GHC/Tc/TyCl/Build.hs

    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
    -}

    {-# LANGUAGE CPP #-}

    {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}

    module GHC.Tc.TyCl.Build (
            buildDataCon,
            buildPatSyn,
            TcMethInfo, MethInfo, buildClass,
            mkNewTyConRhs,
            newImplicitBinder, newTyConRepName
        ) where

    #include "HsVersions.h"

    import GHC.Prelude

    import GHC.Iface.Env
    import GHC.Core.FamInstEnv( FamInstEnvs, mkNewTypeCoAxiom )
    import GHC.Builtin.Types( isCTupleTyConName )
    import GHC.Builtin.Types.Prim ( voidPrimTy )
    import GHC.Core.DataCon
    import GHC.Core.PatSyn
    import GHC.Types.Var
    import GHC.Types.Var.Set
    import GHC.Types.Basic
    import GHC.Types.Name
    import GHC.Types.Name.Env
    import GHC.Types.Id.Make
    import GHC.Core.Class
    import GHC.Core.TyCon
    import GHC.Core.Type
    import GHC.Types.Id
    import GHC.Tc.Utils.TcType
    import GHC.Core.Multiplicity

    import GHC.Types.SrcLoc( SrcSpan, noSrcSpan )
    import GHC.Driver.Session
    import GHC.Tc.Utils.Monad
    import GHC.Types.Unique.Supply
    import GHC.Utils.Misc
    import GHC.Utils.Outputable

    mkNewTyConRhs :: Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
    -- ^ Monadic because it makes a Name for the coercion TyCon
    --   We pass the Name of the parent TyCon, as well as the TyCon itself,
    --   because the latter is part of a knot, whereas the former is not.
    mkNewTyConRhs tycon_name tycon con
      = do  { co_tycon_name <- newImplicitBinder tycon_name mkNewTyCoOcc
            ; let nt_ax = mkNewTypeCoAxiom co_tycon_name tycon etad_tvs etad_roles etad_rhs
            ; traceIf (text "mkNewTyConRhs" <+> ppr nt_ax)
            ; return (NewTyCon { data_con    = con,
                                 nt_rhs      = rhs_ty,
                                 nt_etad_rhs = (etad_tvs, etad_rhs),
                                 nt_co       = nt_ax,
                                 nt_lev_poly = isKindLevPoly res_kind } ) }
                                 -- Coreview looks through newtypes with a Nothing
                                 -- for nt_co, or uses explicit coercions otherwise
      where
        tvs      = tyConTyVars tycon
        roles    = tyConRoles tycon
        res_kind = tyConResKind tycon
        con_arg_ty = case dataConRepArgTys con of
                       [arg_ty] -> scaledThing arg_ty
                       tys -> pprPanic "mkNewTyConRhs" (ppr con <+> ppr tys)
        rhs_ty = substTyWith (dataConUnivTyVars con)
                             (mkTyVarTys tvs) con_arg_ty
            -- Instantiate the newtype's RHS with the
            -- type variables from the tycon
            -- NB: a newtype DataCon has a type that must look like
            --        forall tvs.  <arg-ty> -> T tvs
            -- Note that we *can't* use dataConInstOrigArgTys here because
            -- the newtype arising from   class Foo a => Bar a where {}
            -- has a single argument (Foo a) that is a *type class*, so
            -- dataConInstOrigArgTys returns [].

        etad_tvs   :: [TyVar]  -- Matched lazily, so that mkNewTypeCo can
        etad_roles :: [Role]   -- return a TyCon without pulling on rhs_ty
        etad_rhs   :: Type     -- See Note [Tricky iface loop] in GHC.Iface.Load
        (etad_tvs, etad_roles, etad_rhs) = eta_reduce (reverse tvs) (reverse roles) rhs_ty

        eta_reduce :: [TyVar]       -- Reversed
                   -> [Role]        -- also reversed
                   -> Type          -- Rhs type
                   -> ([TyVar], [Role], Type)  -- Eta-reduced version
                                               -- (tyvars in normal order)
        eta_reduce (a:as) (_:rs) ty | Just (fun, arg) <- splitAppTy_maybe ty,
                                      Just tv <- getTyVar_maybe arg,
                                      tv == a,
                                      not (a `elemVarSet` tyCoVarsOfType fun)
                                    = eta_reduce as rs fun
        eta_reduce tvs rs ty = (reverse tvs, reverse rs, ty)

    ------------------------------------------------------
    buildDataCon :: FamInstEnvs
                -> Name
                -> Bool                     -- Declared infix
                -> TyConRepName
                -> [HsSrcBang]
                -> Maybe [HsImplBang]
                    -- See Note [Bangs on imported data constructors] in GHC.Types.Id.Make
               -> [FieldLabel]             -- Field labels
               -> [TyVar]                  -- Universals
               -> [TyCoVar]                -- Existentials
               -> [InvisTVBinder]          -- User-written 'TyVarBinder's
               -> [EqSpec]                 -- Equality spec
               -> KnotTied ThetaType       -- Does not include the "stupid theta"
                                           -- or the GADT equalities
               -> [KnotTied (Scaled Type)] -- Arguments
               -> KnotTied Type            -- Result types
               -> KnotTied TyCon           -- Rep tycon
               -> NameEnv ConTag           -- Maps the Name of each DataCon to its
                                           -- ConTag
               -> TcRnIf m n DataCon
    -- A wrapper for DataCon.mkDataCon that
    --   a) makes the worker Id
    --   b) makes the wrapper Id if necessary, including
    --      allocating its unique (hence monadic)
    buildDataCon fam_envs src_name declared_infix prom_info src_bangs impl_bangs
                 field_lbls univ_tvs ex_tvs user_tvbs eq_spec ctxt arg_tys res_ty
                 rep_tycon tag_map
      = do  { wrap_name <- newImplicitBinder src_name mkDataConWrapperOcc
            ; work_name <- newImplicitBinder src_name mkDataConWorkerOcc
            -- This last one takes the name of the data constructor in the source
            -- code, which (for Haskell source anyway) will be in the DataName name
            -- space, and puts it into the VarName name space

            ; traceIf (text "buildDataCon 1" <+> ppr src_name)
            ; us <- newUniqueSupply
            ; dflags <- getDynFlags
            ; let stupid_ctxt = mkDataConStupidTheta rep_tycon (map scaledThing arg_tys) univ_tvs
                  tag = lookupNameEnv_NF tag_map src_name
                  -- See Note [Constructor tag allocation], fixes #14657
                  data_con = mkDataCon src_name declared_infix prom_info
                                       src_bangs field_lbls
                                       univ_tvs ex_tvs user_tvbs eq_spec ctxt
                                       arg_tys res_ty NoRRI rep_tycon tag
                                       stupid_ctxt dc_wrk dc_rep
                  dc_wrk = mkDataConWorkId work_name data_con
                  dc_rep = initUs_ us (mkDataConRep dflags fam_envs wrap_name
                                                    impl_bangs data_con)

            ; traceIf (text "buildDataCon 2" <+> ppr src_name)
            ; return data_con }

    -- The stupid context for a data constructor should be limited to
    -- the type variables mentioned in the arg_tys
    -- ToDo: Or functionally dependent on?
    --       This whole stupid theta thing is, well, stupid.
    mkDataConStupidTheta :: TyCon -> [Type] -> [TyVar] -> [PredType]
    mkDataConStupidTheta tycon arg_tys univ_tvs
      | null stupid_theta = []      -- The common case
      | otherwise         = filter in_arg_tys stupid_theta
      where
        tc_subst     = zipTvSubst (tyConTyVars tycon)
                                  (mkTyVarTys univ_tvs)
        stupid_theta = substTheta tc_subst (tyConStupidTheta tycon)
            -- Start by instantiating the master copy of the
            -- stupid theta, taken from the TyCon

        arg_tyvars      = tyCoVarsOfTypes arg_tys
        in_arg_tys pred = tyCoVarsOfType pred `intersectsVarSet` arg_tyvars

    ------------------------------------------------------
    buildPatSyn :: Name -> Bool
                -> (Id,Bool) -> Maybe (Id, Bool)
                -> ([InvisTVBinder], ThetaType) -- ^ Univ and req
                -> ([InvisTVBinder], ThetaType) -- ^ Ex and prov
                -> [Type]                       -- ^ Argument types
                -> Type                         -- ^ Result type
                -> [FieldLabel]                 -- ^ Field labels for
                                                --   a record pattern synonym
                -> PatSyn
    buildPatSyn src_name declared_infix matcher@(matcher_id,_) builder
                (univ_tvs, req_theta) (ex_tvs, prov_theta) arg_tys
                pat_ty field_labels
      = -- The assertion checks that the matcher is
        -- compatible with the pattern synonym
        ASSERT2((and [ univ_tvs `equalLength` univ_tvs1
                     , ex_tvs `equalLength` ex_tvs1
                     , pat_ty `eqType` substTy subst (scaledThing pat_ty1)
                     , prov_theta `eqTypes` substTys subst prov_theta1
                     , req_theta `eqTypes` substTys subst req_theta1
                     , compareArgTys arg_tys (substTys subst (map scaledThing arg_tys1))
                     ])
                , (vcat [ ppr univ_tvs <+> twiddle <+> ppr univ_tvs1
                        , ppr ex_tvs <+> twiddle <+> ppr ex_tvs1
                        , ppr pat_ty <+> twiddle <+> ppr pat_ty1
                        , ppr prov_theta <+> twiddle <+> ppr prov_theta1
                        , ppr req_theta <+> twiddle <+> ppr req_theta1
                        , ppr arg_tys <+> twiddle <+> ppr arg_tys1]))
        mkPatSyn src_name declared_infix
                 (univ_tvs, req_theta) (ex_tvs, prov_theta)
                 arg_tys pat_ty
                 matcher builder field_labels
      where
        ((_:_:univ_tvs1), req_theta1, tau) = tcSplitSigmaTy $ idType matcher_id
        ([pat_ty1, cont_sigma, _], _)      = tcSplitFunTys tau
        (ex_tvs1, prov_theta1, cont_tau)   = tcSplitSigmaTy (scaledThing cont_sigma)
        (arg_tys1, _) = (tcSplitFunTys cont_tau)
        twiddle = char '~'
        subst = zipTvSubst (univ_tvs1 ++ ex_tvs1)
                           (mkTyVarTys (binderVars (univ_tvs ++ ex_tvs)))

        -- For a nullary pattern synonym we add a single void argument to the
        -- matcher to preserve laziness in the case of unlifted types.
        -- See #12746
        compareArgTys :: [Type] -> [Type] -> Bool
        compareArgTys [] [x] = x `eqType` voidPrimTy
        compareArgTys arg_tys matcher_arg_tys = arg_tys `eqTypes` matcher_arg_tys

    ------------------------------------------------------
    type TcMethInfo = MethInfo  -- this variant needs zonking
    type MethInfo       -- A temporary intermediate, to communicate
                        -- between tcClassSigs and buildClass.
      = ( Name   -- Name of the class op
        , Type   -- Type of the class op
        , Maybe (DefMethSpec (SrcSpan, Type)))
             -- Nothing                    => no default method
             --
             -- Just VanillaDM             => There is an ordinary
             --                               polymorphic default method
             --
             -- Just (GenericDM (loc, ty)) => There is a generic default metho
             --                               Here is its type, and the location
             --                               of the type signature
             --    We need that location /only/ to attach it to the
             --    generic default method's Name; and we need /that/
             --    only to give the right location of an ambiguity error
             --    for the generic default method, spat out by checkValidClass

    buildClass :: Name  -- Name of the class/tycon (they have the same Name)
               -> [TyConBinder]                -- Of the tycon
               -> [Role]
               -> [FunDep TyVar]               -- Functional dependencies
               -- Super classes, associated types, method info, minimal complete def.
               -- This is Nothing if the class is abstract.
               -> Maybe (KnotTied ThetaType, [ClassATItem], [KnotTied MethInfo], ClassMinimalDef)
               -> TcRnIf m n Class

    buildClass tycon_name binders roles fds Nothing
      = fixM  $ \ rec_clas ->       -- Only name generation inside loop
        do  { traceIf (text "buildClass")

            ; tc_rep_name  <- newTyConRepName tycon_name
            ; let univ_tvs = binderVars binders
                  tycon = mkClassTyCon tycon_name binders roles
                                       AbstractTyCon rec_clas tc_rep_name
                  result = mkAbstractClass tycon_name univ_tvs fds tycon
            ; traceIf (text "buildClass" <+> ppr tycon)
            ; return result }

    buildClass tycon_name binders roles fds
               (Just (sc_theta, at_items, sig_stuff, mindef))
      = fixM  $ \ rec_clas ->       -- Only name generation inside loop
        do  { traceIf (text "buildClass")

            ; datacon_name <- newImplicitBinder tycon_name mkClassDataConOcc
            ; tc_rep_name  <- newTyConRepName tycon_name

            ; op_items <- mapM (mk_op_item rec_clas) sig_stuff
                            -- Build the selector id and default method id

                  -- Make selectors for the superclasses
            ; sc_sel_names <- mapM  (newImplicitBinder tycon_name . mkSuperDictSelOcc)
                                    (takeList sc_theta [fIRST_TAG..])
            ; let sc_sel_ids = [ mkDictSelId sc_name rec_clas
                               | sc_name <- sc_sel_names]
                  -- We number off the Dict superclass selectors, 1, 2, 3 etc so that we
                  -- can construct names for the selectors. Thus
                  --      class (C a, C b) => D a b where ...
                  -- gives superclass selectors
                  --      D_sc1, D_sc2
                  -- (We used to call them D_C, but now we can have two different
                  --  superclasses both called C!)

            ; let use_newtype = isSingleton arg_tys
                    -- Use a newtype if the data constructor
                    --   (a) has exactly one value field
                    --       i.e. exactly one operation or superclass taken together
                    --   (b) that value is of lifted type (which they always are, because
                    --       we box equality superclasses)
                    -- See note [Class newtypes and equality predicates]

                    -- We treat the dictionary superclasses as ordinary arguments.
                    -- That means that in the case of
                    --     class C a => D a
                    -- we don't get a newtype with no arguments!
                  args       = sc_sel_names ++ op_names
                  op_tys     = [ty | (_,ty,_) <- sig_stuff]
                  op_names   = [op | (op,_,_) <- sig_stuff]
                  arg_tys    = sc_theta ++ op_tys
                  rec_tycon  = classTyCon rec_clas
                  univ_bndrs = tyConInvisTVBinders binders
                  univ_tvs   = binderVars univ_bndrs

            ; rep_nm   <- newTyConRepName datacon_name
            ; dict_con <- buildDataCon (panic "buildClass: FamInstEnvs")
                                       datacon_name
                                       False        -- Not declared infix
                                       rep_nm
                                       (map (const no_bang) args)
                                       (Just (map (const HsLazy) args))
                                       [{- No fields -}]
                                       univ_tvs
                                       [{- no existentials -}]
                                       univ_bndrs
                                       [{- No GADT equalities -}]
                                       [{- No theta -}]
                                       (map unrestricted arg_tys) -- type classes are unrestricted
                                       (mkTyConApp rec_tycon (mkTyVarTys univ_tvs))
                                       rec_tycon
                                       (mkTyConTagMap rec_tycon)

            ; rhs <- case () of
                      _ | use_newtype
                        -> mkNewTyConRhs tycon_name rec_tycon dict_con
                        | isCTupleTyConName tycon_name
                        -> return (TupleTyCon { data_con = dict_con
                                              , tup_sort = ConstraintTuple })
                        | otherwise
                        -> return (mkDataTyConRhs [dict_con])

            ; let { tycon = mkClassTyCon tycon_name binders roles
                                         rhs rec_clas tc_rep_name
                    -- A class can be recursive, and in the case of newtypes
                    -- this matters.  For example
                    --      class C a where { op :: C b => a -> b -> Int }
                    -- Because C has only one operation, it is represented by
                    -- a newtype, and it should be a *recursive* newtype.
                    -- [If we don't make it a recursive newtype, we'll expand the
                    -- newtype like a synonym, but that will lead to an infinite
                    -- type]

                  ; result = mkClass tycon_name univ_tvs fds
                                     sc_theta sc_sel_ids at_items
                                     op_items mindef tycon
                  }
            ; traceIf (text "buildClass" <+> ppr tycon)
            ; return result }
      where
        no_bang = HsSrcBang NoSourceText NoSrcUnpack NoSrcStrict

        mk_op_item :: Class -> TcMethInfo -> TcRnIf n m ClassOpItem
        mk_op_item rec_clas (op_name, _, dm_spec)
          = do { dm_info <- mk_dm_info op_name dm_spec
               ; return (mkDictSelId op_name rec_clas, dm_info) }

        mk_dm_info :: Name -> Maybe (DefMethSpec (SrcSpan, Type))
                   -> TcRnIf n m (Maybe (Name, DefMethSpec Type))
        mk_dm_info _ Nothing
          = return Nothing
        mk_dm_info op_name (Just VanillaDM)
          = do { dm_name <- newImplicitBinder op_name mkDefaultMethodOcc
               ; return (Just (dm_name, VanillaDM)) }
        mk_dm_info op_name (Just (GenericDM (loc, dm_ty)))
          = do { dm_name <- newImplicitBinderLoc op_name mkDefaultMethodOcc loc
               ; return (Just (dm_name, GenericDM dm_ty)) }

    {-
    Note [Class newtypes and equality predicates]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
            class (a ~ F b) => C a b where
              op :: a -> b

    We cannot represent this by a newtype, even though it's not
    existential, because there are two value fields (the equality
    predicate and op. See #2238

    Moreover,
              class (a ~ F b) => C a b where {}
    Here we can't use a newtype either, even though there is only
    one field, because equality predicates are unboxed, and classes
    are boxed.
    -}

    newImplicitBinder :: Name                       -- Base name
                      -> (OccName -> OccName)       -- Occurrence name modifier
                      -> TcRnIf m n Name            -- Implicit name
    -- Called in GHC.Tc.TyCl.Build to allocate the implicit binders of type/class decls
    -- For source type/class decls, this is the first occurrence
    -- For iface ones, GHC.Iface.Load has already allocated a suitable name in the cache
    newImplicitBinder base_name mk_sys_occ
      = newImplicitBinderLoc base_name mk_sys_occ (nameSrcSpan base_name)

    newImplicitBinderLoc :: Name                       -- Base name
                         -> (OccName -> OccName)       -- Occurrence name modifier
                         -> SrcSpan
                         -> TcRnIf m n Name            -- Implicit name
    -- Just the same, but lets you specify the SrcSpan
    newImplicitBinderLoc base_name mk_sys_occ loc
      | Just mod <- nameModule_maybe base_name
      = newGlobalBinder mod occ loc
      | otherwise           -- When typechecking a [d| decl bracket |],
                            -- TH generates types, classes etc with Internal names,
                            -- so we follow suit for the implicit binders
      = do  { uniq <- newUnique
            ; return (mkInternalName uniq occ loc) }
      where
        occ = mk_sys_occ (nameOccName base_name)

    -- | Make the 'TyConRepName' for this 'TyCon'
    newTyConRepName :: Name -> TcRnIf gbl lcl TyConRepName
    newTyConRepName tc_name
      | Just mod <- nameModule_maybe tc_name
      , (mod, occ) <- tyConRepModOcc mod (nameOccName tc_name)
      = newGlobalBinder mod occ noSrcSpan
      | otherwise
      = newImplicitBinder tc_name mkTyConRepOcc