diff options
Diffstat (limited to 'compiler/GHC/Tc/Module.hs')
| -rw-r--r-- | compiler/GHC/Tc/Module.hs | 616 |
1 files changed, 315 insertions, 301 deletions
diff --git a/compiler/GHC/Tc/Module.hs b/compiler/GHC/Tc/Module.hs index ecb2e4241e..e9cca205d1 100644 --- a/compiler/GHC/Tc/Module.hs +++ b/compiler/GHC/Tc/Module.hs @@ -13,6 +13,7 @@ {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE ViewPatterns #-} +{-# LANGUAGE MultiWayIf #-} {-# OPTIONS_GHC -Wno-incomplete-record-updates #-} @@ -56,7 +57,7 @@ import GHC.Iface.Env ( externaliseName ) import GHC.Tc.Gen.HsType import GHC.Tc.Validity( checkValidType ) import GHC.Tc.Gen.Match -import GHC.Tc.Utils.Unify( checkConstraints ) +import GHC.Tc.Utils.Unify( checkConstraints, tcSubTypeSigma ) import GHC.Rename.HsType import GHC.Rename.Expr import GHC.Rename.Utils ( HsDocContext(..) ) @@ -129,7 +130,7 @@ import GHC.Core.Class import GHC.Types.Basic hiding( SuccessFlag(..) ) import GHC.Core.Coercion.Axiom import GHC.Types.Annotations -import Data.List ( find, sortBy, sort ) +import Data.List ( sortBy, sort ) import Data.Ord import GHC.Data.FastString import GHC.Data.Maybe @@ -266,9 +267,16 @@ tcRnModuleTcRnM hsc_env mod_sum $ do { -- Rename and type check the declarations traceRn "rn1a" empty ; tcg_env <- if isHsBootOrSig hsc_src - then tcRnHsBootDecls hsc_src local_decls + then do { + ; tcg_env <- tcRnHsBootDecls hsc_src local_decls + ; traceRn "rn4a: before exports" empty + ; tcg_env <- setGblEnv tcg_env $ + rnExports explicit_mod_hdr export_ies + ; traceRn "rn4b: after exports" empty + ; return tcg_env + } else {-# SCC "tcRnSrcDecls" #-} - tcRnSrcDecls explicit_mod_hdr local_decls export_ies + tcRnSrcDecls explicit_mod_hdr export_ies local_decls ; whenM (goptM Opt_DoCoreLinting) $ do { let (warns, errs) = lintGblEnv (hsc_dflags hsc_env) tcg_env @@ -278,12 +286,7 @@ tcRnModuleTcRnM hsc_env mod_sum -- going to get in deeper trouble by proceeding ; setGblEnv tcg_env - $ do { -- Process the export list - traceRn "rn4a: before exports" empty - ; tcg_env <- tcRnExports explicit_mod_hdr export_ies - tcg_env - ; traceRn "rn4b: after exports" empty - ; -- Compare hi-boot iface (if any) with the real thing + $ do { -- Compare hi-boot iface (if any) with the real thing -- Must be done after processing the exports tcg_env <- checkHiBootIface tcg_env boot_info ; -- The new type env is already available to stuff @@ -407,104 +410,117 @@ tcRnImports hsc_env import_decls -} tcRnSrcDecls :: Bool -- False => no 'module M(..) where' header at all - -> [LHsDecl GhcPs] -- Declarations -> Maybe (Located [LIE GhcPs]) + -> [LHsDecl GhcPs] -- Declarations -> TcM TcGblEnv -tcRnSrcDecls explicit_mod_hdr decls export_ies +tcRnSrcDecls explicit_mod_hdr export_ies decls = do { -- Do all the declarations ; (tcg_env, tcl_env, lie) <- tc_rn_src_decls decls - -- Check for the 'main' declaration - -- Must do this inside the captureTopConstraints - -- NB: always set envs *before* captureTopConstraints - ; (tcg_env, lie_main) <- setEnvs (tcg_env, tcl_env) $ - captureTopConstraints $ - checkMain explicit_mod_hdr export_ies - - ; setEnvs (tcg_env, tcl_env) $ do { - - -- Simplify constraints - -- - -- We do this after checkMain, so that we use the type info - -- that checkMain adds - -- - -- We do it with both global and local env in scope: - -- * the global env exposes the instances to simplifyTop - -- * the local env exposes the local Ids to simplifyTop, - -- so that we get better error messages (monomorphism restriction) + ------ Simplify constraints --------- + -- + -- We do this after checkMainType, so that we use the type + -- info that checkMainType adds + -- + -- We do it with both global and local env in scope: + -- * the global env exposes the instances to simplifyTop, + -- and affects how names are rendered in error messages + -- * the local env exposes the local Ids to simplifyTop, + -- so that we get better error messages (monomorphism restriction) ; new_ev_binds <- {-# SCC "simplifyTop" #-} - simplifyTop (lie `andWC` lie_main) + setEnvs (tcg_env, tcl_env) $ + do { lie_main <- checkMainType tcg_env + ; simplifyTop (lie `andWC` lie_main) } -- Emit Typeable bindings - ; tcg_env <- mkTypeableBinds - + ; tcg_env <- setGblEnv tcg_env $ + mkTypeableBinds ; traceTc "Tc9" empty - ; failIfErrsM -- Don't zonk if there have been errors - -- It's a waste of time; and we may get debug warnings - -- about strangely-typed TyCons! - ; traceTc "Tc10" empty - -- Zonk the final code. This must be done last. -- Even simplifyTop may do some unification. -- This pass also warns about missing type signatures - ; (bind_env, ev_binds', binds', fords', imp_specs', rules') + ; (id_env, ev_binds', binds', fords', imp_specs', rules') <- zonkTcGblEnv new_ev_binds tcg_env - -- Finalizers must run after constraints are simplified, or some types - -- might not be complete when using reify (see #12777). - -- and also after we zonk the first time because we run typed splices - -- in the zonker which gives rise to the finalisers. - ; (tcg_env_mf, _) <- setGblEnv (clearTcGblEnv tcg_env) - run_th_modfinalizers + --------- Run finalizers -------------- + -- Finalizers must run after constraints are simplified, lest types + -- might not be complete when using reify (see #12777). + -- and also after we zonk the first time because we run typed splices + -- in the zonker which gives rise to the finalisers. + ; let -- init_tcg_env: + -- * Remove accumulated bindings, rules and so on from + -- TcGblEnv. They are now in ev_binds', binds', etc. + -- * Add the zonked Ids from the value bindings to tcg_type_env + -- Up to now these Ids are only in tcl_env's type-envt + init_tcg_env = tcg_env { tcg_binds = emptyBag + , tcg_ev_binds = emptyBag + , tcg_imp_specs = [] + , tcg_rules = [] + , tcg_fords = [] + , tcg_type_env = tcg_type_env tcg_env + `plusTypeEnv` id_env } + ; (tcg_env, tcl_env) <- setGblEnv init_tcg_env + run_th_modfinalizers ; finishTH ; traceTc "Tc11" empty - ; -- zonk the new bindings arising from running the finalisers. - -- This won't give rise to any more finalisers as you can't nest - -- finalisers inside finalisers. - ; (bind_env_mf, ev_binds_mf, binds_mf, fords_mf, imp_specs_mf, rules_mf) - <- zonkTcGblEnv emptyBag tcg_env_mf - - - ; let { final_type_env = plusTypeEnv (tcg_type_env tcg_env) - (plusTypeEnv bind_env_mf bind_env) - ; tcg_env' = tcg_env_mf - { tcg_binds = binds' `unionBags` binds_mf, - tcg_ev_binds = ev_binds' `unionBags` ev_binds_mf , - tcg_imp_specs = imp_specs' ++ imp_specs_mf , - tcg_rules = rules' ++ rules_mf , - tcg_fords = fords' ++ fords_mf } } ; + --------- Deal with the exports ---------- + -- Can't be done earlier, because the export list must "see" + -- the declarations created by the finalizers + ; tcg_env <- setEnvs (tcg_env, tcl_env) $ + rnExports explicit_mod_hdr export_ies + + --------- Emit the ':Main.main = runMainIO main' declaration ---------- + -- Do this /after/ rnExports, so that it can consult + -- the tcg_exports created by rnExports + ; (tcg_env, main_ev_binds) + <- setEnvs (tcg_env, tcl_env) $ + do { (tcg_env, lie) <- captureTopConstraints $ + checkMain explicit_mod_hdr export_ies + ; ev_binds <- simplifyTop lie + ; return (tcg_env, ev_binds) } + + ---------- Final zonking --------------- + -- Zonk the new bindings arising from running the finalisers, + -- and main. This won't give rise to any more finalisers as you + -- can't nest finalisers inside finalisers. + ; (id_env_mf, ev_binds_mf, binds_mf, fords_mf, imp_specs_mf, rules_mf) + <- zonkTcGblEnv main_ev_binds tcg_env + + ; let { !final_type_env = tcg_type_env tcg_env + `plusTypeEnv` id_env_mf + -- Add the zonked Ids from the value bindings (they were in tcl_env) + -- Force !final_type_env, lest we retain an old reference + -- to the previous tcg_env + + ; tcg_env' = tcg_env + { tcg_binds = binds' `unionBags` binds_mf + , tcg_ev_binds = ev_binds' `unionBags` ev_binds_mf + , tcg_imp_specs = imp_specs' ++ imp_specs_mf + , tcg_rules = rules' ++ rules_mf + , tcg_fords = fords' ++ fords_mf } } ; ; setGlobalTypeEnv tcg_env' final_type_env - - } } + } zonkTcGblEnv :: Bag EvBind -> TcGblEnv -> TcM (TypeEnv, Bag EvBind, LHsBinds GhcTc, [LForeignDecl GhcTc], [LTcSpecPrag], [LRuleDecl GhcTc]) -zonkTcGblEnv new_ev_binds tcg_env = - let TcGblEnv { tcg_binds = binds, - tcg_ev_binds = cur_ev_binds, - tcg_imp_specs = imp_specs, - tcg_rules = rules, - tcg_fords = fords } = tcg_env - - all_ev_binds = cur_ev_binds `unionBags` new_ev_binds - - in {-# SCC "zonkTopDecls" #-} - zonkTopDecls all_ev_binds binds rules imp_specs fords - - --- | Remove accumulated bindings, rules and so on from TcGblEnv -clearTcGblEnv :: TcGblEnv -> TcGblEnv -clearTcGblEnv tcg_env - = tcg_env { tcg_binds = emptyBag, - tcg_ev_binds = emptyBag , - tcg_imp_specs = [], - tcg_rules = [], - tcg_fords = [] } +zonkTcGblEnv ev_binds tcg_env@(TcGblEnv { tcg_binds = binds + , tcg_ev_binds = cur_ev_binds + , tcg_imp_specs = imp_specs + , tcg_rules = rules + , tcg_fords = fords }) + = {-# SCC "zonkTopDecls" #-} + setGblEnv tcg_env $ -- This sets the GlobalRdrEnv which is used when rendering + -- error messages during zonking (notably levity errors) + do { failIfErrsM -- Don't zonk if there have been errors + -- It's a waste of time; and we may get debug warnings + -- about strangely-typed TyCons! + ; let all_ev_binds = cur_ev_binds `unionBags` ev_binds + ; zonkTopDecls all_ev_binds binds rules imp_specs fords } -- | Runs TH finalizers and renames and typechecks the top-level declarations -- that they could introduce. @@ -608,12 +624,9 @@ tc_rn_src_decls ds ; (spliced_decls, splice_fvs) <- rnTopSpliceDecls splice -- Glue them on the front of the remaining decls and loop - ; (tcg_env, tcl_env, lie2) <- - setGblEnv (tcg_env `addTcgDUs` usesOnly splice_fvs) $ - addTopEvBinds ev_binds1 $ - tc_rn_src_decls (spliced_decls ++ rest_ds) - - ; return (tcg_env, tcl_env, lie2) + ; setGblEnv (tcg_env `addTcgDUs` usesOnly splice_fvs) $ + addTopEvBinds ev_binds1 $ + tc_rn_src_decls (spliced_decls ++ rest_ds) } } } @@ -1722,185 +1735,233 @@ tcTyClsInstDecls tycl_decls deriv_decls binds ************************************************************************ -} +checkMainType :: TcGblEnv -> TcRn WantedConstraints +-- If this is the Main module, and it defines a function main, +-- check that its type is of form IO tau. +-- If not, do nothing +-- See Note [Dealing with main] +checkMainType tcg_env + = do { dflags <- getDynFlags + ; if tcg_mod tcg_env /= mainModIs dflags + then return emptyWC else + + do { rdr_env <- getGlobalRdrEnv + ; let main_occ = getMainOcc dflags + main_gres = lookupGlobalRdrEnv rdr_env main_occ + ; case filter isLocalGRE main_gres of { + [] -> return emptyWC ; + (_:_:_) -> return emptyWC ; + [main_gre] -> + + do { let main_name = gre_name main_gre + ctxt = FunSigCtxt main_name False + ; main_id <- tcLookupId main_name + ; (io_ty,_) <- getIOType + ; (_, lie) <- captureTopConstraints $ + setMainCtxt main_name io_ty $ + tcSubTypeSigma ctxt (idType main_id) io_ty + ; return lie } } } } + checkMain :: Bool -- False => no 'module M(..) where' header at all -> Maybe (Located [LIE GhcPs]) -- Export specs of Main module -> TcM TcGblEnv --- If we are in module Main, check that 'main' is defined and exported. +-- If we are in module Main, check that 'main' is exported, +-- and generate the runMainIO binding that calls it +-- See Note [Dealing with main] checkMain explicit_mod_hdr export_ies - = do { dflags <- getDynFlags - ; tcg_env <- getGblEnv - ; check_main dflags tcg_env explicit_mod_hdr export_ies } - -check_main :: DynFlags -> TcGblEnv -> Bool -> Maybe (Located [LIE GhcPs]) - -> TcM TcGblEnv -check_main dflags tcg_env explicit_mod_hdr export_ies - | mod /= main_mod - = traceTc "checkMain not" (ppr main_mod <+> ppr mod) >> - return tcg_env - - | otherwise - -- Compare the list of main functions in scope with those - -- specified in the export list. - = do mains_all <- lookupInfoOccRn main_fn - -- get all 'main' functions in scope - -- They may also be imported from other modules! - case exportedMains of -- check the main(s) specified in the export list - [ ] -> do - -- The module has no main functions in the export spec, so we must give - -- some kind of error message. The tricky part is giving an error message - -- that accurately characterizes what the problem is. - -- See Note [Main module without a main function in the export spec] - traceTc "checkMain no main module exported" ppr_mod_mainfn - complain_no_main - -- In order to reduce the number of potential error messages, we check - -- to see if there are any main functions defined (but not exported)... - case getSomeMain mains_all of - Nothing -> return tcg_env - -- ...if there are no such main functions, there is nothing we can do... - Just some_main -> use_as_main some_main - -- ...if there is such a main function, then communicate this to the - -- typechecker. This can prevent a spurious "Ambiguous type variable" - -- error message in certain cases, as described in - -- Note [Main module without a main function in the export spec]. - _ -> do -- The module has one or more main functions in the export spec - let mains = filterInsMains exportedMains mains_all - case mains of - [] -> do -- - traceTc "checkMain fail" ppr_mod_mainfn - complain_no_main - return tcg_env - [main_name] -> use_as_main main_name - _ -> do -- multiple main functions are exported - addAmbiguousNameErr main_fn -- issue error msg + = do { dflags <- getDynFlags + ; tcg_env <- getGblEnv + + ; let main_mod = mainModIs dflags + main_occ = getMainOcc dflags + + exported_mains :: [Name] + -- Exported things that are called 'main' + exported_mains = [ name | avail <- tcg_exports tcg_env + , name <- availNames avail + , nameOccName name == main_occ ] + + ; if | tcg_mod tcg_env /= main_mod + -> -- Not the main module return tcg_env + + | [main_name] <- exported_mains + -> -- The module indeed exports a function called 'main' + generateMainBinding tcg_env main_name + + | otherwise + -> ASSERT( null exported_mains ) + -- A fully-checked export list can't contain more + -- than one function with the same OccName + do { complain_no_main dflags main_mod main_occ + ; return tcg_env } } where - mod = tcg_mod tcg_env - main_mod = mainModIs dflags - main_mod_nm = moduleName main_mod - main_fn = getMainFun dflags - occ_main_fn = occName main_fn - interactive = ghcLink dflags == LinkInMemory - exportedMains = selExportMains export_ies - ppr_mod_mainfn = ppr main_mod <+> ppr main_fn - - -- There is a single exported 'main' function. - use_as_main :: Name -> TcM TcGblEnv - use_as_main main_name = do - { traceTc "checkMain found" (ppr main_mod <+> ppr main_fn) - ; let loc = srcLocSpan (getSrcLoc main_name) - ; ioTyCon <- tcLookupTyCon ioTyConName - ; res_ty <- newFlexiTyVarTy liftedTypeKind - ; let io_ty = mkTyConApp ioTyCon [res_ty] - skol_info = SigSkol (FunSigCtxt main_name False) io_ty [] - main_expr_rn = L loc (HsVar noExtField (L loc main_name)) - ; (ev_binds, main_expr) - <- checkConstraints skol_info [] [] $ - addErrCtxt mainCtxt $ - tcCheckMonoExpr main_expr_rn io_ty - - -- See Note [Root-main Id] - -- Construct the binding - -- :Main.main :: IO res_ty = runMainIO res_ty main - ; run_main_id <- tcLookupId runMainIOName - ; let { root_main_name = mkExternalName rootMainKey rOOT_MAIN - (mkVarOccFS (fsLit "main")) - (getSrcSpan main_name) - ; root_main_id = Id.mkExportedVanillaId root_main_name - (mkTyConApp ioTyCon [res_ty]) - ; co = mkWpTyApps [res_ty] - -- The ev_binds of the `main` function may contain deferred - -- type error when type of `main` is not `IO a`. The `ev_binds` - -- must be put inside `runMainIO` to ensure the deferred type - -- error can be emitted correctly. See #13838. - ; rhs = nlHsApp (mkLHsWrap co (nlHsVar run_main_id)) $ - mkHsDictLet ev_binds main_expr - ; main_bind = mkVarBind root_main_id rhs } - - ; return (tcg_env { tcg_main = Just main_name, - tcg_binds = tcg_binds tcg_env - `snocBag` main_bind, - tcg_dus = tcg_dus tcg_env - `plusDU` usesOnly (unitFV main_name) - -- Record the use of 'main', so that we don't - -- complain about it being defined but not used - })} - - complain_no_main = unless (interactive && not explicit_mod_hdr) - (addErrTc noMainMsg) -- #12906 - -- Without an explicit module header... - -- in interactive mode, don't worry about the absence of 'main'. - -- in other modes, add error message and go on with typechecking. - - mainCtxt = text "When checking the type of the" <+> pp_main_fn - noMainMsg = text "The" <+> pp_main_fn - <+> text "is not" <+> text defOrExp <+> text "module" - <+> quotes (ppr main_mod) - defOrExp = if null exportedMains then "exported by" else "defined in" - - pp_main_fn = ppMainFn main_fn - - -- Select the main functions from the export list. - -- Only the module name is needed, the function name is fixed. - selExportMains :: Maybe (Located [LIE GhcPs]) -> [ModuleName] -- #16453 - selExportMains Nothing = [main_mod_nm] - -- no main specified, but there is a header. - selExportMains (Just exps) = fmap fst $ - filter (\(_,n) -> n == occ_main_fn ) texp - where - ies = fmap unLoc $ unLoc exps - texp = mapMaybe transExportIE ies - - -- Filter all main functions in scope that match the export specs - filterInsMains :: [ModuleName] -> [Name] -> [Name] -- #16453 - filterInsMains export_mains inscope_mains = - [mod | mod <- inscope_mains, - (moduleName . nameModule) mod `elem` export_mains] - - -- Transform an export_ie to a (ModuleName, OccName) pair. - -- 'IEVar' constructors contain exported values (functions), eg '(Main.main)' - -- 'IEModuleContents' constructors contain fully exported modules, eg '(Main)' - -- All other 'IE...' constructors are not used and transformed to Nothing. - transExportIE :: IE GhcPs -> Maybe (ModuleName, OccName) -- #16453 - transExportIE (IEVar _ var) = isQual_maybe $ - upqual $ ieWrappedName $ unLoc var - where - -- A module name is always needed, so qualify 'UnQual' rdr names. - upqual (Unqual occ) = Qual main_mod_nm occ - upqual rdr = rdr - transExportIE (IEModuleContents _ mod) = Just (unLoc mod, occ_main_fn) - transExportIE _ = Nothing - - -- Get a main function that is in scope. - -- See Note [Main module without a main function in the export spec] - getSomeMain :: [Name] -> Maybe Name -- #16453 - getSomeMain all_mains = case all_mains of - [] -> Nothing -- No main function in scope - [m] -> Just m -- Just one main function in scope - _ -> case mbMainOfMain of - Nothing -> listToMaybe all_mains -- Take the first main function in scope or Nothing - _ -> mbMainOfMain -- Take the Main module's main function or Nothing + complain_no_main dflags main_mod main_occ + = unless (interactive && not explicit_mod_hdr) $ + addErrTc (noMainMsg main_mod main_occ) -- #12906 where - mbMainOfMain = find (\n -> (moduleName . nameModule) n == main_mod_nm ) - all_mains -- the main function of the Main module + interactive = ghcLink dflags == LinkInMemory + -- Without an explicit module header... + -- in interactive mode, don't worry about the absence of 'main'. + -- in other modes, add error message and go on with typechecking. + + noMainMsg main_mod main_occ + = text "The" <+> ppMainFn main_occ + <+> text "is not" <+> text defOrExp <+> text "module" + <+> quotes (ppr main_mod) + + defOrExp | explicit_export_list = "exported by" + | otherwise = "defined in" + explicit_export_list = explicit_mod_hdr && isJust export_ies -- | Get the unqualified name of the function to use as the \"main\" for the main module. -- Either returns the default name or the one configured on the command line with -main-is -getMainFun :: DynFlags -> RdrName -getMainFun dflags = case mainFunIs dflags of - Just fn -> mkRdrUnqual (mkVarOccFS (mkFastString fn)) - Nothing -> main_RDR_Unqual - -ppMainFn :: RdrName -> SDoc -ppMainFn main_fn - | rdrNameOcc main_fn == mainOcc - = text "IO action" <+> quotes (ppr main_fn) +getMainOcc :: DynFlags -> OccName +getMainOcc dflags = case mainFunIs dflags of + Just fn -> mkVarOccFS (mkFastString fn) + Nothing -> mainOcc + +ppMainFn :: OccName -> SDoc +ppMainFn main_occ + | main_occ == mainOcc + = text "IO action" <+> quotes (ppr main_occ) | otherwise - = text "main IO action" <+> quotes (ppr main_fn) + = text "main IO action" <+> quotes (ppr main_occ) mainOcc :: OccName mainOcc = mkVarOccFS (fsLit "main") -{- +generateMainBinding :: TcGblEnv -> Name -> TcM TcGblEnv +-- There is a single exported 'main' function, called 'foo' (say), +-- which may be locally defined or imported +-- Define and typecheck the binding +-- :Main.main :: IO res_ty = runMainIO res_ty foo +-- This wraps the user's main function in the top-level stuff +-- defined in runMainIO (eg catching otherwise un-caught exceptions) +-- See Note [Dealing with main] +generateMainBinding tcg_env main_name = do + { traceTc "checkMain found" (ppr main_name) + ; (io_ty, res_ty) <- getIOType + ; let loc = getSrcSpan main_name + main_expr_rn = L loc (HsVar noExtField (L loc main_name)) + ; (ev_binds, main_expr) <- setMainCtxt main_name io_ty $ + tcCheckMonoExpr main_expr_rn io_ty + + -- See Note [Root-main Id] + -- Construct the binding + -- :Main.main :: IO res_ty = runMainIO res_ty main + ; run_main_id <- tcLookupId runMainIOName + ; let { root_main_name = mkExternalName rootMainKey rOOT_MAIN + (mkVarOccFS (fsLit "main")) + (getSrcSpan main_name) + ; root_main_id = Id.mkExportedVanillaId root_main_name io_ty + ; co = mkWpTyApps [res_ty] + -- The ev_binds of the `main` function may contain deferred + -- type errors when type of `main` is not `IO a`. The `ev_binds` + -- must be put inside `runMainIO` to ensure the deferred type + -- error can be emitted correctly. See #13838. + ; rhs = nlHsApp (mkLHsWrap co (nlHsVar run_main_id)) $ + mkHsDictLet ev_binds main_expr + ; main_bind = mkVarBind root_main_id rhs } + + ; return (tcg_env { tcg_main = Just main_name + , tcg_binds = tcg_binds tcg_env + `snocBag` main_bind + , tcg_dus = tcg_dus tcg_env + `plusDU` usesOnly (unitFV main_name) }) + -- Record the use of 'main', so that we don't + -- complain about it being defined but not used + } + +getIOType :: TcM (TcType, TcType) +-- Return (IO alpha, alpha) for fresh alpha +getIOType = do { ioTyCon <- tcLookupTyCon ioTyConName + ; res_ty <- newFlexiTyVarTy liftedTypeKind + ; return (mkTyConApp ioTyCon [res_ty], res_ty) } + +setMainCtxt :: Name -> TcType -> TcM a -> TcM (TcEvBinds, a) +setMainCtxt main_name io_ty thing_inside + = setSrcSpan (getSrcSpan main_name) $ + addErrCtxt main_ctxt $ + checkConstraints skol_info [] [] $ -- Builds an implication if necessary + thing_inside -- e.g. with -fdefer-type-errors + where + skol_info = SigSkol (FunSigCtxt main_name False) io_ty [] + main_ctxt = text "When checking the type of the" + <+> ppMainFn (nameOccName main_name) + +{- Note [Dealing with main] +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Dealing with the 'main' declaration is surprisingly tricky. Here are +the moving parts: + +* The flag -main-is=M.foo allows you to set the main module to 'M', + and the main function to 'foo'. We access them through + mainModIs :: DynFlags -> Module -- returns M + getMainOcc :: DynFlags -> OccName -- returns foo + Of course usually M = Main, and foo = main. + +* checkMainType: when typechecking module M, we add an extra check that + foo :: IO tau, for some type tau. + This avoids getting ambiguous-type errors from the monomorphism restriction + applying to things like + main = return () + Note that checkMainType does not consult the export list because + we have not yet done rnExports (and can't do it until later). + +* rnExports: checks the export list. Very annoyingly, we can only do + this after running any finalisers, which may add new declarations. + That's why checkMainType and checkMain have to be separate. + +* checkMain: does two things: + - check that the export list does indeed export something called 'foo' + - generateMainBinding: generate the root-main binding + :Main.main = runMainIO M.foo + See Note [Root-main id] + +An annoying consequence of having both checkMainType and checkMain is +that, when (but only when) -fdefer-type-errors is on, we may report an +ill-typed 'main' twice (as warnings): once in checkMainType and once +in checkMain. See test typecheck/should_fail/T13292. + +We have the following tests to check this processing: +----------------+----------------------------------------------------------------------------------+ + | Module Header: | + +-------------+-------------+-------------+-------------+-------------+------------+ + | module | module Main | <No Header> | module Main |module |module Main | + | Main(main) | | | (module X)| Main () | (Sub.main)| +----------------+==================================================================================+ +`main` function | ERROR: | Main.main | ERROR: | Main.main | ERROR: | Sub.main | +in Main module | Ambiguous | | Ambiguous | | `main` not | | +and in imported | | | | | exported | | +module Sub. | T19397E1 | T16453M0 | T19397E2 | T16453M3 | | T16453M1 | + | | | | X = Main | Remark 2) | | +----------------+-------------+-------------+-------------+-------------+-------------+------------+ +`main`function | Sub.main | ERROR: | Sub.main | Sub.main | ERROR: | Sub.main | +only in imported| | No `main` in| | | `main` not | | +submodule Sub. | | `Main` | | | exported | | + | T19397M0 | T16453E1 | T19397M1 | T16453M4 | | T16453M5 | + | | | | X = Sub | Remark 2) | | +----------------+-------------+-------------+-------------+-------------+-------------+------------+ +`foo` function | Sub.foo | ERROR: | Sub.foo | Sub.foo | ERROR: | Sub.foo | +in submodule | | No `foo` in | | | `foo` not | | +Sub. | | `Main` | | | exported | | +GHC option: | | | | | | | + -main-is foo | T19397M2 | T19397E3 | T19397M3 | T19397M4 | T19397E4 | T16453M6 | + | Remark 1) | | | X = Sub | | Remark 3) | +----------------+-------------+-------------+-------------+-------------+-------------+------------+ + +Remarks: +* The first line shows the exported `main` function or the error. +* The second line shows the coresponding test case. +* The module `Sub` contains the following functions: + main :: IO () + foo :: IO () +* Remark 1) Here the header is `Main (foo)`. +* Remark 2) Here we have no extra test case. It would exercise the same code path as `T19397E4`. +* Remark 3) Here the header is `Main (Sub.foo)`. + + Note [Root-main Id] ~~~~~~~~~~~~~~~~~~~ The function that the RTS invokes is always :Main.main, which we call @@ -1914,53 +1975,6 @@ module. Tiresomely, we must filter it out again in GHC.Iface.Make, less we get two defns for 'main' in the interface file! -Note [Main module without a main function in the export spec] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Giving accurate error messages for a Main module that does not export a main -function is surprisingly tricky. To see why, consider a module in a file -`Foo.hs` that has no `main` function in the explicit export specs of the module -header: - - module Main () where - foo = return () - -This does not export a main function and therefore should be rejected, per -chapter 5 of the Haskell Report 2010: - - A Haskell program is a collection of modules, one of which, by convention, - must be called Main and must export the value main. The value of the - program is the value of the identifier main in module Main, which must be - a computation of type IO τ for some type τ. - -In fact, when you compile the program above using `ghc Foo.hs`, you will -actually get *two* errors: - - - The IO action ‘main’ is not defined in module ‘Main’ - - - Ambiguous type variable ‘m0’ arising from a use of ‘return’ - prevents the constraint ‘(Monad m0)’ from being solved. - -The first error is self-explanatory, while the second error message occurs -due to the monomorphism restriction. - -Now consider what would happen if the program above were compiled with -`ghc -main-is foo Foo`. The has the effect of `foo` being designated as the -main function. The program will still be rejected since it does not export -`foo` (and therefore does not export its main function), but there is one -important difference: `foo` will be checked against the type `IO τ`. As a -result, we would *not* expect the monomorphism restriction error message -to occur, since the typechecker should have no trouble figuring out the type -of `foo`. In other words, we should only throw the former error message, -not the latter. - -The implementation uses the function `getSomeMain` to find a potential main -function that is defined but not exported. If one is found, it is passed to -`use_as_main` to inform the typechecker that the main function should be of -type `IO τ`. See also the `T414` and `T17171a` test cases for similar examples -of programs whose error messages are influenced by the situation described in -this Note. - - ********************************************************* * * GHCi stuff @@ -2715,7 +2729,7 @@ tcRnDeclsi :: HscEnv -> IO (Messages, Maybe TcGblEnv) tcRnDeclsi hsc_env local_decls = runTcInteractive hsc_env $ - tcRnSrcDecls False local_decls Nothing + tcRnSrcDecls False Nothing local_decls externaliseAndTidyId :: Module -> Id -> TcM Id externaliseAndTidyId this_mod id |