{-# LANGUAGE MultiWayIf #-} -- | Checking for representation-polymorphism using the Concrete mechanism. -- -- This module contains the logic for enforcing the representation-polymorphism -- invariants by way of emitting constraints. module GHC.Tc.Utils.Concrete ( -- * Ensuring that a type has a fixed runtime representation hasFixedRuntimeRep , hasFixedRuntimeRep_syntactic -- * Making a type concrete , makeTypeConcrete ) where import GHC.Prelude import GHC.Builtin.Types ( liftedTypeKindTyCon, unliftedTypeKindTyCon ) import GHC.Core.Coercion ( coToMCo, mkCastTyMCo , mkGReflRightMCo, mkNomReflCo ) import GHC.Core.TyCo.Rep ( Type(..), MCoercion(..) ) import GHC.Core.TyCon ( isConcreteTyCon ) import GHC.Core.Type ( isConcrete, typeKind, tyVarKind, coreView , mkTyVarTy, mkTyConApp, mkFunTy, mkAppTy ) import GHC.Tc.Types ( TcM, ThStage(..), PendingStuff(..) ) import GHC.Tc.Types.Constraint ( NotConcreteError(..), NotConcreteReason(..) ) import GHC.Tc.Types.Evidence ( Role(..), TcCoercionN, TcMCoercionN ) import GHC.Tc.Types.Origin ( CtOrigin(..), FixedRuntimeRepContext, FixedRuntimeRepOrigin(..) ) import GHC.Tc.Utils.Monad ( emitNotConcreteError, setTcLevel, getCtLocM, getStage, traceTc ) import GHC.Tc.Utils.TcType ( TcType, TcKind, TcTypeFRR , MetaInfo(..), ConcreteTvOrigin(..) , isMetaTyVar, metaTyVarInfo, tcTyVarLevel ) import GHC.Tc.Utils.TcMType ( newConcreteTyVar, isFilledMetaTyVar_maybe, writeMetaTyVar , emitWantedEq ) import GHC.Types.Basic ( TypeOrKind(..) ) import GHC.Utils.Misc ( HasDebugCallStack ) import GHC.Utils.Outputable import Control.Monad ( void ) import Data.Functor ( ($>) ) import Data.List.NonEmpty ( NonEmpty((:|)) ) import Control.Monad.Trans.Class ( lift ) import Control.Monad.Trans.Writer.CPS ( WriterT, runWriterT, tell ) {- Note [Concrete overview] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ GHC ensures that certain types have a fixed runtime representation in the typechecker, by emitting certain constraints. Emitting constraints to be solved later allows us to accept more programs: if we directly inspected the type (using e.g. `typePrimRep`), we might not have enough information available (e.g. if the type has kind `TYPE r` for a metavariable `r` which has not yet been filled in.) We give here an overview of the various moving parts, to serve as a central point of reference for this topic. * Representation polymorphism Note [Representation polymorphism invariants] in GHC.Core Note [Representation polymorphism checking] The first note explains why we require that certain types have a fixed runtime representation. The second note details why we sometimes need a constraint to perform such checks in the typechecker: we might not know immediately whether a type has a fixed runtime representation. For example, we might need further unification to take place before being able to decide. So, instead of checking immediately, we emit a constraint. * What does it mean for a type to be concrete? Note [Concrete types] explains what it means for a type to be concrete. To compute which representation to use for a type, `typePrimRep` expects its kind to be concrete: something specific like `BoxedRep Lifted` or `IntRep`; certainly not a type involving type variables or type families. * What constraints do we emit? Note [The Concrete mechanism] Instead of simply checking that a type `ty` is concrete (i.e. computing 'isConcrete`), we emit an equality constraint: co :: ty ~# concrete_ty where 'concrete_ty' is a concrete metavariable: a metavariable whose 'MetaInfo' is 'ConcreteTv', signifying that it can only be unified with a concrete type. The Note explains that this allows us to accept more programs. The Note also explains that the implementation is happening in two phases (PHASE 1 and PHASE 2). In PHASE 1 (the current implementation) we only allow trivial evidence of the form `co = Refl`. * Fixed runtime representation vs fixed RuntimeRep Note [Fixed RuntimeRep] We currently enforce the representation-polymorphism invariants by checking that binders and function arguments have a "fixed RuntimeRep". This is slightly less general than we might like, as this rules out types with kind `TYPE (BoxedRep l)`: we know that this will be represented by a pointer, which should be enough to go on in many situations. * When do we emit these constraints? Note [hasFixedRuntimeRep] We introduce constraints to satisfy the representation-polymorphism invariants outlined in Note [Representation polymorphism invariants] in GHC.Core, which mostly amounts to the following two cases: - checking that a binder has a fixed runtime representation, - checking that a function argument has a fixed runtime representation. The Note explains precisely how and where these constraints are emitted. * Reporting unsolved constraints Note [Reporting representation-polymorphism errors] in GHC.Tc.Types.Origin When we emit a constraint to enforce a fixed representation, we also provide a 'FixedRuntimeRepOrigin' which gives context about the check being done. This origin gets reported to the user if we end up with such an an unsolved Wanted constraint. Note [Representation polymorphism checking] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ According to the "Levity Polymorphism" paper (PLDI '17), there are two places in which we must know that a type has a fixed runtime representation, as explained in Note [Representation polymorphism invariants] in GHC.Core: I1. the type of a bound term-level variable, I2. the type of an argument to a function. The paper explains the restrictions more fully, but briefly: expressions in these contexts need to be stored in registers, and it's hard (read: impossible) to store something that does not have a fixed runtime representation. In practice, we enforce these types to have a /fixed RuntimeRep/, which is slightly stronger, as explained in Note [Fixed RuntimeRep]. There are two different ways we check whether a given type has a fixed runtime representation, both in the typechecker: 1. When typechecking type declarations (e.g. datatypes, typeclass, pattern synonyms), under the GHC.Tc.TyCl module hierarchy. In these situations, we can immediately reject bad representation polymorphism. For instance, the following datatype declaration data Foo (r :: RuntimeRep) (a :: TYPE r) = Foo a is rejected in GHC.Tc.TyCl.checkValidDataCon upon seeing that the type 'a' is representation-polymorphic. Such checks are done using `GHC.Tc.Utils.TcMType.checkTypeHasFixedRuntimeRep`, with `GHC.Tc.Errors.Types.FixedRuntimeRepProvenance` describing the different contexts in which bad representation polymorphism can occur while validity checking. 2. When typechecking value-level declarations (functions, expressions, patterns, ...), under the GHC.Tc.Gen module hierarchy. In these situations, the typechecker might need to do some work to figure out whether a type has a fixed runtime representation or not. For instance, GHC might introduce a metavariable (rr :: RuntimeRep), which is only later (through constraint solving) discovered to be equal to FloatRep. This is handled by the Concrete mechanism outlined in Note [The Concrete mechanism] in GHC.Tc.Utils.Concrete. See Note [Concrete overview] in GHC.Tc.Utils.Concrete for an overview of the various moving parts. Note [Concrete types] ~~~~~~~~~~~~~~~~~~~~~ Definition: a type is /concrete/ iff it is: - a concrete type constructor (as defined below), or - a concrete type variable (see Note [ConcreteTv] below), or - an application of a concrete type to another concrete type GHC.Core.Type.isConcrete checks whether a type meets this definition. Definition: a /concrete type constructor/ is defined by - a promoted data constructor - a class, data type or newtype - a primitive type like Array# or Int# - an abstract type as defined in a Backpack signature file (see Note [Synonyms implement abstract data] in GHC.Tc.Module) In particular, type and data families are not concrete. GHC.Core.TyCon.isConcreteTyCon checks whether a TyCon meets this definition. Examples of concrete types: Lifted, BoxedRep Lifted, TYPE (BoxedRep Lifted) are all concrete Examples of non-concrete types F Int, TYPE (F Int), TYPE r, a[sk] NB: (F Int) is not concrete because F is a type function The recursive definition of concreteness entails the following property: Concrete Congruence Property (CCP) All sub-trees of a concrete type tree are concrete. The following property also holds due to the invariant that the kind of a concrete metavariable is itself concrete (see Note [ConcreteTv]): Concrete Kinds Property (CKP) The kind of a concrete type is concrete. Note [ConcreteTv] ~~~~~~~~~~~~~~~~~ A concrete metavariable is a metavariable whose 'MetaInfo' is 'ConcreteTv'. Similar to 'TyVarTv's which are type variables which can only be unified with other type variables, a 'ConcreteTv' type variable is a type variable which can only be unified with a concrete type (in the sense of Note [Concrete types]). INVARIANT: the kind of a concrete metavariable is concrete. This invariant is upheld at the time of creation of a new concrete metavariable. Concrete metavariables are useful for representation-polymorphism checks: they allow us to refer to a type whose representation is not yet known but will be figured out by the typechecker (see Note [The Concrete mechanism]). Note [The Concrete mechanism] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To check (ty :: ki) has a fixed runtime representation, we proceed as follows: - Create a new concrete metavariable `concrete_tv`, i.e. a metavariable with 'ConcreteTv' 'MetaInfo' (see Note [ConcreteTv]). - Emit an equality constraint: ki ~# concrete_tv The origin for such an equality constraint uses `GHC.Tc.Types.Origin.FixedRuntimeRepOrigin`, so that we can report the appropriate representation-polymorphism error if any such constraint goes unsolved. To solve `ki ~# concrete_ki`, we must unify `concrete_tv := concrete_ki`, where `concrete_ki` is some concrete type. We can then compute `kindPrimRep` on `concrete_ki` to compute the representation: this means `ty` indeed has a fixed runtime representation. ------------------------- -- PHASE 1 and PHASE 2 -- ------------------------- The Concrete mechanism is being implemented in two separate phases. In PHASE 1, we enforce that we only solve the emitted constraints `co :: ki ~# concrete_tv` with `Refl`. This forbids any program which requires type family evaluation in order to determine that a 'RuntimeRep' is fixed. To achieve this, instead of creating a new concrete metavariable, we directly ensure that 'ki' is concrete, using 'makeTypeConcrete'. If it fails, then we report an error (even though rewriting might have allowed us to proceed). In PHASE 2, we lift this restriction. This means we replace a call to `hasFixedRuntimeRep_syntactic` with a call to `hasFixedRuntimeRep`, and insert the obtained coercion in the typechecked result. To illustrate what this entails, recall that the code generator needs to be able to compute 'PrimRep's, so that it can put function arguments in the correct registers, etc. As a result, we must insert additional casts in Core to ensure that no type family reduction is needed to be able to compute 'PrimRep's. For example, the Core f = /\ ( a :: F Int ). \ ( x :: a ). some_expression is problematic when 'F' is a type family: we don't know what runtime representation to use for 'x', so we can't compile this function (we can't evaluate type family applications after we are done with typechecking). Instead, we ensure the 'RuntimeRep' is always explicitly visible: f = /\ ( a :: F Int ). \ ( x :: ( a |> kco ) ). some_expression where 'kco' is the appropriate coercion; for example if `F Int = TYPE Int#` this would be: kco :: F Int ~# TYPE Int# As `( a |> kco ) :: TYPE Int#`, the code generator knows to use a machine-sized integer register for `x`, and all is good again. Because we can convert calls from hasFixedRuntimeRep_syntactic to hasFixedRuntimeRep one at a time, we can migrate from PHASE 1 to PHASE 2 incrementally. Example test cases that require PHASE 2: T13105, T17021, T20363b. Note [Fixed RuntimeRep] ~~~~~~~~~~~~~~~~~~~~~~~ Definitions: FRR. The type `ty :: ki` has a /syntactically fixed RuntimeRep/ (we also say that `ty` is an `FRRType`) <=> the kind `ki` is concrete (in the sense of Note [Concrete types]) <=> `typePrimRep ty` (= `kindPrimRep ki`) does not crash (assuming that typechecking succeeded, so that all metavariables in `ty` have been filled) Fixed RuntimeRep. The type `ty :: ki` has a /fixed RuntimeRep/ <=> there exists an FRR type `ty'` with `ty ~# ty'` <=> there exists a concrete type `concrete_ki` such that `ki ~ concrete_ki` These definitions are crafted to be useful to satisfy the invariants of Core; see Note [Representation polymorphism invariants] in GHC.Core. Notice that "fixed RuntimeRep" means (for now anyway) that * we know the runtime representation, and * we know the levity. For example (ty :: TYPE (BoxedRep l)), where `l` is a levity variable is /not/ "fixed RuntimeRep", even though it is always represented by a heap pointer, because we don't know the levity. In due course we will want to make finer distinctions, as explained in the paper Kinds are Calling Conventions [ICFP'20], but this suffices for now. Note [hasFixedRuntimeRep] ~~~~~~~~~~~~~~~~~~~~~~~~~ The 'hasFixedRuntimeRep' function is responsible for taking a type 'ty' and emitting a constraint to ensure that 'ty' has a fixed `RuntimeRep`, as outlined in Note [The Concrete mechanism]. To do so, we compute the kind 'ki' of 'ty', create a new concrete metavariable `concrete_tv` of kind `ki`, and emit a constraint `ki ~# concrete_tv`, which will only be solved if we can prove that 'ty' indeed has a fixed RuntimeRep. If we can solve the equality constraint, i.e. produce a coercion `kco :: ki ~# concrete_tv`, then 'hasFixedRuntimeRep' returns the coercion co = GRefl ty kco :: ty ~# ty |> kco The RHS of the coercion `co` is `ty |> kco`. The kind of this type is concrete (by construction), which means that `ty |> kco` is an FRRType in the sense of Note [Fixed RuntimeRep], so that we can directely compute its runtime representation using `typePrimRep`. [Wrinkle: Typed Template Haskell] We don't perform any checks when type-checking a typed Template Haskell quote: we want to allow representation polymorphic quotes, as long as they are monomorphised at splice site. Example: Module1 repPolyId :: forall r (a :: TYPE r). CodeQ (a -> a) repPolyId = [|| \ x -> x ||] Module2 import Module1 id1 :: Int -> Int id1 = $$repPolyId id2 :: Int# -> Int# id2 = $$repPolyId We implement this skip by inspecting the TH stage in `hasFixedRuntimeRep`. A better solution would be to use 'CodeC' constraints, as in the paper "Staging With Class", POPL 2022 by Ningning Xie, Matthew Pickering, Andres Löh, Nicolas Wu, Jeremy Yallop, Meng Wang but for the moment, as we will typecheck again when splicing, this shouldn't cause any problems in practice. See ticket #18170. Test case: rep-poly/T18170a. -} -- | Given a type @ty :: ki@, this function ensures that @ty@ -- has a __fixed__ 'RuntimeRep', by emitting a new equality constraint -- @ki ~ concrete_tv@ for a concrete metavariable @concrete_tv@. -- -- Returns a coercion @co :: ty ~# concrete_ty@ as evidence. -- If @ty@ obviously has a fixed 'RuntimeRep', e.g @ki = IntRep@, -- then this function immediately returns 'MRefl', -- without emitting any constraints. hasFixedRuntimeRep :: HasDebugCallStack => FixedRuntimeRepContext -- ^ Context to be reported to the user -- if the type ends up not having a fixed -- 'RuntimeRep'. -> TcType -- ^ The type to check (we only look at its kind). -> TcM (TcCoercionN, TcTypeFRR) -- ^ @(co, ty')@ where @ty' :: ki'@, -- @ki@ is concrete, and @co :: ty ~# ty'@. -- That is, @ty'@ has a syntactically fixed RuntimeRep -- in the sense of Note [Fixed RuntimeRep]. hasFixedRuntimeRep :: (() :: Constraint) => FixedRuntimeRepContext -> TcType -> TcM (TcCoercionN, TcType) hasFixedRuntimeRep FixedRuntimeRepContext frr_ctxt TcType ty = (() :: Constraint) => (FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN) -> FixedRuntimeRepContext -> TcType -> TcM (TcCoercionN, TcType) (FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN) -> FixedRuntimeRepContext -> TcType -> TcM (TcCoercionN, TcType) checkFRR_with (() :: Constraint) => FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN unifyConcrete FixedRuntimeRepContext frr_ctxt TcType ty -- | Like 'hasFixedRuntimeRep', but we perform an eager syntactic check. -- -- Throws an error in the 'TcM' monad if the check fails. -- -- This is useful if we are not actually going to use the coercion returned -- from 'hasFixedRuntimeRep'; it would generally be unsound to allow a non-reflexive -- coercion but not actually make use of it in a cast. -- -- The goal is to eliminate all uses of this function and replace them with -- 'hasFixedRuntimeRep', making use of the returned coercion. This is what -- is meant by going from PHASE 1 to PHASE 2, in Note [The Concrete mechanism]. hasFixedRuntimeRep_syntactic :: HasDebugCallStack => FixedRuntimeRepContext -- ^ Context to be reported to the user -- if the type does not have a syntactically -- fixed 'RuntimeRep'. -> TcType -- ^ The type to check (we only look at its kind). -> TcM () hasFixedRuntimeRep_syntactic :: (() :: Constraint) => FixedRuntimeRepContext -> TcType -> TcM () hasFixedRuntimeRep_syntactic FixedRuntimeRepContext frr_ctxt TcType ty = TcM (TcCoercionN, TcType) -> TcM () forall (f :: * -> *) a. Functor f => f a -> f () void (TcM (TcCoercionN, TcType) -> TcM ()) -> TcM (TcCoercionN, TcType) -> TcM () forall a b. (a -> b) -> a -> b $ (() :: Constraint) => (FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN) -> FixedRuntimeRepContext -> TcType -> TcM (TcCoercionN, TcType) (FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN) -> FixedRuntimeRepContext -> TcType -> TcM (TcCoercionN, TcType) checkFRR_with FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN ensure_conc FixedRuntimeRepContext frr_ctxt TcType ty where ensure_conc :: FixedRuntimeRepOrigin -> TcKind -> TcM TcMCoercionN ensure_conc :: FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN ensure_conc FixedRuntimeRepOrigin frr_orig TcType ki = (() :: Constraint) => FixedRuntimeRepOrigin -> TcType -> TcM TcType FixedRuntimeRepOrigin -> TcType -> TcM TcType ensureConcrete FixedRuntimeRepOrigin frr_orig TcType ki TcM TcType -> TcMCoercionN -> TcM TcMCoercionN forall (f :: * -> *) a b. Functor f => f a -> b -> f b $> TcMCoercionN MRefl -- | Internal function to check whether the given type has a fixed 'RuntimeRep'. -- -- Use 'hasFixedRuntimeRep' to allow rewriting, or 'hasFixedRuntimeRep_syntactic' -- to perform a syntactic check. checkFRR_with :: HasDebugCallStack => (FixedRuntimeRepOrigin -> TcKind -> TcM TcMCoercionN) -- ^ The check to perform on the kind. -> FixedRuntimeRepContext -- ^ The context which required a fixed 'RuntimeRep', -- e.g. an application, a lambda abstraction, ... -> TcType -- ^ The type @ty@ to check (the check itself only looks at its kind). -> TcM (TcCoercionN, TcTypeFRR) -- ^ Returns @(co, frr_ty)@ with @co :: ty ~# frr_ty@ -- and @frr_@ty has a fixed 'RuntimeRep'. checkFRR_with :: (() :: Constraint) => (FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN) -> FixedRuntimeRepContext -> TcType -> TcM (TcCoercionN, TcType) checkFRR_with FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN check_kind FixedRuntimeRepContext frr_ctxt TcType ty = do { ThStage th_stage <- TcM ThStage getStage ; if -- Shortcut: check for 'Type' and 'UnliftedType' type synonyms. | TyConApp TyCon tc [] <- TcType ki , TyCon tc TyCon -> TyCon -> Bool forall a. Eq a => a -> a -> Bool == TyCon liftedTypeKindTyCon Bool -> Bool -> Bool || TyCon tc TyCon -> TyCon -> Bool forall a. Eq a => a -> a -> Bool == TyCon unliftedTypeKindTyCon -> (TcCoercionN, TcType) -> TcM (TcCoercionN, TcType) forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a forall (m :: * -> *) a. Monad m => a -> m a return (TcCoercionN, TcType) refl -- See [Wrinkle: Typed Template Haskell] in Note [hasFixedRuntimeRep]. | Brack ThStage _ (TcPending {}) <- ThStage th_stage -> (TcCoercionN, TcType) -> TcM (TcCoercionN, TcType) forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a forall (m :: * -> *) a. Monad m => a -> m a return (TcCoercionN, TcType) refl -- Otherwise: ensure that the kind 'ki' of 'ty' is concrete. | Bool otherwise -> do { TcMCoercionN kco <- FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN check_kind FixedRuntimeRepOrigin frr_orig TcType ki ; (TcCoercionN, TcType) -> TcM (TcCoercionN, TcType) forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a forall (m :: * -> *) a. Monad m => a -> m a return ( Role -> TcType -> TcMCoercionN -> TcCoercionN mkGReflRightMCo Role Nominal TcType ty TcMCoercionN kco , TcType -> TcMCoercionN -> TcType mkCastTyMCo TcType ty TcMCoercionN kco ) } } where refl :: (TcCoercionN, TcType) refl :: (TcCoercionN, TcType) refl = (TcType -> TcCoercionN mkNomReflCo TcType ty, TcType ty) ki :: TcKind ki :: TcType ki = (() :: Constraint) => TcType -> TcType TcType -> TcType typeKind TcType ty frr_orig :: FixedRuntimeRepOrigin frr_orig :: FixedRuntimeRepOrigin frr_orig = FixedRuntimeRepOrigin { frr_type :: TcType frr_type = TcType ty, frr_context :: FixedRuntimeRepContext frr_context = FixedRuntimeRepContext frr_ctxt } -- | Ensure that the given type @ty@ can unify with a concrete type, -- in the sense of Note [Concrete types]. -- -- Returns a coercion @co :: ty ~# conc_ty@, where @conc_ty@ is -- concrete. -- -- If the type is already syntactically concrete, this -- immediately returns a reflexive coercion. Otherwise, -- it creates a new concrete metavariable @concrete_tv@ -- and emits an equality constraint @ty ~# concrete_tv@, -- to be handled by the constraint solver. -- -- Invariant: the kind of the supplied type must be concrete. -- -- We assume the provided type is already at the kind-level -- (this only matters for error messages). unifyConcrete :: HasDebugCallStack => FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN unifyConcrete :: (() :: Constraint) => FixedRuntimeRepOrigin -> TcType -> TcM TcMCoercionN unifyConcrete FixedRuntimeRepOrigin frr_orig TcType ty = do { (TcType ty, [NotConcreteReason] errs) <- ConcreteTvOrigin -> TcType -> TcM (TcType, [NotConcreteReason]) makeTypeConcrete (FixedRuntimeRepOrigin -> ConcreteTvOrigin ConcreteFRR FixedRuntimeRepOrigin frr_orig) TcType ty ; case [NotConcreteReason] errs of -- We were able to make the type fully concrete. { [] -> TcMCoercionN -> TcM TcMCoercionN forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a forall (m :: * -> *) a. Monad m => a -> m a return TcMCoercionN MRefl -- The type could not be made concrete; perhaps it contains -- a skolem type variable, a type family application, ... -- -- Create a new ConcreteTv metavariable @concrete_tv@ -- and unify @ty ~# concrete_tv@. ; [NotConcreteReason] _ -> do { TcTyVar conc_tv <- (() :: Constraint) => ConcreteTvOrigin -> TcType -> TcM TcTyVar ConcreteTvOrigin -> TcType -> TcM TcTyVar newConcreteTyVar (FixedRuntimeRepOrigin -> ConcreteTvOrigin ConcreteFRR FixedRuntimeRepOrigin frr_orig) TcType ki -- NB: newConcreteTyVar asserts that 'ki' is concrete. ; TcCoercionN -> TcMCoercionN coToMCo (TcCoercionN -> TcMCoercionN) -> IOEnv (Env TcGblEnv TcLclEnv) TcCoercionN -> TcM TcMCoercionN forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b <$> CtOrigin -> TypeOrKind -> Role -> TcType -> TcType -> IOEnv (Env TcGblEnv TcLclEnv) TcCoercionN emitWantedEq CtOrigin orig TypeOrKind KindLevel Role Nominal TcType ty (TcTyVar -> TcType mkTyVarTy TcTyVar conc_tv) } } } where ki :: TcKind ki :: TcType ki = (() :: Constraint) => TcType -> TcType TcType -> TcType typeKind TcType ty orig :: CtOrigin orig :: CtOrigin orig = FixedRuntimeRepOrigin -> CtOrigin FRROrigin FixedRuntimeRepOrigin frr_orig -- | Ensure that the given type is concrete. -- -- This is an eager syntactic check, and never defers -- any work to the constraint solver. -- -- Invariant: the kind of the supplied type must be concrete. -- Invariant: the output type is equal to the input type, -- up to zonking. -- -- We assume the provided type is already at the kind-level -- (this only matters for error messages). ensureConcrete :: HasDebugCallStack => FixedRuntimeRepOrigin -> TcType -> TcM TcType ensureConcrete :: (() :: Constraint) => FixedRuntimeRepOrigin -> TcType -> TcM TcType ensureConcrete FixedRuntimeRepOrigin frr_orig TcType ty = do { (TcType ty', [NotConcreteReason] errs) <- ConcreteTvOrigin -> TcType -> TcM (TcType, [NotConcreteReason]) makeTypeConcrete ConcreteTvOrigin conc_orig TcType ty ; case [NotConcreteReason] errs of { NotConcreteReason err:[NotConcreteReason] errs -> do { String -> SDoc -> TcM () traceTc String "ensureConcrete } failure" (SDoc -> TcM ()) -> SDoc -> TcM () forall a b. (a -> b) -> a -> b $ [SDoc] -> SDoc forall doc. IsDoc doc => [doc] -> doc vcat [ String -> SDoc forall doc. IsLine doc => String -> doc text String "ty:" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> TcType -> SDoc forall a. Outputable a => a -> SDoc ppr TcType ty , String -> SDoc forall doc. IsLine doc => String -> doc text String "ty':" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> TcType -> SDoc forall a. Outputable a => a -> SDoc ppr TcType ty' ] ; CtLoc loc <- CtOrigin -> Maybe TypeOrKind -> TcM CtLoc getCtLocM (FixedRuntimeRepOrigin -> CtOrigin FRROrigin FixedRuntimeRepOrigin frr_orig) (TypeOrKind -> Maybe TypeOrKind forall a. a -> Maybe a Just TypeOrKind KindLevel) ; NotConcreteError -> TcM () emitNotConcreteError (NotConcreteError -> TcM ()) -> NotConcreteError -> TcM () forall a b. (a -> b) -> a -> b $ NCE_FRR { nce_loc :: CtLoc nce_loc = CtLoc loc , nce_frr_origin :: FixedRuntimeRepOrigin nce_frr_origin = FixedRuntimeRepOrigin frr_orig , nce_reasons :: NonEmpty NotConcreteReason nce_reasons = NotConcreteReason err NotConcreteReason -> [NotConcreteReason] -> NonEmpty NotConcreteReason forall a. a -> [a] -> NonEmpty a :| [NotConcreteReason] errs } } ; [] -> String -> SDoc -> TcM () traceTc String "ensureConcrete } success" (SDoc -> TcM ()) -> SDoc -> TcM () forall a b. (a -> b) -> a -> b $ [SDoc] -> SDoc forall doc. IsDoc doc => [doc] -> doc vcat [ String -> SDoc forall doc. IsLine doc => String -> doc text String "ty: " SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> TcType -> SDoc forall a. Outputable a => a -> SDoc ppr TcType ty , String -> SDoc forall doc. IsLine doc => String -> doc text String "ty':" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> TcType -> SDoc forall a. Outputable a => a -> SDoc ppr TcType ty' ] } ; TcType -> TcM TcType forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a forall (m :: * -> *) a. Monad m => a -> m a return TcType ty' } where conc_orig :: ConcreteTvOrigin conc_orig :: ConcreteTvOrigin conc_orig = FixedRuntimeRepOrigin -> ConcreteTvOrigin ConcreteFRR FixedRuntimeRepOrigin frr_orig {-*********************************************************************** %* * Making a type concrete %* * %************************************************************************ Note [Unifying concrete metavariables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Unifying concrete metavariables (as defined in Note [ConcreteTv]) is not an all-or-nothing affair as it is for other sorts of metavariables. Consider the following unification problem in which all metavariables are unfilled (and ignoring any TcLevel considerations): alpha[conc] ~# TYPE (TupleRep '[ beta[conc], IntRep, gamma[tau] ]) We can't immediately unify `alpha` with the RHS, because the RHS is not a concrete type (in the sense of Note [Concrete types]). Instead, we proceed as follows: - create a fresh concrete metavariable variable `gamma'[conc]`, - write gamma[tau] := gamma'[conc], - write alpha[conc] := TYPE (TupleRep '[ beta[conc], IntRep, gamma'[conc] ]). Thus, in general, to unify `alpha[conc] ~# rhs`, we first try to turn `rhs` into a concrete type (see the 'makeTypeConcrete' function). If this succeeds, resulting in a concrete type `rhs'`, we simply fill `alpha[conc] := rhs'`. If it fails, then syntactic unification fails. Example 1: alpha[conc] ~# TYPE (TupleRep '[ beta[conc], IntRep, gamma[tau] ]) We proceed by filling metavariables: gamma[tau] := gamma[conc] alpha[conc] := TYPE (TupleRep '[ beta[conc], IntRep, gamma[conc] ]) This successfully unifies alpha. Example 2: For a type family `F :: Type -> Type`: delta[conc] ~# TYPE (SumRep '[ zeta[tau], a[sk], F omega[tau] ]) We write zeta[tau] := zeta[conc], and then fail, providing the following two reasons: - `a[sk]` is not a concrete type variable, so the overall type cannot be concrete - `F` is not a concrete type constructor, in the sense of Note [Concrete types]. So we keep it as is; in particular, we /should not/ try to make its argument `omega[tau]` into a ConcreteTv. Note that making zeta concrete allows us to propagate information. For example, after more typechecking, we might try to unify `zeta ~# rr[sk]`. If we made zeta a ConcreteTv, we will report this unsolved equality using the 'ConcreteTvOrigin' stored in zeta[conc]. This allows us to report ALL the problems in a representation-polymorphism check (instead of only a non-empty subset). -} -- | Try to turn the provided type into a concrete type, by ensuring -- unfilled metavariables are appropriately marked as concrete. -- -- Returns a zonked type which is "as concrete as possible", and -- a list of problems encountered when trying to make it concrete. -- -- INVARIANT: the returned type is equal to the input type, up to zonking. -- INVARIANT: if this function returns an empty list of 'NotConcreteReasons', -- then the returned type is concrete, in the sense of Note [Concrete types]. makeTypeConcrete :: ConcreteTvOrigin -> TcType -> TcM (TcType, [NotConcreteReason]) -- TODO: it could be worthwhile to return enough information to continue solving. -- Consider unifying `alpha[conc] ~# TupleRep '[ beta[tau], F Int ]` for -- a type family 'F'. -- This function will concretise `beta[tau] := beta[conc]` and return -- that `TupleRep '[ beta[conc], F Int ]` is not concrete because of the -- type family application `F Int`. But we could decompose by setting -- alpha := TupleRep '[ beta, gamma[conc] ] and emitting `[W] gamma[conc] ~ F Int`. -- -- This would be useful in startSolvingByUnification. makeTypeConcrete :: ConcreteTvOrigin -> TcType -> TcM (TcType, [NotConcreteReason]) makeTypeConcrete ConcreteTvOrigin conc_orig TcType ty = do { res :: (TcType, [NotConcreteReason]) res@(TcType ty', [NotConcreteReason] _) <- WriterT [NotConcreteReason] TcM TcType -> TcM (TcType, [NotConcreteReason]) forall w (m :: * -> *) a. Monoid w => WriterT w m a -> m (a, w) runWriterT (WriterT [NotConcreteReason] TcM TcType -> TcM (TcType, [NotConcreteReason])) -> WriterT [NotConcreteReason] TcM TcType -> TcM (TcType, [NotConcreteReason]) forall a b. (a -> b) -> a -> b $ TcType -> WriterT [NotConcreteReason] TcM TcType go TcType ty ; String -> SDoc -> TcM () traceTc String "makeTypeConcrete" (SDoc -> TcM ()) -> SDoc -> TcM () forall a b. (a -> b) -> a -> b $ [SDoc] -> SDoc forall doc. IsDoc doc => [doc] -> doc vcat [ String -> SDoc forall doc. IsLine doc => String -> doc text String "ty:" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> TcType -> SDoc forall a. Outputable a => a -> SDoc ppr TcType ty , String -> SDoc forall doc. IsLine doc => String -> doc text String "ty':" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> TcType -> SDoc forall a. Outputable a => a -> SDoc ppr TcType ty' ] ; (TcType, [NotConcreteReason]) -> TcM (TcType, [NotConcreteReason]) forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a forall (m :: * -> *) a. Monad m => a -> m a return (TcType, [NotConcreteReason]) res } where go :: TcType -> WriterT [NotConcreteReason] TcM TcType go :: TcType -> WriterT [NotConcreteReason] TcM TcType go TcType ty | Just TcType ty <- TcType -> Maybe TcType coreView TcType ty = TcType -> WriterT [NotConcreteReason] TcM TcType go TcType ty | TcType -> Bool isConcrete TcType ty = TcType -> WriterT [NotConcreteReason] TcM TcType forall a. a -> WriterT [NotConcreteReason] TcM a forall (f :: * -> *) a. Applicative f => a -> f a pure TcType ty go ty :: TcType ty@(TyVarTy TcTyVar tv) -- not a ConcreteTv (already handled above) = do { Maybe TcType mb_filled <- IOEnv (Env TcGblEnv TcLclEnv) (Maybe TcType) -> WriterT [NotConcreteReason] TcM (Maybe TcType) forall (m :: * -> *) a. Monad m => m a -> WriterT [NotConcreteReason] m a forall (t :: (* -> *) -> * -> *) (m :: * -> *) a. (MonadTrans t, Monad m) => m a -> t m a lift (IOEnv (Env TcGblEnv TcLclEnv) (Maybe TcType) -> WriterT [NotConcreteReason] TcM (Maybe TcType)) -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe TcType) -> WriterT [NotConcreteReason] TcM (Maybe TcType) forall a b. (a -> b) -> a -> b $ TcTyVar -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe TcType) isFilledMetaTyVar_maybe TcTyVar tv ; case Maybe TcType mb_filled of { Just TcType ty -> TcType -> WriterT [NotConcreteReason] TcM TcType go TcType ty ; Maybe TcType Nothing | TcTyVar -> Bool isMetaTyVar TcTyVar tv , MetaInfo TauTv <- TcTyVar -> MetaInfo metaTyVarInfo TcTyVar tv -> -- Change the MetaInfo to ConcreteTv, but retain the TcLevel do { TcType kind <- TcType -> WriterT [NotConcreteReason] TcM TcType go (TcTyVar -> TcType tyVarKind TcTyVar tv) ; TcM TcType -> WriterT [NotConcreteReason] TcM TcType forall (m :: * -> *) a. Monad m => m a -> WriterT [NotConcreteReason] m a forall (t :: (* -> *) -> * -> *) (m :: * -> *) a. (MonadTrans t, Monad m) => m a -> t m a lift (TcM TcType -> WriterT [NotConcreteReason] TcM TcType) -> TcM TcType -> WriterT [NotConcreteReason] TcM TcType forall a b. (a -> b) -> a -> b $ do { TcTyVar conc_tv <- TcLevel -> TcM TcTyVar -> TcM TcTyVar forall a. TcLevel -> TcM a -> TcM a setTcLevel (TcTyVar -> TcLevel tcTyVarLevel TcTyVar tv) (TcM TcTyVar -> TcM TcTyVar) -> TcM TcTyVar -> TcM TcTyVar forall a b. (a -> b) -> a -> b $ (() :: Constraint) => ConcreteTvOrigin -> TcType -> TcM TcTyVar ConcreteTvOrigin -> TcType -> TcM TcTyVar newConcreteTyVar ConcreteTvOrigin conc_orig TcType kind ; let conc_ty :: TcType conc_ty = TcTyVar -> TcType mkTyVarTy TcTyVar conc_tv ; TcTyVar -> TcType -> TcM () writeMetaTyVar TcTyVar tv TcType conc_ty ; TcType -> TcM TcType forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a forall (m :: * -> *) a. Monad m => a -> m a return TcType conc_ty } } | Bool otherwise -- Don't attempt to make other type variables concrete -- (e.g. SkolemTv, TyVarTv, CycleBreakerTv, RuntimeUnkTv). -> TcType -> NotConcreteReason -> WriterT [NotConcreteReason] TcM TcType bale_out TcType ty (TcTyVar -> NotConcreteReason NonConcretisableTyVar TcTyVar tv) } } go ty :: TcType ty@(TyConApp TyCon tc [TcType] tys) | TyCon -> Bool isConcreteTyCon TyCon tc = TyCon -> [TcType] -> TcType mkTyConApp TyCon tc ([TcType] -> TcType) -> WriterT [NotConcreteReason] TcM [TcType] -> WriterT [NotConcreteReason] TcM TcType forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b <$> (TcType -> WriterT [NotConcreteReason] TcM TcType) -> [TcType] -> WriterT [NotConcreteReason] TcM [TcType] forall (t :: * -> *) (m :: * -> *) a b. (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b) forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b] mapM TcType -> WriterT [NotConcreteReason] TcM TcType go [TcType] tys | Bool otherwise = TcType -> NotConcreteReason -> WriterT [NotConcreteReason] TcM TcType bale_out TcType ty (TyCon -> [TcType] -> NotConcreteReason NonConcreteTyCon TyCon tc [TcType] tys) go (FunTy FunTyFlag af TcType w TcType ty1 TcType ty2) = do { TcType w <- TcType -> WriterT [NotConcreteReason] TcM TcType go TcType w ; TcType ty1 <- TcType -> WriterT [NotConcreteReason] TcM TcType go TcType ty1 ; TcType ty2 <- TcType -> WriterT [NotConcreteReason] TcM TcType go TcType ty2 ; TcType -> WriterT [NotConcreteReason] TcM TcType forall a. a -> WriterT [NotConcreteReason] TcM a forall (m :: * -> *) a. Monad m => a -> m a return (TcType -> WriterT [NotConcreteReason] TcM TcType) -> TcType -> WriterT [NotConcreteReason] TcM TcType forall a b. (a -> b) -> a -> b $ (() :: Constraint) => FunTyFlag -> TcType -> TcType -> TcType -> TcType FunTyFlag -> TcType -> TcType -> TcType -> TcType mkFunTy FunTyFlag af TcType w TcType ty1 TcType ty2 } go (AppTy TcType ty1 TcType ty2) = do { TcType ty1 <- TcType -> WriterT [NotConcreteReason] TcM TcType go TcType ty1 ; TcType ty2 <- TcType -> WriterT [NotConcreteReason] TcM TcType go TcType ty2 ; TcType -> WriterT [NotConcreteReason] TcM TcType forall a. a -> WriterT [NotConcreteReason] TcM a forall (m :: * -> *) a. Monad m => a -> m a return (TcType -> WriterT [NotConcreteReason] TcM TcType) -> TcType -> WriterT [NotConcreteReason] TcM TcType forall a b. (a -> b) -> a -> b $ TcType -> TcType -> TcType mkAppTy TcType ty1 TcType ty2 } go ty :: TcType ty@(LitTy {}) = TcType -> WriterT [NotConcreteReason] TcM TcType forall a. a -> WriterT [NotConcreteReason] TcM a forall (m :: * -> *) a. Monad m => a -> m a return TcType ty go ty :: TcType ty@(CastTy TcType cast_ty TcCoercionN kco) = TcType -> NotConcreteReason -> WriterT [NotConcreteReason] TcM TcType bale_out TcType ty (TcType -> TcCoercionN -> NotConcreteReason ContainsCast TcType cast_ty TcCoercionN kco) go ty :: TcType ty@(ForAllTy ForAllTyBinder tcv TcType body) = TcType -> NotConcreteReason -> WriterT [NotConcreteReason] TcM TcType bale_out TcType ty (ForAllTyBinder -> TcType -> NotConcreteReason ContainsForall ForAllTyBinder tcv TcType body) go ty :: TcType ty@(CoercionTy TcCoercionN co) = TcType -> NotConcreteReason -> WriterT [NotConcreteReason] TcM TcType bale_out TcType ty (TcCoercionN -> NotConcreteReason ContainsCoercionTy TcCoercionN co) bale_out :: TcType -> NotConcreteReason -> WriterT [NotConcreteReason] TcM TcType bale_out :: TcType -> NotConcreteReason -> WriterT [NotConcreteReason] TcM TcType bale_out TcType ty NotConcreteReason reason = do { [NotConcreteReason] -> WriterT [NotConcreteReason] TcM () forall w (m :: * -> *). (Monoid w, Monad m) => w -> WriterT w m () tell [NotConcreteReason reason]; TcType -> WriterT [NotConcreteReason] TcM TcType forall a. a -> WriterT [NotConcreteReason] TcM a forall (m :: * -> *) a. Monad m => a -> m a return TcType ty }