{- % (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 -} {-# LANGUAGE CPP, TupleSections, ScopedTypeVariables #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE TypeFamilies, DataKinds, TypeApplications #-} {-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow] -- in module GHC.Hs.Extension {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-} module GHC.Tc.Gen.Expr ( tcCheckPolyExpr, tcCheckMonoExpr, tcCheckMonoExprNC, tcMonoExpr, tcMonoExprNC, tcInferSigma, tcInferRho, tcInferRhoNC, tcExpr, tcSyntaxOp, tcSyntaxOpGen, SyntaxOpType(..), synKnownType, tcCheckId, addAmbiguousNameErr, getFixedTyVars ) where #include "HsVersions.h" import GHC.Prelude import {-# SOURCE #-} GHC.Tc.Gen.Splice( tcSpliceExpr, tcTypedBracket, tcUntypedBracket ) import GHC.Builtin.Names.TH( liftStringName, liftName ) import GHC.Hs import GHC.Tc.Utils.Zonk import GHC.Tc.Utils.Monad import GHC.Tc.Utils.Unify import GHC.Types.Basic import GHC.Core.Multiplicity import GHC.Core.UsageEnv import GHC.Tc.Utils.Instantiate import GHC.Tc.Gen.Bind ( chooseInferredQuantifiers, tcLocalBinds ) import GHC.Tc.Gen.Sig ( tcUserTypeSig, tcInstSig ) import GHC.Tc.Solver ( simplifyInfer, InferMode(..) ) import GHC.Tc.Instance.Family ( tcGetFamInstEnvs, tcLookupDataFamInst, tcLookupDataFamInst_maybe ) import GHC.Core.FamInstEnv ( FamInstEnvs ) import GHC.Rename.Env ( addUsedGRE ) import GHC.Rename.Utils ( addNameClashErrRn, unknownSubordinateErr ) import GHC.Tc.Utils.Env import GHC.Tc.Gen.Arrow import GHC.Tc.Gen.Match import GHC.Tc.Gen.HsType import GHC.Tc.TyCl.PatSyn ( tcPatSynBuilderOcc, nonBidirectionalErr ) import GHC.Tc.Gen.Pat import GHC.Tc.Utils.TcMType import GHC.Tc.Types.Origin import GHC.Tc.Utils.TcType as TcType import GHC.Types.Id import GHC.Types.Id.Info import GHC.Core.ConLike import GHC.Core.DataCon import GHC.Core.PatSyn import GHC.Types.Name import GHC.Types.Name.Env import GHC.Types.Name.Set import GHC.Types.Name.Reader import GHC.Core.TyCon import GHC.Core.TyCo.Rep import GHC.Core.TyCo.Ppr import GHC.Core.TyCo.Subst (substTyWithInScope) import GHC.Core.Type import GHC.Tc.Types.Evidence import GHC.Types.Var.Set import GHC.Builtin.Types import GHC.Builtin.PrimOps( tagToEnumKey ) import GHC.Builtin.Names import GHC.Driver.Session import GHC.Types.SrcLoc import GHC.Utils.Misc import GHC.Types.Var.Env ( emptyTidyEnv, mkInScopeSet ) import GHC.Data.List.SetOps import GHC.Data.Maybe import GHC.Utils.Outputable as Outputable import GHC.Data.FastString import Control.Monad import GHC.Core.Class(classTyCon) import GHC.Types.Unique.Set ( nonDetEltsUniqSet ) import qualified GHC.LanguageExtensions as LangExt import Data.Function import Data.List (partition, sortBy, groupBy, intersect) import qualified Data.Set as Set {- ************************************************************************ * * \subsection{Main wrappers} * * ************************************************************************ -} tcCheckPolyExpr, tcCheckPolyExprNC :: LHsExpr GhcRn -- Expression to type check -> TcSigmaType -- Expected type (could be a polytype) -> TcM (LHsExpr GhcTc) -- Generalised expr with expected type -- tcCheckPolyExpr is a convenient place (frequent but not too frequent) -- place to add context information. -- The NC version does not do so, usually because the caller wants -- to do so himself. tcCheckPolyExpr expr res_ty = tcPolyExpr expr (mkCheckExpType res_ty) tcCheckPolyExprNC expr res_ty = tcPolyExprNC expr (mkCheckExpType res_ty) -- These versions take an ExpType tcPolyExpr, tcPolyExprNC :: LHsExpr GhcRn -> ExpSigmaType -> TcM (LHsExpr GhcTc) tcPolyExpr expr res_ty = addExprCtxt expr $ do { traceTc "tcPolyExpr" (ppr res_ty) ; tcPolyExprNC expr res_ty } tcPolyExprNC (L loc expr) res_ty = set_loc_and_ctxt loc expr $ do { traceTc "tcPolyExprNC" (ppr res_ty) ; (wrap, expr') <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty -> tcExpr expr res_ty ; return $ L loc (mkHsWrap wrap expr') } where -- See Note [Rebindable syntax and HsExpansion), which describes -- the logic behind this location/context tweaking. set_loc_and_ctxt l e m = do inGenCode <- inGeneratedCode if inGenCode && not (isGeneratedSrcSpan l) then setSrcSpan l $ addExprCtxt (L l e) m else setSrcSpan l m --------------- tcInferSigma :: LHsExpr GhcRn -> TcM (LHsExpr GhcTc, TcSigmaType) -- Used by tcRnExpr to implement GHCi :type -- It goes against the principle of eager instantiation, -- so we expect very very few calls to this function -- Most clients will want tcInferRho tcInferSigma le@(L loc expr) = addExprCtxt le $ setSrcSpan loc $ do { (fun, args, ty) <- tcInferApp expr ; return (L loc (applyHsArgs fun args), ty) } --------------- tcCheckMonoExpr, tcCheckMonoExprNC :: LHsExpr GhcRn -- Expression to type check -> TcRhoType -- Expected type -- Definitely no foralls at the top -> TcM (LHsExpr GhcTc) tcCheckMonoExpr expr res_ty = tcMonoExpr expr (mkCheckExpType res_ty) tcCheckMonoExprNC expr res_ty = tcMonoExprNC expr (mkCheckExpType res_ty) tcMonoExpr, tcMonoExprNC :: LHsExpr GhcRn -- Expression to type check -> ExpRhoType -- Expected type -- Definitely no foralls at the top -> TcM (LHsExpr GhcTc) tcMonoExpr expr res_ty = addExprCtxt expr $ tcMonoExprNC expr res_ty tcMonoExprNC (L loc expr) res_ty = setSrcSpan loc $ do { expr' <- tcExpr expr res_ty ; return (L loc expr') } --------------- tcInferRho, tcInferRhoNC :: LHsExpr GhcRn -> TcM (LHsExpr GhcTc, TcRhoType) -- Infer a *rho*-type. The return type is always instantiated. tcInferRho le = addExprCtxt le (tcInferRhoNC le) tcInferRhoNC (L loc expr) = setSrcSpan loc $ do { (expr', rho) <- tcInfer (tcExpr expr) ; return (L loc expr', rho) } {- ********************************************************************* * * tcExpr: the main expression typechecker * * ********************************************************************* -} tcLExpr, tcLExprNC :: LHsExpr GhcRn -- Expression to type check -> ExpRhoType -- Expected type -- Definitely no foralls at the top -> TcM (LHsExpr GhcTc) tcLExpr expr res_ty = setSrcSpan (getLoc expr) $ addExprCtxt expr (tcLExprNC expr res_ty) tcLExprNC (L loc expr) res_ty = setSrcSpan loc $ do { expr' <- tcExpr expr res_ty ; return (L loc expr') } tcExpr :: HsExpr GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc) tcExpr (HsVar _ (L _ name)) res_ty = tcCheckId name res_ty tcExpr e@(HsUnboundVar _ uv) res_ty = tcUnboundId e uv res_ty tcExpr e@(HsApp {}) res_ty = tcApp e res_ty tcExpr e@(HsAppType {}) res_ty = tcApp e res_ty tcExpr e@(HsLit x lit) res_ty = do { let lit_ty = hsLitType lit ; tcWrapResult e (HsLit x (convertLit lit)) lit_ty res_ty } tcExpr (HsPar x expr) res_ty = do { expr' <- tcLExprNC expr res_ty ; return (HsPar x expr') } tcExpr (HsPragE x prag expr) res_ty = do { expr' <- tcLExpr expr res_ty ; return (HsPragE x (tcExprPrag prag) expr') } tcExpr (HsOverLit x lit) res_ty = do { lit' <- newOverloadedLit lit res_ty ; return (HsOverLit x lit') } tcExpr (NegApp x expr neg_expr) res_ty = do { (expr', neg_expr') <- tcSyntaxOp NegateOrigin neg_expr [SynAny] res_ty $ \[arg_ty] [arg_mult] -> tcScalingUsage arg_mult $ tcLExpr expr (mkCheckExpType arg_ty) ; return (NegApp x expr' neg_expr') } tcExpr e@(HsIPVar _ x) res_ty = do { {- Implicit parameters must have a *tau-type* not a type scheme. We enforce this by creating a fresh type variable as its type. (Because res_ty may not be a tau-type.) -} ip_ty <- newOpenFlexiTyVarTy ; let ip_name = mkStrLitTy (hsIPNameFS x) ; ipClass <- tcLookupClass ipClassName ; ip_var <- emitWantedEvVar origin (mkClassPred ipClass [ip_name, ip_ty]) ; tcWrapResult e (fromDict ipClass ip_name ip_ty (HsVar noExtField (noLoc ip_var))) ip_ty res_ty } where -- Coerces a dictionary for `IP "x" t` into `t`. fromDict ipClass x ty = mkHsWrap $ mkWpCastR $ unwrapIP $ mkClassPred ipClass [x,ty] origin = IPOccOrigin x tcExpr e@(HsOverLabel _ mb_fromLabel l) res_ty = do { -- See Note [Type-checking overloaded labels] loc <- getSrcSpanM ; case mb_fromLabel of Just fromLabel -> tcExpr (applyFromLabel loc fromLabel) res_ty Nothing -> do { isLabelClass <- tcLookupClass isLabelClassName ; alpha <- newFlexiTyVarTy liftedTypeKind ; let pred = mkClassPred isLabelClass [lbl, alpha] ; loc <- getSrcSpanM ; var <- emitWantedEvVar origin pred ; tcWrapResult e (fromDict pred (HsVar noExtField (L loc var))) alpha res_ty } } where -- Coerces a dictionary for `IsLabel "x" t` into `t`, -- or `HasField "x" r a into `r -> a`. fromDict pred = mkHsWrap $ mkWpCastR $ unwrapIP pred origin = OverLabelOrigin l lbl = mkStrLitTy l applyFromLabel loc fromLabel = HsAppType noExtField (L loc (HsVar noExtField (L loc fromLabel))) (mkEmptyWildCardBndrs (L loc (HsTyLit noExtField (HsStrTy NoSourceText l)))) tcExpr (HsLam x match) res_ty = do { (wrap, match') <- tcMatchLambda herald match_ctxt match res_ty ; return (mkHsWrap wrap (HsLam x match')) } where match_ctxt = MC { mc_what = LambdaExpr, mc_body = tcBody } herald = sep [ text "The lambda expression" <+> quotes (pprSetDepth (PartWay 1) $ pprMatches match), -- The pprSetDepth makes the abstraction print briefly text "has"] tcExpr e@(HsLamCase x matches) res_ty = do { (wrap, matches') <- tcMatchLambda msg match_ctxt matches res_ty -- The laziness annotation is because we don't want to fail here -- if there are multiple arguments ; return (mkHsWrap wrap $ HsLamCase x matches') } where msg = sep [ text "The function" <+> quotes (ppr e) , text "requires"] match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody } tcExpr e@(ExprWithTySig _ expr hs_ty) res_ty = do { (expr', poly_ty) <- tcExprWithSig expr hs_ty ; tcWrapResult e expr' poly_ty res_ty } {- Note [Type-checking overloaded labels] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Recall that we have module GHC.OverloadedLabels where class IsLabel (x :: Symbol) a where fromLabel :: a We translate `#foo` to `fromLabel @"foo"`, where we use * the in-scope `fromLabel` if `RebindableSyntax` is enabled; or if not * `GHC.OverloadedLabels.fromLabel`. In the `RebindableSyntax` case, the renamer will have filled in the first field of `HsOverLabel` with the `fromLabel` function to use, and we simply apply it to the appropriate visible type argument. In the `OverloadedLabels` case, when we see an overloaded label like `#foo`, we generate a fresh variable `alpha` for the type and emit an `IsLabel "foo" alpha` constraint. Because the `IsLabel` class has a single method, it is represented by a newtype, so we can coerce `IsLabel "foo" alpha` to `alpha` (just like for implicit parameters). -} {- ************************************************************************ * * Infix operators and sections * * ************************************************************************ Note [Left sections] ~~~~~~~~~~~~~~~~~~~~ Left sections, like (4 *), are equivalent to \ x -> (*) 4 x, or, if PostfixOperators is enabled, just (*) 4 With PostfixOperators we don't actually require the function to take two arguments at all. For example, (x `not`) means (not x); you get postfix operators! Not Haskell 98, but it's less work and kind of useful. Note [Typing rule for ($)] ~~~~~~~~~~~~~~~~~~~~~~~~~~ People write runST $ blah so much, where runST :: (forall s. ST s a) -> a that I have finally given in and written a special type-checking rule just for saturated applications of ($). * Infer the type of the first argument * Decompose it; should be of form (arg2_ty -> res_ty), where arg2_ty might be a polytype * Use arg2_ty to typecheck arg2 -} tcExpr expr@(OpApp fix arg1 op arg2) res_ty | (L loc (HsVar _ (L lv op_name))) <- op , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)] = do { traceTc "Application rule" (ppr op) ; (arg1', arg1_ty) <- addErrCtxt (funAppCtxt op arg1 1) $ tcInferRhoNC arg1 ; let doc = text "The first argument of ($) takes" orig1 = lexprCtOrigin arg1 ; (wrap_arg1, [arg2_sigma], op_res_ty) <- matchActualFunTysRho doc orig1 (Just (unLoc arg1)) 1 arg1_ty ; mult_wrap <- tcSubMult AppOrigin Many (scaledMult arg2_sigma) -- See Note [Wrapper returned from tcSubMult] in GHC.Tc.Utils.Unify. -- -- When ($) becomes multiplicity-polymorphic, then the above check will -- need to go. But in the meantime, it would produce ill-typed -- desugared code to accept linear functions to the left of a ($). -- We have (arg1 $ arg2) -- So: arg1_ty = arg2_ty -> op_res_ty -- where arg2_sigma maybe polymorphic; that's the point ; arg2' <- tcArg nl_op arg2 arg2_sigma 2 -- Make sure that the argument type has kind '*' -- ($) :: forall (r:RuntimeRep) (a:*) (b:TYPE r). (a->b) -> a -> b -- Eg we do not want to allow (D# $ 4.0#) #5570 -- (which gives a seg fault) ; _ <- unifyKind (Just (XHsType $ NHsCoreTy (scaledThing arg2_sigma))) (tcTypeKind (scaledThing arg2_sigma)) liftedTypeKind -- Ignore the evidence. arg2_sigma must have type * or #, -- because we know (arg2_sigma -> op_res_ty) is well-kinded -- (because otherwise matchActualFunTysRho would fail) -- So this 'unifyKind' will either succeed with Refl, or will -- produce an insoluble constraint * ~ #, which we'll report later. -- NB: unlike the argument type, the *result* type, op_res_ty can -- have any kind (#8739), so we don't need to check anything for that ; op_id <- tcLookupId op_name ; let op' = L loc (mkHsWrap (mkWpTyApps [ getRuntimeRep op_res_ty , scaledThing arg2_sigma , op_res_ty]) (HsVar noExtField (L lv op_id))) -- arg1' :: arg1_ty -- wrap_arg1 :: arg1_ty "->" (arg2_sigma -> op_res_ty) -- op' :: (a2_ty -> op_res_ty) -> a2_ty -> op_res_ty expr' = OpApp fix (mkLHsWrap (wrap_arg1 <.> mult_wrap) arg1') op' arg2' ; tcWrapResult expr expr' op_res_ty res_ty } | L loc (HsRecFld _ (Ambiguous _ lbl)) <- op , Just sig_ty <- obviousSig (unLoc arg1) -- See Note [Disambiguating record fields] = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty ; sel_name <- disambiguateSelector lbl sig_tc_ty ; let op' = L loc (HsRecFld noExtField (Unambiguous sel_name lbl)) ; tcExpr (OpApp fix arg1 op' arg2) res_ty } | otherwise = do { traceTc "Non Application rule" (ppr op) ; (op', op_ty) <- tcInferRhoNC op ; (wrap_fun, [arg1_ty, arg2_ty], op_res_ty) <- matchActualFunTysRho (mk_op_msg op) fn_orig (Just (unLoc op)) 2 op_ty -- You might think we should use tcInferApp here, but there is -- too much impedance-matching, because tcApp may return wrappers as -- well as type-checked arguments. ; arg1' <- tcArg nl_op arg1 arg1_ty 1 ; arg2' <- tcArg nl_op arg2 arg2_ty 2 ; let expr' = OpApp fix arg1' (mkLHsWrap wrap_fun op') arg2' ; tcWrapResult expr expr' op_res_ty res_ty } where fn_orig = exprCtOrigin nl_op nl_op = unLoc op -- Right sections, equivalent to \ x -> x `op` expr, or -- \ x -> op x expr tcExpr expr@(SectionR x op arg2) res_ty = do { (op', op_ty) <- tcInferRhoNC op ; (wrap_fun, [Scaled arg1_mult arg1_ty, arg2_ty], op_res_ty) <- matchActualFunTysRho (mk_op_msg op) fn_orig (Just (unLoc op)) 2 op_ty ; arg2' <- tcArg (unLoc op) arg2 arg2_ty 2 ; let expr' = SectionR x (mkLHsWrap wrap_fun op') arg2' act_res_ty = mkVisFunTy arg1_mult arg1_ty op_res_ty ; tcWrapResultMono expr expr' act_res_ty res_ty } where fn_orig = lexprCtOrigin op -- It's important to use the origin of 'op', so that call-stacks -- come out right; they are driven by the OccurrenceOf CtOrigin -- See #13285 tcExpr expr@(SectionL x arg1 op) res_ty = do { (op', op_ty) <- tcInferRhoNC op ; dflags <- getDynFlags -- Note [Left sections] ; let n_reqd_args | xopt LangExt.PostfixOperators dflags = 1 | otherwise = 2 ; (wrap_fn, (arg1_ty:arg_tys), op_res_ty) <- matchActualFunTysRho (mk_op_msg op) fn_orig (Just (unLoc op)) n_reqd_args op_ty ; arg1' <- tcArg (unLoc op) arg1 arg1_ty 1 ; let expr' = SectionL x arg1' (mkLHsWrap wrap_fn op') act_res_ty = mkVisFunTys arg_tys op_res_ty ; tcWrapResultMono expr expr' act_res_ty res_ty } where fn_orig = lexprCtOrigin op -- It's important to use the origin of 'op', so that call-stacks -- come out right; they are driven by the OccurrenceOf CtOrigin -- See #13285 tcExpr expr@(ExplicitTuple x tup_args boxity) res_ty | all tupArgPresent tup_args = do { let arity = length tup_args tup_tc = tupleTyCon boxity arity -- NB: tupleTyCon doesn't flatten 1-tuples -- See Note [Don't flatten tuples from HsSyn] in GHC.Core.Make ; res_ty <- expTypeToType res_ty ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty -- Unboxed tuples have RuntimeRep vars, which we -- don't care about here -- See Note [Unboxed tuple RuntimeRep vars] in GHC.Core.TyCon ; let arg_tys' = case boxity of Unboxed -> drop arity arg_tys Boxed -> arg_tys ; tup_args1 <- tcTupArgs tup_args arg_tys' ; return $ mkHsWrapCo coi (ExplicitTuple x tup_args1 boxity) } | otherwise = -- The tup_args are a mixture of Present and Missing (for tuple sections) do { let arity = length tup_args ; arg_tys <- case boxity of { Boxed -> newFlexiTyVarTys arity liftedTypeKind ; Unboxed -> replicateM arity newOpenFlexiTyVarTy } -- Handle tuple sections where ; tup_args1 <- tcTupArgs tup_args arg_tys ; let expr' = ExplicitTuple x tup_args1 boxity missing_tys = [Scaled mult ty | (L _ (Missing (Scaled mult _)), ty) <- zip tup_args1 arg_tys] -- See Note [Linear fields generalization] act_res_ty = mkVisFunTys missing_tys (mkTupleTy1 boxity arg_tys) -- See Note [Don't flatten tuples from HsSyn] in GHC.Core.Make ; traceTc "ExplicitTuple" (ppr act_res_ty $$ ppr res_ty) ; tcWrapResultMono expr expr' act_res_ty res_ty } tcExpr (ExplicitSum _ alt arity expr) res_ty = do { let sum_tc = sumTyCon arity ; res_ty <- expTypeToType res_ty ; (coi, arg_tys) <- matchExpectedTyConApp sum_tc res_ty ; -- Drop levity vars, we don't care about them here let arg_tys' = drop arity arg_tys ; expr' <- tcCheckPolyExpr expr (arg_tys' `getNth` (alt - 1)) ; return $ mkHsWrapCo coi (ExplicitSum arg_tys' alt arity expr' ) } -- This will see the empty list only when -XOverloadedLists. -- See Note [Empty lists] in GHC.Hs.Expr. tcExpr (ExplicitList _ witness exprs) res_ty = case witness of Nothing -> do { res_ty <- expTypeToType res_ty ; (coi, elt_ty) <- matchExpectedListTy res_ty ; exprs' <- mapM (tc_elt elt_ty) exprs ; return $ mkHsWrapCo coi $ ExplicitList elt_ty Nothing exprs' } Just fln -> do { ((exprs', elt_ty), fln') <- tcSyntaxOp ListOrigin fln [synKnownType intTy, SynList] res_ty $ \ [elt_ty] [_int_mul, list_mul] -> -- We ignore _int_mul because the integer (first -- argument of fromListN) is statically known: it -- is desugared to a literal. Therefore there is -- no variable of which to scale the usage in that -- first argument, and `_int_mul` is completely -- free in this expression. do { exprs' <- mapM (tcScalingUsage list_mul . tc_elt elt_ty) exprs ; return (exprs', elt_ty) } ; return $ ExplicitList elt_ty (Just fln') exprs' } where tc_elt elt_ty expr = tcCheckPolyExpr expr elt_ty {- ************************************************************************ * * Let, case, if, do * * ************************************************************************ -} tcExpr (HsLet x (L l binds) expr) res_ty = do { (binds', expr') <- tcLocalBinds binds $ tcLExpr expr res_ty ; return (HsLet x (L l binds') expr') } tcExpr (HsCase x scrut matches) res_ty = do { -- We used to typecheck the case alternatives first. -- The case patterns tend to give good type info to use -- when typechecking the scrutinee. For example -- case (map f) of -- (x:xs) -> ... -- will report that map is applied to too few arguments -- -- But now, in the GADT world, we need to typecheck the scrutinee -- first, to get type info that may be refined in the case alternatives let mult = Many -- There is not yet syntax or inference mechanism for case -- expressions to be anything else than unrestricted. -- Typecheck the scrutinee. We use tcInferRho but tcInferSigma -- would also be possible (tcMatchesCase accepts sigma-types) -- Interesting litmus test: do these two behave the same? -- case id of {..} -- case (\v -> v) of {..} -- This design choice is discussed in #17790 ; (scrut', scrut_ty) <- tcScalingUsage mult $ tcInferRho scrut ; traceTc "HsCase" (ppr scrut_ty) ; matches' <- tcMatchesCase match_ctxt (Scaled mult scrut_ty) matches res_ty ; return (HsCase x scrut' matches') } where match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody } tcExpr (HsIf x pred b1 b2) res_ty = do { pred' <- tcLExpr pred (mkCheckExpType boolTy) ; (u1,b1') <- tcCollectingUsage $ tcLExpr b1 res_ty ; (u2,b2') <- tcCollectingUsage $ tcLExpr b2 res_ty ; tcEmitBindingUsage (supUE u1 u2) ; return (HsIf x pred' b1' b2') } tcExpr (HsMultiIf _ alts) res_ty = do { alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts ; res_ty <- readExpType res_ty ; return (HsMultiIf res_ty alts') } where match_ctxt = MC { mc_what = IfAlt, mc_body = tcBody } tcExpr (HsDo _ do_or_lc stmts) res_ty = do { expr' <- tcDoStmts do_or_lc stmts res_ty ; return expr' } tcExpr (HsProc x pat cmd) res_ty = do { (pat', cmd', coi) <- tcProc pat cmd res_ty ; return $ mkHsWrapCo coi (HsProc x pat' cmd') } -- Typechecks the static form and wraps it with a call to 'fromStaticPtr'. -- See Note [Grand plan for static forms] in GHC.Iface.Tidy.StaticPtrTable for an overview. -- To type check -- (static e) :: p a -- we want to check (e :: a), -- and wrap (static e) in a call to -- fromStaticPtr :: IsStatic p => StaticPtr a -> p a tcExpr (HsStatic fvs expr) res_ty = do { res_ty <- expTypeToType res_ty ; (co, (p_ty, expr_ty)) <- matchExpectedAppTy res_ty ; (expr', lie) <- captureConstraints $ addErrCtxt (hang (text "In the body of a static form:") 2 (ppr expr) ) $ tcCheckPolyExprNC expr expr_ty -- Check that the free variables of the static form are closed. -- It's OK to use nonDetEltsUniqSet here as the only side effects of -- checkClosedInStaticForm are error messages. ; mapM_ checkClosedInStaticForm $ nonDetEltsUniqSet fvs -- Require the type of the argument to be Typeable. -- The evidence is not used, but asking the constraint ensures that -- the current implementation is as restrictive as future versions -- of the StaticPointers extension. ; typeableClass <- tcLookupClass typeableClassName ; _ <- emitWantedEvVar StaticOrigin $ mkTyConApp (classTyCon typeableClass) [liftedTypeKind, expr_ty] -- Insert the constraints of the static form in a global list for later -- validation. ; emitStaticConstraints lie -- Wrap the static form with the 'fromStaticPtr' call. ; fromStaticPtr <- newMethodFromName StaticOrigin fromStaticPtrName [p_ty] ; let wrap = mkWpTyApps [expr_ty] ; loc <- getSrcSpanM ; return $ mkHsWrapCo co $ HsApp noExtField (L loc $ mkHsWrap wrap fromStaticPtr) (L loc (HsStatic fvs expr')) } {- ************************************************************************ * * Record construction and update * * ************************************************************************ -} tcExpr expr@(RecordCon { rcon_con_name = L loc con_name , rcon_flds = rbinds }) res_ty = do { con_like <- tcLookupConLike con_name -- Check for missing fields ; checkMissingFields con_like rbinds ; (con_expr, con_sigma) <- tcInferId con_name ; (con_wrap, con_tau) <- topInstantiate orig con_sigma -- a shallow instantiation should really be enough for -- a data constructor. ; let arity = conLikeArity con_like Right (arg_tys, actual_res_ty) = tcSplitFunTysN arity con_tau ; case conLikeWrapId_maybe con_like of { Nothing -> nonBidirectionalErr (conLikeName con_like) ; Just con_id -> do { rbinds' <- tcRecordBinds con_like (map scaledThing arg_tys) rbinds -- It is currently not possible for a record to have -- multiplicities. When they do, `tcRecordBinds` will take -- scaled types instead. Meanwhile, it's safe to take -- `scaledThing` above, as we know all the multiplicities are -- Many. ; let rcon_tc = RecordConTc { rcon_con_like = con_like , rcon_con_expr = mkHsWrap con_wrap con_expr } expr' = RecordCon { rcon_ext = rcon_tc , rcon_con_name = L loc con_id , rcon_flds = rbinds' } ; tcWrapResultMono expr expr' actual_res_ty res_ty } } } where orig = OccurrenceOf con_name {- Note [Type of a record update] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The main complication with RecordUpd is that we need to explicitly handle the *non-updated* fields. Consider: data T a b c = MkT1 { fa :: a, fb :: (b,c) } | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c } | MkT3 { fd :: a } upd :: T a b c -> (b',c) -> T a b' c upd t x = t { fb = x} The result type should be (T a b' c) not (T a b c), because 'b' *is not* mentioned in a non-updated field not (T a b' c'), because 'c' *is* mentioned in a non-updated field NB that it's not good enough to look at just one constructor; we must look at them all; cf #3219 After all, upd should be equivalent to: upd t x = case t of MkT1 p q -> MkT1 p x MkT2 a b -> MkT2 p b MkT3 d -> error ... So we need to give a completely fresh type to the result record, and then constrain it by the fields that are *not* updated ("p" above). We call these the "fixed" type variables, and compute them in getFixedTyVars. Note that because MkT3 doesn't contain all the fields being updated, its RHS is simply an error, so it doesn't impose any type constraints. Hence the use of 'relevant_cont'. Note [Implicit type sharing] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ We also take into account any "implicit" non-update fields. For example data T a b where { MkT { f::a } :: T a a; ... } So the "real" type of MkT is: forall ab. (a~b) => a -> T a b Then consider upd t x = t { f=x } We infer the type upd :: T a b -> a -> T a b upd (t::T a b) (x::a) = case t of { MkT (co:a~b) (_:a) -> MkT co x } We can't give it the more general type upd :: T a b -> c -> T c b Note [Criteria for update] ~~~~~~~~~~~~~~~~~~~~~~~~~~ We want to allow update for existentials etc, provided the updated field isn't part of the existential. For example, this should be ok. data T a where { MkT { f1::a, f2::b->b } :: T a } f :: T a -> b -> T b f t b = t { f1=b } The criterion we use is this: The types of the updated fields mention only the universally-quantified type variables of the data constructor NB: this is not (quite) the same as being a "naughty" record selector (See Note [Naughty record selectors]) in GHC.Tc.TyCl), at least in the case of GADTs. Consider data T a where { MkT :: { f :: a } :: T [a] } Then f is not "naughty" because it has a well-typed record selector. But we don't allow updates for 'f'. (One could consider trying to allow this, but it makes my head hurt. Badly. And no one has asked for it.) In principle one could go further, and allow g :: T a -> T a g t = t { f2 = \x -> x } because the expression is polymorphic...but that seems a bridge too far. Note [Data family example] ~~~~~~~~~~~~~~~~~~~~~~~~~~ data instance T (a,b) = MkT { x::a, y::b } ---> data :TP a b = MkT { a::a, y::b } coTP a b :: T (a,b) ~ :TP a b Suppose r :: T (t1,t2), e :: t3 Then r { x=e } :: T (t3,t1) ---> case r |> co1 of MkT x y -> MkT e y |> co2 where co1 :: T (t1,t2) ~ :TP t1 t2 co2 :: :TP t3 t2 ~ T (t3,t2) The wrapping with co2 is done by the constructor wrapper for MkT Outgoing invariants ~~~~~~~~~~~~~~~~~~~ In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys): * cons are the data constructors to be updated * in_inst_tys, out_inst_tys have same length, and instantiate the *representation* tycon of the data cons. In Note [Data family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2] Note [Mixed Record Field Updates] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider the following pattern synonym. data MyRec = MyRec { foo :: Int, qux :: String } pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2} This allows updates such as the following updater :: MyRec -> MyRec updater a = a {f1 = 1 } It would also make sense to allow the following update (which we reject). updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two" This leads to confusing behaviour when the selectors in fact refer the same field. updater a = a {f1 = 1, foo = 2} ==? ??? For this reason, we reject a mixture of pattern synonym and normal record selectors in the same update block. Although of course we still allow the following. updater a = (a {f1 = 1}) {foo = 2} > updater (MyRec 0 "str") MyRec 2 "str" -} tcExpr expr@(RecordUpd { rupd_expr = record_expr, rupd_flds = rbnds }) res_ty = ASSERT( notNull rbnds ) do { -- STEP -2: typecheck the record_expr, the record to be updated (record_expr', record_rho) <- tcScalingUsage Many $ tcInferRho record_expr -- Record update drops some of the content of the record (namely the -- content of the field being updated). As a consequence, unless the -- field being updated is unrestricted in the record, or we need an -- unrestricted record. Currently, we simply always require an -- unrestricted record. -- -- Consider the following example: -- -- data R a = R { self :: a } -- bad :: a ⊸ () -- bad x = let r = R x in case r { self = () } of { R x' -> x' } -- -- This should definitely *not* typecheck. -- STEP -1 See Note [Disambiguating record fields] -- After this we know that rbinds is unambiguous ; rbinds <- disambiguateRecordBinds record_expr record_rho rbnds res_ty ; let upd_flds = map (unLoc . hsRecFieldLbl . unLoc) rbinds upd_fld_occs = map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc) upd_flds sel_ids = map selectorAmbiguousFieldOcc upd_flds -- STEP 0 -- Check that the field names are really field names -- and they are all field names for proper records or -- all field names for pattern synonyms. ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name) | fld <- rbinds, -- Excludes class ops let L loc sel_id = hsRecUpdFieldId (unLoc fld), not (isRecordSelector sel_id), let fld_name = idName sel_id ] ; unless (null bad_guys) (sequence bad_guys >> failM) -- See note [Mixed Record Selectors] ; let (data_sels, pat_syn_sels) = partition isDataConRecordSelector sel_ids ; MASSERT( all isPatSynRecordSelector pat_syn_sels ) ; checkTc ( null data_sels || null pat_syn_sels ) ( mixedSelectors data_sels pat_syn_sels ) -- STEP 1 -- Figure out the tycon and data cons from the first field name ; let -- It's OK to use the non-tc splitters here (for a selector) sel_id : _ = sel_ids mtycon :: Maybe TyCon mtycon = case idDetails sel_id of RecSelId (RecSelData tycon) _ -> Just tycon _ -> Nothing con_likes :: [ConLike] con_likes = case idDetails sel_id of RecSelId (RecSelData tc) _ -> map RealDataCon (tyConDataCons tc) RecSelId (RecSelPatSyn ps) _ -> [PatSynCon ps] _ -> panic "tcRecordUpd" -- NB: for a data type family, the tycon is the instance tycon relevant_cons = conLikesWithFields con_likes upd_fld_occs -- A constructor is only relevant to this process if -- it contains *all* the fields that are being updated -- Other ones will cause a runtime error if they occur -- Step 2 -- Check that at least one constructor has all the named fields -- i.e. has an empty set of bad fields returned by badFields ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds con_likes) -- Take apart a representative constructor ; let con1 = ASSERT( not (null relevant_cons) ) head relevant_cons (con1_tvs, _, _, _prov_theta, req_theta, scaled_con1_arg_tys, _) = conLikeFullSig con1 con1_arg_tys = map scaledThing scaled_con1_arg_tys -- We can safely drop the fields' multiplicities because -- they are currently always 1: there is no syntax for record -- fields with other multiplicities yet. This way we don't need -- to handle it in the rest of the function con1_flds = map flLabel $ conLikeFieldLabels con1 con1_tv_tys = mkTyVarTys con1_tvs con1_res_ty = case mtycon of Just tc -> mkFamilyTyConApp tc con1_tv_tys Nothing -> conLikeResTy con1 con1_tv_tys -- Check that we're not dealing with a unidirectional pattern -- synonym ; unless (isJust $ conLikeWrapId_maybe con1) (nonBidirectionalErr (conLikeName con1)) -- STEP 3 Note [Criteria for update] -- Check that each updated field is polymorphic; that is, its type -- mentions only the universally-quantified variables of the data con ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys bad_upd_flds = filter bad_fld flds1_w_tys con1_tv_set = mkVarSet con1_tvs bad_fld (fld, ty) = fld `elem` upd_fld_occs && not (tyCoVarsOfType ty `subVarSet` con1_tv_set) ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds) -- STEP 4 Note [Type of a record update] -- Figure out types for the scrutinee and result -- Both are of form (T a b c), with fresh type variables, but with -- common variables where the scrutinee and result must have the same type -- These are variables that appear in *any* arg of *any* of the -- relevant constructors *except* in the updated fields -- ; let fixed_tvs = getFixedTyVars upd_fld_occs con1_tvs relevant_cons is_fixed_tv tv = tv `elemVarSet` fixed_tvs mk_inst_ty :: TCvSubst -> (TyVar, TcType) -> TcM (TCvSubst, TcType) -- Deals with instantiation of kind variables -- c.f. GHC.Tc.Utils.TcMType.newMetaTyVars mk_inst_ty subst (tv, result_inst_ty) | is_fixed_tv tv -- Same as result type = return (extendTvSubst subst tv result_inst_ty, result_inst_ty) | otherwise -- Fresh type, of correct kind = do { (subst', new_tv) <- newMetaTyVarX subst tv ; return (subst', mkTyVarTy new_tv) } ; (result_subst, con1_tvs') <- newMetaTyVars con1_tvs ; let result_inst_tys = mkTyVarTys con1_tvs' init_subst = mkEmptyTCvSubst (getTCvInScope result_subst) ; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty init_subst (con1_tvs `zip` result_inst_tys) ; let rec_res_ty = TcType.substTy result_subst con1_res_ty scrut_ty = TcType.substTy scrut_subst con1_res_ty con1_arg_tys' = map (TcType.substTy result_subst) con1_arg_tys ; co_scrut <- unifyType (Just (unLoc record_expr)) record_rho scrut_ty -- NB: normal unification is OK here (as opposed to subsumption), -- because for this to work out, both record_rho and scrut_ty have -- to be normal datatypes -- no contravariant stuff can go on -- STEP 5 -- Typecheck the bindings ; rbinds' <- tcRecordUpd con1 con1_arg_tys' rbinds -- STEP 6: Deal with the stupid theta ; let theta' = substThetaUnchecked scrut_subst (conLikeStupidTheta con1) ; instStupidTheta RecordUpdOrigin theta' -- Step 7: make a cast for the scrutinee, in the -- case that it's from a data family ; let fam_co :: HsWrapper -- RepT t1 .. tn ~R scrut_ty fam_co | Just tycon <- mtycon , Just co_con <- tyConFamilyCoercion_maybe tycon = mkWpCastR (mkTcUnbranchedAxInstCo co_con scrut_inst_tys []) | otherwise = idHsWrapper -- Step 8: Check that the req constraints are satisfied -- For normal data constructors req_theta is empty but we must do -- this check for pattern synonyms. ; let req_theta' = substThetaUnchecked scrut_subst req_theta ; req_wrap <- instCallConstraints RecordUpdOrigin req_theta' -- Phew! ; let upd_tc = RecordUpdTc { rupd_cons = relevant_cons , rupd_in_tys = scrut_inst_tys , rupd_out_tys = result_inst_tys , rupd_wrap = req_wrap } expr' = RecordUpd { rupd_expr = mkLHsWrap fam_co $ mkLHsWrapCo co_scrut record_expr' , rupd_flds = rbinds' , rupd_ext = upd_tc } ; tcWrapResult expr expr' rec_res_ty res_ty } tcExpr e@(HsRecFld _ f) res_ty = tcCheckRecSelId e f res_ty {- ************************************************************************ * * Arithmetic sequences e.g. [a,b..] and their parallel-array counterparts e.g. [: a,b.. :] * * ************************************************************************ -} tcExpr (ArithSeq _ witness seq) res_ty = tcArithSeq witness seq res_ty {- ************************************************************************ * * Template Haskell * * ************************************************************************ -} -- HsSpliced is an annotation produced by 'GHC.Rename.Splice.rnSpliceExpr'. -- Here we get rid of it and add the finalizers to the global environment. -- -- See Note [Delaying modFinalizers in untyped splices] in GHC.Rename.Splice. tcExpr (HsSpliceE _ (HsSpliced _ mod_finalizers (HsSplicedExpr expr))) res_ty = do addModFinalizersWithLclEnv mod_finalizers tcExpr expr res_ty tcExpr (HsSpliceE _ splice) res_ty = tcSpliceExpr splice res_ty tcExpr e@(HsBracket _ brack) res_ty = tcTypedBracket e brack res_ty tcExpr e@(HsRnBracketOut _ brack ps) res_ty = tcUntypedBracket e brack ps res_ty {- ************************************************************************ * * Rebindable syntax * * ************************************************************************ -} -- See Note [Rebindable syntax and HsExpansion]. tcExpr (XExpr (HsExpanded a b)) t = fmap (XExpr . ExpansionExpr . HsExpanded a) $ setSrcSpan generatedSrcSpan (tcExpr b t) {- ************************************************************************ * * Catch-all * * ************************************************************************ -} tcExpr other _ = pprPanic "tcLExpr" (ppr other) -- Include ArrForm, ArrApp, which shouldn't appear at all -- Also HsTcBracketOut, HsQuasiQuoteE {- ********************************************************************* * * Pragmas on expressions * * ********************************************************************* -} tcExprPrag :: HsPragE GhcRn -> HsPragE GhcTc tcExprPrag (HsPragSCC x1 src ann) = HsPragSCC x1 src ann tcExprPrag (HsPragTick x1 src info srcInfo) = HsPragTick x1 src info srcInfo {- ********************************************************************* * * Expression with type signature e::ty * * ********************************************************************* -} 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 expr sig_info ; return (ExprWithTySig noExtField expr' hs_ty, poly_ty) } where loc = getLoc (hsSigWcType hs_ty) {- ************************************************************************ * * Arithmetic sequences [a..b] etc * * ************************************************************************ -} tcArithSeq :: Maybe (SyntaxExpr GhcRn) -> ArithSeqInfo GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc) tcArithSeq witness seq@(From expr) res_ty = do { (wrap, elt_mult, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr' <-tcScalingUsage elt_mult $ tcCheckPolyExpr expr elt_ty ; enum_from <- newMethodFromName (ArithSeqOrigin seq) enumFromName [elt_ty] ; return $ mkHsWrap wrap $ ArithSeq enum_from wit' (From expr') } tcArithSeq witness seq@(FromThen expr1 expr2) res_ty = do { (wrap, elt_mult, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr1 elt_ty ; expr2' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr2 elt_ty ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq) enumFromThenName [elt_ty] ; return $ mkHsWrap wrap $ ArithSeq enum_from_then wit' (FromThen expr1' expr2') } tcArithSeq witness seq@(FromTo expr1 expr2) res_ty = do { (wrap, elt_mult, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr1 elt_ty ; expr2' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr2 elt_ty ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq) enumFromToName [elt_ty] ; return $ mkHsWrap wrap $ ArithSeq enum_from_to wit' (FromTo expr1' expr2') } tcArithSeq witness seq@(FromThenTo expr1 expr2 expr3) res_ty = do { (wrap, elt_mult, elt_ty, wit') <- arithSeqEltType witness res_ty ; expr1' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr1 elt_ty ; expr2' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr2 elt_ty ; expr3' <- tcScalingUsage elt_mult $ tcCheckPolyExpr expr3 elt_ty ; eft <- newMethodFromName (ArithSeqOrigin seq) enumFromThenToName [elt_ty] ; return $ mkHsWrap wrap $ ArithSeq eft wit' (FromThenTo expr1' expr2' expr3') } ----------------- arithSeqEltType :: Maybe (SyntaxExpr GhcRn) -> ExpRhoType -> TcM (HsWrapper, Mult, TcType, Maybe (SyntaxExpr GhcTc)) arithSeqEltType Nothing res_ty = do { res_ty <- expTypeToType res_ty ; (coi, elt_ty) <- matchExpectedListTy res_ty ; return (mkWpCastN coi, One, elt_ty, Nothing) } arithSeqEltType (Just fl) res_ty = do { ((elt_mult, elt_ty), fl') <- tcSyntaxOp ListOrigin fl [SynList] res_ty $ \ [elt_ty] [elt_mult] -> return (elt_mult, elt_ty) ; return (idHsWrapper, elt_mult, elt_ty, Just fl') } {- ************************************************************************ * * Applications * * ************************************************************************ -} {- Note [Typechecking applications] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We typecheck application chains (f e1 @ty e2) specially: * So we can report errors like "in the third arument of a call of f" * So we can do Visible Type Application (VTA), for which we must not eagerly instantiate the function part of the application. * So that we can do Quick Look impredicativity. The idea is: * Use collectHsArgs, which peels off HsApp, HsTypeApp, HsPrag, HsPar returning the function in the corner and the arguments * Use tcInferAppHead to infer the type of the fuction, as an (uninstantiated) TcSigmaType There are special cases for HsVar, HsREcFld, and ExprWithTySig Otherwise, delegate back to tcExpr, which infers an (instantiated) TcRhoType Some cases that /won't/ work: 1. Consider this (which uses visible type application): (let { f :: forall a. a -> a; f x = x } in f) @Int Since 'let' is not among the special cases for tcInferAppHead, we'll delegate back to tcExpr, which will instantiate f's type and the type application to @Int will fail. Too bad! -} -- HsExprArg is a very local type, used only within this module. -- It's really a zipper for an application chain -- It's a GHC-specific type, so using TTG only where necessary data HsExprArg id = HsEValArg SrcSpan -- Of the function (LHsExpr (GhcPass id)) | HsETypeArg SrcSpan -- Of the function (LHsWcType (NoGhcTc (GhcPass id))) !(XExprTypeArg id) | HsEPrag SrcSpan (HsPragE (GhcPass id)) | HsEPar SrcSpan -- Of the nested expr | HsEWrap !(XArgWrap id) -- Wrapper, after typechecking only -- The outer location is the location of the application itself type LHsExprArgIn = HsExprArg 'Renamed type LHsExprArgOut = HsExprArg 'Typechecked instance OutputableBndrId id => Outputable (HsExprArg id) where ppr (HsEValArg _ tm) = ppr tm ppr (HsEPrag _ p) = text "HsPrag" <+> ppr p ppr (HsETypeArg _ hs_ty _) = char '@' <> ppr hs_ty ppr (HsEPar _) = text "HsEPar" ppr (HsEWrap w) = case ghcPass @id of GhcTc -> text "HsEWrap" <+> ppr w _ -> empty type family XExprTypeArg id where XExprTypeArg 'Parsed = NoExtField XExprTypeArg 'Renamed = NoExtField XExprTypeArg 'Typechecked = Type type family XArgWrap id where XArgWrap 'Parsed = NoExtCon XArgWrap 'Renamed = NoExtCon XArgWrap 'Typechecked = HsWrapper addArgWrap :: HsWrapper -> [LHsExprArgOut] -> [LHsExprArgOut] addArgWrap wrap args | isIdHsWrapper wrap = args | otherwise = HsEWrap wrap : args collectHsArgs :: HsExpr GhcRn -> (HsExpr GhcRn, [LHsExprArgIn]) collectHsArgs e = go e [] where go (HsPar _ (L l fun)) args = go fun (HsEPar l : args) go (HsPragE _ p (L l fun)) args = go fun (HsEPrag l p : args) go (HsApp _ (L l fun) arg) args = go fun (HsEValArg l arg : args) go (HsAppType _ (L l fun) hs_ty) args = go fun (HsETypeArg l hs_ty noExtField : args) go e args = (e,args) applyHsArgs :: HsExpr GhcTc -> [LHsExprArgOut]-> HsExpr GhcTc applyHsArgs fun args = go fun args where go fun [] = fun go fun (HsEWrap wrap : args) = go (mkHsWrap wrap fun) args go fun (HsEValArg l arg : args) = go (HsApp noExtField (L l fun) arg) args go fun (HsETypeArg l hs_ty ty : args) = go (HsAppType ty (L l fun) hs_ty) args go fun (HsEPar l : args) = go (HsPar noExtField (L l fun)) args go fun (HsEPrag l p : args) = go (HsPragE noExtField p (L l fun)) args isHsValArg :: HsExprArg id -> Bool isHsValArg (HsEValArg {}) = True isHsValArg _ = False isArgPar :: HsExprArg id -> Bool isArgPar (HsEPar {}) = True isArgPar _ = False getFunLoc :: [HsExprArg 'Renamed] -> Maybe SrcSpan getFunLoc [] = Nothing getFunLoc (a:_) = Just $ case a of HsEValArg l _ -> l HsETypeArg l _ _ -> l HsEPrag l _ -> l HsEPar l -> l --------------------------- tcApp :: HsExpr GhcRn -- either HsApp or HsAppType -> ExpRhoType -> TcM (HsExpr GhcTc) -- See Note [Typechecking applications] tcApp expr res_ty = do { (fun, args, app_res_ty) <- tcInferApp expr ; if isTagToEnum fun then tcTagToEnum expr fun args app_res_ty res_ty -- Done here because we have res_ty, -- whereas tcInferApp does not else -- The wildly common case do { let expr' = applyHsArgs fun args ; addFunResCtxt True fun app_res_ty res_ty $ tcWrapResult expr expr' app_res_ty res_ty } } --------------------------- tcInferApp :: HsExpr GhcRn -> TcM ( HsExpr GhcTc -- Function , [LHsExprArgOut] -- Arguments , TcSigmaType) -- Inferred type: a sigma-type! -- Also used by Module.tcRnExpr to implement GHCi :type tcInferApp expr | -- Gruesome special case for ambiguous record selectors HsRecFld _ fld_lbl <- fun , Ambiguous _ lbl <- fld_lbl -- Still ambiguous , HsEValArg _ (L _ arg) : _ <- filterOut isArgPar args -- A value arg is first , Just sig_ty <- obviousSig arg -- A type sig on the arg disambiguates = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty ; sel_name <- disambiguateSelector lbl sig_tc_ty ; (tc_fun, fun_ty) <- tcInferRecSelId (Unambiguous sel_name lbl) ; tcInferApp_finish fun tc_fun fun_ty args } | otherwise -- The wildly common case = do { (tc_fun, fun_ty) <- set_fun_loc (tcInferAppHead fun) ; tcInferApp_finish fun tc_fun fun_ty args } where (fun, args) = collectHsArgs expr set_fun_loc thing_inside = case getFunLoc args of Nothing -> thing_inside -- Don't set the location twice Just loc -> setSrcSpan loc thing_inside tcInferApp_finish :: HsExpr GhcRn -- Renamed function -> HsExpr GhcTc -> TcSigmaType -- Function and its type -> [LHsExprArgIn] -- Arguments -> TcM (HsExpr GhcTc, [LHsExprArgOut], TcSigmaType) tcInferApp_finish rn_fun tc_fun fun_sigma rn_args = do { (tc_args, actual_res_ty) <- tcArgs rn_fun fun_sigma rn_args ; return (tc_fun, tc_args, actual_res_ty) } mk_op_msg :: LHsExpr GhcRn -> SDoc mk_op_msg op = text "The operator" <+> quotes (ppr op) <+> text "takes" ---------------- tcInferAppHead :: HsExpr GhcRn -> TcM (HsExpr GhcTc, TcSigmaType) -- Infer type of the head of an application, returning a /SigmaType/ -- i.e. the 'f' in (f e1 ... en) -- We get back a SigmaType because we have special cases for -- * A bare identifier (just look it up) -- This case also covers a record selectro HsRecFld -- * An expression with a type signature (e :: ty) -- -- 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 collectHsArgs. -- -- See Note [Typechecking applications] tcInferAppHead e = case e of HsVar _ (L _ nm) -> tcInferId nm HsRecFld _ f -> tcInferRecSelId f ExprWithTySig _ e hs_ty -> add_ctxt $ tcExprWithSig e hs_ty _ -> add_ctxt $ tcInfer (tcExpr e) where add_ctxt thing = addErrCtxt (exprCtxt e) thing ---------------- -- | Type-check the arguments to a function, possibly including visible type -- applications tcArgs :: HsExpr GhcRn -- ^ The function itself (for err msgs only) -> TcSigmaType -- ^ the (uninstantiated) type of the function -> [LHsExprArgIn] -- ^ the args -> TcM ([LHsExprArgOut], TcSigmaType) -- ^ (a wrapper for the function, the tc'd args, result type) tcArgs fun orig_fun_ty orig_args = go 1 [] orig_fun_ty orig_args where fun_orig = exprCtOrigin fun herald = sep [ text "The function" <+> quotes (ppr fun) , text "is applied to"] -- Count value args only when complaining about a function -- applied to too many value args -- See Note [Herald for matchExpectedFunTys] in GHC.Tc.Utils.Unify. n_val_args = count isHsValArg orig_args fun_is_out_of_scope -- See Note [VTA for out-of-scope functions] = case fun of HsUnboundVar {} -> True _ -> False go :: Int -- Which argment number this is (incl type args) -> [Scaled TcSigmaType] -- Value args to which applied so far -> TcSigmaType -> [LHsExprArgIn] -> TcM ([LHsExprArgOut], TcSigmaType) go _ _ fun_ty [] = traceTc "tcArgs:ret" (ppr fun_ty) >> return ([], fun_ty) go n so_far fun_ty (HsEPar sp : args) = do { (args', res_ty) <- go n so_far fun_ty args ; return (HsEPar sp : args', res_ty) } go n so_far fun_ty (HsEPrag sp prag : args) = do { (args', res_ty) <- go n so_far fun_ty args ; return (HsEPrag sp (tcExprPrag prag) : args', res_ty) } go n so_far fun_ty (HsETypeArg loc hs_ty_arg _ : args) | fun_is_out_of_scope -- See Note [VTA for out-of-scope functions] = go (n+1) so_far fun_ty args | otherwise = do { (wrap1, upsilon_ty) <- topInstantiateInferred fun_orig fun_ty -- wrap1 :: fun_ty "->" upsilon_ty ; case tcSplitForAllTy_maybe upsilon_ty of Just (tvb, inner_ty) | binderArgFlag tvb == Specified -> -- It really can't be Inferred, because we've justn -- instantiated those. But, oddly, it might just be Required. -- See Note [Required quantifiers in the type of a term] do { let tv = binderVar tvb kind = tyVarKind tv ; ty_arg <- tcHsTypeApp hs_ty_arg kind ; inner_ty <- zonkTcType inner_ty -- See Note [Visible type application zonk] ; let in_scope = mkInScopeSet (tyCoVarsOfTypes [upsilon_ty, ty_arg]) insted_ty = substTyWithInScope in_scope [tv] [ty_arg] inner_ty -- NB: tv and ty_arg have the same kind, so this -- substitution is kind-respecting ; traceTc "VTA" (vcat [ppr tv, debugPprType kind , debugPprType ty_arg , debugPprType (tcTypeKind ty_arg) , debugPprType inner_ty , debugPprType insted_ty ]) ; (args', res_ty) <- go (n+1) so_far insted_ty args ; return ( addArgWrap wrap1 $ HsETypeArg loc hs_ty_arg ty_arg : args' , res_ty ) } _ -> ty_app_err upsilon_ty hs_ty_arg } go n so_far fun_ty (HsEValArg loc arg : args) = do { (wrap, arg_ty, res_ty) <- matchActualFunTySigma herald fun_orig (Just fun) (n_val_args, so_far) fun_ty ; arg' <- tcArg fun arg arg_ty n ; (args', inner_res_ty) <- go (n+1) (arg_ty:so_far) res_ty args ; return ( addArgWrap wrap $ HsEValArg loc arg' : args' , inner_res_ty ) } ty_app_err ty arg = do { (_, ty) <- zonkTidyTcType emptyTidyEnv ty ; failWith $ text "Cannot apply expression of type" <+> quotes (ppr ty) $$ text "to a visible type argument" <+> quotes (ppr arg) } {- Note [Required quantifiers in the type of a term] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider (#15859) data A k :: k -> Type -- A :: forall k -> k -> Type type KindOf (a :: k) = k -- KindOf :: forall k. k -> Type a = (undefind :: KindOf A) @Int With ImpredicativeTypes (thin ice, I know), we instantiate KindOf at type (forall k -> k -> Type), so KindOf A = forall k -> k -> Type whose first argument is Required We want to reject this type application to Int, but in earlier GHCs we had an ASSERT that Required could not occur here. The ice is thin; c.f. Note [No Required TyCoBinder in terms] in GHC.Core.TyCo.Rep. Note [VTA for out-of-scope functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose 'wurble' is not in scope, and we have (wurble @Int @Bool True 'x') Then the renamer will make (HsUnboundVar "wurble) for 'wurble', and the typechecker will typecheck it with tcUnboundId, giving it a type 'alpha', and emitting a deferred Hole, to be reported later. But then comes the visible type application. If we do nothing, we'll generate an immediate failure (in tc_app_err), saying that a function of type 'alpha' can't be applied to Bool. That's insane! And indeed users complain bitterly (#13834, #17150.) The right error is the Hole, which has /already/ been emitted by tcUnboundId. It later reports 'wurble' as out of scope, and tries to give its type. Fortunately in tcArgs we still have access to the function, so we can check if it is a HsUnboundVar. We use this info to simply skip over any visible type arguments. We've already inferred the type of the function, so we'll /already/ have emitted a Hole; failing preserves that constraint. We do /not/ want to fail altogether in this case (via failM) becuase that may abandon an entire instance decl, which (in the presence of -fdefer-type-errors) leads to leading to #17792. Downside; the typechecked term has lost its visible type arguments; we don't even kind-check them. But let's jump that bridge if we come to it. Meanwhile, let's not crash! Note [Visible type application zonk] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * Substitutions should be kind-preserving, so we need kind(tv) = kind(ty_arg). * tcHsTypeApp only guarantees that - ty_arg is zonked - kind(zonk(tv)) = kind(ty_arg) (checkExpectedKind zonks as it goes). So we must zonk inner_ty as well, to guarantee consistency between zonk(tv) and inner_ty. Otherwise we can build an ill-kinded type. An example was #14158, where we had: id :: forall k. forall (cat :: k -> k -> *). forall (a :: k). cat a a and we had the visible type application id @(->) * We instantiated k := kappa, yielding forall (cat :: kappa -> kappa -> *). forall (a :: kappa). cat a a * Then we called tcHsTypeApp (->) with expected kind (kappa -> kappa -> *). * That instantiated (->) as ((->) q1 q1), and unified kappa := q1, Here q1 :: RuntimeRep * Now we substitute cat :-> (->) q1 q1 :: TYPE q1 -> TYPE q1 -> * but we must first zonk the inner_ty to get forall (a :: TYPE q1). cat a a so that the result of substitution is well-kinded Failing to do so led to #14158. -} ---------------- tcArg :: HsExpr GhcRn -- The function (for error messages) -> LHsExpr GhcRn -- Actual arguments -> Scaled TcSigmaType -- expected arg type -> Int -- # of argument -> TcM (LHsExpr GhcTc) -- Resulting argument tcArg fun arg (Scaled mult ty) arg_no = addErrCtxt (funAppCtxt fun arg arg_no) $ do { traceTc "tcArg" $ vcat [ ppr arg_no <+> text "of" <+> ppr fun , text "arg type:" <+> ppr ty , text "arg:" <+> ppr arg ] ; tcScalingUsage mult $ tcCheckPolyExprNC arg ty } ---------------- tcTupArgs :: [LHsTupArg GhcRn] -> [TcSigmaType] -> TcM [LHsTupArg GhcTc] tcTupArgs args tys = ASSERT( equalLength args tys ) mapM go (args `zip` tys) where go (L l (Missing {}), arg_ty) = do { mult <- newFlexiTyVarTy multiplicityTy ; return (L l (Missing (Scaled mult arg_ty))) } go (L l (Present x expr), arg_ty) = do { expr' <- tcCheckPolyExpr expr arg_ty ; return (L l (Present x expr')) } --------------------------- -- See TcType.SyntaxOpType also for commentary tcSyntaxOp :: CtOrigin -> SyntaxExprRn -> [SyntaxOpType] -- ^ shape of syntax operator arguments -> ExpRhoType -- ^ overall result type -> ([TcSigmaType] -> [Mult] -> TcM a) -- ^ Type check any arguments, -- takes a type per hole and a -- multiplicity per arrow in -- the shape. -> TcM (a, SyntaxExprTc) -- ^ Typecheck a syntax operator -- The operator is a variable or a lambda at this stage (i.e. renamer -- output) tcSyntaxOp orig expr arg_tys res_ty = tcSyntaxOpGen orig expr arg_tys (SynType res_ty) -- | Slightly more general version of 'tcSyntaxOp' that allows the caller -- to specify the shape of the result of the syntax operator tcSyntaxOpGen :: CtOrigin -> SyntaxExprRn -> [SyntaxOpType] -> SyntaxOpType -> ([TcSigmaType] -> [Mult] -> TcM a) -> TcM (a, SyntaxExprTc) tcSyntaxOpGen orig (SyntaxExprRn op) arg_tys res_ty thing_inside = do { (expr, sigma) <- tcInferAppHead op ; traceTc "tcSyntaxOpGen" (ppr op $$ ppr expr $$ ppr sigma) ; (result, expr_wrap, arg_wraps, res_wrap) <- tcSynArgA orig sigma arg_tys res_ty $ thing_inside ; traceTc "tcSyntaxOpGen" (ppr op $$ ppr expr $$ ppr sigma ) ; return (result, SyntaxExprTc { syn_expr = mkHsWrap expr_wrap expr , syn_arg_wraps = arg_wraps , syn_res_wrap = res_wrap }) } tcSyntaxOpGen _ NoSyntaxExprRn _ _ _ = panic "tcSyntaxOpGen" {- Note [tcSynArg] ~~~~~~~~~~~~~~~ Because of the rich structure of SyntaxOpType, we must do the contra-/covariant thing when working down arrows, to get the instantiation vs. skolemisation decisions correct (and, more obviously, the orientation of the HsWrappers). We thus have two tcSynArgs. -} -- works on "expected" types, skolemising where necessary -- See Note [tcSynArg] tcSynArgE :: CtOrigin -> TcSigmaType -> SyntaxOpType -- ^ shape it is expected to have -> ([TcSigmaType] -> [Mult] -> TcM a) -- ^ check the arguments -> TcM (a, HsWrapper) -- ^ returns a wrapper :: (type of right shape) "->" (type passed in) tcSynArgE orig sigma_ty syn_ty thing_inside = do { (skol_wrap, (result, ty_wrapper)) <- tcSkolemise GenSigCtxt sigma_ty $ \ rho_ty -> go rho_ty syn_ty ; return (result, skol_wrap <.> ty_wrapper) } where go rho_ty SynAny = do { result <- thing_inside [rho_ty] [] ; return (result, idHsWrapper) } go rho_ty SynRho -- same as SynAny, because we skolemise eagerly = do { result <- thing_inside [rho_ty] [] ; return (result, idHsWrapper) } go rho_ty SynList = do { (list_co, elt_ty) <- matchExpectedListTy rho_ty ; result <- thing_inside [elt_ty] [] ; return (result, mkWpCastN list_co) } go rho_ty (SynFun arg_shape res_shape) = do { ( match_wrapper -- :: (arg_ty -> res_ty) "->" rho_ty , ( ( (result, arg_ty, res_ty, op_mult) , res_wrapper ) -- :: res_ty_out "->" res_ty , arg_wrapper1, [], arg_wrapper2 ) ) -- :: arg_ty "->" arg_ty_out <- matchExpectedFunTys herald GenSigCtxt 1 (mkCheckExpType rho_ty) $ \ [arg_ty] res_ty -> do { arg_tc_ty <- expTypeToType (scaledThing arg_ty) ; res_tc_ty <- expTypeToType res_ty -- another nested arrow is too much for now, -- but I bet we'll never need this ; MASSERT2( case arg_shape of SynFun {} -> False; _ -> True , text "Too many nested arrows in SyntaxOpType" $$ pprCtOrigin orig ) ; let arg_mult = scaledMult arg_ty ; tcSynArgA orig arg_tc_ty [] arg_shape $ \ arg_results arg_res_mults -> tcSynArgE orig res_tc_ty res_shape $ \ res_results res_res_mults -> do { result <- thing_inside (arg_results ++ res_results) ([arg_mult] ++ arg_res_mults ++ res_res_mults) ; return (result, arg_tc_ty, res_tc_ty, arg_mult) }} ; return ( result , match_wrapper <.> mkWpFun (arg_wrapper2 <.> arg_wrapper1) res_wrapper (Scaled op_mult arg_ty) res_ty doc ) } where herald = text "This rebindable syntax expects a function with" doc = text "When checking a rebindable syntax operator arising from" <+> ppr orig go rho_ty (SynType the_ty) = do { wrap <- tcSubTypePat orig GenSigCtxt the_ty rho_ty ; result <- thing_inside [] [] ; return (result, wrap) } -- works on "actual" types, instantiating where necessary -- See Note [tcSynArg] tcSynArgA :: CtOrigin -> TcSigmaType -> [SyntaxOpType] -- ^ argument shapes -> SyntaxOpType -- ^ result shape -> ([TcSigmaType] -> [Mult] -> TcM a) -- ^ check the arguments -> TcM (a, HsWrapper, [HsWrapper], HsWrapper) -- ^ returns a wrapper to be applied to the original function, -- wrappers to be applied to arguments -- and a wrapper to be applied to the overall expression tcSynArgA orig sigma_ty arg_shapes res_shape thing_inside = do { (match_wrapper, arg_tys, res_ty) <- matchActualFunTysRho herald orig Nothing (length arg_shapes) sigma_ty -- match_wrapper :: sigma_ty "->" (arg_tys -> res_ty) ; ((result, res_wrapper), arg_wrappers) <- tc_syn_args_e (map scaledThing arg_tys) arg_shapes $ \ arg_results arg_res_mults -> tc_syn_arg res_ty res_shape $ \ res_results -> thing_inside (arg_results ++ res_results) (map scaledMult arg_tys ++ arg_res_mults) ; return (result, match_wrapper, arg_wrappers, res_wrapper) } where herald = text "This rebindable syntax expects a function with" tc_syn_args_e :: [TcSigmaType] -> [SyntaxOpType] -> ([TcSigmaType] -> [Mult] -> TcM a) -> TcM (a, [HsWrapper]) -- the wrappers are for arguments tc_syn_args_e (arg_ty : arg_tys) (arg_shape : arg_shapes) thing_inside = do { ((result, arg_wraps), arg_wrap) <- tcSynArgE orig arg_ty arg_shape $ \ arg1_results arg1_mults -> tc_syn_args_e arg_tys arg_shapes $ \ args_results args_mults -> thing_inside (arg1_results ++ args_results) (arg1_mults ++ args_mults) ; return (result, arg_wrap : arg_wraps) } tc_syn_args_e _ _ thing_inside = (, []) <$> thing_inside [] [] tc_syn_arg :: TcSigmaType -> SyntaxOpType -> ([TcSigmaType] -> TcM a) -> TcM (a, HsWrapper) -- the wrapper applies to the overall result tc_syn_arg res_ty SynAny thing_inside = do { result <- thing_inside [res_ty] ; return (result, idHsWrapper) } tc_syn_arg res_ty SynRho thing_inside = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty -- inst_wrap :: res_ty "->" rho_ty ; result <- thing_inside [rho_ty] ; return (result, inst_wrap) } tc_syn_arg res_ty SynList thing_inside = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty -- inst_wrap :: res_ty "->" rho_ty ; (list_co, elt_ty) <- matchExpectedListTy rho_ty -- list_co :: [elt_ty] ~N rho_ty ; result <- thing_inside [elt_ty] ; return (result, mkWpCastN (mkTcSymCo list_co) <.> inst_wrap) } tc_syn_arg _ (SynFun {}) _ = pprPanic "tcSynArgA hits a SynFun" (ppr orig) tc_syn_arg res_ty (SynType the_ty) thing_inside = do { wrap <- tcSubType orig GenSigCtxt res_ty the_ty ; result <- thing_inside [] ; return (result, wrap) } {- Note [Push result type in] ~~~~~~~~~~~~~~~~~~~~~~~~~~ Unify with expected result before type-checking the args so that the info from res_ty percolates to args. This is when we might detect a too-few args situation. (One can think of cases when the opposite order would give a better error message.) experimenting with putting this first. Here's an example where it actually makes a real difference class C t a b | t a -> b instance C Char a Bool data P t a = forall b. (C t a b) => MkP b data Q t = MkQ (forall a. P t a) f1, f2 :: Q Char; f1 = MkQ (MkP True) f2 = MkQ (MkP True :: forall a. P Char a) With the change, f1 will type-check, because the 'Char' info from the signature is propagated into MkQ's argument. With the check in the other order, the extra signature in f2 is reqd. ************************************************************************ * * Expressions with a type signature expr :: type * * ********************************************************************* -} tcExprSig :: LHsExpr GhcRn -> TcIdSigInfo -> TcM (LHsExpr GhcTc, TcType) tcExprSig 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 ExprSigCtxt 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, _) <- 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 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 ExprSigCtxt 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. -} {- ********************************************************************* * * tcInferId * * ********************************************************************* -} tcCheckId :: Name -> ExpRhoType -> TcM (HsExpr GhcTc) tcCheckId name res_ty | name `hasKey` tagToEnumKey = failWithTc (text "tagToEnum# must appear applied to one argument") -- tcApp catches the case (tagToEnum# arg) | otherwise = do { (expr, actual_res_ty) <- tcInferId name ; traceTc "tcCheckId" (vcat [ppr name, ppr actual_res_ty, ppr res_ty]) ; addFunResCtxt False expr actual_res_ty res_ty $ tcWrapResultO (OccurrenceOf name) (HsVar noExtField (noLoc name)) expr actual_res_ty res_ty } tcCheckRecSelId :: HsExpr GhcRn -> AmbiguousFieldOcc GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc) tcCheckRecSelId rn_expr f@(Unambiguous {}) res_ty = do { (expr, actual_res_ty) <- tcInferRecSelId f ; tcWrapResult rn_expr expr actual_res_ty res_ty } tcCheckRecSelId rn_expr (Ambiguous _ lbl) res_ty = case tcSplitFunTy_maybe =<< checkingExpType_maybe res_ty of Nothing -> ambiguousSelector lbl Just (arg, _) -> do { sel_name <- disambiguateSelector lbl (scaledThing arg) ; tcCheckRecSelId rn_expr (Unambiguous sel_name lbl) res_ty } ------------------------ tcInferRecSelId :: AmbiguousFieldOcc GhcRn -> TcM (HsExpr GhcTc, TcRhoType) tcInferRecSelId (Unambiguous sel (L _ lbl)) = do { (expr', ty) <- tc_infer_id lbl sel ; return (expr', ty) } tcInferRecSelId (Ambiguous _ lbl) = ambiguousSelector lbl ------------------------ 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 (nameRdrName id_name) id_name else tc_infer_assert id_name } | otherwise = do { (expr, ty) <- tc_infer_id (nameRdrName id_name) 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 (noLoc assert_error_id)), id_rho) } tc_infer_id :: RdrName -> Name -> TcM (HsExpr GhcTc, TcSigmaType) tc_infer_id lbl id_name = do { thing <- tcLookup id_name ; case thing of ATcId { tct_id = id } -> do { check_naughty id -- Note [Local record selectors] ; checkThLocalId id ; tcEmitBindingUsage $ unitUE id_name One ; return_id id } AGlobal (AnId id) -> do { check_naughty 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 cl) -> case cl of RealDataCon con -> return_data_con con PatSynCon ps -> tcPatSynBuilderOcc ps _ -> failWithTc $ ppr thing <+> text "used where a value identifier was expected" } where return_id id = return (HsVar noExtField (noLoc id), idType id) return_data_con con = do { let tvs = dataConUserTyVarBinders con theta = dataConOtherTheta con args = dataConOrigArgTys con res = dataConOrigResTy con -- See Note [Linear fields generalization] ; mul_vars <- newFlexiTyVarTys (length args) multiplicityTy ; let scaleArgs args' = zipWithEqual "return_data_con" combine mul_vars args' combine var (Scaled One ty) = Scaled var ty combine _ scaled_ty = scaled_ty -- The combine function implements the fact that, as -- described in Note [Linear fields generalization], if a -- field is not linear (last line) it isn't made polymorphic. etaWrapper arg_tys = foldr (\scaled_ty wr -> WpFun WpHole wr scaled_ty empty) WpHole arg_tys -- See Note [Instantiating stupid theta] ; let shouldInstantiate = (not (null (dataConStupidTheta con)) || isKindLevPoly (tyConResKind (dataConTyCon con))) ; case shouldInstantiate of True -> do { (subst, tvs') <- newMetaTyVars (binderVars tvs) ; let tys' = mkTyVarTys tvs' theta' = substTheta subst theta args' = substScaledTys subst args res' = substTy subst res ; wrap <- instCall (OccurrenceOf id_name) tys' theta' ; let scaled_arg_tys = scaleArgs args' eta_wrap = etaWrapper scaled_arg_tys ; addDataConStupidTheta con tys' ; return ( mkHsWrap (eta_wrap <.> wrap) (HsConLikeOut noExtField (RealDataCon con)) , mkVisFunTys scaled_arg_tys res') } False -> let scaled_arg_tys = scaleArgs args wrap1 = mkWpTyApps (mkTyVarTys $ binderVars tvs) eta_wrap = etaWrapper (map unrestricted theta ++ scaled_arg_tys) wrap2 = mkWpTyLams $ binderVars tvs in return ( mkHsWrap (wrap2 <.> eta_wrap <.> wrap1) (HsConLikeOut noExtField (RealDataCon con)) , mkInvisForAllTys tvs $ mkInvisFunTysMany theta $ mkVisFunTys scaled_arg_tys res) } check_naughty id | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel lbl) | otherwise = return () tcUnboundId :: HsExpr GhcRn -> OccName -> ExpRhoType -> TcM (HsExpr GhcTc) -- Typecheck an occurrence of an unbound Id -- -- Some of these started life as a true expression hole "_". -- Others might simply be variables that accidentally have no binding site -- -- We turn all of them into HsVar, since HsUnboundVar can't contain an -- Id; and indeed the evidence for the ExprHole does bind it, so it's -- not unbound any more! tcUnboundId rn_expr occ res_ty = do { ty <- newOpenFlexiTyVarTy -- Allow Int# etc (#12531) ; name <- newSysName occ ; let ev = mkLocalId name Many ty ; emitNewExprHole occ ev ty ; tcWrapResultO (UnboundOccurrenceOf occ) rn_expr (HsVar noExtField (noLoc ev)) ty res_ty } {- 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 [tagToEnum#] ~~~~~~~~~~~~~~~~~ Nasty check to ensure that tagToEnum# is applied to a type that is an enumeration TyCon. Unification may refine the type later, but this check won't see that, alas. It's crude, because it relies on our knowing *now* that the type is ok, which in turn relies on the eager-unification part of the type checker pushing enough information here. In theory the Right Thing to do is to have a new form of constraint but I definitely cannot face that! And it works ok as-is. Here's are two cases that should fail f :: forall a. a f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable g :: Int g = tagToEnum# 0 -- Int is not an enumeration When data type families are involved it's a bit more complicated. data family F a data instance F [Int] = A | B | C Then we want to generate something like tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int] Usually that coercion is hidden inside the wrappers for constructors of F [Int] but here we have to do it explicitly. It's all grotesquely complicated. Note [Instantiating stupid theta] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Normally, when we infer the type of an Id, we don't instantiate, because we wish to allow for visible type application later on. But if a datacon has a stupid theta, we're a bit stuck. We need to emit the stupid theta constraints with instantiated types. It's difficult to defer this to the lazy instantiation, because a stupid theta has no spot to put it in a type. So we just instantiate eagerly in this case. Thus, users cannot use visible type application with a data constructor sporting a stupid theta. I won't feel so bad for the users that complain. Note [Linear fields generalization] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ As per Note [Polymorphisation of linear fields], linear field of data constructors get a polymorphic type when the data constructor is used as a term. Just :: forall {p} a. a #p-> Maybe a This rule is known only to the typechecker: Just keeps its linear type in Core. In order to desugar this generalised typing rule, we simply eta-expand: \a (x # p :: a) -> Just @a x has the appropriate type. We insert these eta-expansion with WpFun wrappers. A small hitch: if the constructor is levity-polymorphic (unboxed tuples, sums, certain newtypes with -XUnliftedNewtypes) then this strategy produces \r1 r2 a b (x # p :: a) (y # q :: b) -> (# a, b #) Which has type forall r1 r2 a b. a #p-> b #q-> (# a, b #) Which violates the levity-polymorphism restriction see Note [Levity polymorphism checking] in DsMonad. So we really must instantiate r1 and r2 rather than quantify over them. For simplicity, we just instantiate the entire type, as described in Note [Instantiating stupid theta]. It breaks visible type application with unboxed tuples, sums and levity-polymorphic newtypes, but this doesn't appear to be used anywhere. A better plan: let's force all representation variable to be *inferred*, so that they are not subject to visible type applications. Then we can instantiate inferred argument eagerly. -} isTagToEnum :: HsExpr GhcTc -> Bool isTagToEnum (HsVar _ (L _ fun_id)) = fun_id `hasKey` tagToEnumKey isTagToEnum _ = False tcTagToEnum :: HsExpr GhcRn -> HsExpr GhcTc -> [LHsExprArgOut] -> TcSigmaType -> ExpRhoType -> TcM (HsExpr GhcTc) -- tagToEnum# :: forall a. Int# -> a -- See Note [tagToEnum#] Urgh! tcTagToEnum expr fun args app_res_ty res_ty = do { res_ty <- readExpType res_ty ; ty' <- zonkTcType res_ty -- Check that the type is algebraic ; case tcSplitTyConApp_maybe ty' of { Nothing -> do { addErrTc (mk_error ty' doc1) ; vanilla_result } ; Just (tc, tc_args) -> do { -- Look through any type family ; fam_envs <- tcGetFamInstEnvs ; case tcLookupDataFamInst_maybe fam_envs tc tc_args of { Nothing -> do { check_enumeration ty' tc ; vanilla_result } ; Just (rep_tc, rep_args, coi) -> do { -- coi :: tc tc_args ~R rep_tc rep_args check_enumeration ty' rep_tc ; let val_arg = dropWhile (not . isHsValArg) args rep_ty = mkTyConApp rep_tc rep_args fun' = mkHsWrap (WpTyApp rep_ty) fun expr' = applyHsArgs fun' val_arg df_wrap = mkWpCastR (mkTcSymCo coi) ; return (mkHsWrap df_wrap expr') }}}}} where vanilla_result = do { let expr' = applyHsArgs fun args ; tcWrapResult expr expr' app_res_ty res_ty } check_enumeration ty' tc | isEnumerationTyCon tc = return () | otherwise = addErrTc (mk_error ty' doc2) doc1 = vcat [ text "Specify the type by giving a type signature" , text "e.g. (tagToEnum# x) :: Bool" ] doc2 = text "Result type must be an enumeration type" mk_error :: TcType -> SDoc -> SDoc mk_error ty what = hang (text "Bad call to tagToEnum#" <+> text "at type" <+> ppr ty) 2 what {- ************************************************************************ * * Template Haskell checks * * ************************************************************************ -} checkThLocalId :: Id -> TcM () -- The renamer has already done checkWellStaged, -- in 'GHC.Rename.Splice.checkThLocalName', so don't repeat that here. -- Here we just add constraints fro 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 (noLoc 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] -- Update the pending splices ; ps <- readMutVar ps_var ; let pending_splice = PendingTcSplice id_name (nlHsApp (mkLHsWrap (applyQuoteWrapper q) (noLoc lift)) (nlHsVar id)) ; writeMutVar ps_var (pending_splice : ps) ; return () } where id_name = idName id checkCrossStageLifting _ _ _ = return () polySpliceErr :: Id -> SDoc polySpliceErr id = 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 "GHC.ThToHs" 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. TcTyClsBindings.mkAuxBinds. ************************************************************************ * * \subsection{Record bindings} * * ************************************************************************ -} getFixedTyVars :: [FieldLabelString] -> [TyVar] -> [ConLike] -> TyVarSet -- These tyvars must not change across the updates getFixedTyVars upd_fld_occs univ_tvs cons = mkVarSet [tv1 | con <- cons , let (u_tvs, _, eqspec, prov_theta , req_theta, arg_tys, _) = conLikeFullSig con theta = eqSpecPreds eqspec ++ prov_theta ++ req_theta flds = conLikeFieldLabels con fixed_tvs = exactTyCoVarsOfTypes (map scaledThing fixed_tys) -- fixed_tys: See Note [Type of a record update] `unionVarSet` tyCoVarsOfTypes theta -- Universally-quantified tyvars that -- appear in any of the *implicit* -- arguments to the constructor are fixed -- See Note [Implicit type sharing] fixed_tys = [ty | (fl, ty) <- zip flds arg_tys , not (flLabel fl `elem` upd_fld_occs)] , (tv1,tv) <- univ_tvs `zip` u_tvs , tv `elemVarSet` fixed_tvs ] {- Note [Disambiguating record fields] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When the -XDuplicateRecordFields extension is used, and the renamer encounters a record selector or update that it cannot immediately disambiguate (because it involves fields that belong to multiple datatypes), it will defer resolution of the ambiguity to the typechecker. In this case, the `Ambiguous` constructor of `AmbiguousFieldOcc` is used. Consider the following definitions: data S = MkS { foo :: Int } data T = MkT { foo :: Int, bar :: Int } data U = MkU { bar :: Int, baz :: Int } When the renamer sees `foo` as a selector or an update, it will not know which parent datatype is in use. For selectors, there are two possible ways to disambiguate: 1. Check if the pushed-in type is a function whose domain is a datatype, for example: f s = (foo :: S -> Int) s g :: T -> Int g = foo This is checked by `tcCheckRecSelId` when checking `HsRecFld foo`. 2. Check if the selector is applied to an argument that has a type signature, for example: h = foo (s :: S) This is checked by `tcApp`. Updates are slightly more complex. The `disambiguateRecordBinds` function tries to determine the parent datatype in three ways: 1. Check for types that have all the fields being updated. For example: f x = x { foo = 3, bar = 2 } Here `f` must be updating `T` because neither `S` nor `U` have both fields. This may also discover that no possible type exists. For example the following will be rejected: f' x = x { foo = 3, baz = 3 } 2. Use the type being pushed in, if it is already a TyConApp. The following are valid updates to `T`: g :: T -> T g x = x { foo = 3 } g' x = x { foo = 3 } :: T 3. Use the type signature of the record expression, if it exists and is a TyConApp. Thus this is valid update to `T`: h x = (x :: T) { foo = 3 } Note that we do not look up the types of variables being updated, and no constraint-solving is performed, so for example the following will be rejected as ambiguous: let bad (s :: S) = foo s let r :: T r = blah in r { foo = 3 } \r. (r { foo = 3 }, r :: T ) We could add further tests, of a more heuristic nature. For example, rather than looking for an explicit signature, we could try to infer the type of the argument to a selector or the record expression being updated, in case we are lucky enough to get a TyConApp straight away. However, it might be hard for programmers to predict whether a particular update is sufficiently obvious for the signature to be omitted. Moreover, this might change the behaviour of typechecker in non-obvious ways. See also Note [HsRecField and HsRecUpdField] in GHC.Hs.Pat. -} -- Given a RdrName that refers to multiple record fields, and the type -- of its argument, try to determine the name of the selector that is -- meant. disambiguateSelector :: Located RdrName -> Type -> TcM Name disambiguateSelector lr@(L _ rdr) parent_type = do { fam_inst_envs <- tcGetFamInstEnvs ; case tyConOf fam_inst_envs parent_type of Nothing -> ambiguousSelector lr Just p -> do { xs <- lookupParents rdr ; let parent = RecSelData p ; case lookup parent xs of Just gre -> do { addUsedGRE True gre ; return (gre_name gre) } Nothing -> failWithTc (fieldNotInType parent rdr) } } -- This field name really is ambiguous, so add a suitable "ambiguous -- occurrence" error, then give up. ambiguousSelector :: Located RdrName -> TcM a ambiguousSelector (L _ rdr) = do { addAmbiguousNameErr rdr ; failM } -- | This name really is ambiguous, so add a suitable "ambiguous -- occurrence" error, then continue addAmbiguousNameErr :: RdrName -> TcM () addAmbiguousNameErr rdr = do { env <- getGlobalRdrEnv ; let gres = lookupGRE_RdrName rdr env ; setErrCtxt [] $ addNameClashErrRn rdr gres} -- Disambiguate the fields in a record update. -- See Note [Disambiguating record fields] disambiguateRecordBinds :: LHsExpr GhcRn -> TcRhoType -> [LHsRecUpdField GhcRn] -> ExpRhoType -> TcM [LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)] disambiguateRecordBinds record_expr record_rho rbnds res_ty -- Are all the fields unambiguous? = case mapM isUnambiguous rbnds of -- If so, just skip to looking up the Ids -- Always the case if DuplicateRecordFields is off Just rbnds' -> mapM lookupSelector rbnds' Nothing -> -- If not, try to identify a single parent do { fam_inst_envs <- tcGetFamInstEnvs -- Look up the possible parents for each field ; rbnds_with_parents <- getUpdFieldsParents ; let possible_parents = map (map fst . snd) rbnds_with_parents -- Identify a single parent ; p <- identifyParent fam_inst_envs possible_parents -- Pick the right selector with that parent for each field ; checkNoErrs $ mapM (pickParent p) rbnds_with_parents } where -- Extract the selector name of a field update if it is unambiguous isUnambiguous :: LHsRecUpdField GhcRn -> Maybe (LHsRecUpdField GhcRn,Name) isUnambiguous x = case unLoc (hsRecFieldLbl (unLoc x)) of Unambiguous sel_name _ -> Just (x, sel_name) Ambiguous{} -> Nothing -- Look up the possible parents and selector GREs for each field getUpdFieldsParents :: TcM [(LHsRecUpdField GhcRn , [(RecSelParent, GlobalRdrElt)])] getUpdFieldsParents = fmap (zip rbnds) $ mapM (lookupParents . unLoc . hsRecUpdFieldRdr . unLoc) rbnds -- Given a the lists of possible parents for each field, -- identify a single parent identifyParent :: FamInstEnvs -> [[RecSelParent]] -> TcM RecSelParent identifyParent fam_inst_envs possible_parents = case foldr1 intersect possible_parents of -- No parents for all fields: record update is ill-typed [] -> failWithTc (noPossibleParents rbnds) -- Exactly one datatype with all the fields: use that [p] -> return p -- Multiple possible parents: try harder to disambiguate -- Can we get a parent TyCon from the pushed-in type? _:_ | Just p <- tyConOfET fam_inst_envs res_ty -> return (RecSelData p) -- Does the expression being updated have a type signature? -- If so, try to extract a parent TyCon from it | Just {} <- obviousSig (unLoc record_expr) , Just tc <- tyConOf fam_inst_envs record_rho -> return (RecSelData tc) -- Nothing else we can try... _ -> failWithTc badOverloadedUpdate -- Make a field unambiguous by choosing the given parent. -- Emits an error if the field cannot have that parent, -- e.g. if the user writes -- r { x = e } :: T -- where T does not have field x. pickParent :: RecSelParent -> (LHsRecUpdField GhcRn, [(RecSelParent, GlobalRdrElt)]) -> TcM (LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)) pickParent p (upd, xs) = case lookup p xs of -- Phew! The parent is valid for this field. -- Previously ambiguous fields must be marked as -- used now that we know which one is meant, but -- unambiguous ones shouldn't be recorded again -- (giving duplicate deprecation warnings). Just gre -> do { unless (null (tail xs)) $ do let L loc _ = hsRecFieldLbl (unLoc upd) setSrcSpan loc $ addUsedGRE True gre ; lookupSelector (upd, gre_name gre) } -- The field doesn't belong to this parent, so report -- an error but keep going through all the fields Nothing -> do { addErrTc (fieldNotInType p (unLoc (hsRecUpdFieldRdr (unLoc upd)))) ; lookupSelector (upd, gre_name (snd (head xs))) } -- Given a (field update, selector name) pair, look up the -- selector to give a field update with an unambiguous Id lookupSelector :: (LHsRecUpdField GhcRn, Name) -> TcM (LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)) lookupSelector (L l upd, n) = do { i <- tcLookupId n ; let L loc af = hsRecFieldLbl upd lbl = rdrNameAmbiguousFieldOcc af ; return $ L l upd { hsRecFieldLbl = L loc (Unambiguous i (L loc lbl)) } } -- 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 :: RdrName -> RnM [(RecSelParent, GlobalRdrElt)] lookupParents rdr = do { env <- getGlobalRdrEnv ; let gres = lookupGRE_RdrName rdr env ; mapM lookupParent gres } where lookupParent :: GlobalRdrElt -> RnM (RecSelParent, GlobalRdrElt) lookupParent gre = do { id <- tcLookupId (gre_name gre) ; if isRecordSelector id then return (recordSelectorTyCon id, gre) else failWithTc (notSelector (gre_name gre)) } -- 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 _ = Nothing {- Game plan for record bindings ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1. Find the TyCon for the bindings, from the first field label. 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty. For each binding field = value 3. Instantiate the field type (from the field label) using the type envt from step 2. 4 Type check the value using tcArg, passing the field type as the expected argument type. This extends OK when the field types are universally quantified. -} tcRecordBinds :: ConLike -> [TcType] -- Expected type for each field -> HsRecordBinds GhcRn -> TcM (HsRecordBinds GhcTc) tcRecordBinds con_like arg_tys (HsRecFields rbinds dd) = do { mb_binds <- mapM do_bind rbinds ; return (HsRecFields (catMaybes mb_binds) dd) } where fields = map flSelector $ conLikeFieldLabels con_like flds_w_tys = zipEqual "tcRecordBinds" fields arg_tys do_bind :: LHsRecField GhcRn (LHsExpr GhcRn) -> TcM (Maybe (LHsRecField GhcTc (LHsExpr GhcTc))) do_bind (L l fld@(HsRecField { hsRecFieldLbl = f , hsRecFieldArg = rhs })) = do { mb <- tcRecordField con_like flds_w_tys f rhs ; case mb of Nothing -> return Nothing Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = f' , hsRecFieldArg = rhs' }))) } tcRecordUpd :: ConLike -> [TcType] -- Expected type for each field -> [LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)] -> TcM [LHsRecUpdField GhcTc] tcRecordUpd con_like arg_tys rbinds = fmap catMaybes $ mapM do_bind rbinds where fields = map flSelector $ conLikeFieldLabels con_like flds_w_tys = zipEqual "tcRecordUpd" fields arg_tys do_bind :: LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn) -> TcM (Maybe (LHsRecUpdField GhcTc)) do_bind (L l fld@(HsRecField { hsRecFieldLbl = L loc af , hsRecFieldArg = rhs })) = do { let lbl = rdrNameAmbiguousFieldOcc af sel_id = selectorAmbiguousFieldOcc af f = L loc (FieldOcc (idName sel_id) (L loc lbl)) ; mb <- tcRecordField con_like flds_w_tys f rhs ; case mb of Nothing -> return Nothing Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = L loc (Unambiguous (extFieldOcc (unLoc f')) (L loc lbl)) , hsRecFieldArg = rhs' }))) } tcRecordField :: ConLike -> Assoc Name Type -> LFieldOcc GhcRn -> LHsExpr GhcRn -> TcM (Maybe (LFieldOcc GhcTc, LHsExpr GhcTc)) tcRecordField con_like flds_w_tys (L loc (FieldOcc sel_name lbl)) rhs | Just field_ty <- assocMaybe flds_w_tys sel_name = addErrCtxt (fieldCtxt field_lbl) $ do { rhs' <- tcCheckPolyExprNC rhs field_ty ; let field_id = mkUserLocal (nameOccName sel_name) (nameUnique sel_name) Many field_ty loc -- Yuk: the field_id has the *unique* of the selector Id -- (so we can find it easily) -- but is a LocalId with the appropriate type of the RHS -- (so the desugarer knows the type of local binder to make) ; return (Just (L loc (FieldOcc field_id lbl), rhs')) } | otherwise = do { addErrTc (badFieldCon con_like field_lbl) ; return Nothing } where field_lbl = occNameFS $ rdrNameOcc (unLoc lbl) checkMissingFields :: ConLike -> HsRecordBinds GhcRn -> TcM () checkMissingFields con_like rbinds | null field_labels -- Not declared as a record; -- But C{} is still valid if no strict fields = if any isBanged field_strs then -- Illegal if any arg is strict addErrTc (missingStrictFields con_like []) else do warn <- woptM Opt_WarnMissingFields when (warn && notNull field_strs && null field_labels) (warnTc (Reason Opt_WarnMissingFields) True (missingFields con_like [])) | otherwise = do -- A record unless (null missing_s_fields) (addErrTc (missingStrictFields con_like missing_s_fields)) warn <- woptM Opt_WarnMissingFields when (warn && notNull missing_ns_fields) (warnTc (Reason Opt_WarnMissingFields) True (missingFields con_like missing_ns_fields)) where missing_s_fields = [ flLabel fl | (fl, str) <- field_info, isBanged str, not (fl `elemField` field_names_used) ] missing_ns_fields = [ flLabel fl | (fl, str) <- field_info, not (isBanged str), not (fl `elemField` field_names_used) ] field_names_used = hsRecFields rbinds field_labels = conLikeFieldLabels con_like field_info = zipEqual "missingFields" field_labels field_strs field_strs = conLikeImplBangs con_like fl `elemField` flds = any (\ fl' -> flSelector fl == fl') flds {- ************************************************************************ * * \subsection{Errors and contexts} * * ************************************************************************ Boring and alphabetical: -} fieldCtxt :: FieldLabelString -> SDoc fieldCtxt field_name = text "In the" <+> quotes (ppr field_name) <+> ptext (sLit "field of a record") addExprCtxt :: LHsExpr GhcRn -> TcRn a -> TcRn a addExprCtxt e thing_inside = addErrCtxt (exprCtxt (unLoc e)) thing_inside exprCtxt :: HsExpr GhcRn -> SDoc exprCtxt expr = hang (text "In the expression:") 2 (ppr (stripParensHsExpr expr)) addFunResCtxt :: Bool -- There is at least one argument -> HsExpr GhcTc -> 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 -- -- Used for naked variables too; but with has_args = False addFunResCtxt has_args fun fun_res_ty env_ty = addLandmarkErrCtxtM (\env -> (env, ) <$> mk_msg) -- 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' -- No need to call tcSplitNestedSigmaTys here, since env_ty is -- an ExpRhoTy, i.e., it's already instantiated. (_, _, env_tau) = tcSplitSigmaTy env' (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 | n_fun == n_env = Outputable.empty | n_fun > n_env , not_fun res_env = text "Probable cause:" <+> quotes (ppr fun) <+> text "is applied to too few arguments" | has_args , not_fun res_fun = text "Possible cause:" <+> quotes (ppr fun) <+> text "is applied to too many arguments" | otherwise = Outputable.empty -- Never suggest that a naked variable is -- applied to too many args! ; return info } where 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 Trac #13311, for instance: f :: forall a. (Monoid a) => 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: 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: [Maybe a] Return type: Maybe b So now GHC recognizes that `f` has one more argument type than it was actually provided. -} badFieldTypes :: [(FieldLabelString,TcType)] -> SDoc badFieldTypes prs = hang (text "Record update for insufficiently polymorphic field" <> plural prs <> colon) 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ]) badFieldsUpd :: [LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)] -- Field names that don't belong to a single datacon -> [ConLike] -- Data cons of the type which the first field name belongs to -> SDoc badFieldsUpd rbinds data_cons = hang (text "No constructor has all these fields:") 2 (pprQuotedList conflictingFields) -- See Note [Finding the conflicting fields] where -- A (preferably small) set of fields such that no constructor contains -- all of them. See Note [Finding the conflicting fields] conflictingFields = case nonMembers of -- nonMember belongs to a different type. (nonMember, _) : _ -> [aMember, nonMember] [] -> let -- All of rbinds belong to one type. In this case, repeatedly add -- a field to the set until no constructor contains the set. -- Each field, together with a list indicating which constructors -- have all the fields so far. growingSets :: [(FieldLabelString, [Bool])] growingSets = scanl1 combine membership combine (_, setMem) (field, fldMem) = (field, zipWith (&&) setMem fldMem) in -- Fields that don't change the membership status of the set -- are redundant and can be dropped. map (fst . head) $ groupBy ((==) `on` snd) growingSets aMember = ASSERT( not (null members) ) fst (head members) (members, nonMembers) = partition (or . snd) membership -- For each field, which constructors contain the field? membership :: [(FieldLabelString, [Bool])] membership = sortMembership $ map (\fld -> (fld, map (Set.member fld) fieldLabelSets)) $ map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) rbinds fieldLabelSets :: [Set.Set FieldLabelString] fieldLabelSets = map (Set.fromList . map flLabel . conLikeFieldLabels) data_cons -- Sort in order of increasing number of True, so that a smaller -- conflicting set can be found. sortMembership = map snd . sortBy (compare `on` fst) . map (\ item@(_, membershipRow) -> (countTrue membershipRow, item)) countTrue = count id {- Note [Finding the conflicting fields] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Suppose we have data A = A {a0, a1 :: Int} | B {b0, b1 :: Int} and we see a record update x { a0 = 3, a1 = 2, b0 = 4, b1 = 5 } Then we'd like to find the smallest subset of fields that no constructor has all of. Here, say, {a0,b0}, or {a0,b1}, etc. We don't really want to report that no constructor has all of {a0,a1,b0,b1}, because when there are hundreds of fields it's hard to see what was really wrong. We may need more than two fields, though; eg data T = A { x,y :: Int, v::Int } | B { y,z :: Int, v::Int } | C { z,x :: Int, v::Int } with update r { x=e1, y=e2, z=e3 }, we Finding the smallest subset is hard, so the code here makes a decent stab, no more. See #7989. -} naughtyRecordSel :: RdrName -> SDoc naughtyRecordSel sel_id = text "Cannot use record selector" <+> quotes (ppr sel_id) <+> text "as a function due to escaped type variables" $$ text "Probable fix: use pattern-matching syntax instead" notSelector :: Name -> SDoc notSelector field = hsep [quotes (ppr field), text "is not a record selector"] mixedSelectors :: [Id] -> [Id] -> SDoc mixedSelectors data_sels@(dc_rep_id:_) pat_syn_sels@(ps_rep_id:_) = ptext (sLit "Cannot use a mixture of pattern synonym and record selectors") $$ text "Record selectors defined by" <+> quotes (ppr (tyConName rep_dc)) <> text ":" <+> pprWithCommas ppr data_sels $$ text "Pattern synonym selectors defined by" <+> quotes (ppr (patSynName rep_ps)) <> text ":" <+> pprWithCommas ppr pat_syn_sels where RecSelPatSyn rep_ps = recordSelectorTyCon ps_rep_id RecSelData rep_dc = recordSelectorTyCon dc_rep_id mixedSelectors _ _ = panic "GHC.Tc.Gen.Expr: mixedSelectors emptylists" missingStrictFields :: ConLike -> [FieldLabelString] -> SDoc missingStrictFields con fields = header <> rest where rest | null fields = Outputable.empty -- Happens for non-record constructors -- with strict fields | otherwise = colon <+> pprWithCommas ppr fields header = text "Constructor" <+> quotes (ppr con) <+> text "does not have the required strict field(s)" missingFields :: ConLike -> [FieldLabelString] -> SDoc missingFields con fields = header <> rest where rest | null fields = Outputable.empty | otherwise = colon <+> pprWithCommas ppr fields header = text "Fields of" <+> quotes (ppr con) <+> text "not initialised" -- callCtxt fun args = text "In the call" <+> parens (ppr (foldl' mkHsApp fun args)) noPossibleParents :: [LHsRecUpdField GhcRn] -> SDoc noPossibleParents rbinds = hang (text "No type has all these fields:") 2 (pprQuotedList fields) where fields = map (hsRecFieldLbl . unLoc) rbinds badOverloadedUpdate :: SDoc badOverloadedUpdate = text "Record update is ambiguous, and requires a type signature" fieldNotInType :: RecSelParent -> RdrName -> SDoc fieldNotInType p rdr = unknownSubordinateErr (text "field of type" <+> quotes (ppr p)) rdr {- ************************************************************************ * * \subsection{Static Pointers} * * ************************************************************************ -} -- | A data type to describe why a variable is not closed. data NotClosedReason = NotLetBoundReason | NotTypeClosed VarSet | NotClosed Name NotClosedReason -- | Checks if the given name is closed and emits an error if not. -- -- See Note [Not-closed error messages]. checkClosedInStaticForm :: Name -> TcM () checkClosedInStaticForm name = do type_env <- getLclTypeEnv case checkClosed type_env name of Nothing -> return () Just reason -> addErrTc $ explain name reason where -- See Note [Checking closedness]. checkClosed :: TcTypeEnv -> Name -> Maybe NotClosedReason checkClosed type_env n = checkLoop type_env (unitNameSet n) n checkLoop :: TcTypeEnv -> NameSet -> Name -> Maybe NotClosedReason checkLoop type_env visited n = do -- The @visited@ set is an accumulating parameter that contains the set of -- visited nodes, so we avoid repeating cycles in the traversal. case lookupNameEnv type_env n of Just (ATcId { tct_id = tcid, tct_info = info }) -> case info of ClosedLet -> Nothing NotLetBound -> Just NotLetBoundReason NonClosedLet fvs type_closed -> listToMaybe $ -- Look for a non-closed variable in fvs [ NotClosed n' reason | n' <- nameSetElemsStable fvs , not (elemNameSet n' visited) , Just reason <- [checkLoop type_env (extendNameSet visited n') n'] ] ++ if type_closed then [] else -- We consider non-let-bound variables easier to figure out than -- non-closed types, so we report non-closed types to the user -- only if we cannot spot the former. [ NotTypeClosed $ tyCoVarsOfType (idType tcid) ] -- The binding is closed. _ -> Nothing -- Converts a reason into a human-readable sentence. -- -- @explain name reason@ starts with -- -- " is used in a static form but it is not closed because it" -- -- and then follows a list of causes. For each id in the path, the text -- -- "uses which" -- -- is appended, yielding something like -- -- "uses which uses which uses which" -- -- until the end of the path is reached, which is reported as either -- -- "is not let-bound" -- -- when the final node is not let-bound, or -- -- "has a non-closed type because it contains the type variables: -- v1, v2, v3" -- -- when the final node has a non-closed type. -- explain :: Name -> NotClosedReason -> SDoc explain name reason = quotes (ppr name) <+> text "is used in a static form but it is not closed" <+> text "because it" $$ sep (causes reason) causes :: NotClosedReason -> [SDoc] causes NotLetBoundReason = [text "is not let-bound."] causes (NotTypeClosed vs) = [ text "has a non-closed type because it contains the" , text "type variables:" <+> pprVarSet vs (hsep . punctuate comma . map (quotes . ppr)) ] causes (NotClosed n reason) = let msg = text "uses" <+> quotes (ppr n) <+> text "which" in case reason of NotClosed _ _ -> msg : causes reason _ -> let (xs0, xs1) = splitAt 1 $ causes reason in fmap (msg <+>) xs0 ++ xs1 -- Note [Not-closed error messages] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- When variables in a static form are not closed, we go through the trouble -- of explaining why they aren't. -- -- Thus, the following program -- -- > {-# LANGUAGE StaticPointers #-} -- > module M where -- > -- > f x = static g -- > where -- > g = h -- > h = x -- -- produces the error -- -- 'g' is used in a static form but it is not closed because it -- uses 'h' which uses 'x' which is not let-bound. -- -- And a program like -- -- > {-# LANGUAGE StaticPointers #-} -- > module M where -- > -- > import Data.Typeable -- > import GHC.StaticPtr -- > -- > f :: Typeable a => a -> StaticPtr TypeRep -- > f x = const (static (g undefined)) (h x) -- > where -- > g = h -- > h = typeOf -- -- produces the error -- -- 'g' is used in a static form but it is not closed because it -- uses 'h' which has a non-closed type because it contains the -- type variables: 'a' -- -- Note [Checking closedness] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- @checkClosed@ checks if a binding is closed and returns a reason if it is -- not. -- -- The bindings define a graph where the nodes are ids, and there is an edge -- from @id1@ to @id2@ if the rhs of @id1@ contains @id2@ among its free -- variables. -- -- When @n@ is not closed, it has to exist in the graph some node reachable -- from @n@ that it is not a let-bound variable or that it has a non-closed -- type. Thus, the "reason" is a path from @n@ to this offending node. -- -- When @n@ is not closed, we traverse the graph reachable from @n@ to build -- the reason. --