{-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeFamilies #-} module GHC.Tc.Gen.Export (rnExports, exports_from_avail, classifyGREs) where import GHC.Prelude import GHC.Hs import GHC.Builtin.Names import GHC.Tc.Errors.Types import GHC.Tc.Utils.Monad import GHC.Tc.Utils.Env ( TyThing(AConLike, AnId), tcLookupGlobal, tcLookupTyCon ) import GHC.Tc.Utils.TcType import GHC.Rename.Doc import GHC.Rename.Names import GHC.Rename.Env import GHC.Rename.Unbound ( reportUnboundName ) import GHC.Utils.Error import GHC.Unit.Module import GHC.Unit.Module.Imported import GHC.Core.TyCon import GHC.Utils.Outputable import GHC.Utils.Panic import GHC.Core.ConLike import GHC.Core.PatSyn import GHC.Data.Maybe import GHC.Data.FastString (fsLit) import GHC.Driver.Env import GHC.Driver.Session import GHC.Parser.PostProcess ( setRdrNameSpace ) import qualified GHC.LanguageExtensions as LangExt import GHC.Types.Unique.Set import GHC.Types.SrcLoc as SrcLoc import GHC.Types.Name import GHC.Types.Name.Env import GHC.Types.Name.Set import GHC.Types.Avail import GHC.Types.SourceFile import GHC.Types.Id import GHC.Types.Id.Info import GHC.Types.Name.Reader import Control.Arrow ( first ) import Control.Monad ( when ) import qualified Data.List.NonEmpty as NE import Data.Traversable ( for ) {- ************************************************************************ * * \subsection{Export list processing} * * ************************************************************************ Processing the export list. You might think that we should record things that appear in the export list as ``occurrences'' (using @addOccurrenceName@), but you'd be wrong. We do check (here) that they are in scope, but there is no need to slurp in their actual declaration (which is what @addOccurrenceName@ forces). Indeed, doing so would big trouble when compiling @PrelBase@, because it re-exports @GHC@, which includes @takeMVar#@, whose type includes @ConcBase.StateAndSynchVar#@, and so on... Note [Exports of data families] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose you see (#5306) module M where import X( F ) data instance F Int = FInt What does M export? AvailTC F [FInt] or AvailTC F [F,FInt]? The former is strictly right because F isn't defined in this module. But then you can never do an explicit import of M, thus import M( F( FInt ) ) because F isn't exported by M. Nor can you import FInt alone from here import M( FInt ) because we don't have syntax to support that. (It looks like an import of the type FInt.) At one point I implemented a compromise: * When constructing exports with no export list, or with module M( module M ), we add the parent to the exports as well. * But not when you see module M( f ), even if f is a class method with a parent. * Nor when you see module M( module N ), with N /= M. But the compromise seemed too much of a hack, so we backed it out. You just have to use an explicit export list: module M( F(..) ) where ... Note [Avails of associated data families] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose you have (#16077) {-# LANGUAGE TypeFamilies #-} module A (module A) where class C a where { data T a } instance C () where { data T () = D } Because @A@ is exported explicitly, GHC tries to produce an export list from the @GlobalRdrEnv@. In this case, it pulls out the following: [ C defined at A.hs:4:1 , T parent:C defined at A.hs:4:23 , D parent:T defined at A.hs:5:35 ] If map these directly into avails, (via 'availFromGRE'), we get @[C{C;}, C{T;}, T{D;}]@, which eventually gets merged into @[C{C, T;}, T{D;}]@. That's not right, because @T{D;}@ violates the AvailTC invariant: @T@ is exported, but it isn't the first entry in the avail! We work around this issue by expanding GREs where the parent and child are both type constructors into two GRES. T parent:C defined at A.hs:4:23 => [ T parent:C defined at A.hs:4:23 , T defined at A.hs:4:23 ] Then, we get @[C{C;}, C{T;}, T{T;}, T{D;}]@, which eventually gets merged into @[C{C, T;}, T{T, D;}]@ (which satisfies the AvailTC invariant). -} data ExportAccum -- The type of the accumulating parameter of -- the main worker function in rnExports = ExportAccum ExportOccMap -- Tracks exported occurrence names (UniqSet ModuleName) -- Tracks (re-)exported module names emptyExportAccum :: ExportAccum emptyExportAccum = ExportAccum emptyOccEnv emptyUniqSet accumExports :: (ExportAccum -> x -> TcRn (Maybe (ExportAccum, y))) -> [x] -> TcRn [y] accumExports f = fmap (catMaybes . snd) . mapAccumLM f' emptyExportAccum where f' acc x = do m <- attemptM (f acc x) pure $ case m of Just (Just (acc', y)) -> (acc', Just y) _ -> (acc, Nothing) type ExportOccMap = OccEnv (Name, IE GhcPs) -- 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 (LocatedL [LIE GhcPs]) -- Nothing => no explicit export list -> 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 = checkNoErrs $ -- Fail if anything in rnExports finds -- an error fails, to avoid error cascade do { hsc_env <- getTopEnv ; tcg_env <- getGblEnv ; let dflags = hsc_dflags hsc_env TcGblEnv { tcg_mod = this_mod , tcg_rdr_env = rdr_env , tcg_imports = imports , tcg_src = hsc_src } = tcg_env default_main | mainModIs (hsc_HUE hsc_env) == this_mod , Just main_fun <- mainFunIs dflags = mkUnqual varName (fsLit main_fun) | otherwise = main_RDR_Unqual ; has_main <- (not . null) <$> lookupInfoOccRn default_main -- #17832 -- If a module has no explicit header, and it has one or more main -- functions in scope, then add a header like -- "module Main(main) where ..." #13839 -- See Note [Modules without a module header] ; let real_exports | explicit_mod = exports | has_main = Just (noLocA [noLocA (IEVar noExtField (noLocA (IEName noExtField $ noLocA default_main)))]) -- ToDo: the 'noLoc' here is unhelpful if 'main' -- turns out to be out of scope | otherwise = Nothing -- Rename the export list ; let do_it = exports_from_avail real_exports rdr_env imports this_mod ; (rn_exports, final_avails) <- if hsc_src == HsigFile then do (mb_r, msgs) <- tryTc do_it case mb_r of Just r -> return r Nothing -> addMessages msgs >> failM else checkNoErrs do_it -- Final processing ; let final_ns = availsToNameSet final_avails ; traceRn "rnExports: Exports:" (ppr final_avails) ; 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 final_ns }) } exports_from_avail :: Maybe (LocatedL [LIE GhcPs]) -- ^ 'Nothing' means no explicit export list -> GlobalRdrEnv -> ImportAvails -- ^ Imported modules; this is used to test if a -- @module Foo@ export is valid (it's not valid -- if we didn't import @Foo@!) -> Module -> RnM (Maybe [(LIE GhcRn, Avails)], Avails) -- (Nothing, _) <=> no explicit export list -- if explicit export list is present it contains -- each renamed export item together with its exported -- names. 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, except we also export the data family -- when a data instance is exported. = do { ; addDiagnostic (TcRnMissingExportList $ moduleName _this_mod) ; let avails = map fix_faminst . gresToAvailInfo . filter isLocalGRE . globalRdrEnvElts $ rdr_env ; return (Nothing, avails) } where -- #11164: when we define a data instance -- but not data family, re-export the family -- Even though we don't check whether this is actually a data family -- only data families can locally define subordinate things (`ns` here) -- without locally defining (and instead importing) the parent (`n`) fix_faminst avail@(AvailTC n ns) | availExportsDecl avail = avail | otherwise = AvailTC n (n:ns) fix_faminst avail = avail exports_from_avail (Just (L _ rdr_items)) rdr_env imports this_mod = do ie_avails <- accumExports do_litem rdr_items let final_exports = nubAvails (concatMap snd ie_avails) -- Combine families return (Just ie_avails, final_exports) where do_litem :: ExportAccum -> LIE GhcPs -> RnM (Maybe (ExportAccum, (LIE GhcRn, Avails))) do_litem acc lie = setSrcSpan (getLocA lie) (exports_from_item acc lie) -- Maps a parent to its in-scope children kids_env :: NameEnv [GlobalRdrElt] kids_env = mkChildEnv (globalRdrEnvElts rdr_env) -- See Note [Avails of associated data families] expand_tyty_gre :: GlobalRdrElt -> [GlobalRdrElt] expand_tyty_gre (gre@GRE { gre_par = ParentIs p }) | isTyConName p , isTyConName (greName gre) = [gre, gre{ gre_par = NoParent }] expand_tyty_gre gre = [gre] imported_modules = [ imv_name imv | xs <- moduleEnvElts $ imp_mods imports , imv <- importedByUser xs ] exports_from_item :: ExportAccum -> LIE GhcPs -> RnM (Maybe (ExportAccum, (LIE GhcRn, Avails))) exports_from_item (ExportAccum occs earlier_mods) (L loc ie@(IEModuleContents _ lmod@(L _ mod))) | mod `elementOfUniqSet` earlier_mods -- Duplicate export of M = do { addDiagnostic (TcRnDupeModuleExport mod) ; return Nothing} | otherwise = do { let { exportValid = (mod `elem` imported_modules) || (moduleName this_mod == mod) ; gre_prs = pickGREsModExp mod (globalRdrEnvElts rdr_env) ; new_gres = [ gre' | (gre, _) <- gre_prs , gre' <- expand_tyty_gre gre ] ; new_exports = map availFromGRE new_gres ; all_gres = foldr (\(gre1,gre2) gres -> gre1 : gre2 : gres) [] gre_prs ; mods = addOneToUniqSet earlier_mods mod } ; checkErr exportValid (TcRnExportedModNotImported mod) ; warnIf (exportValid && null gre_prs) (TcRnNullExportedModule mod) ; traceRn "efa" (ppr mod $$ ppr all_gres) ; addUsedGREs all_gres ; occs' <- check_occs occs ie new_gres -- 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. ; traceRn "export_mod" (vcat [ ppr mod , ppr new_exports ]) ; return $ Just $ ( ExportAccum occs' mods , ( L loc (IEModuleContents noExtField lmod) , new_exports) ) } exports_from_item acc@(ExportAccum occs mods) (L loc ie) = do m_new_ie <- lookup_doc_ie ie case m_new_ie of Just new_ie -> return $ Just (acc, (L loc new_ie, [])) Nothing -> do let finish (occs', new_ie, avail) = (ExportAccum occs' mods, (L loc new_ie, [avail])) fmap finish <$> lookup_ie occs ie ------------- lookup_ie :: ExportOccMap -> IE GhcPs -> RnM (Maybe (ExportOccMap, IE GhcRn, AvailInfo)) lookup_ie occs ie@(IEVar ann l) = do mb_gre <- lookupGreAvailRn $ lieWrappedName l for mb_gre $ \ gre -> do let avail = availFromGRE gre name = greName gre occs' <- check_occs occs ie [gre] return (occs', IEVar ann (replaceLWrappedName l name), avail) lookup_ie occs ie@(IEThingAbs ann l) = do mb_gre <- lookupGreAvailRn $ lieWrappedName l for mb_gre $ \ gre -> do let avail = availFromGRE gre name = greName gre occs' <- check_occs occs ie [gre] return ( occs' , IEThingAbs ann (replaceLWrappedName l name) , avail) lookup_ie occs ie@(IEThingAll ann l) = do mb_gre <- lookupGreAvailRn $ lieWrappedName l for mb_gre $ \ par -> do all_kids <- lookup_ie_kids_all ie l par let name = greName par kids_avails = map greName all_kids occs' <- check_occs occs ie (par:all_kids) return ( occs' , IEThingAll ann (replaceLWrappedName l name) , AvailTC name (name:kids_avails)) lookup_ie occs ie@(IEThingWith ann l wc sub_rdrs) = do mb_gre <- addExportErrCtxt ie $ lookupGreAvailRn $ lieWrappedName l for mb_gre $ \ par -> do (subs, with_kids) <- addExportErrCtxt ie $ lookup_ie_kids_with par sub_rdrs wc_kids <- case wc of NoIEWildcard -> return [] IEWildcard _ -> lookup_ie_kids_all ie l par let name = greName par all_kids = with_kids ++ wc_kids kids_avails = map greName all_kids occs' <- check_occs occs ie (par:all_kids) return ( occs' , IEThingWith ann (replaceLWrappedName l name) wc subs , AvailTC name (name:kids_avails)) lookup_ie _ _ = panic "lookup_ie" -- Other cases covered earlier lookup_ie_kids_with :: GlobalRdrElt -> [LIEWrappedName GhcPs] -> RnM ([LIEWrappedName GhcRn], [GlobalRdrElt]) lookup_ie_kids_with gre sub_rdrs = do { let name = greName gre ; kids <- lookupChildrenExport name sub_rdrs ; return (map fst kids, map snd kids) } lookup_ie_kids_all :: IE GhcPs -> LIEWrappedName GhcPs -> GlobalRdrElt -> RnM [GlobalRdrElt] lookup_ie_kids_all ie (L _ rdr) gre = do { let name = greName gre gres = findChildren kids_env name ; addUsedKids (ieWrappedName rdr) gres ; when (null gres) $ if isTyConName name then addTcRnDiagnostic (TcRnDodgyExports gre) else -- This occurs when you export T(..), but -- only import T abstractly, or T is a synonym. addErr (TcRnExportHiddenComponents ie) ; return gres } ------------- lookup_doc_ie :: IE GhcPs -> RnM (Maybe (IE GhcRn)) lookup_doc_ie (IEGroup _ lev doc) = do doc' <- rnLHsDoc doc pure $ Just (IEGroup noExtField lev doc') lookup_doc_ie (IEDoc _ doc) = do doc' <- rnLHsDoc doc pure $ Just (IEDoc noExtField doc') lookup_doc_ie (IEDocNamed _ str) = pure $ Just (IEDocNamed noExtField str) lookup_doc_ie _ = pure Nothing -- In an export item M.T(A,B,C), we want to treat the uses of -- A,B,C as if they were M.A, M.B, M.C -- Happily pickGREs does just the right thing addUsedKids :: RdrName -> [GlobalRdrElt] -> RnM () addUsedKids parent_rdr kid_gres = addUsedGREs (pickGREs parent_rdr kid_gres) -- Renaming and typechecking of exports happens after everything else has -- been typechecked. {- Note [Modules without a module header] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The Haskell 2010 report says in section 5.1: >> An abbreviated form of module, consisting only of the module body, is >> permitted. If this is used, the header is assumed to be >> ‘module Main(main) where’. For modules without a module header, this is implemented the following way: If the module has a main function in scope: Then create a module header and export the main function, as if a module header like ‘module Main(main) where...’ would exist. This has the effect to mark the main function and all top level functions called directly or indirectly via main as 'used', and later on, unused top-level functions can be reported correctly. There is no distinction between GHC and GHCi. If the module has several main functions in scope: Then generate a header as above. The ambiguity is reported later in module `GHC.Tc.Module` function `check_main`. If the module has NO main function: Then export all top-level functions. This marks all top level functions as 'used'. In GHCi this has the effect, that we don't get any 'non-used' warnings. In GHC, however, the 'has-main-module' check in GHC.Tc.Module.checkMain fires, and we get the error: The IO action ‘main’ is not defined in module ‘Main’ -} -- Renaming exports lists is a minefield. Five different things can appear in -- children export lists ( T(A, B, C) ). -- 1. Record selectors -- 2. Type constructors -- 3. Data constructors -- 4. Pattern Synonyms -- 5. Pattern Synonym Selectors -- -- However, things get put into weird name spaces. -- 1. Some type constructors are parsed as variables (-.->) for example. -- 2. All data constructors are parsed as type constructors -- 3. When there is ambiguity, we default type constructors to data -- constructors and require the explicit `type` keyword for type -- constructors. -- -- This function first establishes the possible namespaces that an -- identifier might be in (`choosePossibleNameSpaces`). -- -- Then for each namespace in turn, tries to find the correct identifier -- there returning the first positive result or the first terminating -- error. -- lookupChildrenExport :: Name -> [LIEWrappedName GhcPs] -> RnM ([(LIEWrappedName GhcRn, GlobalRdrElt)]) lookupChildrenExport spec_parent rdr_items = mapAndReportM doOne rdr_items where -- Pick out the possible namespaces in order of priority -- This is a consequence of how the parser parses all -- data constructors as type constructors. choosePossibleNamespaces :: NameSpace -> [NameSpace] choosePossibleNamespaces ns | ns == varName = [varName, tcName] -- NB: for varName, we will also end up looking in the -- record field namespaces. | ns == tcName = [dataName, tcName] | otherwise = [ns] -- Process an individual child doOne :: LIEWrappedName GhcPs -> RnM (LIEWrappedName GhcRn, GlobalRdrElt) doOne n = do let bareName = (ieWrappedName . unLoc) n lkup v = lookupSubBndrOcc_helper False DisableDeprecationWarnings -- Do not report export list deprecations spec_parent (setRdrNameSpace bareName v) name <- combineChildLookupResult $ map lkup $ choosePossibleNamespaces (rdrNameSpace bareName) traceRn "lookupChildrenExport" (ppr name) -- Default to data constructors for slightly better error -- messages let unboundName :: RdrName unboundName = if rdrNameSpace bareName == varName then bareName else setRdrNameSpace bareName dataName case name of NameNotFound -> do { ub <- reportUnboundName unboundName ; let l = getLoc n gre = localVanillaGRE NoParent ub ; return (L l (IEName noExtField (L (la2na l) ub)), gre)} FoundChild child@(GRE { gre_par = par }) -> do { checkPatSynParent spec_parent par child ; let child_nm = greName child ; return (replaceLWrappedName n child_nm, child) } IncorrectParent p c gs -> failWithDcErr p c gs -- Note [Typing Pattern Synonym Exports] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- It proved quite a challenge to precisely specify which pattern synonyms -- should be allowed to be bundled with which type constructors. -- In the end it was decided to be quite liberal in what we allow. Below is -- how Simon described the implementation. -- -- "Personally I think we should Keep It Simple. All this talk of -- satisfiability makes me shiver. I suggest this: allow T( P ) in all -- situations except where `P`'s type is ''visibly incompatible'' with -- `T`. -- -- What does "visibly incompatible" mean? `P` is visibly incompatible -- with -- `T` if -- * `P`'s type is of form `... -> S t1 t2` -- * `S` is a data/newtype constructor distinct from `T` -- -- Nothing harmful happens if we allow `P` to be exported with -- a type it can't possibly be useful for, but specifying a tighter -- relationship is very awkward as you have discovered." -- -- Note that this allows *any* pattern synonym to be bundled with any -- datatype type constructor. For example, the following pattern `P` can be -- bundled with any type. -- -- ``` -- pattern P :: (A ~ f) => f -- ``` -- -- So we provide basic type checking in order to help the user out, most -- pattern synonyms are defined with definite type constructors, but don't -- actually prevent a library author completely confusing their users if -- they want to. -- -- So, we check for exactly four things -- 1. The name arises from a pattern synonym definition. (Either a pattern -- synonym constructor or a pattern synonym selector) -- 2. The pattern synonym is only bundled with a datatype or newtype. -- 3. Check that the head of the result type constructor is an actual type -- constructor and not a type variable. (See above example) -- 4. Is so, check that this type constructor is the same as the parent -- type constructor. -- -- -- Note [Types of TyCon] -- ~~~~~~~~~~~~~~~~~~~~~ -- This check appears to be overly complicated, Richard asked why it -- is not simply just `isAlgTyCon`. The answer for this is that -- a classTyCon is also an `AlgTyCon` which we explicitly want to disallow. -- (It is either a newtype or data depending on the number of methods) -- -- | Given a resolved name in the children export list and a parent. Decide -- whether we are allowed to export the child with the parent. -- Invariant: gre_par == NoParent -- See Note [Typing Pattern Synonym Exports] checkPatSynParent :: Name -- ^ Alleged parent type constructor -- User wrote T( P, Q ) -> Parent -- The parent of P we discovered -> GlobalRdrElt -- ^ Either a -- a) Pattern Synonym Constructor -- b) A pattern synonym selector -> TcM () -- Fails if wrong parent checkPatSynParent _ (ParentIs {}) _ = return () checkPatSynParent parent NoParent gre | isUnboundName parent -- Avoid an error cascade = return () | otherwise = do { parent_ty_con <- tcLookupTyCon parent ; let nm = greName gre ; mpat_syn_thing <- tcLookupGlobal nm -- 1. Check that the Id was actually from a thing associated with patsyns ; case mpat_syn_thing of AnId i | isId i , RecSelId { sel_tycon = RecSelPatSyn p } <- idDetails i -> handle_pat_syn (selErr nm) parent_ty_con p AConLike (PatSynCon p) -> handle_pat_syn (psErr p) parent_ty_con p _ -> failWithDcErr parent gre [] } where psErr = exportErrCtxt "pattern synonym" selErr = exportErrCtxt "pattern synonym record selector" handle_pat_syn :: SDoc -> TyCon -- Parent TyCon -> PatSyn -- Corresponding bundled PatSyn -- and pretty printed origin -> TcM () handle_pat_syn doc ty_con pat_syn -- 2. See Note [Types of TyCon] | not $ isTyConWithSrcDataCons ty_con = addErrCtxt doc $ failWithTc TcRnPatSynBundledWithNonDataCon -- 3. Is the head a type variable? | Nothing <- mtycon = return () -- 4. Ok. Check they are actually the same type constructor. | Just p_ty_con <- mtycon, p_ty_con /= ty_con = addErrCtxt doc $ failWithTc (TcRnPatSynBundledWithWrongType expected_res_ty res_ty) -- 5. We passed! | otherwise = return () where expected_res_ty = mkTyConApp ty_con (mkTyVarTys (tyConTyVars ty_con)) (_, _, _, _, _, res_ty) = patSynSig pat_syn mtycon = fst <$> tcSplitTyConApp_maybe res_ty {-===========================================================================-} -- | Insert the given 'GlobalRdrElt's into the 'ExportOccMap', checking that -- each of the given 'GlobalRdrElt's does not appear multiple times in -- the 'ExportOccMap', as per Note [Exporting duplicate declarations]. check_occs :: ExportOccMap -> IE GhcPs -> [GlobalRdrElt] -> RnM ExportOccMap check_occs occs ie gres -- 'gres' are the entities specified by 'ie' = do { drf <- xoptM LangExt.DuplicateRecordFields ; foldlM (check drf) occs gres } where -- Check for distinct children exported with the same OccName (an error) or -- for duplicate exports of the same child (a warning). -- -- See Note [Exporting duplicate declarations]. check :: Bool -> ExportOccMap -> GlobalRdrElt -> RnM ExportOccMap check drf_enabled occs gre = case try_insert occs gre of Right occs' -- If DuplicateRecordFields is not enabled, also make sure -- that we are not exporting two fields with the same occNameFS -- under different namespaces. -- -- See Note [Exporting duplicate record fields]. | drf_enabled || not (isFieldOcc child_occ) -> return occs' | otherwise -> do { let flds = filter (\(_,ie') -> not $ dupFieldExport_ok ie ie') $ lookupFieldsOccEnv occs (occNameFS child_occ) ; case flds of { [] -> return occs'; clash1:clashes -> do { addDuplicateFieldExportErr (gre,ie) (clash1 NE.:| clashes) ; return occs } } } Left (child', ie') | child == child' -- Duplicate export of a single Name: a warning. -> do { warnIf (not (dupExport_ok child ie ie')) (TcRnDuplicateExport gre ie ie') ; return occs } | otherwise -- Same OccName but different Name: an error. -> do { global_env <- getGlobalRdrEnv ; addErr (exportClashErr global_env child' child ie' ie) ; return occs } where child = greName gre child_occ = occName child -- Try to insert a child into the map, returning Left if there is something -- already exported with the same OccName. try_insert :: ExportOccMap -> GlobalRdrElt -> Either (Name, IE GhcPs) ExportOccMap try_insert occs child = case lookupOccEnv occs occ of Nothing -> Right (extendOccEnv occs occ (greName child, ie)) Just x -> Left x where occ = greOccName child -- | Is it OK for the given name to be exported by both export items? -- -- See Note [Exporting duplicate declarations]. dupExport_ok :: Name -> IE GhcPs -> IE GhcPs -> Bool dupExport_ok child ie1 ie2 = not ( single ie1 || single ie2 || (explicit_in ie1 && explicit_in ie2) ) where explicit_in (IEModuleContents {}) = False -- module M explicit_in (IEThingAll _ r) = occName child == rdrNameOcc (ieWrappedName $ unLoc r) -- T(..) explicit_in _ = True single IEVar {} = True single IEThingAbs {} = True single _ = False exportErrCtxt :: Outputable o => String -> o -> SDoc exportErrCtxt herald exp = text "In the" <+> text (herald ++ ":") <+> ppr exp addExportErrCtxt :: (OutputableBndrId p) => IE (GhcPass p) -> TcM a -> TcM a addExportErrCtxt ie = addErrCtxt exportCtxt where exportCtxt = text "In the export:" <+> ppr ie failWithDcErr :: Name -> GlobalRdrElt -> [Name] -> TcM a failWithDcErr parent child parents = do ty_thing <- tcLookupGlobal (greName child) failWithTc $ TcRnExportedParentChildMismatch parent ty_thing child parents exportClashErr :: GlobalRdrEnv -> Name -> Name -> IE GhcPs -> IE GhcPs -> TcRnMessage exportClashErr global_env child1 child2 ie1 ie2 = TcRnConflictingExports occ gre1' ie1' gre2' ie2' where occ = occName child1 -- get_gre finds a GRE for the Name, so that we can show its provenance gre1 = get_gre child1 gre2 = get_gre child2 get_gre child = fromMaybe (pprPanic "exportClashErr" (ppr child)) (lookupGRE_Name global_env child) (gre1', ie1', gre2', ie2') = case SrcLoc.leftmost_smallest (greSrcSpan gre1) (greSrcSpan gre2) of LT -> (gre1, ie1, gre2, ie2) GT -> (gre2, ie2, gre1, ie1) EQ -> panic "exportClashErr: clashing exports have identical location" addDuplicateFieldExportErr :: (GlobalRdrElt, IE GhcPs) -> NE.NonEmpty (Name, IE GhcPs) -> RnM () addDuplicateFieldExportErr gre others = do { rdr_env <- getGlobalRdrEnv ; let lkup = expectJust "addDuplicateFieldExportErr" . lookupGRE_Name rdr_env other_gres = fmap (first lkup) others ; addErr (TcRnDuplicateFieldExport gre other_gres) } -- | Is it OK to export two clashing duplicate record fields coming from the -- given export items, with @-XDisambiguateRecordFields@ disabled? -- -- See Note [Exporting duplicate record fields]. dupFieldExport_ok :: IE GhcPs -> IE GhcPs -> Bool dupFieldExport_ok ie1 ie2 | IEModuleContents {} <- ie1 , ie2 == ie1 = True | otherwise = False {- Note [Exporting duplicate declarations] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We want to check that two different export items don't have both attempt to export the same thing. What do we mean precisely? There are three main situations to consider: 1. We export two distinct Names with identical OccNames. This is an error. 2. We export the same Name in two different export items. This is usually a warning, but see below. 3. We export a duplicate record field, and DuplicateRecordFields is not enabled. See Note [Exporting duplicate record fields]. Concerning (2), we sometimes want to allow a duplicate export of a given Name, as #4478 points out. The logic, as implemented in dupExport_ok, is that we do not allow a given Name to be exported by two IEs iff either: - the Name is mentioned explicitly in both IEs, or - one of the IEs mentions the name *alone*. Examples: NOT OK: module M( f, f ) f is mentioned explicitly in both NOT OK: module M( fmap, Functor(..) ) NOT OK: module M( module Data.Functor, fmap ) One of the import items mentions fmap alone, which is also exported by the other export item. OK: module M( module A, module B ) where import A( f ) import B( f ) OK: (#2436) module M( C(..), T(..) ) where class C a where { data T a } instance C Int where { data T Int = TInt } OK: (#2436) module Foo ( T ) where data family T a module Bar ( T(..), module Foo ) where import Foo data instance T Int = TInt Note [Exporting duplicate record fields] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Record fields belonging to different datatypes belong to different namespaces, as explained in Note [Record field namespacing] in GHC.Types.Name.Occurrence. However, when the DuplicateRecordFields extension is NOT enabled, we want to prevent users from exporting record fields that share the same underlying occNameFS. To enforce this, in check_occs, when inserting a new record field into the ExportOccMap and DuplicateRecordFields is not enabled, we also look up any clashing record fields, and report an error. Note however that the clash check has an extra wrinkle, similar to dupExport_ok, as we want to allow the following: {-# LANGUAGE DuplicateRecordFields #-} module M1 where data D1 = MkD1 { foo :: Int } data D2 = MkD2 { foo :: Bool } --------------------------------------------- module M2 ( module M1 ) where import M1 That is, we should be allowed to re-export the whole module M1, without reporting any nameclashes, even though M1 exports duplicate record fields and we have not enabled -XDuplicateRecordFields in M2. This logic is implemented in dupFieldExport_ok. See test case NoDRFModuleExport. Note that this logic only applies to whole-module imports, as we don't want to allow the following: module N0 where data family D a module N1 where import N0 data instance D Int = MkDInt { foo :: Int } module N2 where import N0 data instance D Bool = MkDBool { foo :: Int } module N (D(..)) where import N1 import N2 Here, the single export item D(..) of N exports both record fields, `$fld:MkDInt:foo` and `$fld:MkDBool:foo`, so we have to reject the program. See test overloadedrecfldsfail10. -}