{- (c) The University of Glasgow 2006-2012 (c) The GRASP Project, Glasgow University, 1992-2002 -} {-# LANGUAGE CPP #-} {-# LANGUAGE TypeFamilies #-} module GHC.Tc.Gen.Sig( TcSigInfo(..), TcIdSigInfo(..), TcIdSigInst, TcPatSynInfo(..), TcSigFun, isPartialSig, hasCompleteSig, tcIdSigName, tcSigInfoName, completeSigPolyId_maybe, isCompleteHsSig, tcTySigs, tcUserTypeSig, completeSigFromId, tcInstSig, TcPragEnv, emptyPragEnv, lookupPragEnv, extendPragEnv, mkPragEnv, tcSpecPrags, tcSpecWrapper, tcImpPrags, addInlinePrags ) where #include "HsVersions.h" import GHC.Prelude import GHC.Hs import GHC.Tc.Gen.HsType import GHC.Tc.Types import GHC.Tc.Solver( pushLevelAndSolveEqualitiesX, reportUnsolvedEqualities ) import GHC.Tc.Utils.Monad import GHC.Tc.Utils.Zonk import GHC.Tc.Types.Origin import GHC.Tc.Utils.TcType import GHC.Tc.Utils.TcMType import GHC.Tc.Validity ( checkValidType ) import GHC.Tc.Utils.Unify( tcSkolemise, unifyType ) import GHC.Tc.Utils.Instantiate( topInstantiate, tcInstTypeBndrs ) import GHC.Tc.Utils.Env( tcLookupId ) import GHC.Tc.Types.Evidence( HsWrapper, (<.>) ) import GHC.Core( hasSomeUnfolding ) import GHC.Core.Type ( mkTyVarBinders ) import GHC.Core.Multiplicity import GHC.Driver.Session import GHC.Driver.Backend import GHC.Driver.Ppr import GHC.Types.Var ( TyVar, Specificity(..), tyVarKind, binderVars ) import GHC.Types.Id ( Id, idName, idType, setInlinePragma , mkLocalId, realIdUnfolding ) import GHC.Builtin.Names( mkUnboundName ) import GHC.Types.Basic import GHC.Unit.Module( getModule ) import GHC.Types.Name import GHC.Types.Name.Env import GHC.Utils.Outputable import GHC.Utils.Panic import GHC.Types.SrcLoc import GHC.Utils.Misc as Utils ( singleton ) import GHC.Data.Maybe( orElse ) import Data.Maybe( mapMaybe ) import Control.Monad( unless ) {- ------------------------------------------------------------- Note [Overview of type signatures] ---------------------------------------------------------------- Type signatures, including partial signatures, are jolly tricky, especially on value bindings. Here's an overview. f :: forall a. [a] -> [a] g :: forall b. _ -> b f = ...g... g = ...f... * HsSyn: a signature in a binding starts off as a TypeSig, in type HsBinds.Sig * When starting a mutually recursive group, like f/g above, we call tcTySig on each signature in the group. * tcTySig: Sig -> TcIdSigInfo - For a /complete/ signature, like 'f' above, tcTySig kind-checks the HsType, producing a Type, and wraps it in a CompleteSig, and extend the type environment with this polymorphic 'f'. - For a /partial/signature, like 'g' above, tcTySig does nothing Instead it just wraps the pieces in a PartialSig, to be handled later. * tcInstSig: TcIdSigInfo -> TcIdSigInst In tcMonoBinds, when looking at an individual binding, we use tcInstSig to instantiate the signature forall's in the signature, and attribute that instantiated (monomorphic) type to the binder. You can see this in GHC.Tc.Gen.Bind.tcLhsId. The instantiation does the obvious thing for complete signatures, but for /partial/ signatures it starts from the HsSyn, so it has to kind-check it etc: tcHsPartialSigType. It's convenient to do this at the same time as instantiation, because we can make the wildcards into unification variables right away, raather than somehow quantifying over them. And the "TcLevel" of those unification variables is correct because we are in tcMonoBinds. Note [Binding scoped type variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The type variables *brought into lexical scope* by a type signature may be a subset of the *quantified type variables* of the signatures, for two reasons: * With kind polymorphism a signature like f :: forall f a. f a -> f a may actually give rise to f :: forall k. forall (f::k -> *) (a:k). f a -> f a So the sig_tvs will be [k,f,a], but only f,a are scoped. NB: the scoped ones are not necessarily the *initial* ones! * Even aside from kind polymorphism, there may be more instantiated type variables than lexically-scoped ones. For example: type T a = forall b. b -> (a,b) f :: forall c. T c Here, the signature for f will have one scoped type variable, c, but two instantiated type variables, c' and b'. However, all of this only applies to the renamer. The typechecker just puts all of them into the type environment; any lexical-scope errors were dealt with by the renamer. -} {- ********************************************************************* * * Utility functions for TcSigInfo * * ********************************************************************* -} tcIdSigName :: TcIdSigInfo -> Name tcIdSigName (CompleteSig { sig_bndr = id }) = idName id tcIdSigName (PartialSig { psig_name = n }) = n tcSigInfoName :: TcSigInfo -> Name tcSigInfoName (TcIdSig idsi) = tcIdSigName idsi tcSigInfoName (TcPatSynSig tpsi) = patsig_name tpsi completeSigPolyId_maybe :: TcSigInfo -> Maybe TcId completeSigPolyId_maybe sig | TcIdSig sig_info <- sig , CompleteSig { sig_bndr = id } <- sig_info = Just id | otherwise = Nothing {- ********************************************************************* * * Typechecking user signatures * * ********************************************************************* -} tcTySigs :: [LSig GhcRn] -> TcM ([TcId], TcSigFun) tcTySigs hs_sigs = checkNoErrs $ do { -- Fail if any of the signatures is duff -- Hence mapAndReportM -- See Note [Fail eagerly on bad signatures] ty_sigs_s <- mapAndReportM tcTySig hs_sigs ; let ty_sigs = concat ty_sigs_s poly_ids = mapMaybe completeSigPolyId_maybe ty_sigs -- The returned [TcId] are the ones for which we have -- a complete type signature. -- See Note [Complete and partial type signatures] env = mkNameEnv [(tcSigInfoName sig, sig) | sig <- ty_sigs] ; return (poly_ids, lookupNameEnv env) } tcTySig :: LSig GhcRn -> TcM [TcSigInfo] tcTySig (L _ (IdSig _ id)) = do { let ctxt = FunSigCtxt (idName id) False -- False: do not report redundant constraints -- The user has no control over the signature! sig = completeSigFromId ctxt id ; return [TcIdSig sig] } tcTySig (L loc (TypeSig _ names sig_ty)) = setSrcSpanA loc $ do { sigs <- sequence [ tcUserTypeSig (locA loc) sig_ty (Just name) | L _ name <- names ] ; return (map TcIdSig sigs) } tcTySig (L loc (PatSynSig _ names sig_ty)) = setSrcSpanA loc $ do { tpsigs <- sequence [ tcPatSynSig name sig_ty | L _ name <- names ] ; return (map TcPatSynSig tpsigs) } tcTySig _ = return [] tcUserTypeSig :: SrcSpan -> LHsSigWcType GhcRn -> Maybe Name -> TcM TcIdSigInfo -- A function or expression type signature -- Returns a fully quantified type signature; even the wildcards -- are quantified with ordinary skolems that should be instantiated -- -- The SrcSpan is what to declare as the binding site of the -- any skolems in the signature. For function signatures we -- use the whole `f :: ty' signature; for expression signatures -- just the type part. -- -- Just n => Function type signature name :: type -- Nothing => Expression type signature <expr> :: type tcUserTypeSig loc hs_sig_ty mb_name | isCompleteHsSig hs_sig_ty = do { sigma_ty <- tcHsSigWcType ctxt_F hs_sig_ty ; traceTc "tcuser" (ppr sigma_ty) ; return $ CompleteSig { sig_bndr = mkLocalId name Many sigma_ty -- We use `Many' as the multiplicity here, -- as if this identifier corresponds to -- anything, it is a top-level -- definition. Which are all unrestricted in -- the current implementation. , sig_ctxt = ctxt_T , sig_loc = loc } } -- Location of the <type> in f :: <type> -- Partial sig with wildcards | otherwise = return (PartialSig { psig_name = name, psig_hs_ty = hs_sig_ty , sig_ctxt = ctxt_F, sig_loc = loc }) where name = case mb_name of Just n -> n Nothing -> mkUnboundName (mkVarOcc "<expression>") ctxt_F = case mb_name of Just n -> FunSigCtxt n False Nothing -> ExprSigCtxt ctxt_T = case mb_name of Just n -> FunSigCtxt n True Nothing -> ExprSigCtxt completeSigFromId :: UserTypeCtxt -> Id -> TcIdSigInfo -- Used for instance methods and record selectors completeSigFromId ctxt id = CompleteSig { sig_bndr = id , sig_ctxt = ctxt , sig_loc = getSrcSpan id } isCompleteHsSig :: LHsSigWcType GhcRn -> Bool -- ^ If there are no wildcards, return a LHsSigWcType isCompleteHsSig (HsWC { hswc_ext = wcs, hswc_body = hs_sig_ty }) = null wcs && no_anon_wc_sig_ty hs_sig_ty no_anon_wc_sig_ty :: LHsSigType GhcRn -> Bool no_anon_wc_sig_ty (L _ (HsSig{sig_bndrs = outer_bndrs, sig_body = body})) = all no_anon_wc_tvb (hsOuterExplicitBndrs outer_bndrs) && no_anon_wc_ty body no_anon_wc_ty :: LHsType GhcRn -> Bool no_anon_wc_ty lty = go lty where go (L _ ty) = case ty of HsWildCardTy _ -> False HsAppTy _ ty1 ty2 -> go ty1 && go ty2 HsAppKindTy _ ty ki -> go ty && go ki HsFunTy _ w ty1 ty2 -> go ty1 && go ty2 && go (arrowToHsType w) HsListTy _ ty -> go ty HsTupleTy _ _ tys -> gos tys HsSumTy _ tys -> gos tys HsOpTy _ ty1 _ ty2 -> go ty1 && go ty2 HsParTy _ ty -> go ty HsIParamTy _ _ ty -> go ty HsKindSig _ ty kind -> go ty && go kind HsDocTy _ ty _ -> go ty HsBangTy _ _ ty -> go ty HsRecTy _ flds -> gos $ map (cd_fld_type . unLoc) flds HsExplicitListTy _ _ tys -> gos tys HsExplicitTupleTy _ tys -> gos tys HsForAllTy { hst_tele = tele , hst_body = ty } -> no_anon_wc_tele tele && go ty HsQualTy { hst_ctxt = ctxt , hst_body = ty } -> gos (fromMaybeContext ctxt) && go ty HsSpliceTy _ (HsSpliced _ _ (HsSplicedTy ty)) -> go $ L noSrcSpanA ty HsSpliceTy{} -> True HsTyLit{} -> True HsTyVar{} -> True HsStarTy{} -> True XHsType{} -> True -- HsCoreTy, which does not have any wildcard gos = all go no_anon_wc_tele :: HsForAllTelescope GhcRn -> Bool no_anon_wc_tele tele = case tele of HsForAllVis { hsf_vis_bndrs = ltvs } -> all no_anon_wc_tvb ltvs HsForAllInvis { hsf_invis_bndrs = ltvs } -> all no_anon_wc_tvb ltvs no_anon_wc_tvb :: LHsTyVarBndr flag GhcRn -> Bool no_anon_wc_tvb (L _ tvb) = case tvb of UserTyVar _ _ _ -> True KindedTyVar _ _ _ ki -> no_anon_wc_ty ki {- Note [Fail eagerly on bad signatures] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If a type signature is wrong, fail immediately: * the type sigs may bind type variables, so proceeding without them can lead to a cascade of errors * the type signature might be ambiguous, in which case checking the code against the signature will give a very similar error to the ambiguity error. ToDo: this means we fall over if any top-level type signature in the module is wrong, because we typecheck all the signatures together (see GHC.Tc.Gen.Bind.tcValBinds). Moreover, because of top-level captureTopConstraints, only insoluble constraints will be reported. We typecheck all signatures at the same time because a signature like f,g :: blah might have f and g from different SCCs. So it's a bit awkward to get better error recovery, and no one has complained! -} {- ********************************************************************* * * Type checking a pattern synonym signature * * ************************************************************************ Note [Pattern synonym signatures] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Pattern synonym signatures are surprisingly tricky (see #11224 for example). In general they look like this: pattern P :: forall univ_tvs. req_theta => forall ex_tvs. prov_theta => arg1 -> .. -> argn -> res_ty For parsing and renaming we treat the signature as an ordinary LHsSigType. Once we get to type checking, we decompose it into its parts, in tcPatSynSig. * Note that 'forall univ_tvs' and 'req_theta =>' and 'forall ex_tvs' and 'prov_theta =>' are all optional. We gather the pieces at the top of tcPatSynSig * Initially the implicitly-bound tyvars (added by the renamer) include both universal and existential vars. * After we kind-check the pieces and convert to Types, we do kind generalisation. Note [Report unsolved equalities in tcPatSynSig] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It's important that we solve /all/ the equalities in a pattern synonym signature, because we are going to zonk the signature to a Type (not a TcType), in GHC.Tc.TyCl.PatSyn.tc_patsyn_finish, and that fails if there are un-filled-in coercion variables mentioned in the type (#15694). So we solve all the equalities we can, and report any unsolved ones, rather than leaving them in the ambient constraints to be solved later. Pattern synonyms are top-level, so there's no problem with completely solving them. -} tcPatSynSig :: Name -> LHsSigType GhcRn -> TcM TcPatSynInfo -- See Note [Pattern synonym signatures] -- See Note [Recipe for checking a signature] in GHC.Tc.Gen.HsType tcPatSynSig name sig_ty@(L _ (HsSig{sig_bndrs = hs_outer_bndrs, sig_body = hs_ty})) | (hs_req, hs_ty1) <- splitLHsQualTy hs_ty , (ex_hs_tvbndrs, hs_prov, hs_body_ty) <- splitLHsSigmaTyInvis hs_ty1 = do { traceTc "tcPatSynSig 1" (ppr sig_ty) ; let skol_info = DataConSkol name ; (tclvl, wanted, (outer_bndrs, (ex_bndrs, (req, prov, body_ty)))) <- pushLevelAndSolveEqualitiesX "tcPatSynSig" $ -- See Note [solveEqualities in tcPatSynSig] tcOuterTKBndrs skol_info hs_outer_bndrs $ tcExplicitTKBndrs ex_hs_tvbndrs $ do { req <- tcHsContext hs_req ; prov <- tcHsContext hs_prov ; body_ty <- tcHsOpenType hs_body_ty -- A (literal) pattern can be unlifted; -- e.g. pattern Zero <- 0# (#12094) ; return (req, prov, body_ty) } ; let implicit_tvs :: [TcTyVar] univ_bndrs :: [TcInvisTVBinder] (implicit_tvs, univ_bndrs) = case outer_bndrs of HsOuterImplicit{hso_ximplicit = implicit_tvs} -> (implicit_tvs, []) HsOuterExplicit{hso_xexplicit = univ_bndrs} -> ([], univ_bndrs) ; implicit_tvs <- zonkAndScopedSort implicit_tvs ; let implicit_bndrs = mkTyVarBinders SpecifiedSpec implicit_tvs -- Kind generalisation ; let ungen_patsyn_ty = build_patsyn_type implicit_bndrs univ_bndrs req ex_bndrs prov body_ty ; traceTc "tcPatSynSig" (ppr ungen_patsyn_ty) ; kvs <- kindGeneralizeAll ungen_patsyn_ty ; reportUnsolvedEqualities skol_info kvs tclvl wanted -- See Note [Report unsolved equalities in tcPatSynSig] -- These are /signatures/ so we zonk to squeeze out any kind -- unification variables. Do this after kindGeneralizeAll which may -- default kind variables to *. ; ze <- mkEmptyZonkEnv NoFlexi ; (ze, kv_bndrs) <- zonkTyVarBindersX ze (mkTyVarBinders InferredSpec kvs) ; (ze, implicit_bndrs) <- zonkTyVarBindersX ze implicit_bndrs ; (ze, univ_bndrs) <- zonkTyVarBindersX ze univ_bndrs ; (ze, ex_bndrs) <- zonkTyVarBindersX ze ex_bndrs ; req <- zonkTcTypesToTypesX ze req ; prov <- zonkTcTypesToTypesX ze prov ; body_ty <- zonkTcTypeToTypeX ze body_ty -- Now do validity checking ; checkValidType ctxt $ build_patsyn_type implicit_bndrs univ_bndrs req ex_bndrs prov body_ty -- arguments become the types of binders. We thus cannot allow -- levity polymorphism here ; let (arg_tys, _) = tcSplitFunTys body_ty ; mapM_ (checkForLevPoly empty . scaledThing) arg_tys ; traceTc "tcTySig }" $ vcat [ text "kvs" <+> ppr_tvs (binderVars kv_bndrs) , text "implicit_tvs" <+> ppr_tvs (binderVars implicit_bndrs) , text "univ_tvs" <+> ppr_tvs (binderVars univ_bndrs) , text "req" <+> ppr req , text "ex_tvs" <+> ppr_tvs (binderVars ex_bndrs) , text "prov" <+> ppr prov , text "body_ty" <+> ppr body_ty ] ; return (TPSI { patsig_name = name , patsig_implicit_bndrs = kv_bndrs ++ implicit_bndrs , patsig_univ_bndrs = univ_bndrs , patsig_req = req , patsig_ex_bndrs = ex_bndrs , patsig_prov = prov , patsig_body_ty = body_ty }) } where ctxt = PatSynCtxt name build_patsyn_type implicit_bndrs univ_bndrs req ex_bndrs prov body = mkInvisForAllTys implicit_bndrs $ mkInvisForAllTys univ_bndrs $ mkPhiTy req $ mkInvisForAllTys ex_bndrs $ mkPhiTy prov $ body ppr_tvs :: [TyVar] -> SDoc ppr_tvs tvs = braces (vcat [ ppr tv <+> dcolon <+> ppr (tyVarKind tv) | tv <- tvs]) {- ********************************************************************* * * Instantiating user signatures * * ********************************************************************* -} tcInstSig :: TcIdSigInfo -> TcM TcIdSigInst -- Instantiate a type signature; only used with plan InferGen tcInstSig sig@(CompleteSig { sig_bndr = poly_id, sig_loc = loc }) = setSrcSpan loc $ -- Set the binding site of the tyvars do { (tv_prs, theta, tau) <- tcInstTypeBndrs poly_id -- See Note [Pattern bindings and complete signatures] ; return (TISI { sig_inst_sig = sig , sig_inst_skols = tv_prs , sig_inst_wcs = [] , sig_inst_wcx = Nothing , sig_inst_theta = theta , sig_inst_tau = tau }) } tcInstSig hs_sig@(PartialSig { psig_hs_ty = hs_ty , sig_ctxt = ctxt , sig_loc = loc }) = setSrcSpan loc $ -- Set the binding site of the tyvars do { traceTc "Staring partial sig {" (ppr hs_sig) ; (wcs, wcx, tv_prs, theta, tau) <- tcHsPartialSigType ctxt hs_ty -- See Note [Checking partial type signatures] in GHC.Tc.Gen.HsType ; let inst_sig = TISI { sig_inst_sig = hs_sig , sig_inst_skols = tv_prs , sig_inst_wcs = wcs , sig_inst_wcx = wcx , sig_inst_theta = theta , sig_inst_tau = tau } ; traceTc "End partial sig }" (ppr inst_sig) ; return inst_sig } {- Note [Pattern bindings and complete signatures] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data T a = MkT a a f :: forall a. a->a g :: forall b. b->b MkT f g = MkT (\x->x) (\y->y) Here we'll infer a type from the pattern of 'T a', but if we feed in the signature types for f and g, we'll end up unifying 'a' and 'b' So we instantiate f and g's signature with TyVarTv skolems (newMetaTyVarTyVars) that can unify with each other. If too much unification takes place, we'll find out when we do the final impedance-matching check in GHC.Tc.Gen.Bind.mkExport See Note [TyVarTv] in GHC.Tc.Utils.TcMType None of this applies to a function binding with a complete signature, which doesn't use tcInstSig. See GHC.Tc.Gen.Bind.tcPolyCheck. -} {- ********************************************************************* * * Pragmas and PragEnv * * ********************************************************************* -} type TcPragEnv = NameEnv [LSig GhcRn] emptyPragEnv :: TcPragEnv emptyPragEnv = emptyNameEnv lookupPragEnv :: TcPragEnv -> Name -> [LSig GhcRn] lookupPragEnv prag_fn n = lookupNameEnv prag_fn n `orElse` [] extendPragEnv :: TcPragEnv -> (Name, LSig GhcRn) -> TcPragEnv extendPragEnv prag_fn (n, sig) = extendNameEnv_Acc (:) Utils.singleton prag_fn n sig --------------- mkPragEnv :: [LSig GhcRn] -> LHsBinds GhcRn -> TcPragEnv mkPragEnv sigs binds = foldl' extendPragEnv emptyNameEnv prs where prs = mapMaybe get_sig sigs get_sig :: LSig GhcRn -> Maybe (Name, LSig GhcRn) get_sig (L l (SpecSig x lnm@(L _ nm) ty inl)) = Just (nm, L l $ SpecSig x lnm ty (add_arity nm inl)) get_sig (L l (InlineSig x lnm@(L _ nm) inl)) = Just (nm, L l $ InlineSig x lnm (add_arity nm inl)) get_sig (L l (SCCFunSig x st lnm@(L _ nm) str)) = Just (nm, L l $ SCCFunSig x st lnm str) get_sig _ = Nothing add_arity n inl_prag -- Adjust inl_sat field to match visible arity of function | Inline <- inl_inline inl_prag -- add arity only for real INLINE pragmas, not INLINABLE = case lookupNameEnv ar_env n of Just ar -> inl_prag { inl_sat = Just ar } Nothing -> WARN( True, text "mkPragEnv no arity" <+> ppr n ) -- There really should be a binding for every INLINE pragma inl_prag | otherwise = inl_prag -- ar_env maps a local to the arity of its definition ar_env :: NameEnv Arity ar_env = foldr lhsBindArity emptyNameEnv binds lhsBindArity :: LHsBind GhcRn -> NameEnv Arity -> NameEnv Arity lhsBindArity (L _ (FunBind { fun_id = id, fun_matches = ms })) env = extendNameEnv env (unLoc id) (matchGroupArity ms) lhsBindArity _ env = env -- PatBind/VarBind ----------------- addInlinePrags :: TcId -> [LSig GhcRn] -> TcM TcId addInlinePrags poly_id prags_for_me | inl@(L _ prag) : inls <- inl_prags = do { traceTc "addInlinePrag" (ppr poly_id $$ ppr prag) ; unless (null inls) (warn_multiple_inlines inl inls) ; return (poly_id `setInlinePragma` prag) } | otherwise = return poly_id where inl_prags = [L loc prag | L loc (InlineSig _ _ prag) <- prags_for_me] warn_multiple_inlines _ [] = return () warn_multiple_inlines inl1@(L loc prag1) (inl2@(L _ prag2) : inls) | inlinePragmaActivation prag1 == inlinePragmaActivation prag2 , noUserInlineSpec (inlinePragmaSpec prag1) = -- Tiresome: inl1 is put there by virtue of being in a hs-boot loop -- and inl2 is a user NOINLINE pragma; we don't want to complain warn_multiple_inlines inl2 inls | otherwise = setSrcSpanA loc $ addWarnTc NoReason (hang (text "Multiple INLINE pragmas for" <+> ppr poly_id) 2 (vcat (text "Ignoring all but the first" : map pp_inl (inl1:inl2:inls)))) pp_inl (L loc prag) = ppr prag <+> parens (ppr loc) {- ********************************************************************* * * SPECIALISE pragmas * * ************************************************************************ Note [Handling SPECIALISE pragmas] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The basic idea is this: foo :: Num a => a -> b -> a {-# SPECIALISE foo :: Int -> b -> Int #-} We check that (forall a b. Num a => a -> b -> a) is more polymorphic than forall b. Int -> b -> Int (for which we could use tcSubType, but see below), generating a HsWrapper to connect the two, something like wrap = /\b. <hole> Int b dNumInt This wrapper is put in the TcSpecPrag, in the ABExport record of the AbsBinds. f :: (Eq a, Ix b) => a -> b -> Bool {-# SPECIALISE f :: (Ix p, Ix q) => Int -> (p,q) -> Bool #-} f = <poly_rhs> From this the typechecker generates AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds SpecPrag (wrap_fn :: forall a b. (Eq a, Ix b) => XXX -> forall p q. (Ix p, Ix q) => XXX[ Int/a, (p,q)/b ]) From these we generate: Rule: forall p, q, (dp:Ix p), (dq:Ix q). f Int (p,q) dInt ($dfInPair dp dq) = f_spec p q dp dq Spec bind: f_spec = wrap_fn <poly_rhs> Note that * The LHS of the rule may mention dictionary *expressions* (eg $dfIxPair dp dq), and that is essential because the dp, dq are needed on the RHS. * The RHS of f_spec, <poly_rhs> has a *copy* of 'binds', so that it can fully specialise it. From the TcSpecPrag, in GHC.HsToCore.Binds we generate a binding for f_spec and a RULE: f_spec :: Int -> b -> Int f_spec = wrap<f rhs> RULE: forall b (d:Num b). f b d = f_spec b The RULE is generated by taking apart the HsWrapper, which is a little delicate, but works. Some wrinkles 1. In tcSpecWrapper, rather than calling tcSubType, we directly call skolemise/instantiate. That is mainly because of wrinkle (2). Historical note: in the past, tcSubType did co/contra stuff, which could generate too complex a LHS for the RULE, which was another reason for not using tcSubType. But that reason has gone away with simple subsumption (#17775). 2. We need to take care with type families (#5821). Consider type instance F Int = Bool f :: Num a => a -> F a {-# SPECIALISE foo :: Int -> Bool #-} We *could* try to generate an f_spec with precisely the declared type: f_spec :: Int -> Bool f_spec = <f rhs> Int dNumInt |> co RULE: forall d. f Int d = f_spec |> sym co but the 'co' and 'sym co' are (a) playing no useful role, and (b) are hard to generate. At all costs we must avoid this: RULE: forall d. f Int d |> co = f_spec because the LHS will never match (indeed it's rejected in decomposeRuleLhs). So we simply do this: - Generate a constraint to check that the specialised type (after skolemisation) is equal to the instantiated function type. - But *discard* the evidence (coercion) for that constraint, so that we ultimately generate the simpler code f_spec :: Int -> F Int f_spec = <f rhs> Int dNumInt RULE: forall d. f Int d = f_spec You can see this discarding happening in tcSpecPrag 3. Note that the HsWrapper can transform *any* function with the right type prefix forall ab. (Eq a, Ix b) => XXX regardless of XXX. It's sort of polymorphic in XXX. This is useful: we use the same wrapper to transform each of the class ops, as well as the dict. That's what goes on in GHC.Tc.TyCl.Instance.mk_meth_spec_prags -} tcSpecPrags :: Id -> [LSig GhcRn] -> TcM [LTcSpecPrag] -- Add INLINE and SPECIALSE pragmas -- INLINE prags are added to the (polymorphic) Id directly -- SPECIALISE prags are passed to the desugarer via TcSpecPrags -- Pre-condition: the poly_id is zonked -- Reason: required by tcSubExp tcSpecPrags poly_id prag_sigs = do { traceTc "tcSpecPrags" (ppr poly_id <+> ppr spec_sigs) ; unless (null bad_sigs) warn_discarded_sigs ; pss <- mapAndRecoverM (wrapLocMA (tcSpecPrag poly_id)) spec_sigs ; return $ concatMap (\(L l ps) -> map (L (locA l)) ps) pss } where spec_sigs = filter isSpecLSig prag_sigs bad_sigs = filter is_bad_sig prag_sigs is_bad_sig s = not (isSpecLSig s || isInlineLSig s || isSCCFunSig s) warn_discarded_sigs = addWarnTc NoReason (hang (text "Discarding unexpected pragmas for" <+> ppr poly_id) 2 (vcat (map (ppr . getLoc) bad_sigs))) -------------- tcSpecPrag :: TcId -> Sig GhcRn -> TcM [TcSpecPrag] tcSpecPrag poly_id prag@(SpecSig _ fun_name hs_tys inl) -- See Note [Handling SPECIALISE pragmas] -- -- The Name fun_name in the SpecSig may not be the same as that of the poly_id -- Example: SPECIALISE for a class method: the Name in the SpecSig is -- for the selector Id, but the poly_id is something like $cop -- However we want to use fun_name in the error message, since that is -- what the user wrote (#8537) = addErrCtxt (spec_ctxt prag) $ do { warnIf (not (isOverloadedTy poly_ty || isInlinePragma inl)) (text "SPECIALISE pragma for non-overloaded function" <+> quotes (ppr fun_name)) -- Note [SPECIALISE pragmas] ; spec_prags <- mapM tc_one hs_tys ; traceTc "tcSpecPrag" (ppr poly_id $$ nest 2 (vcat (map ppr spec_prags))) ; return spec_prags } where name = idName poly_id poly_ty = idType poly_id spec_ctxt prag = hang (text "In the pragma:") 2 (ppr prag) tc_one hs_ty = do { spec_ty <- tcHsSigType (FunSigCtxt name False) hs_ty ; wrap <- tcSpecWrapper (FunSigCtxt name True) poly_ty spec_ty ; return (SpecPrag poly_id wrap inl) } tcSpecPrag _ prag = pprPanic "tcSpecPrag" (ppr prag) -------------- tcSpecWrapper :: UserTypeCtxt -> TcType -> TcType -> TcM HsWrapper -- A simpler variant of tcSubType, used for SPECIALISE pragmas -- See Note [Handling SPECIALISE pragmas], wrinkle 1 tcSpecWrapper ctxt poly_ty spec_ty = do { (sk_wrap, inst_wrap) <- tcSkolemise ctxt spec_ty $ \ spec_tau -> do { (inst_wrap, tau) <- topInstantiate orig poly_ty ; _ <- unifyType Nothing spec_tau tau -- Deliberately ignore the evidence -- See Note [Handling SPECIALISE pragmas], -- wrinkle (2) ; return inst_wrap } ; return (sk_wrap <.> inst_wrap) } where orig = SpecPragOrigin ctxt -------------- tcImpPrags :: [LSig GhcRn] -> TcM [LTcSpecPrag] -- SPECIALISE pragmas for imported things tcImpPrags prags = do { this_mod <- getModule ; dflags <- getDynFlags ; if (not_specialising dflags) then return [] else do { pss <- mapAndRecoverM (wrapLocMA tcImpSpec) [L loc (name,prag) | (L loc prag@(SpecSig _ (L _ name) _ _)) <- prags , not (nameIsLocalOrFrom this_mod name) ] ; return $ concatMap (\(L l ps) -> map (L (locA l)) ps) pss } } where -- Ignore SPECIALISE pragmas for imported things -- when we aren't specialising, or when we aren't generating -- code. The latter happens when Haddocking the base library; -- we don't want complaints about lack of INLINABLE pragmas not_specialising dflags | not (gopt Opt_Specialise dflags) = True | otherwise = case backend dflags of NoBackend -> True Interpreter -> True _other -> False tcImpSpec :: (Name, Sig GhcRn) -> TcM [TcSpecPrag] tcImpSpec (name, prag) = do { id <- tcLookupId name ; if hasSomeUnfolding (realIdUnfolding id) -- See Note [SPECIALISE pragmas for imported Ids] then tcSpecPrag id prag else do { addWarnTc NoReason (impSpecErr name) ; return [] } } impSpecErr :: Name -> SDoc impSpecErr name = hang (text "You cannot SPECIALISE" <+> quotes (ppr name)) 2 (vcat [ text "because its definition is not visible in this module" , text "Hint: make sure" <+> ppr mod <+> text "is compiled with -O" , text " and that" <+> quotes (ppr name) <+> text "has an INLINABLE pragma" ]) where mod = nameModule name {- Note [SPECIALISE pragmas for imported Ids] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ An imported Id may or may not have an unfolding. If not, we obviously can't specialise it here; indeed the desugar falls over (#18118). We used to test whether it had a user-specified INLINABLE pragma but, because of Note [Worker-wrapper for INLINABLE functions] in GHC.Core.Opt.WorkWrap, even an INLINABLE function may end up with a wrapper that has no pragma, just an unfolding (#19246). So now we just test whether the function has an unfolding. There's a risk that a pragma-free function may have an unfolding now (because it is fairly small), and then gets a bit bigger, and no longer has an unfolding in the future. But then you'll get a helpful error message suggesting an INLINABLE pragma, which you can follow. That seems enough for now. -}