data constructors.
    -}

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

    filterImports iface decl_spec (Just (want_hiding, L l import_items))
      = do  -- check for errors, convert RdrNames to Names
            items1 <- mapM lookup_lie 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_spec = ImpSpec { is_decl = decl_spec, is_item = ImpAll }

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

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

            -- See Note [Dealing with imports]
        imp_occ_env :: OccEnv (Name,        -- the name
                               AvailInfo,   -- the export item providing the name
                               Maybe Name)  -- the parent of associated types
        imp_occ_env = mkOccEnv_C combine [ (nameOccName n, (n, a, Nothing))
                                         | a <- all_avails, n <- availNames a]
          where
            -- See Note [Dealing with imports]
            -- 'combine' is only called for associated data types which appear
            -- twice in the all_avails. In the example, we combine
            --    T(T,T1,T2,T3) and C(C,T)  to give   (T, T(T,T1,T2,T3), Just C)
            -- NB: the AvailTC can have fields as well as data constructors (Trac #12127)
            combine (name1, a1@(AvailTC p1 _ _), mp1)
                    (name2, a2@(AvailTC p2 _ _), mp2)
              = ASSERT2( name1 == name2 && isNothing mp1 && isNothing mp2
                       , ppr name1 <+> ppr name2 <+> ppr mp1 <+> ppr mp2 )
                if p1 == name1 then (name1, a1, Just p2)
                               else (name1, a2, Just p1)
            combine x y = pprPanic "filterImports/combine" (ppr x $$ ppr y)

        lookup_name :: RdrName -> IELookupM (Name, AvailInfo, Maybe Name)
        lookup_name rdr | isQual rdr              = failLookupWith (QualImportError rdr)
                        | Just succ <- mb_success = return succ
                        | otherwise               = failLookupWith BadImport
          where
            mb_success = lookupOccEnv imp_occ_env (rdrNameOcc rdr)

        lookup_lie :: LIE RdrName -> TcRn [(LIE Name, AvailInfo)]
        lookup_lie (L loc ieRdr)
            = do (stuff, warns) <- setSrcSpan loc $
                                   liftM (fromMaybe ([],[])) $
                                   run_lookup (lookup_ie ieRdr)
                 mapM_ emit_warning warns
                 return [ (L loc ie, avail) | (ie,avail) <- stuff ]
            where
                -- Warn when importing T(..) if T was exported abstractly
                emit_warning (DodgyImport n) = whenWOptM Opt_WarnDodgyImports $
                  addWarn (Reason Opt_WarnDodgyImports) (dodgyImportWarn n)
                emit_warning MissingImportList = whenWOptM Opt_WarnMissingImportList $
                  addWarn (Reason Opt_WarnMissingImportList) (missingImportListItem ieRdr)
                emit_warning BadImportW = whenWOptM Opt_WarnDodgyImports $
                  addWarn (Reason Opt_WarnDodgyImports) (lookup_err_msg BadImport)

                run_lookup :: IELookupM a -> TcRn (Maybe a)
                run_lookup m = case m of
                  Failed err -> addErr (lookup_err_msg err) >> return Nothing
                  Succeeded a -> return (Just a)

                lookup_err_msg err = case err of
                  BadImport -> badImportItemErr iface decl_spec ieRdr all_avails
                  IllegalImport -> illegalImportItemErr
                  QualImportError rdr -> qualImportItemErr rdr

            -- 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 Note [Dealing with imports]
        lookup_ie :: IE RdrName -> IELookupM ([(IE Name, AvailInfo)], [IELookupWarning])
        lookup_ie ie = handle_bad_import $ do
          case ie of
            IEVar (L l n) -> do
                (name, avail, _) <- lookup_name $ ieWrappedName n
                return ([(IEVar (L l (replaceWrappedName n name)),
                                                      trimAvail avail name)], [])

            IEThingAll (L l tc) -> do
                (name, avail, mb_parent) <- lookup_name $ ieWrappedName tc
                let warns = case avail of
                              Avail {}                     -- e.g. f(..)
                                -> [DodgyImport $ ieWrappedName tc]

                              AvailTC _ subs fs
                                | null (drop 1 subs) && null fs -- e.g. T(..) where T is a synonym
                                -> [DodgyImport $ ieWrappedName tc]

                                | not (is_qual decl_spec)  -- e.g. import M( T(..) )
                                -> [MissingImportList]

                                | otherwise
                                -> []

                    renamed_ie = IEThingAll (L l (replaceWrappedName tc name))
                    sub_avails = case avail of
                                   Avail {}              -> []
                                   AvailTC name2 subs fs -> [(renamed_ie, AvailTC name2 (subs \\ [name]) fs)]
                case mb_parent of
                  Nothing     -> return ([(renamed_ie, avail)], warns)
                                 -- non-associated ty/cls
                  Just parent -> return ((renamed_ie, AvailTC parent [name] []) : sub_avails, warns)
                                 -- associated type

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

            IEThingWith (L l rdr_tc) wc rdr_ns' rdr_fs ->
              ASSERT2(null rdr_fs, ppr rdr_fs) do
               (name, AvailTC _ ns subflds, mb_parent)
                                             <- lookup_name (ieWrappedName rdr_tc)

               -- Look up the children in the sub-names of the parent
               let subnames = case ns of   -- The tc is first in ns,
                                [] -> []   -- if it is there at all
                                           -- See the AvailTC Invariant in Avail.hs
                                (n1:ns1) | n1 == name -> ns1
                                         | otherwise  -> ns
                   rdr_ns = map ieLWrappedName rdr_ns'
               case lookupChildren (map Left subnames ++ map Right subflds) rdr_ns of
                 Nothing                      -> failLookupWith BadImport
                 Just (childnames, childflds) ->
                   case mb_parent of
                     -- non-associated ty/cls
                     Nothing
                       -> return ([(IEThingWith (L l name') wc childnames'
                                                               childflds,
                                   AvailTC name (name:map unLoc childnames) (map unLoc childflds))],
                                  [])
                       where name' = replaceWrappedName rdr_tc name
                             childnames' = map to_ie_post_rn childnames
                             -- childnames' = postrn_ies childnames
                     -- associated ty
                     Just parent
                       -> return ([(IEThingWith (L l name') wc childnames'
                                                               childflds,
                                    AvailTC name (map unLoc childnames) (map unLoc childflds)),
                                   (IEThingWith (L l name') wc childnames'
                                                               childflds,
                                    AvailTC parent [name] [])],
                                  [])
                       where name' = replaceWrappedName rdr_tc name
                             childnames' = map to_ie_post_rn childnames

            _other -> failLookupWith IllegalImport
            -- could be IEModuleContents, IEGroup, IEDoc, IEDocNamed
            -- all errors.

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

            handle_bad_import m = catchIELookup m $ \err -> case err of
              BadImport | want_hiding -> return ([], [BadImportW])
              _                       -> failLookupWith err

    type IELookupM = MaybeErr IELookupError

    data IELookupWarning
      = BadImportW
      | MissingImportList
      | DodgyImport RdrName
      -- NB. use the RdrName for reporting a "dodgy" import

    data IELookupError
      = QualImportError RdrName
      | BadImport
      | IllegalImport

    failLookupWith :: IELookupError -> IELookupM a
    failLookupWith err = Failed err

    catchIELookup :: IELookupM a -> (IELookupError -> IELookupM a) -> IELookupM a
    catchIELookup m h = case m of
      Succeeded r -> return r
      Failed err  -> h err

    catIELookupM :: [IELookupM a] -> [a]
    catIELookupM ms = [ a | Succeeded a <- ms ]

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Import/Export Utils}
    *                                                                      *
    ************************************************************************
    -}

    -- | 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 (L _ name) -> \n -> n == ieWrappedName name
                        _                     -> \_ -> True
        prov_fn name
          = Just (ImpSpec { is_decl = decl_spec, is_item = item_spec })
          where
            item_spec = ImpSome { is_explicit = is_explicit name, is_iloc = loc }

    {-
    Note [Children for duplicate record fields]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider the module

        {-# LANGUAGE DuplicateRecordFields #-}
        module M (F(foo, MkFInt, MkFBool)) where
          data family F a
          data instance F Int = MkFInt { foo :: Int }
          data instance F Bool = MkFBool { foo :: Bool }

    The `foo` in the export list refers to *both* selectors! For this
    reason, lookupChildren builds an environment that maps the FastString
    to a list of items, rather than a single item.
    -}

    mkChildEnv :: [GlobalRdrElt] -> NameEnv [GlobalRdrElt]
    mkChildEnv gres = foldr add emptyNameEnv gres
      where
        add gre env = case gre_par gre of
            FldParent p _  -> extendNameEnv_Acc (:) singleton env p gre
            ParentIs  p    -> extendNameEnv_Acc (:) singleton env p gre
            NoParent       -> env

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

    lookupChildren :: [Either Name FieldLabel] -> [Located RdrName]
                   -> Maybe ([Located Name], [Located FieldLabel])
    -- (lookupChildren all_kids rdr_items) maps each rdr_item to its
    -- corresponding Name all_kids, if the former exists
    -- The matching is done by FastString, not OccName, so that
    --    Cls( meth, AssocTy )
    -- will correctly find AssocTy among the all_kids of Cls, even though
    -- the RdrName for AssocTy may have a (bogus) DataName namespace
    -- (Really the rdr_items should be FastStrings in the first place.)
    lookupChildren all_kids rdr_items
      = do xs <- mapM doOne rdr_items
           return (fmap concat (partitionEithers xs))
      where
        doOne (L l r) = case (lookupFsEnv kid_env . occNameFS . rdrNameOcc) r of
          Just [Left n]            -> Just (Left (L l n))
          Just rs | all isRight rs -> Just (Right (map (L l) (rights rs)))
          _                        -> Nothing

        -- See Note [Children for duplicate record fields]
        kid_env = extendFsEnvList_C (++) emptyFsEnv
                          [(either (occNameFS . nameOccName) flLabel x, [x]) | x <- all_kids]

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

    {-
    *********************************************************
    *                                                       *
    \subsection{Unused names}
    *                                                       *
    *********************************************************
    -}

    reportUnusedNames :: Maybe (Located [LIE RdrName])  -- Export list
                      -> TcGblEnv -> RnM ()
    reportUnusedNames _export_decls gbl_env
      = do  { traceRn "RUN" (ppr (tcg_dus gbl_env))
            ; warnUnusedImportDecls gbl_env
            ; warnUnusedTopBinds unused_locals
            ; warnMissingSignatures gbl_env }
      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 (\ gre -> gre_name gre `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)

    {-
    *********************************************************
    *                                                       *
    \subsection{Unused imports}
    *                                                       *
    *********************************************************

    This code finds which import declarations are unused.  The
    specification and implementation notes are here:
      http://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/UnusedImports
    -}

    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_gres gbl_env)
           ; let user_imports = filterOut (ideclImplicit . unLoc) (tcg_rn_imports gbl_env)
                                -- This whole function deals only with *user* imports
                                -- both for warning about unnecessary ones, and for
                                -- deciding the minimal ones
                 rdr_env = tcg_rdr_env gbl_env
                 fld_env = mkFieldEnv rdr_env

           ; let usage :: [ImportDeclUsage]
                 usage = findImportUsage user_imports uses

           ; traceRn "warnUnusedImportDecls" $
                           (vcat [ text "Uses:" <+> ppr uses
                           , text "Import usage" <+> ppr usage])
           ; whenWOptM Opt_WarnUnusedImports $
             mapM_ (warnUnusedImport Opt_WarnUnusedImports fld_env) usage

           ; whenGOptM Opt_D_dump_minimal_imports $
             printMinimalImports usage }

    -- | Warn the user about top level binders that lack type signatures.
    -- Called /after/ type inference, so that we can report the
    -- inferred type of the function
    warnMissingSignatures :: TcGblEnv -> RnM ()
    warnMissingSignatures gbl_env
      = do { let exports = availsToNameSet (tcg_exports gbl_env)
                 sig_ns  = tcg_sigs gbl_env
                   -- We use sig_ns to exclude top-level bindings that are generated by GHC
                 binds    = collectHsBindsBinders $ tcg_binds gbl_env
                 pat_syns = tcg_patsyns gbl_env

             -- Warn about missing signatures
             -- Do this only when we we have a type to offer
           ; warn_missing_sigs  <- woptM Opt_WarnMissingSignatures
           ; warn_only_exported <- woptM Opt_WarnMissingExportedSignatures
           ; warn_pat_syns      <- woptM Opt_WarnMissingPatternSynonymSignatures

           ; let add_sig_warns
                   | warn_only_exported = add_warns Opt_WarnMissingExportedSignatures
                   | warn_missing_sigs  = add_warns Opt_WarnMissingSignatures
                   | warn_pat_syns      = add_warns Opt_WarnMissingPatternSynonymSignatures
                   | otherwise          = return ()

                 add_warns flag
                    = when warn_pat_syns
                           (mapM_ add_pat_syn_warn pat_syns) >>
                      when (warn_missing_sigs || warn_only_exported)
                           (mapM_ add_bind_warn binds)
                    where
                      add_pat_syn_warn p
                        = add_warn name $
                          hang (text "Pattern synonym with no type signature:")
                             2 (text "pattern" <+> pprPrefixName name <+> dcolon <+> pp_ty)
                        where
                          name  = patSynName p
                          pp_ty = pprPatSynType p

                      add_bind_warn id
                        = do { env <- tcInitTidyEnv     -- Why not use emptyTidyEnv?
                             ; let name    = idName id
                                   (_, ty) = tidyOpenType env (idType id)
                                   ty_msg  = pprSigmaType ty
                             ; add_warn name $
                               hang (text "Top-level binding with no type signature:")
                                  2 (pprPrefixName name <+> dcolon <+> ty_msg) }

                      add_warn name msg
                        = when (name `elemNameSet` sig_ns && export_check name)
                               (addWarnAt (Reason flag) (getSrcSpan name) msg)

                      export_check name
                        = not warn_only_exported || name `elemNameSet` exports

           ; add_sig_warns }

    {-
    Note [The ImportMap]
    ~~~~~~~~~~~~~~~~~~~~
    The ImportMap is a short-lived 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 END of a particular 'import'
    declaration.  Why *END*?  Because we don't want to get confused
    by the implicit Prelude import. Consider (Trac #7476) the module
        import Foo( foo )
        main = print foo
    There is an implicit 'import Prelude(print)', and it gets a SrcSpan
    of line 1:1 (just the point, not a span). If we use the *START* of
    the SrcSpan to identify the import decl, we'll confuse the implicit
    import Prelude with the explicit 'import Foo'.  So we use the END.
    It's just a cheap hack; we could equally well use the Span too.

    The AvailInfos are the things imported from that decl (just a list,
    not normalised).
    -}

    type ImportMap = Map SrcLoc [AvailInfo]  -- See [The ImportMap]

    findImportUsage :: [LImportDecl Name]
                    -> [GlobalRdrElt]
                    -> [ImportDeclUsage]

    findImportUsage imports used_gres
      = map unused_decl imports
      where
        import_usage :: ImportMap
        import_usage
          = foldr extendImportMap Map.empty used_gres

        unused_decl decl@(L loc (ImportDecl { ideclHiding = imps }))
          = (decl, nubAvails used_avails, nameSetElemsStable unused_imps)
          where
            used_avails = Map.lookup (srcSpanEnd loc) import_usage `orElse` []
                          -- srcSpanEnd: see Note [The ImportMap]
            used_names   = availsToNameSetWithSelectors used_avails
            used_parents = mkNameSet [n | AvailTC n _ _ <- used_avails]

            unused_imps   -- Not trivial; see eg Trac #7454
              = case imps of
                  Just (False, L _ imp_ies) ->
                                     foldr (add_unused . unLoc) emptyNameSet imp_ies
                  _other -> emptyNameSet -- No explicit import list => no unused-name list

            add_unused :: IE Name -> NameSet -> NameSet
            add_unused (IEVar (L _ n))      acc
                                           = add_unused_name (ieWrappedName n) acc
            add_unused (IEThingAbs (L _ n)) acc
                                           = add_unused_name (ieWrappedName n) acc
            add_unused (IEThingAll (L _ n)) acc
                                           = add_unused_all  (ieWrappedName n) acc
            add_unused (IEThingWith (L _ p) wc ns fs) acc =
              add_wc_all (add_unused_with (ieWrappedName p) xs acc)
              where xs = map (ieWrappedName . unLoc) ns
                              ++ map (flSelector . unLoc) fs
                    add_wc_all = case wc of
                                NoIEWildcard -> id
                                IEWildcard _ -> add_unused_all (ieWrappedName p)
            add_unused _ acc = acc

            add_unused_name n acc
              | n `elemNameSet` used_names = acc
              | otherwise                  = acc `extendNameSet` n
            add_unused_all n acc
              | n `elemNameSet` used_names   = acc
              | n `elemNameSet` used_parents = acc
              | otherwise                    = acc `extendNameSet` n
            add_unused_with p ns acc
              | all (`elemNameSet` acc1) ns = add_unused_name p acc1
              | otherwise = acc1
              where
                acc1 = foldr add_unused_name acc 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 the two cases in add_unused_with.

    extendImportMap :: GlobalRdrElt -> ImportMap -> ImportMap
    -- For each of a list of used GREs, 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
    extendImportMap gre imp_map
       = add_imp gre (bestImport (gre_imp gre)) 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 = srcSpanEnd (is_dloc imp_decl_spec)
                       -- For srcSpanEnd see Note [The ImportMap]
            avail    = availFromGRE gre

    warnUnusedImport :: WarningFlag -> NameEnv (FieldLabelString, Name)
                     -> ImportDeclUsage -> RnM ()
    warnUnusedImport flag fld_env (L loc decl, used, unused)
      | Just (False,L _ []) <- ideclHiding decl
                    = return ()            -- Do not warn for 'import M()'

      | Just (True, L _ hides) <- ideclHiding decl
      , not (null hides)
      , pRELUDE_NAME == unLoc (ideclName decl)
                    = return ()            -- Note [Do not warn about Prelude hiding]
      | null used   = addWarnAt (Reason flag) loc msg1 -- Nothing used; drop entire decl
      | null unused = return ()            -- Everything imported is used; nop
      | otherwise   = addWarnAt (Reason flag) loc msg2 -- Some imports are unused
      where
        msg1 = vcat [pp_herald <+> quotes pp_mod <+> pp_not_used,
                     nest 2 (text "except perhaps to import instances from"
                                       <+> quotes pp_mod),
                     text "To import instances alone, use:"
                                       <+> text "import" <+> pp_mod <> parens Outputable.empty ]
        msg2 = sep [pp_herald <+> quotes sort_unused,
                        text "from module" <+> quotes pp_mod <+> pp_not_used]
        pp_herald  = text "The" <+> pp_qual <+> text "import of"
        pp_qual
          | ideclQualified decl = text "qualified"
          | otherwise           = Outputable.empty
        pp_mod      = ppr (unLoc (ideclName decl))
        pp_not_used = text "is redundant"

        ppr_possible_field n = case lookupNameEnv fld_env n of
                                   Just (fld, p) -> ppr p <> parens (ppr fld)
                                   Nothing  -> ppr n

        -- Print unused names in a deterministic (lexicographic) order
        sort_unused = pprWithCommas ppr_possible_field $
                        sortBy (comparing nameOccName) unused

    {-
    Note [Do not warn about Prelude hiding]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We do not warn about
       import Prelude hiding( x, y )
    because even if nothing else from Prelude is used, it may be essential to hide
    x,y to avoid name-shadowing warnings.  Example (Trac #9061)
       import Prelude hiding( log )
       f x = log where log = ()

    Note [Printing minimal imports]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    To print the minimal imports we walk over the user-supplied import
    decls, and simply trim their import lists.  NB that

      * We do *not* change the 'qualified' or 'as' parts!

      * We do not disard a decl altogether; we might need instances
        from it.  Instead we just trim to an empty import list
    -}

    printMinimalImports :: [ImportDeclUsage] -> RnM ()
    -- See Note [Printing minimal imports]
    printMinimalImports imports_w_usage
      = do { imports' <- mapM mk_minimal imports_w_usage
           ; this_mod <- getModule
           ; dflags   <- getDynFlags
           ; liftIO $
             do { h <- openFile (mkFilename dflags this_mod) WriteMode
                ; printForUser dflags 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 dflags this_mod
          | Just d <- dumpDir dflags = d </> basefn
          | otherwise                = basefn
          where
            basefn = 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 (fmap sl_fs mb_pkg)
               ; let lies = map (L l) (concatMap (to_ie iface) used)
               ; return (L l (decl { ideclHiding = Just (False, L l 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 (to_ie_post_rn $ noLoc n)]
        to_ie _ (AvailTC n [m] [])
           | n==m = [IEThingAbs (to_ie_post_rn $ noLoc n)]
        to_ie iface (AvailTC n ns fs)
          = case [(xs,gs) |  AvailTC x xs gs <- mi_exports iface
                     , x == n
                     , x `elem` xs    -- Note [Partial export]
                     ] of
               [xs] | all_used xs -> [IEThingAll (to_ie_post_rn $ noLoc n)]
                    | otherwise   ->
                       [IEThingWith (to_ie_post_rn $ noLoc n) NoIEWildcard
                                    (map (to_ie_post_rn . noLoc) (filter (/= n) ns))
                                    (map noLoc fs)]
                                              -- Note [Overloaded field import]
               _other | all_non_overloaded fs
                                  -> map (IEVar . to_ie_post_rn_var . noLoc) $ ns
                                     ++ map flSelector fs
                      | otherwise ->
                          [IEThingWith (to_ie_post_rn $ noLoc n) NoIEWildcard
                                    (map (to_ie_post_rn . noLoc) (filter (/= n) ns))
                                    (map noLoc fs)]
            where

              fld_lbls = map flLabel fs

              all_used (avail_occs, avail_flds)
                  = all (`elem` ns) avail_occs
                        && all (`elem` fld_lbls) (map flLabel avail_flds)

              all_non_overloaded = all (not . flIsOverloaded)

    to_ie_post_rn_var :: (HasOccName name) => Located name -> LIEWrappedName name
    to_ie_post_rn_var (L l n)
      | isDataOcc $ occName n = L l (IEPattern (L l n))
      | otherwise             = L l (IEName    (L l n))

    to_ie_post_rn :: (HasOccName name) => Located name -> LIEWrappedName name
    to_ie_post_rn (L l n)
      | isTcOcc occ && isSymOcc occ = L l (IEType (L l n))
      | otherwise                   = L l (IEName (L l n))
      where occ = occName n

    {-
    Note [Partial export]
    ~~~~~~~~~~~~~~~~~~~~~
    Suppose we have

       module A( op ) where
         class C a where
           op :: a -> a

       module B where
       import A
       f = ..op...

    Then the minimal import for module B is
       import A( op )
    not
       import A( C( op ) )
    which we would usually generate if C was exported from B.  Hence
    the (x `elem` xs) test when deciding what to generate.

    Note [Overloaded field import]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    On the other hand, if we have

        {-# LANGUAGE DuplicateRecordFields #-}
        module A where
          data T = MkT { foo :: Int }

        module B where
          import A
          f = ...foo...

    then the minimal import for module B must be
        import A ( T(foo) )
    because when DuplicateRecordFields is enabled, field selectors are
    not in scope without their enclosing datatype.

    ************************************************************************
    *                                                                      *
    \subsection{Errors}
    *                                                                      *
    ************************************************************************
    -}

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

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

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

    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 = text "Illegal import item"

    dodgyImportWarn :: RdrName -> SDoc
    dodgyImportWarn item = dodgyMsg (text "import") item

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

    addDupDeclErr :: [GlobalRdrElt] -> TcRn ()
    addDupDeclErr [] = panic "addDupDeclErr: empty list"
    addDupDeclErr gres@(gre : _)
      = addErrAt (getSrcSpan (last sorted_names)) $
        -- Report the error at the later location
        vcat [text "Multiple declarations of" <+>
                 quotes (ppr (nameOccName name)),
                 -- NB. print the OccName, not the Name, because the
                 -- latter might not be in scope in the RdrEnv and so will
                 -- be printed qualified.
              text "Declared at:" <+>
                       vcat (map (ppr . nameSrcLoc) sorted_names)]
      where
        name = gre_name gre
        sorted_names = sortWith nameSrcLoc (map gre_name gres)

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

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

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

    packageImportErr :: SDoc
    packageImportErr
      = text "Package-qualified imports are not enabled; use PackageImports"

    -- This data decl will parse OK
    --      data T = a Int
    -- treating "a" as the constructor.
    -- It is really hard to make the parser spot this malformation.
    -- So the renamer has to check that the constructor is legal
    --
    -- We can get an operator as the constructor, even in the prefix form:
    --      data T = :% Int Int
    -- from interface files, which always print in prefix form

    checkConName :: RdrName -> TcRn ()
    checkConName name = checkErr (isRdrDataCon name) (badDataCon name)

    badDataCon :: RdrName -> SDoc
    badDataCon name
       = hsep [text "Illegal data constructor name", quotes (ppr name)]