{-# LANGUAGE DataKinds #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TupleSections #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow] {-# LANGUAGE ViewPatterns #-} {-# LANGUAGE DisambiguateRecordFields #-} {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-} {- % (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 -} module GHC.Tc.Gen.Head ( HsExprArg(..), EValArg(..), TcPass(..) , AppCtxt(..), appCtxtLoc, insideExpansion , splitHsApps, rebuildHsApps , addArgWrap, isHsValArg , countLeadingValArgs, isVisibleArg, pprHsExprArgTc , countVisAndInvisValArgs, countHsWrapperInvisArgs , tcInferAppHead, tcInferAppHead_maybe , tcInferId, tcCheckId , obviousSig , tyConOf, tyConOfET, lookupParents, fieldNotInType , notSelector, nonBidirectionalErr , addExprCtxt, addFunResCtxt ) where import {-# SOURCE #-} GHC.Tc.Gen.Expr( tcExpr, tcCheckMonoExprNC, tcCheckPolyExprNC ) import GHC.Tc.Gen.HsType import GHC.Tc.Gen.Bind( chooseInferredQuantifiers ) import GHC.Tc.Gen.Sig( tcUserTypeSig, tcInstSig, lhsSigWcTypeContextSpan ) import GHC.Tc.TyCl.PatSyn( patSynBuilderOcc ) import GHC.Tc.Utils.Monad import GHC.Tc.Utils.Unify import GHC.Types.Basic import GHC.Types.Error import GHC.Tc.Utils.Instantiate import GHC.Tc.Instance.Family ( tcLookupDataFamInst ) import GHC.Core.FamInstEnv ( FamInstEnvs ) import GHC.Core.UsageEnv ( unitUE ) import GHC.Rename.Unbound ( unknownNameSuggestions, WhatLooking(..) ) import GHC.Unit.Module ( getModule ) import GHC.Tc.Errors.Types import GHC.Tc.Solver ( InferMode(..), simplifyInfer ) import GHC.Tc.Utils.Env import GHC.Tc.Utils.TcMType import GHC.Tc.Types.Origin import GHC.Tc.Utils.TcType as TcType import GHC.Hs import GHC.Hs.Syn.Type import GHC.Types.Id import GHC.Types.Id.Info import GHC.Core.PatSyn( PatSyn ) import GHC.Core.ConLike( ConLike(..) ) import GHC.Core.DataCon import GHC.Types.Name import GHC.Types.Name.Reader import GHC.Core.TyCon import GHC.Core.TyCo.Rep import GHC.Core.Type import GHC.Tc.Types.Evidence import GHC.Builtin.Types( multiplicityTy ) import GHC.Builtin.Names import GHC.Builtin.Names.TH( liftStringName, liftName ) import GHC.Driver.Env import GHC.Driver.Session import GHC.Types.SrcLoc import GHC.Utils.Misc import GHC.Data.Maybe import GHC.Utils.Outputable as Outputable import GHC.Utils.Panic import GHC.Utils.Panic.Plain import Control.Monad import Data.Function import GHC.Prelude {- ********************************************************************* * * HsExprArg: auxiliary data type * * ********************************************************************* -} {- Note [HsExprArg] ~~~~~~~~~~~~~~~~~~~ The data type HsExprArg :: TcPass -> Type is a very local type, used only within this module and GHC.Tc.Gen.App * It's really a zipper for an application chain See Note [Application chains and heads] in GHC.Tc.Gen.App for what an "application chain" is. * It's a GHC-specific type, so using TTG only where necessary * It is indexed by TcPass, meaning - HsExprArg TcpRn: The result of splitHsApps, which decomposes a HsExpr GhcRn - HsExprArg TcpInst: The result of tcInstFun, which instantiates the function type Adds EWrap nodes, the argument type in EValArg, and the kind-checked type in ETypeArg - HsExprArg TcpTc: The result of tcArg, which typechecks the value args In EValArg we now have a (LHsExpr GhcTc) * rebuildPrefixApps is dual to splitHsApps, and zips an application back into a HsExpr Note [EValArg] ~~~~~~~~~~~~~~ The data type EValArg is the payload of the EValArg constructor of HsExprArg; i.e. a value argument of the application. EValArg has two forms: * ValArg: payload is just the expression itself. Simple. * ValArgQL: captures the results of applying quickLookArg to the argument in a ValArg. When we later want to typecheck that argument we can just carry on from where quick-look left off. The fields of ValArgQL exactly capture what is needed to complete the job. Invariants: 1. With QL switched off, all arguments are ValArg; no ValArgQL 2. With QL switched on, tcInstFun converts some ValArgs to ValArgQL, under the conditions when quick-look should happen (eg the argument type is guarded) -- see quickLookArg Note [splitHsApps] ~~~~~~~~~~~~~~~~~~ The key function splitHsApps :: HsExpr GhcRn -> (HsExpr GhcRn, HsExpr GhcRn, [HsExprArg 'TcpRn]) takes apart either an HsApp, or an infix OpApp, returning * The "head" of the application, an expression that is often a variable; this is used for typechecking * The "user head" or "error head" of the application, to be reported to the user in case of an error. Example: (`op` e) expands (via HsExpanded) to (rightSection op e) but we don't want to see 'rightSection' in error messages. So we keep the innermost un-expanded head as the "error head". * A list of HsExprArg, the arguments -} data TcPass = TcpRn -- Arguments decomposed | TcpInst -- Function instantiated | TcpTc -- Typechecked data HsExprArg (p :: TcPass) = -- See Note [HsExprArg] EValArg { eva_ctxt :: AppCtxt , eva_arg :: EValArg p , eva_arg_ty :: !(XEVAType p) } | ETypeArg { eva_ctxt :: AppCtxt , eva_hs_ty :: LHsWcType GhcRn -- The type arg , eva_ty :: !(XETAType p) } -- Kind-checked type arg | EPrag AppCtxt (HsPragE (GhcPass (XPass p))) | EWrap EWrap data EWrap = EPar AppCtxt | EExpand (HsExpr GhcRn) | EHsWrap HsWrapper data EValArg (p :: TcPass) where -- See Note [EValArg] ValArg :: LHsExpr (GhcPass (XPass p)) -> EValArg p ValArgQL :: { va_expr :: LHsExpr GhcRn -- Original application -- For location and error msgs , va_fun :: (HsExpr GhcTc, AppCtxt) -- Function of the application, -- typechecked, plus its context , va_args :: [HsExprArg 'TcpInst] -- Args, instantiated , va_ty :: TcRhoType } -- Result type -> EValArg 'TcpInst -- Only exists in TcpInst phase data AppCtxt = VAExpansion (HsExpr GhcRn) -- Inside an expansion of this expression SrcSpan -- The SrcSpan of the expression -- noSrcSpan if outermost | VACall (HsExpr GhcRn) Int -- In the third argument of function f SrcSpan -- The SrcSpan of the application (f e1 e2 e3) appCtxtLoc :: AppCtxt -> SrcSpan appCtxtLoc (VAExpansion _ l) = l appCtxtLoc (VACall _ _ l) = l insideExpansion :: AppCtxt -> Bool insideExpansion (VAExpansion {}) = True insideExpansion (VACall {}) = False instance Outputable AppCtxt where ppr (VAExpansion e _) = text "VAExpansion" <+> ppr e ppr (VACall f n _) = text "VACall" <+> int n <+> ppr f type family XPass p where XPass 'TcpRn = 'Renamed XPass 'TcpInst = 'Renamed XPass 'TcpTc = 'Typechecked type family XETAType p where -- Type arguments XETAType 'TcpRn = NoExtField XETAType _ = Type type family XEVAType p where -- Value arguments XEVAType 'TcpRn = NoExtField XEVAType _ = Scaled Type mkEValArg :: AppCtxt -> LHsExpr GhcRn -> HsExprArg 'TcpRn mkEValArg ctxt e = EValArg { eva_arg = ValArg e, eva_ctxt = ctxt , eva_arg_ty = noExtField } mkETypeArg :: AppCtxt -> LHsWcType GhcRn -> HsExprArg 'TcpRn mkETypeArg ctxt hs_ty = ETypeArg { eva_ctxt = ctxt, eva_hs_ty = hs_ty , eva_ty = noExtField } addArgWrap :: HsWrapper -> [HsExprArg 'TcpInst] -> [HsExprArg 'TcpInst] addArgWrap wrap args | isIdHsWrapper wrap = args | otherwise = EWrap (EHsWrap wrap) : args splitHsApps :: HsExpr GhcRn -> ( (HsExpr GhcRn, AppCtxt) -- Head , [HsExprArg 'TcpRn]) -- Args -- See Note [splitHsApps] splitHsApps e = go e (top_ctxt 0 e) [] where top_ctxt n (HsPar _ _ fun _) = top_lctxt n fun top_ctxt n (HsPragE _ _ fun) = top_lctxt n fun top_ctxt n (HsAppType _ fun _) = top_lctxt (n+1) fun top_ctxt n (HsApp _ fun _) = top_lctxt (n+1) fun top_ctxt n (XExpr (HsExpanded orig _)) = VACall orig n noSrcSpan top_ctxt n other_fun = VACall other_fun n noSrcSpan top_lctxt n (L _ fun) = top_ctxt n fun go :: HsExpr GhcRn -> AppCtxt -> [HsExprArg 'TcpRn] -> ((HsExpr GhcRn, AppCtxt), [HsExprArg 'TcpRn]) go (HsPar _ _ (L l fun) _) ctxt args = go fun (set l ctxt) (EWrap (EPar ctxt) : args) go (HsPragE _ p (L l fun)) ctxt args = go fun (set l ctxt) (EPrag ctxt p : args) go (HsAppType _ (L l fun) ty) ctxt args = go fun (dec l ctxt) (mkETypeArg ctxt ty : args) go (HsApp _ (L l fun) arg) ctxt args = go fun (dec l ctxt) (mkEValArg ctxt arg : args) -- See Note [Looking through HsExpanded] go (XExpr (HsExpanded orig fun)) ctxt args = go fun (VAExpansion orig (appCtxtLoc ctxt)) (EWrap (EExpand orig) : args) -- See Note [Desugar OpApp in the typechecker] go e@(OpApp _ arg1 (L l op) arg2) _ args = ( (op, VACall op 0 (locA l)) , mkEValArg (VACall op 1 generatedSrcSpan) arg1 : mkEValArg (VACall op 2 generatedSrcSpan) arg2 : EWrap (EExpand e) : args ) go e ctxt args = ((e,ctxt), args) set :: SrcSpanAnnA -> AppCtxt -> AppCtxt set l (VACall f n _) = VACall f n (locA l) set _ ctxt@(VAExpansion {}) = ctxt dec :: SrcSpanAnnA -> AppCtxt -> AppCtxt dec l (VACall f n _) = VACall f (n-1) (locA l) dec _ ctxt@(VAExpansion {}) = ctxt rebuildHsApps :: HsExpr GhcTc -> AppCtxt -> [HsExprArg 'TcpTc]-> HsExpr GhcTc rebuildHsApps fun _ [] = fun rebuildHsApps fun ctxt (arg : args) = case arg of EValArg { eva_arg = ValArg arg, eva_ctxt = ctxt' } -> rebuildHsApps (HsApp noAnn lfun arg) ctxt' args ETypeArg { eva_hs_ty = hs_ty, eva_ty = ty, eva_ctxt = ctxt' } -> rebuildHsApps (HsAppType ty lfun hs_ty) ctxt' args EPrag ctxt' p -> rebuildHsApps (HsPragE noExtField p lfun) ctxt' args EWrap (EPar ctxt') -> rebuildHsApps (gHsPar lfun) ctxt' args EWrap (EExpand orig) -> rebuildHsApps (XExpr (ExpansionExpr (HsExpanded orig fun))) ctxt args EWrap (EHsWrap wrap) -> rebuildHsApps (mkHsWrap wrap fun) ctxt args where lfun = L (noAnnSrcSpan $ appCtxtLoc ctxt) fun isHsValArg :: HsExprArg id -> Bool isHsValArg (EValArg {}) = True isHsValArg _ = False countLeadingValArgs :: [HsExprArg id] -> Int countLeadingValArgs [] = 0 countLeadingValArgs (EValArg {} : args) = 1 + countLeadingValArgs args countLeadingValArgs (EWrap {} : args) = countLeadingValArgs args countLeadingValArgs (EPrag {} : args) = countLeadingValArgs args countLeadingValArgs (ETypeArg {} : _) = 0 isValArg :: HsExprArg id -> Bool isValArg (EValArg {}) = True isValArg _ = False isVisibleArg :: HsExprArg id -> Bool isVisibleArg (EValArg {}) = True isVisibleArg (ETypeArg {}) = True isVisibleArg _ = False -- | Count visible and invisible value arguments in a list -- of 'HsExprArg' arguments. countVisAndInvisValArgs :: [HsExprArg id] -> Arity countVisAndInvisValArgs [] = 0 countVisAndInvisValArgs (EValArg {} : args) = 1 + countVisAndInvisValArgs args countVisAndInvisValArgs (EWrap wrap : args) = case wrap of { EHsWrap hsWrap -> countHsWrapperInvisArgs hsWrap + countVisAndInvisValArgs args ; EPar {} -> countVisAndInvisValArgs args ; EExpand {} -> countVisAndInvisValArgs args } countVisAndInvisValArgs (EPrag {} : args) = countVisAndInvisValArgs args countVisAndInvisValArgs (ETypeArg {}: args) = countVisAndInvisValArgs args -- | Counts the number of invisible term-level arguments applied by an 'HsWrapper'. -- Precondition: this wrapper contains no abstractions. countHsWrapperInvisArgs :: HsWrapper -> Arity countHsWrapperInvisArgs = go where go WpHole = 0 go (WpCompose wrap1 wrap2) = go wrap1 + go wrap2 go fun@(WpFun {}) = nope fun go (WpCast {}) = 0 go evLam@(WpEvLam {}) = nope evLam go (WpEvApp _) = 1 go tyLam@(WpTyLam {}) = nope tyLam go (WpTyApp _) = 0 go (WpLet _) = 0 go (WpMultCoercion {}) = 0 nope x = pprPanic "countHsWrapperInvisApps" (ppr x) instance OutputableBndrId (XPass p) => Outputable (HsExprArg p) where ppr (EValArg { eva_arg = arg }) = text "EValArg" <+> ppr arg ppr (EPrag _ p) = text "EPrag" <+> ppr p ppr (ETypeArg { eva_hs_ty = hs_ty }) = char '@' <> ppr hs_ty ppr (EWrap wrap) = ppr wrap instance Outputable EWrap where ppr (EPar _) = text "EPar" ppr (EHsWrap w) = text "EHsWrap" <+> ppr w ppr (EExpand orig) = text "EExpand" <+> ppr orig instance OutputableBndrId (XPass p) => Outputable (EValArg p) where ppr (ValArg e) = ppr e ppr (ValArgQL { va_fun = fun, va_args = args, va_ty = ty}) = hang (text "ValArgQL" <+> ppr fun) 2 (vcat [ ppr args, text "va_ty:" <+> ppr ty ]) pprHsExprArgTc :: HsExprArg 'TcpInst -> SDoc pprHsExprArgTc (EValArg { eva_arg = tm, eva_arg_ty = ty }) = text "EValArg" <+> hang (ppr tm) 2 (dcolon <+> ppr ty) pprHsExprArgTc arg = ppr arg {- Note [Desugar OpApp in the typechecker] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Operator sections are desugared in the renamer; see GHC.Rename.Expr Note [Handling overloaded and rebindable constructs]. But for reasons explained there, we rename OpApp to OpApp. Then, here in the typechecker, we desugar it to a use of HsExpanded. That makes it possible to typecheck something like e1 `f` e2 where f :: forall a. t1 -> forall b. t2 -> t3 Note [Looking through HsExpanded] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When creating an application chain in splitHsApps, we must deal with HsExpanded f1 (f `HsApp` e1) `HsApp` e2 `HsApp` e3 as a single application chain `f e1 e2 e3`. Otherwise stuff like overloaded labels (#19154) won't work. It's easy to achieve this: `splitHsApps` unwraps `HsExpanded`. -} {- ********************************************************************* * * tcInferAppHead * * ********************************************************************* -} tcInferAppHead :: (HsExpr GhcRn, AppCtxt) -> [HsExprArg 'TcpRn] -> TcM (HsExpr GhcTc, TcSigmaType) -- Infer type of the head of an application -- i.e. the 'f' in (f e1 ... en) -- See Note [Application chains and heads] in GHC.Tc.Gen.App -- We get back a /SigmaType/ because we have special cases for -- * A bare identifier (just look it up) -- This case also covers a record selector HsRecSel -- * An expression with a type signature (e :: ty) -- See Note [Application chains and heads] in GHC.Tc.Gen.App -- -- Why do we need the arguments to infer the type of the head of the -- application? Simply to inform add_head_ctxt about whether or not -- to put push a new "In the expression..." context. (We don't push a -- new one if there are no arguments, because we already have.) -- -- Note that [] and (,,) are both HsVar: -- see Note [Empty lists] and [ExplicitTuple] in GHC.Hs.Expr -- -- NB: 'e' cannot be HsApp, HsTyApp, HsPrag, HsPar, because those -- cases are dealt with by splitHsApps. -- -- See Note [tcApp: typechecking applications] in GHC.Tc.Gen.App tcInferAppHead (fun,ctxt) args = setSrcSpan (appCtxtLoc ctxt) $ do { mb_tc_fun <- tcInferAppHead_maybe fun args ; case mb_tc_fun of Just (fun', fun_sigma) -> return (fun', fun_sigma) Nothing -> add_head_ctxt fun args $ tcInfer (tcExpr fun) } tcInferAppHead_maybe :: HsExpr GhcRn -> [HsExprArg 'TcpRn] -> TcM (Maybe (HsExpr GhcTc, TcSigmaType)) -- See Note [Application chains and heads] in GHC.Tc.Gen.App -- Returns Nothing for a complicated head tcInferAppHead_maybe fun args = case fun of HsVar _ (L _ nm) -> Just <$> tcInferId nm HsRecSel _ f -> Just <$> tcInferRecSelId f ExprWithTySig _ e hs_ty -> add_head_ctxt fun args $ Just <$> tcExprWithSig e hs_ty HsOverLit _ lit -> Just <$> tcInferOverLit lit HsSpliceE _ (HsSpliced _ _ (HsSplicedExpr e)) -> tcInferAppHead_maybe e args _ -> return Nothing add_head_ctxt :: HsExpr GhcRn -> [HsExprArg 'TcpRn] -> TcM a -> TcM a -- Don't push an expression context if the arguments are empty, -- because it has already been pushed by tcExpr add_head_ctxt fun args thing_inside | null args = thing_inside | otherwise = addExprCtxt fun thing_inside {- ********************************************************************* * * Record selectors * * ********************************************************************* -} tcInferRecSelId :: FieldOcc GhcRn -> TcM (HsExpr GhcTc, TcSigmaType) tcInferRecSelId (FieldOcc sel_name lbl) = do { sel_id <- tc_rec_sel_id ; let expr = HsRecSel noExtField (FieldOcc sel_id lbl) ; return (expr, idType sel_id) } where occ :: OccName occ = rdrNameOcc (unLoc lbl) tc_rec_sel_id :: TcM TcId -- Like tc_infer_id, but returns an Id not a HsExpr, -- so we can wrap it back up into a HsRecSel tc_rec_sel_id = do { thing <- tcLookup sel_name ; case thing of ATcId { tct_id = id } -> do { check_naughty occ id -- See Note [Local record selectors] ; check_local_id id ; return id } AGlobal (AnId id) -> do { check_naughty occ id ; return id } -- A global cannot possibly be ill-staged -- nor does it need the 'lifting' treatment -- hence no checkTh stuff here _ -> failWithTc $ TcRnUnknownMessage $ mkPlainError noHints $ ppr thing <+> text "used where a value identifier was expected" } ------------------------ -- A type signature on the argument of an ambiguous record selector or -- the record expression in an update must be "obvious", i.e. the -- outermost constructor ignoring parentheses. obviousSig :: HsExpr GhcRn -> Maybe (LHsSigWcType GhcRn) obviousSig (ExprWithTySig _ _ ty) = Just ty obviousSig (HsPar _ _ p _) = obviousSig (unLoc p) obviousSig (HsPragE _ _ p) = obviousSig (unLoc p) obviousSig _ = Nothing -- Extract the outermost TyCon of a type, if there is one; for -- data families this is the representation tycon (because that's -- where the fields live). tyConOf :: FamInstEnvs -> TcSigmaType -> Maybe TyCon tyConOf fam_inst_envs ty0 = case tcSplitTyConApp_maybe ty of Just (tc, tys) -> Just (fstOf3 (tcLookupDataFamInst fam_inst_envs tc tys)) Nothing -> Nothing where (_, _, ty) = tcSplitSigmaTy ty0 -- Variant of tyConOf that works for ExpTypes tyConOfET :: FamInstEnvs -> ExpRhoType -> Maybe TyCon tyConOfET fam_inst_envs ty0 = tyConOf fam_inst_envs =<< checkingExpType_maybe ty0 -- For an ambiguous record field, find all the candidate record -- selectors (as GlobalRdrElts) and their parents. lookupParents :: Bool -> RdrName -> RnM [(RecSelParent, GlobalRdrElt)] lookupParents is_selector rdr = do { env <- getGlobalRdrEnv -- Filter by isRecFldGRE because otherwise a non-selector variable with -- an overlapping name can get through when NoFieldSelectors is enabled. -- See Note [NoFieldSelectors] in GHC.Rename.Env. ; let all_gres = lookupGRE_RdrName' rdr env ; let gres | is_selector = filter isFieldSelectorGRE all_gres | otherwise = filter isRecFldGRE all_gres ; mapM lookupParent gres } where lookupParent :: GlobalRdrElt -> RnM (RecSelParent, GlobalRdrElt) lookupParent gre = do { id <- tcLookupId (greMangledName gre) ; case recordSelectorTyCon_maybe id of Just rstc -> return (rstc, gre) Nothing -> failWithTc (notSelector (greMangledName gre)) } fieldNotInType :: RecSelParent -> RdrName -> TcRnMessage fieldNotInType p rdr = mkTcRnNotInScope rdr $ UnknownSubordinate (text "field of type" <+> quotes (ppr p)) notSelector :: Name -> TcRnMessage notSelector field = TcRnUnknownMessage $ mkPlainError noHints $ hsep [quotes (ppr field), text "is not a record selector"] naughtyRecordSel :: OccName -> TcRnMessage naughtyRecordSel lbl = TcRnUnknownMessage $ mkPlainError noHints $ text "Cannot use record selector" <+> quotes (ppr lbl) <+> text "as a function due to escaped type variables" $$ text "Probable fix: use pattern-matching syntax instead" {- ********************************************************************* * * Expressions with a type signature expr :: type * * ********************************************************************* -} tcExprWithSig :: LHsExpr GhcRn -> LHsSigWcType (NoGhcTc GhcRn) -> TcM (HsExpr GhcTc, TcSigmaType) tcExprWithSig expr hs_ty = do { sig_info <- checkNoErrs $ -- Avoid error cascade tcUserTypeSig loc hs_ty Nothing ; (expr', poly_ty) <- tcExprSig ctxt expr sig_info ; return (ExprWithTySig noExtField expr' hs_ty, poly_ty) } where loc = getLocA (dropWildCards hs_ty) ctxt = ExprSigCtxt (lhsSigWcTypeContextSpan hs_ty) tcExprSig :: UserTypeCtxt -> LHsExpr GhcRn -> TcIdSigInfo -> TcM (LHsExpr GhcTc, TcType) tcExprSig ctxt expr (CompleteSig { sig_bndr = poly_id, sig_loc = loc }) = setSrcSpan loc $ -- Sets the location for the implication constraint do { let poly_ty = idType poly_id ; (wrap, expr') <- tcSkolemiseScoped ctxt poly_ty $ \rho_ty -> tcCheckMonoExprNC expr rho_ty ; return (mkLHsWrap wrap expr', poly_ty) } tcExprSig _ expr sig@(PartialSig { psig_name = name, sig_loc = loc }) = setSrcSpan loc $ -- Sets the location for the implication constraint do { (tclvl, wanted, (expr', sig_inst)) <- pushLevelAndCaptureConstraints $ do { sig_inst <- tcInstSig sig ; expr' <- tcExtendNameTyVarEnv (mapSnd binderVar $ sig_inst_skols sig_inst) $ tcExtendNameTyVarEnv (sig_inst_wcs sig_inst) $ tcCheckPolyExprNC expr (sig_inst_tau sig_inst) ; return (expr', sig_inst) } -- See Note [Partial expression signatures] ; let tau = sig_inst_tau sig_inst infer_mode | null (sig_inst_theta sig_inst) , isNothing (sig_inst_wcx sig_inst) = ApplyMR | otherwise = NoRestrictions ; ((qtvs, givens, ev_binds, _), residual) <- captureConstraints $ simplifyInfer tclvl infer_mode [sig_inst] [(name, tau)] wanted ; emitConstraints residual ; tau <- zonkTcType tau ; let inferred_theta = map evVarPred givens tau_tvs = tyCoVarsOfType tau ; (binders, my_theta) <- chooseInferredQuantifiers residual inferred_theta tau_tvs qtvs (Just sig_inst) ; let inferred_sigma = mkInfSigmaTy qtvs inferred_theta tau my_sigma = mkInvisForAllTys binders (mkPhiTy my_theta tau) ; wrap <- if inferred_sigma `eqType` my_sigma -- NB: eqType ignores vis. then return idHsWrapper -- Fast path; also avoids complaint when we infer -- an ambiguous type and have AllowAmbiguousType -- e..g infer x :: forall a. F a -> Int else tcSubTypeSigma ExprSigOrigin (ExprSigCtxt NoRRC) inferred_sigma my_sigma ; traceTc "tcExpSig" (ppr qtvs $$ ppr givens $$ ppr inferred_sigma $$ ppr my_sigma) ; let poly_wrap = wrap <.> mkWpTyLams qtvs <.> mkWpLams givens <.> mkWpLet ev_binds ; return (mkLHsWrap poly_wrap expr', my_sigma) } {- Note [Partial expression signatures] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Partial type signatures on expressions are easy to get wrong. But here is a guiding principile e :: ty should behave like let x :: ty x = e in x So for partial signatures we apply the MR if no context is given. So e :: IO _ apply the MR e :: _ => IO _ do not apply the MR just like in GHC.Tc.Gen.Bind.decideGeneralisationPlan This makes a difference (#11670): peek :: Ptr a -> IO CLong peek ptr = peekElemOff undefined 0 :: _ from (peekElemOff undefined 0) we get type: IO w constraints: Storable w We must NOT try to generalise over 'w' because the signature specifies no constraints so we'll complain about not being able to solve Storable w. Instead, don't generalise; then _ gets instantiated to CLong, as it should. -} {- ********************************************************************* * * Overloaded literals * * ********************************************************************* -} tcInferOverLit :: HsOverLit GhcRn -> TcM (HsExpr GhcTc, TcSigmaType) tcInferOverLit lit@(OverLit { ol_val = val , ol_ext = OverLitRn { ol_rebindable = rebindable , ol_from_fun = L loc from_name } }) = -- Desugar "3" to (fromInteger (3 :: Integer)) -- where fromInteger is gotten by looking up from_name, and -- the (3 :: Integer) is returned by mkOverLit -- Ditto the string literal "foo" to (fromString ("foo" :: String)) do { hs_lit <- mkOverLit val ; from_id <- tcLookupId from_name ; (wrap1, from_ty) <- topInstantiate (LiteralOrigin lit) (idType from_id) ; let thing = NameThing from_name mb_thing = Just thing herald = ExpectedFunTyArg thing (HsLit noAnn hs_lit) ; (wrap2, sarg_ty, res_ty) <- matchActualFunTySigma herald mb_thing (1, []) from_ty ; co <- unifyType mb_thing (hsLitType hs_lit) (scaledThing sarg_ty) ; let lit_expr = L (l2l loc) $ mkHsWrapCo co $ HsLit noAnn hs_lit from_expr = mkHsWrap (wrap2 <.> wrap1) $ HsVar noExtField (L loc from_id) witness = HsApp noAnn (L (l2l loc) from_expr) lit_expr lit' = lit { ol_ext = OverLitTc { ol_rebindable = rebindable , ol_witness = witness , ol_type = res_ty } } ; return (HsOverLit noAnn lit', res_ty) } {- ********************************************************************* * * tcInferId, tcCheckId * * ********************************************************************* -} tcCheckId :: Name -> ExpRhoType -> TcM (HsExpr GhcTc) tcCheckId name res_ty = do { (expr, actual_res_ty) <- tcInferId name ; traceTc "tcCheckId" (vcat [ppr name, ppr actual_res_ty, ppr res_ty]) ; addFunResCtxt rn_fun [] actual_res_ty res_ty $ tcWrapResultO (OccurrenceOf name) rn_fun expr actual_res_ty res_ty } where rn_fun = HsVar noExtField (noLocA name) ------------------------ tcInferId :: Name -> TcM (HsExpr GhcTc, TcSigmaType) -- Look up an occurrence of an Id -- Do not instantiate its type tcInferId id_name | id_name `hasKey` assertIdKey = do { dflags <- getDynFlags ; if gopt Opt_IgnoreAsserts dflags then tc_infer_id id_name else tc_infer_assert id_name } | otherwise = do { (expr, ty) <- tc_infer_id id_name ; traceTc "tcInferId" (ppr id_name <+> dcolon <+> ppr ty) ; return (expr, ty) } tc_infer_assert :: Name -> TcM (HsExpr GhcTc, TcSigmaType) -- Deal with an occurrence of 'assert' -- See Note [Adding the implicit parameter to 'assert'] tc_infer_assert assert_name = do { assert_error_id <- tcLookupId assertErrorName ; (wrap, id_rho) <- topInstantiate (OccurrenceOf assert_name) (idType assert_error_id) ; return (mkHsWrap wrap (HsVar noExtField (noLocA assert_error_id)), id_rho) } tc_infer_id :: Name -> TcM (HsExpr GhcTc, TcSigmaType) tc_infer_id id_name = do { thing <- tcLookup id_name ; case thing of ATcId { tct_id = id } -> do { check_local_id id ; return_id id } AGlobal (AnId id) -> return_id id -- A global cannot possibly be ill-staged -- nor does it need the 'lifting' treatment -- Hence no checkTh stuff here AGlobal (AConLike (RealDataCon con)) -> tcInferDataCon con AGlobal (AConLike (PatSynCon ps)) -> tcInferPatSyn id_name ps (tcTyThingTyCon_maybe -> Just tc) -> fail_tycon tc -- TyCon or TcTyCon ATyVar name _ -> fail_tyvar name _ -> failWithTc $ TcRnUnknownMessage $ mkPlainError noHints $ ppr thing <+> text "used where a value identifier was expected" } where fail_tycon tc = do gre <- getGlobalRdrEnv let nm = tyConName tc pprov = case lookupGRE_Name gre nm of Just gre -> nest 2 (pprNameProvenance gre) Nothing -> empty fail_with_msg dataName nm pprov fail_tyvar nm = let pprov = nest 2 (text "bound at" <+> ppr (getSrcLoc nm)) in fail_with_msg varName nm pprov fail_with_msg whatName nm pprov = do (import_errs, hints) <- get_suggestions whatName unit_state <- hsc_units <$> getTopEnv let -- TODO: unfortunate to have to convert to SDoc here. -- This should go away once we refactor ErrInfo. hint_msg = vcat $ map ppr hints import_err_msg = vcat $ map ppr import_errs info = ErrInfo { errInfoContext = pprov, errInfoSupplementary = import_err_msg $$ hint_msg } msg = TcRnMessageWithInfo unit_state $ TcRnMessageDetailed info (TcRnIncorrectNameSpace nm False) failWithTc msg get_suggestions ns = do let occ = mkOccNameFS ns (occNameFS (occName id_name)) dflags <- getDynFlags rdr_env <- getGlobalRdrEnv lcl_env <- getLocalRdrEnv imp_info <- getImports curr_mod <- getModule hpt <- getHpt return $ unknownNameSuggestions WL_Anything dflags hpt curr_mod rdr_env lcl_env imp_info (mkRdrUnqual occ) return_id id = return (HsVar noExtField (noLocA id), idType id) check_local_id :: Id -> TcM () check_local_id id = do { checkThLocalId id ; tcEmitBindingUsage $ unitUE (idName id) One } check_naughty :: OccName -> TcId -> TcM () check_naughty lbl id | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel lbl) | otherwise = return () tcInferDataCon :: DataCon -> TcM (HsExpr GhcTc, TcSigmaType) -- See Note [Typechecking data constructors] tcInferDataCon con = do { let tvbs = dataConUserTyVarBinders con tvs = binderVars tvbs theta = dataConOtherTheta con args = dataConOrigArgTys con res = dataConOrigResTy con stupid_theta = dataConStupidTheta con ; scaled_arg_tys <- mapM linear_to_poly args ; let full_theta = stupid_theta ++ theta all_arg_tys = map unrestricted full_theta ++ scaled_arg_tys -- stupid-theta must come first -- See Note [Instantiating stupid theta] ; return ( XExpr (ConLikeTc (RealDataCon con) tvs all_arg_tys) , mkInvisForAllTys tvbs $ mkPhiTy full_theta $ mkVisFunTys scaled_arg_tys res ) } where linear_to_poly :: Scaled Type -> TcM (Scaled Type) -- linear_to_poly implements point (3,4) -- of Note [Typechecking data constructors] linear_to_poly (Scaled One ty) = do { mul_var <- newFlexiTyVarTy multiplicityTy ; return (Scaled mul_var ty) } linear_to_poly scaled_ty = return scaled_ty tcInferPatSyn :: Name -> PatSyn -> TcM (HsExpr GhcTc, TcSigmaType) tcInferPatSyn id_name ps = case patSynBuilderOcc ps of Just (expr,ty) -> return (expr,ty) Nothing -> failWithTc (nonBidirectionalErr id_name) nonBidirectionalErr :: Outputable name => name -> TcRnMessage nonBidirectionalErr name = TcRnUnknownMessage $ mkPlainError noHints $ text "non-bidirectional pattern synonym" <+> quotes (ppr name) <+> text "used in an expression" {- Note [Typechecking data constructors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ As per Note [Polymorphisation of linear fields] in GHC.Core.Multiplicity, linear fields of data constructors get a polymorphic multiplicity when the data constructor is used as a term: Just :: forall {p} a. a %p -> Maybe a So at an occurrence of a data constructor we do the following, mostly in tcInferDataCon: 1. Get its type, say K :: forall (r :: RuntimeRep) (a :: TYPE r). a %1 -> T r a Note the %1: it is linear 2. We are going to return a ConLikeTc, thus: XExpr (ConLikeTc K [r,a] [Scaled p a]) :: forall (r :: RuntimeRep) (a :: TYPE r). a %p -> T r a where 'p' is a fresh multiplicity unification variable. To get the returned ConLikeTc, we allocate a fresh multiplicity variable for each linear argument, and store the type, scaled by the fresh multiplicity variable in the ConLikeTc; along with the type of the ConLikeTc. This is done by linear_to_poly. 3. If the argument is not linear (perhaps explicitly declared as non-linear by the user), don't bother with this. 4. The (ConLikeTc K [r,a] [Scaled p a]) is later desugared by GHC.HsToCore.Expr.dsConLike to: (/\r (a :: TYPE r). \(x %p :: a). K @r @a x) which has the desired type given in the previous bullet. The 'p' is the multiplicity unification variable, which will by now have been unified to something, or defaulted in `GHC.Tc.Utils.Zonk.commitFlexi`. So it won't just be an (unbound) variable. Wrinkles * Note that the [TcType] is strictly redundant anyway; those are the type variables from the dataConUserTyVarBinders of the data constructor. Similarly in the [Scaled TcType] field of ConLikeTc, the types come directly from the data constructor. The only bit that /isn't/ redundant is the fresh multiplicity variables! So an alternative would be to define ConLikeTc like this: | ConLikeTc [TcType] -- Just the multiplicity variables But then the desugarer would need to repeat some of the work done here. So for now at least ConLikeTc records this strictly-redundant info. * The lambda expression we produce in (4) can have representation-polymorphic arguments, as indeed in (/\r (a :: TYPE r). \(x %p :: a). K @r @a x), we have a lambda-bound variable x :: (a :: TYPE r). This goes against the representation polymorphism invariants given in Note [Representation polymorphism invariants] in GHC.Core. The trick is that this this lambda will always be instantiated in a way that upholds the invariants. This is achieved as follows: A. Any arguments to such lambda abstractions are guaranteed to have a fixed runtime representation. This is enforced in 'tcApp' by 'matchActualFunTySigma'. B. If there are fewer arguments than there are bound term variables, hasFixedRuntimeRep_remainingValArgs will ensure that we are still instantiating at a representation-monomorphic type, e.g. ( /\r (a :: TYPE r). \ (x %p :: a). K @r @a x) @IntRep @Int# :: Int# -> T IntRep Int# We then rely on the simple optimiser to beta reduce the lambda. * See Note [Instantiating stupid theta] for an extra wrinkle Note [Adding the implicit parameter to 'assert'] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The typechecker transforms (assert e1 e2) to (assertError e1 e2). This isn't really the Right Thing because there's no way to "undo" if you want to see the original source code in the typechecker output. We'll have fix this in due course, when we care more about being able to reconstruct the exact original program. Note [Instantiating stupid theta] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider a data type with a "stupid theta" (see Note [The stupid context] in GHC.Core.DataCon): data Ord a => T a = MkT (Maybe a) We want to generate an Ord constraint for every use of MkT; but we also want to allow visible type application, such as MkT @Int So we generate (ConLikeTc MkT [a] [Ord a, Maybe a]), with type forall a. Ord a => Maybe a -> T a Now visible type application will work fine. But we desugar the ConLikeTc to /\a \(d:Ord a) (x:Maybe a). MkT x Notice that 'd' is dropped in this desugaring. We don't need it; it was only there to generate a Wanted constraint. (That is why it is stupid.) To achieve this: * We put the stupid-thata at the front of the list of argument types in ConLikeTc * GHC.HsToCore.Expr.dsConLike generates /lambdas/ for all the arguments, but drops the stupid-theta arguments when building the /application/. Nice. -} {- ************************************************************************ * * Template Haskell checks * * ************************************************************************ -} checkThLocalId :: Id -> TcM () -- The renamer has already done checkWellStaged, -- in RnSplice.checkThLocalName, so don't repeat that here. -- Here we just add constraints for cross-stage lifting checkThLocalId id = do { mb_local_use <- getStageAndBindLevel (idName id) ; case mb_local_use of Just (top_lvl, bind_lvl, use_stage) | thLevel use_stage > bind_lvl -> checkCrossStageLifting top_lvl id use_stage _ -> return () -- Not a locally-bound thing, or -- no cross-stage link } -------------------------------------- checkCrossStageLifting :: TopLevelFlag -> Id -> ThStage -> TcM () -- If we are inside typed brackets, and (use_lvl > bind_lvl) -- we must check whether there's a cross-stage lift to do -- Examples \x -> [|| x ||] -- [|| map ||] -- -- This is similar to checkCrossStageLifting in GHC.Rename.Splice, but -- this code is applied to *typed* brackets. checkCrossStageLifting top_lvl id (Brack _ (TcPending ps_var lie_var q)) | isTopLevel top_lvl = when (isExternalName id_name) (keepAlive id_name) -- See Note [Keeping things alive for Template Haskell] in GHC.Rename.Splice | otherwise = -- Nested identifiers, such as 'x' in -- E.g. \x -> [|| h x ||] -- We must behave as if the reference to x was -- h $(lift x) -- We use 'x' itself as the splice proxy, used by -- the desugarer to stitch it all back together. -- If 'x' occurs many times we may get many identical -- bindings of the same splice proxy, but that doesn't -- matter, although it's a mite untidy. do { let id_ty = idType id ; checkTc (isTauTy id_ty) (polySpliceErr id) -- If x is polymorphic, its occurrence sites might -- have different instantiations, so we can't use plain -- 'x' as the splice proxy name. I don't know how to -- solve this, and it's probably unimportant, so I'm -- just going to flag an error for now ; lift <- if isStringTy id_ty then do { sid <- tcLookupId GHC.Builtin.Names.TH.liftStringName -- See Note [Lifting strings] ; return (HsVar noExtField (noLocA sid)) } else setConstraintVar lie_var $ -- Put the 'lift' constraint into the right LIE newMethodFromName (OccurrenceOf id_name) GHC.Builtin.Names.TH.liftName [getRuntimeRep id_ty, id_ty] -- Warning for implicit lift (#17804) ; addDetailedDiagnostic (TcRnImplicitLift id) -- Update the pending splices ; ps <- readMutVar ps_var ; let pending_splice = PendingTcSplice id_name (nlHsApp (mkLHsWrap (applyQuoteWrapper q) (noLocA lift)) (nlHsVar id)) ; writeMutVar ps_var (pending_splice : ps) ; return () } where id_name = idName id checkCrossStageLifting _ _ _ = return () polySpliceErr :: Id -> TcRnMessage polySpliceErr id = TcRnUnknownMessage $ mkPlainError noHints $ text "Can't splice the polymorphic local variable" <+> quotes (ppr id) {- Note [Lifting strings] ~~~~~~~~~~~~~~~~~~~~~~ If we see $(... [| s |] ...) where s::String, we don't want to generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc. So this conditional short-circuits the lifting mechanism to generate (liftString "xy") in that case. I didn't want to use overlapping instances for the Lift class in TH.Syntax, because that can lead to overlapping-instance errors in a polymorphic situation. If this check fails (which isn't impossible) we get another chance; see Note [Converting strings] in Convert.hs Note [Local record selectors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Record selectors for TyCons in this module are ordinary local bindings, which show up as ATcIds rather than AGlobals. So we need to check for naughtiness in both branches. c.f. GHC.Tc.TyCl.Utils.mkRecSelBinds. -} {- ********************************************************************* * * Error reporting for function result mis-matches * * ********************************************************************* -} addFunResCtxt :: HsExpr GhcRn -> [HsExprArg 'TcpRn] -> TcType -> ExpRhoType -> TcM a -> TcM a -- When we have a mis-match in the return type of a function -- try to give a helpful message about too many/few arguments -- But not in generated code, where we don't want -- to mention internal (rebindable syntax) function names addFunResCtxt fun args fun_res_ty env_ty thing_inside = addLandmarkErrCtxtM (\env -> (env, ) <$> mk_msg) thing_inside -- NB: use a landmark error context, so that an empty context -- doesn't suppress some more useful context where mk_msg = do { mb_env_ty <- readExpType_maybe env_ty -- by the time the message is rendered, the ExpType -- will be filled in (except if we're debugging) ; fun_res' <- zonkTcType fun_res_ty ; env' <- case mb_env_ty of Just env_ty -> zonkTcType env_ty Nothing -> do { dumping <- doptM Opt_D_dump_tc_trace ; massert dumping ; newFlexiTyVarTy liftedTypeKind } ; let -- See Note [Splitting nested sigma types in mismatched -- function types] (_, _, fun_tau) = tcSplitNestedSigmaTys fun_res' (_, _, env_tau) = tcSplitNestedSigmaTys env' -- env_ty is an ExpRhoTy, but with simple subsumption it -- is not deeply skolemised, so still use tcSplitNestedSigmaTys (args_fun, res_fun) = tcSplitFunTys fun_tau (args_env, res_env) = tcSplitFunTys env_tau n_fun = length args_fun n_env = length args_env info | -- Check for too few args -- fun_tau = a -> b, res_tau = Int n_fun > n_env , not_fun res_env = text "Probable cause:" <+> quotes (ppr fun) <+> text "is applied to too few arguments" | -- Check for too many args -- fun_tau = a -> Int, res_tau = a -> b -> c -> d -- The final guard suppresses the message when there -- aren't enough args to drop; eg. the call is (f e1) n_fun < n_env , not_fun res_fun , (n_fun + count isValArg args) >= n_env -- Never suggest that a naked variable is -- applied to too many args! = text "Possible cause:" <+> quotes (ppr fun) <+> text "is applied to too many arguments" | otherwise = Outputable.empty ; return info } not_fun ty -- ty is definitely not an arrow type, -- and cannot conceivably become one = case tcSplitTyConApp_maybe ty of Just (tc, _) -> isAlgTyCon tc Nothing -> False {- Note [Splitting nested sigma types in mismatched function types] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When one applies a function to too few arguments, GHC tries to determine this fact if possible so that it may give a helpful error message. It accomplishes this by checking if the type of the applied function has more argument types than supplied arguments. Previously, GHC computed the number of argument types through tcSplitSigmaTy. This is incorrect in the face of nested foralls, however! This caused Ticket #13311, for instance: f :: forall a. (Monoid a) => Int -> forall b. (Monoid b) => Maybe a -> Maybe b If one uses `f` like so: do { f; putChar 'a' } Then tcSplitSigmaTy will decompose the type of `f` into: Tyvars: [a] Context: (Monoid a) Argument types: [] Return type: Int -> forall b. Monoid b => Maybe a -> Maybe b That is, it will conclude that there are *no* argument types, and since `f` was given no arguments, it won't print a helpful error message. On the other hand, tcSplitNestedSigmaTys correctly decomposes `f`'s type down to: Tyvars: [a, b] Context: (Monoid a, Monoid b) Argument types: [Int, Maybe a] Return type: Maybe b So now GHC recognizes that `f` has one more argument type than it was actually provided. Notice that tcSplitNestedSigmaTys looks through function arrows too, regardless of simple/deep subsumption. Here we are concerned only whether there is a mis-match in the number of value arguments. -} {- ********************************************************************* * * Misc utility functions * * ********************************************************************* -} addExprCtxt :: HsExpr GhcRn -> TcRn a -> TcRn a addExprCtxt e thing_inside = case e of HsUnboundVar {} -> thing_inside _ -> addErrCtxt (exprCtxt e) thing_inside -- The HsUnboundVar special case addresses situations like -- f x = _ -- when we don't want to say "In the expression: _", -- because it is mentioned in the error message itself exprCtxt :: HsExpr GhcRn -> SDoc exprCtxt expr = hang (text "In the expression:") 2 (ppr (stripParensHsExpr expr))