{-# LANGUAGE CPP                 #-}
{-# LANGUAGE FlexibleContexts    #-}
{-# LANGUAGE ScopedTypeVariables #-}

{-# OPTIONS_GHC -Wno-incomplete-record-updates #-}

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

-}

-- | Types used in the typechecker
--
-- This module provides the Type interface for front-end parts of the
-- compiler.  These parts
--
-- * treat "source types" as opaque:
--         newtypes, and predicates are meaningful.
-- * look through usage types
--
module GHC.Tc.Utils.TcType (
  --------------------------------
  -- Types
  TcType, TcSigmaType, TcRhoType, TcTauType, TcPredType, TcThetaType,
  TcTyVar, TcTyVarSet, TcDTyVarSet, TcTyCoVarSet, TcDTyCoVarSet,
  TcKind, TcCoVar, TcTyCoVar, TcTyVarBinder, TcInvisTVBinder, TcReqTVBinder,
  TcTyCon, KnotTied,

  ExpType(..), InferResult(..), ExpSigmaType, ExpRhoType, mkCheckExpType,

  SyntaxOpType(..), synKnownType, mkSynFunTys,

  -- TcLevel
  TcLevel(..), topTcLevel, pushTcLevel, isTopTcLevel,
  strictlyDeeperThan, deeperThanOrSame, sameDepthAs,
  tcTypeLevel, tcTyVarLevel, maxTcLevel,
  promoteSkolem, promoteSkolemX, promoteSkolemsX,
  --------------------------------
  -- MetaDetails
  TcTyVarDetails(..), pprTcTyVarDetails, vanillaSkolemTv, superSkolemTv,
  MetaDetails(Flexi, Indirect), MetaInfo(..),
  isImmutableTyVar, isSkolemTyVar, isMetaTyVar,  isMetaTyVarTy, isTyVarTy,
  tcIsTcTyVar, isTyVarTyVar, isOverlappableTyVar,  isTyConableTyVar,
  isAmbiguousTyVar, isCycleBreakerTyVar, metaTyVarRef, metaTyVarInfo,
  isFlexi, isIndirect, isRuntimeUnkSkol,
  metaTyVarTcLevel, setMetaTyVarTcLevel, metaTyVarTcLevel_maybe,
  isTouchableMetaTyVar, isPromotableMetaTyVar,
  findDupTyVarTvs, mkTyVarNamePairs,

  --------------------------------
  -- Builders
  mkPhiTy, mkInfSigmaTy, mkSpecSigmaTy, mkSigmaTy,
  mkTcAppTy, mkTcAppTys, mkTcCastTy,

  --------------------------------
  -- Splitters
  -- These are important because they do not look through newtypes
  getTyVar,
  tcSplitForAllTyVarBinder_maybe,
  tcSplitForAllTyVars, tcSplitForAllInvisTyVars, tcSplitSomeForAllTyVars,
  tcSplitForAllReqTVBinders, tcSplitForAllInvisTVBinders,
  tcSplitPiTys, tcSplitPiTy_maybe, tcSplitForAllTyVarBinders,
  tcSplitPhiTy, tcSplitPredFunTy_maybe,
  tcSplitFunTy_maybe, tcSplitFunTys, tcFunArgTy, tcFunResultTy, tcFunResultTyN,
  tcSplitFunTysN,
  tcSplitTyConApp, tcSplitTyConApp_maybe,
  tcTyConAppTyCon, tcTyConAppTyCon_maybe, tcTyConAppArgs,
  tcSplitAppTy_maybe, tcSplitAppTy, tcSplitAppTys, tcRepSplitAppTy_maybe,
  tcRepGetNumAppTys,
  tcGetCastedTyVar_maybe, tcGetTyVar_maybe, tcGetTyVar,
  tcSplitSigmaTy, tcSplitNestedSigmaTys,

  ---------------------------------
  -- Predicates.
  -- Again, newtypes are opaque
  eqType, eqTypes, nonDetCmpType, nonDetCmpTypes, eqTypeX,
  pickyEqType, tcEqType, tcEqKind, tcEqTypeNoKindCheck, tcEqTypeVis,
  tcEqTyConApps,
  isSigmaTy, isRhoTy, isRhoExpTy, isOverloadedTy,
  isFloatingTy, isDoubleTy, isFloatTy, isIntTy, isWordTy, isStringTy,
  isIntegerTy, isNaturalTy,
  isBoolTy, isUnitTy, isCharTy, isCallStackTy, isCallStackPred,
  isTauTy, isTauTyCon, tcIsTyVarTy, tcIsForAllTy,
  isPredTy, isTyVarClassPred,
  checkValidClsArgs, hasTyVarHead,
  isRigidTy,

  ---------------------------------
  -- Misc type manipulators

  deNoteType,
  orphNamesOfType, orphNamesOfCo,
  orphNamesOfTypes, orphNamesOfCoCon,
  getDFunTyKey, evVarPred,

  ---------------------------------
  -- Predicate types
  mkMinimalBySCs, transSuperClasses,
  pickQuantifiablePreds, pickCapturedPreds,
  immSuperClasses, boxEqPred,
  isImprovementPred,

  -- * Finding type instances
  tcTyFamInsts, tcTyFamInstsAndVis, tcTyConAppTyFamInstsAndVis, isTyFamFree,

  -- * Finding "exact" (non-dead) type variables
  exactTyCoVarsOfType, exactTyCoVarsOfTypes,
  anyRewritableTyVar, anyRewritableTyFamApp, anyRewritableCanEqLHS,

  ---------------------------------
  -- Foreign import and export
  isFFIArgumentTy,     -- :: DynFlags -> Safety -> Type -> Bool
  isFFIImportResultTy, -- :: DynFlags -> Type -> Bool
  isFFIExportResultTy, -- :: Type -> Bool
  isFFIExternalTy,     -- :: Type -> Bool
  isFFIDynTy,          -- :: Type -> Type -> Bool
  isFFIPrimArgumentTy, -- :: DynFlags -> Type -> Bool
  isFFIPrimResultTy,   -- :: DynFlags -> Type -> Bool
  isFFILabelTy,        -- :: Type -> Bool
  isFFITy,             -- :: Type -> Bool
  isFunPtrTy,          -- :: Type -> Bool
  tcSplitIOType_maybe, -- :: Type -> Maybe Type

  --------------------------------
  -- Reexported from Kind
  Kind, tcTypeKind,
  liftedTypeKind,
  constraintKind,
  isLiftedTypeKind, isUnliftedTypeKind, classifiesTypeWithValues,

  --------------------------------
  -- Reexported from Type
  Type, PredType, ThetaType, TyCoBinder,
  ArgFlag(..), AnonArgFlag(..),

  mkForAllTy, mkForAllTys, mkInvisForAllTys, mkTyCoInvForAllTys,
  mkSpecForAllTys, mkTyCoInvForAllTy,
  mkInfForAllTy, mkInfForAllTys,
  mkVisFunTy, mkVisFunTys, mkInvisFunTy, mkInvisFunTyMany,
  mkVisFunTyMany, mkVisFunTysMany, mkInvisFunTysMany,
  mkTyConApp, mkAppTy, mkAppTys,
  mkTyConTy, mkTyVarTy, mkTyVarTys,
  mkTyCoVarTy, mkTyCoVarTys,

  isClassPred, isEqPrimPred, isIPLikePred, isEqPred, isEqPredClass,
  mkClassPred,
  tcSplitDFunTy, tcSplitDFunHead, tcSplitMethodTy,
  isRuntimeRepVar, isKindLevPoly,
  isVisibleBinder, isInvisibleBinder,

  -- Type substitutions
  TCvSubst(..),         -- Representation visible to a few friends
  TvSubstEnv, emptyTCvSubst, mkEmptyTCvSubst,
  zipTvSubst,
  mkTvSubstPrs, notElemTCvSubst, unionTCvSubst,
  getTvSubstEnv, setTvSubstEnv, getTCvInScope, extendTCvInScope,
  extendTCvInScopeList, extendTCvInScopeSet, extendTvSubstAndInScope,
  Type.lookupTyVar, Type.extendTCvSubst, Type.substTyVarBndr,
  Type.extendTvSubst,
  isInScope, mkTCvSubst, mkTvSubst, zipTyEnv, zipCoEnv,
  Type.substTy, substTys, substScaledTys, substTyWith, substTyWithCoVars,
  substTyAddInScope,
  substTyUnchecked, substTysUnchecked, substScaledTyUnchecked,
  substThetaUnchecked,
  substTyWithUnchecked,
  substCoUnchecked, substCoWithUnchecked,
  substTheta,

  isUnliftedType,       -- Source types are always lifted
  isUnboxedTupleType,   -- Ditto
  isPrimitiveType,

  tcView, coreView,

  tyCoVarsOfType, tyCoVarsOfTypes, closeOverKinds,
  tyCoFVsOfType, tyCoFVsOfTypes,
  tyCoVarsOfTypeDSet, tyCoVarsOfTypesDSet, closeOverKindsDSet,
  tyCoVarsOfTypeList, tyCoVarsOfTypesList,
  noFreeVarsOfType,

  --------------------------------
  pprKind, pprParendKind, pprSigmaType,
  pprType, pprParendType, pprTypeApp,
  pprTheta, pprParendTheta, pprThetaArrowTy, pprClassPred,
  pprTCvBndr, pprTCvBndrs,

  TypeSize, sizeType, sizeTypes, scopedSort,

  ---------------------------------
  -- argument visibility
  tcTyConVisibilities, isNextTyConArgVisible, isNextArgVisible

  ) where

#include "HsVersions.h"

-- friends:
import GHC.Prelude

import GHC.Core.TyCo.Rep
import GHC.Core.TyCo.Subst ( mkTvSubst, substTyWithCoVars )
import GHC.Core.TyCo.FVs
import GHC.Core.TyCo.Ppr
import GHC.Core.Class
import GHC.Types.Var
import GHC.Types.ForeignCall
import GHC.Types.Var.Set
import GHC.Core.Coercion
import GHC.Core.Type as Type
import GHC.Core.Predicate
import GHC.Types.RepType
import GHC.Core.TyCon

-- others:
import GHC.Driver.Session
import GHC.Core.FVs
import GHC.Types.Name as Name
            -- We use this to make dictionaries for type literals.
            -- Perhaps there's a better way to do this?
import GHC.Types.Name.Set
import GHC.Types.Var.Env
import GHC.Builtin.Names
import GHC.Builtin.Types ( coercibleClass, eqClass, heqClass, unitTyCon, unitTyConKey
                         , listTyCon, constraintKind )
import GHC.Types.Basic
import GHC.Utils.Misc
import GHC.Data.Maybe
import GHC.Data.List.SetOps ( getNth, findDupsEq )
import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Data.FastString
import GHC.Utils.Error( Validity(..), isValid )
import qualified GHC.LanguageExtensions as LangExt

import Data.List  ( mapAccumL )
-- import Data.Functor.Identity( Identity(..) )
import Data.IORef
import Data.List.NonEmpty( NonEmpty(..) )

{-
************************************************************************
*                                                                      *
              Types
*                                                                      *
************************************************************************

The type checker divides the generic Type world into the
following more structured beasts:

sigma ::= forall tyvars. phi
        -- A sigma type is a qualified type
        --
        -- Note that even if 'tyvars' is empty, theta
        -- may not be: e.g.   (?x::Int) => Int

        -- Note that 'sigma' is in prenex form:
        -- all the foralls are at the front.
        -- A 'phi' type has no foralls to the right of
        -- an arrow

phi :: theta => rho

rho ::= sigma -> rho
     |  tau

-- A 'tau' type has no quantification anywhere
-- Note that the args of a type constructor must be taus
tau ::= tyvar
     |  tycon tau_1 .. tau_n
     |  tau_1 tau_2
     |  tau_1 -> tau_2

-- In all cases, a (saturated) type synonym application is legal,
-- provided it expands to the required form.

Note [TcTyVars and TyVars in the typechecker]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The typechecker uses a lot of type variables with special properties,
notably being a unification variable with a mutable reference.  These
use the 'TcTyVar' variant of Var.Var.

Note, though, that a /bound/ type variable can (and probably should)
be a TyVar.  E.g
    forall a. a -> a
Here 'a' is really just a deBruijn-number; it certainly does not have
a significant TcLevel (as every TcTyVar does).  So a forall-bound type
variable should be TyVars; and hence a TyVar can appear free in a TcType.

The type checker and constraint solver can also encounter /free/ type
variables that use the 'TyVar' variant of Var.Var, for a couple of
reasons:

  - When typechecking a class decl, say
       class C (a :: k) where
          foo :: T a -> Int
    We have first kind-check the header; fix k and (a:k) to be
    TyVars, bring 'k' and 'a' into scope, and kind check the
    signature for 'foo'.  In doing so we call solveEqualities to
    solve any kind equalities in foo's signature.  So the solver
    may see free occurrences of 'k'.

    See calls to tcExtendTyVarEnv for other places that ordinary
    TyVars are bought into scope, and hence may show up in the types
    and kinds generated by GHC.Tc.Gen.HsType.

  - The pattern-match overlap checker calls the constraint solver,
    long after TcTyVars have been zonked away

It's convenient to simply treat these TyVars as skolem constants,
which of course they are.  We give them a level number of "outermost",
so they behave as global constants.  Specifically:

* Var.tcTyVarDetails succeeds on a TyVar, returning
  vanillaSkolemTv, as well as on a TcTyVar.

* tcIsTcTyVar returns True for both TyVar and TcTyVar variants
  of Var.Var.  The "tc" prefix means "a type variable that can be
  encountered by the typechecker".

This is a bit of a change from an earlier era when we remoselessly
insisted on real TcTyVars in the type checker.  But that seems
unnecessary (for skolems, TyVars are fine) and it's now very hard
to guarantee, with the advent of kind equalities.

Note [Coercion variables in free variable lists]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are several places in the GHC codebase where functions like
tyCoVarsOfType, tyCoVarsOfCt, et al. are used to compute the free type
variables of a type. The "Co" part of these functions' names shouldn't be
dismissed, as it is entirely possible that they will include coercion variables
in addition to type variables! As a result, there are some places in GHC.Tc.Utils.TcType
where we must take care to check that a variable is a _type_ variable (using
isTyVar) before calling tcTyVarDetails--a partial function that is not defined
for coercion variables--on the variable. Failing to do so led to
GHC #12785.
-}

-- See Note [TcTyVars and TyVars in the typechecker]
type TcCoVar = CoVar    -- Used only during type inference
type TcType = Type      -- A TcType can have mutable type variables
type TcTyCoVar = Var    -- Either a TcTyVar or a CoVar

type TcTyVarBinder     = TyVarBinder
type TcInvisTVBinder   = InvisTVBinder
type TcReqTVBinder     = ReqTVBinder
type TcTyCon           = TyCon   -- these can be the TcTyCon constructor

-- These types do not have boxy type variables in them
type TcPredType     = PredType
type TcThetaType    = ThetaType
type TcSigmaType    = TcType
type TcRhoType      = TcType  -- Note [TcRhoType]
type TcTauType      = TcType
type TcKind         = Kind
type TcTyVarSet     = TyVarSet
type TcTyCoVarSet   = TyCoVarSet
type TcDTyVarSet    = DTyVarSet
type TcDTyCoVarSet  = DTyCoVarSet

{- *********************************************************************
*                                                                      *
          ExpType: an "expected type" in the type checker
*                                                                      *
********************************************************************* -}

-- | An expected type to check against during type-checking.
-- See Note [ExpType] in "GHC.Tc.Utils.TcMType", where you'll also find manipulators.
data ExpType = Check TcType
             | Infer !InferResult

data InferResult
  = IR { InferResult -> Unique
ir_uniq :: Unique  -- For debugging only

       , InferResult -> TcLevel
ir_lvl  :: TcLevel -- See Note [TcLevel of ExpType] in GHC.Tc.Utils.TcMType

       , InferResult -> IORef (Maybe Type)
ir_ref  :: IORef (Maybe TcType) }
         -- The type that fills in this hole should be a Type,
         -- that is, its kind should be (TYPE rr) for some rr

type ExpSigmaType = ExpType
type ExpRhoType   = ExpType

instance Outputable ExpType where
  ppr :: ExpType -> SDoc
ppr (Check Type
ty) = String -> SDoc
text String
"Check" SDoc -> SDoc -> SDoc
<> SDoc -> SDoc
braces (forall a. Outputable a => a -> SDoc
ppr Type
ty)
  ppr (Infer InferResult
ir) = forall a. Outputable a => a -> SDoc
ppr InferResult
ir

instance Outputable InferResult where
  ppr :: InferResult -> SDoc
ppr (IR { ir_uniq :: InferResult -> Unique
ir_uniq = Unique
u, ir_lvl :: InferResult -> TcLevel
ir_lvl = TcLevel
lvl })
    = String -> SDoc
text String
"Infer" SDoc -> SDoc -> SDoc
<> SDoc -> SDoc
braces (forall a. Outputable a => a -> SDoc
ppr Unique
u SDoc -> SDoc -> SDoc
<> SDoc
comma SDoc -> SDoc -> SDoc
<> forall a. Outputable a => a -> SDoc
ppr TcLevel
lvl)

-- | Make an 'ExpType' suitable for checking.
mkCheckExpType :: TcType -> ExpType
mkCheckExpType :: Type -> ExpType
mkCheckExpType = Type -> ExpType
Check


{- *********************************************************************
*                                                                      *
          SyntaxOpType
*                                                                      *
********************************************************************* -}

-- | What to expect for an argument to a rebindable-syntax operator.
-- Quite like 'Type', but allows for holes to be filled in by tcSyntaxOp.
-- The callback called from tcSyntaxOp gets a list of types; the meaning
-- of these types is determined by a left-to-right depth-first traversal
-- of the 'SyntaxOpType' tree. So if you pass in
--
-- > SynAny `SynFun` (SynList `SynFun` SynType Int) `SynFun` SynAny
--
-- you'll get three types back: one for the first 'SynAny', the /element/
-- type of the list, and one for the last 'SynAny'. You don't get anything
-- for the 'SynType', because you've said positively that it should be an
-- Int, and so it shall be.
--
-- You'll also get three multiplicities back: one for each function arrow. See
-- also Note [Linear types] in Multiplicity.
--
-- This is defined here to avoid defining it in "GHC.Tc.Gen.Expr" boot file.
data SyntaxOpType
  = SynAny     -- ^ Any type
  | SynRho     -- ^ A rho type, skolemised or instantiated as appropriate
  | SynList    -- ^ A list type. You get back the element type of the list
  | SynFun SyntaxOpType SyntaxOpType
               -- ^ A function.
  | SynType ExpType   -- ^ A known type.
infixr 0 `SynFun`

-- | Like 'SynType' but accepts a regular TcType
synKnownType :: TcType -> SyntaxOpType
synKnownType :: Type -> SyntaxOpType
synKnownType = ExpType -> SyntaxOpType
SynType forall b c a. (b -> c) -> (a -> b) -> a -> c
. Type -> ExpType
mkCheckExpType

-- | Like 'mkFunTys' but for 'SyntaxOpType'
mkSynFunTys :: [SyntaxOpType] -> ExpType -> SyntaxOpType
mkSynFunTys :: [SyntaxOpType] -> ExpType -> SyntaxOpType
mkSynFunTys [SyntaxOpType]
arg_tys ExpType
res_ty = forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr SyntaxOpType -> SyntaxOpType -> SyntaxOpType
SynFun (ExpType -> SyntaxOpType
SynType ExpType
res_ty) [SyntaxOpType]
arg_tys


{-
Note [TcRhoType]
~~~~~~~~~~~~~~~~
A TcRhoType has no foralls or contexts at the top
  NO     forall a. a ->  Int
  NO     Eq a => a -> a
  YES    a -> a
  YES    (forall a. a->a) -> Int
  YES    Int -> forall a. a -> Int


************************************************************************
*                                                                      *
        TyVarDetails, MetaDetails, MetaInfo
*                                                                      *
************************************************************************

TyVarDetails gives extra info about type variables, used during type
checking.  It's attached to mutable type variables only.
It's knot-tied back to "GHC.Types.Var".  There is no reason in principle
why "GHC.Types.Var" shouldn't actually have the definition, but it "belongs" here.

Note [TyVars and TcTyVars during type checking]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Var type has constructors TyVar and TcTyVar.  They are used
as follows:

* TcTyVar: used /only/ during type checking.  Should never appear
  afterwards.  May contain a mutable field, in the MetaTv case.

* TyVar: is never seen by the constraint solver, except locally
  inside a type like (forall a. [a] ->[a]), where 'a' is a TyVar.
  We instantiate these with TcTyVars before exposing the type
  to the constraint solver.

I have swithered about the latter invariant, excluding TyVars from the
constraint solver.  It's not strictly essential, and indeed
(historically but still there) Var.tcTyVarDetails returns
vanillaSkolemTv for a TyVar.

But ultimately I want to seeparate Type from TcType, and in that case
we would need to enforce the separation.
-}

-- A TyVarDetails is inside a TyVar
-- See Note [TyVars and TcTyVars]
data TcTyVarDetails
  = SkolemTv      -- A skolem
       TcLevel    -- Level of the implication that binds it
                  -- See GHC.Tc.Utils.Unify Note [Deeper level on the left] for
                  --     how this level number is used
       Bool       -- True <=> this skolem type variable can be overlapped
                  --          when looking up instances
                  -- See Note [Binding when looking up instances] in GHC.Core.InstEnv

  | RuntimeUnk    -- Stands for an as-yet-unknown type in the GHCi
                  -- interactive context

  | MetaTv { TcTyVarDetails -> MetaInfo
mtv_info  :: MetaInfo
           , TcTyVarDetails -> IORef MetaDetails
mtv_ref   :: IORef MetaDetails
           , TcTyVarDetails -> TcLevel
mtv_tclvl :: TcLevel }  -- See Note [TcLevel invariants]

vanillaSkolemTv, superSkolemTv :: TcTyVarDetails
-- See Note [Binding when looking up instances] in GHC.Core.InstEnv
vanillaSkolemTv :: TcTyVarDetails
vanillaSkolemTv = TcLevel -> Bool -> TcTyVarDetails
SkolemTv TcLevel
topTcLevel Bool
False  -- Might be instantiated
superSkolemTv :: TcTyVarDetails
superSkolemTv   = TcLevel -> Bool -> TcTyVarDetails
SkolemTv TcLevel
topTcLevel Bool
True   -- Treat this as a completely distinct type
                  -- The choice of level number here is a bit dodgy, but
                  -- topTcLevel works in the places that vanillaSkolemTv is used

instance Outputable TcTyVarDetails where
  ppr :: TcTyVarDetails -> SDoc
ppr = TcTyVarDetails -> SDoc
pprTcTyVarDetails

pprTcTyVarDetails :: TcTyVarDetails -> SDoc
-- For debugging
pprTcTyVarDetails :: TcTyVarDetails -> SDoc
pprTcTyVarDetails (RuntimeUnk {})      = String -> SDoc
text String
"rt"
pprTcTyVarDetails (SkolemTv TcLevel
lvl Bool
True)  = String -> SDoc
text String
"ssk" SDoc -> SDoc -> SDoc
<> SDoc
colon SDoc -> SDoc -> SDoc
<> forall a. Outputable a => a -> SDoc
ppr TcLevel
lvl
pprTcTyVarDetails (SkolemTv TcLevel
lvl Bool
False) = String -> SDoc
text String
"sk"  SDoc -> SDoc -> SDoc
<> SDoc
colon SDoc -> SDoc -> SDoc
<> forall a. Outputable a => a -> SDoc
ppr TcLevel
lvl
pprTcTyVarDetails (MetaTv { mtv_info :: TcTyVarDetails -> MetaInfo
mtv_info = MetaInfo
info, mtv_tclvl :: TcTyVarDetails -> TcLevel
mtv_tclvl = TcLevel
tclvl })
  = forall a. Outputable a => a -> SDoc
ppr MetaInfo
info SDoc -> SDoc -> SDoc
<> SDoc
colon SDoc -> SDoc -> SDoc
<> forall a. Outputable a => a -> SDoc
ppr TcLevel
tclvl

-----------------------------
data MetaDetails
  = Flexi  -- Flexi type variables unify to become Indirects
  | Indirect TcType

data MetaInfo
   = TauTv         -- This MetaTv is an ordinary unification variable
                   -- A TauTv is always filled in with a tau-type, which
                   -- never contains any ForAlls.

   | TyVarTv       -- A variant of TauTv, except that it should not be
                   --   unified with a type, only with a type variable
                   -- See Note [TyVarTv] in GHC.Tc.Utils.TcMType

   | RuntimeUnkTv  -- A unification variable used in the GHCi debugger.
                   -- It /is/ allowed to unify with a polytype, unlike TauTv

   | CycleBreakerTv  -- Used to fix occurs-check problems in Givens
                     -- See Note [Type equality cycles] in
                     -- GHC.Tc.Solver.Canonical

instance Outputable MetaDetails where
  ppr :: MetaDetails -> SDoc
ppr MetaDetails
Flexi         = String -> SDoc
text String
"Flexi"
  ppr (Indirect Type
ty) = String -> SDoc
text String
"Indirect" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr Type
ty

instance Outputable MetaInfo where
  ppr :: MetaInfo -> SDoc
ppr MetaInfo
TauTv          = String -> SDoc
text String
"tau"
  ppr MetaInfo
TyVarTv        = String -> SDoc
text String
"tyv"
  ppr MetaInfo
RuntimeUnkTv   = String -> SDoc
text String
"rutv"
  ppr MetaInfo
CycleBreakerTv = String -> SDoc
text String
"cbv"

{- *********************************************************************
*                                                                      *
                Untouchable type variables
*                                                                      *
********************************************************************* -}

newtype TcLevel = TcLevel Int deriving( TcLevel -> TcLevel -> Bool
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: TcLevel -> TcLevel -> Bool
$c/= :: TcLevel -> TcLevel -> Bool
== :: TcLevel -> TcLevel -> Bool
$c== :: TcLevel -> TcLevel -> Bool
Eq, Eq TcLevel
TcLevel -> TcLevel -> Bool
TcLevel -> TcLevel -> Ordering
TcLevel -> TcLevel -> TcLevel
forall a.
Eq a
-> (a -> a -> Ordering)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> a)
-> (a -> a -> a)
-> Ord a
min :: TcLevel -> TcLevel -> TcLevel
$cmin :: TcLevel -> TcLevel -> TcLevel
max :: TcLevel -> TcLevel -> TcLevel
$cmax :: TcLevel -> TcLevel -> TcLevel
>= :: TcLevel -> TcLevel -> Bool
$c>= :: TcLevel -> TcLevel -> Bool
> :: TcLevel -> TcLevel -> Bool
$c> :: TcLevel -> TcLevel -> Bool
<= :: TcLevel -> TcLevel -> Bool
$c<= :: TcLevel -> TcLevel -> Bool
< :: TcLevel -> TcLevel -> Bool
$c< :: TcLevel -> TcLevel -> Bool
compare :: TcLevel -> TcLevel -> Ordering
$ccompare :: TcLevel -> TcLevel -> Ordering
Ord )
  -- See Note [TcLevel invariants] for what this Int is
  -- See also Note [TcLevel assignment]

{-
Note [TcLevel invariants]
~~~~~~~~~~~~~~~~~~~~~~~~~
* Each unification variable (MetaTv)
  and skolem (SkolemTv)
  and each Implication
  has a level number (of type TcLevel)

* INVARIANTS.  In a tree of Implications,

    (ImplicInv) The level number (ic_tclvl) of an Implication is
                STRICTLY GREATER THAN that of its parent

    (SkolInv)   The level number of the skolems (ic_skols) of an
                Implication is equal to the level of the implication
                itself (ic_tclvl)

    (GivenInv)  The level number of a unification variable appearing
                in the 'ic_given' of an implication I should be
                STRICTLY LESS THAN the ic_tclvl of I
                See Note [GivenInv]

    (WantedInv) The level number of a unification variable appearing
                in the 'ic_wanted' of an implication I should be
                LESS THAN OR EQUAL TO the ic_tclvl of I
                See Note [WantedInv]

The level of a MetaTyVar also governs its untouchability.  See
Note [Unification preconditions] in GHC.Tc.Utils.Unify.

Note [TcLevel assignment]
~~~~~~~~~~~~~~~~~~~~~~~~~
We arrange the TcLevels like this

   0   Top level
   1   First-level implication constraints
   2   Second-level implication constraints
   ...etc...

Note [GivenInv]
~~~~~~~~~~~~~~~
Invariant (GivenInv) is not essential, but it is easy to guarantee, and
it is a useful extra piece of structure.  It ensures that the Givens of
an implication don't change because of unifications /at the same level/
caused by Wanteds.  (Wanteds can also cause unifications at an outer
level, but that will iterate the entire implication; see GHC.Tc.Solver.Monad
Note [The Unification Level Flag].)

Givens can certainly contain meta-tyvars from /outer/ levels.  E.g.
   data T a where
     MkT :: Eq a => a -> MkT a

   f x = case x of MkT y -> y && True

Then we'll infer (x :: T alpha[1]).  The Givens from the implication
arising from the pattern match will look like this:

   forall[2] . Eq alpha[1] => (alpha[1] ~ Bool)

But if we unify alpha (which in this case we will), we'll iterate
the entire implication via Note [The Unification Level Flag] in
GHC.Tc.Solver.Monad.  That isn't true of unifications at the /ambient/
level.

It would be entirely possible to weaken (GivenInv), to LESS THAN OR
EQUAL TO, but we'd need to think carefully about
  - kick-out for Givens
  - GHC.Tc.Solver.Monad.isOuterTyVar
But in fact (GivenInv) is automatically true, so we're adhering to
it for now.  See #18929.

* If a tyvar tv has level n, then the levels of all variables free
  in tv's kind are <= n. Consequence: if tv is untouchable, so are
  all variables in tv's kind.

Note [WantedInv]
~~~~~~~~~~~~~~~~
Why is WantedInv important?  Consider this implication, where
the constraint (C alpha[3]) disobeys WantedInv:

   forall[2] a. blah => (C alpha[3])
                        (forall[3] b. alpha[3] ~ b)

We can unify alpha:=b in the inner implication, because 'alpha' is
touchable; but then 'b' has excaped its scope into the outer implication.
-}

maxTcLevel :: TcLevel -> TcLevel -> TcLevel
maxTcLevel :: TcLevel -> TcLevel -> TcLevel
maxTcLevel (TcLevel Arity
a) (TcLevel Arity
b) = Arity -> TcLevel
TcLevel (Arity
a forall a. Ord a => a -> a -> a
`max` Arity
b)

topTcLevel :: TcLevel
-- See Note [TcLevel assignment]
topTcLevel :: TcLevel
topTcLevel = Arity -> TcLevel
TcLevel Arity
0   -- 0 = outermost level

isTopTcLevel :: TcLevel -> Bool
isTopTcLevel :: TcLevel -> Bool
isTopTcLevel (TcLevel Arity
0) = Bool
True
isTopTcLevel TcLevel
_           = Bool
False

pushTcLevel :: TcLevel -> TcLevel
-- See Note [TcLevel assignment]
pushTcLevel :: TcLevel -> TcLevel
pushTcLevel (TcLevel Arity
us) = Arity -> TcLevel
TcLevel (Arity
us forall a. Num a => a -> a -> a
+ Arity
1)

strictlyDeeperThan :: TcLevel -> TcLevel -> Bool
strictlyDeeperThan :: TcLevel -> TcLevel -> Bool
strictlyDeeperThan (TcLevel Arity
tv_tclvl) (TcLevel Arity
ctxt_tclvl)
  = Arity
tv_tclvl forall a. Ord a => a -> a -> Bool
> Arity
ctxt_tclvl

deeperThanOrSame :: TcLevel -> TcLevel -> Bool
deeperThanOrSame :: TcLevel -> TcLevel -> Bool
deeperThanOrSame (TcLevel Arity
tv_tclvl) (TcLevel Arity
ctxt_tclvl)
  = Arity
tv_tclvl forall a. Ord a => a -> a -> Bool
>= Arity
ctxt_tclvl

sameDepthAs :: TcLevel -> TcLevel -> Bool
sameDepthAs :: TcLevel -> TcLevel -> Bool
sameDepthAs (TcLevel Arity
ctxt_tclvl) (TcLevel Arity
tv_tclvl)
  = Arity
ctxt_tclvl forall a. Eq a => a -> a -> Bool
== Arity
tv_tclvl   -- NB: invariant ctxt_tclvl >= tv_tclvl
                             --     So <= would be equivalent

checkTcLevelInvariant :: TcLevel -> TcLevel -> Bool
-- Checks (WantedInv) from Note [TcLevel invariants]
checkTcLevelInvariant :: TcLevel -> TcLevel -> Bool
checkTcLevelInvariant (TcLevel Arity
ctxt_tclvl) (TcLevel Arity
tv_tclvl)
  = Arity
ctxt_tclvl forall a. Ord a => a -> a -> Bool
>= Arity
tv_tclvl

-- Returns topTcLevel for non-TcTyVars
tcTyVarLevel :: TcTyVar -> TcLevel
tcTyVarLevel :: Var -> TcLevel
tcTyVarLevel Var
tv
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
          MetaTv { mtv_tclvl :: TcTyVarDetails -> TcLevel
mtv_tclvl = TcLevel
tv_lvl } -> TcLevel
tv_lvl
          SkolemTv TcLevel
tv_lvl Bool
_             -> TcLevel
tv_lvl
          TcTyVarDetails
RuntimeUnk                    -> TcLevel
topTcLevel


tcTypeLevel :: TcType -> TcLevel
-- Max level of any free var of the type
tcTypeLevel :: Type -> TcLevel
tcTypeLevel Type
ty
  = forall a. (Var -> a -> a) -> a -> DVarSet -> a
nonDetStrictFoldDVarSet Var -> TcLevel -> TcLevel
add TcLevel
topTcLevel (Type -> DVarSet
tyCoVarsOfTypeDSet Type
ty)
    -- It's safe to use a non-deterministic fold because `maxTcLevel` is
    -- commutative.
  where
    add :: Var -> TcLevel -> TcLevel
add Var
v TcLevel
lvl
      | Var -> Bool
isTcTyVar Var
v = TcLevel
lvl TcLevel -> TcLevel -> TcLevel
`maxTcLevel` Var -> TcLevel
tcTyVarLevel Var
v
      | Bool
otherwise = TcLevel
lvl

instance Outputable TcLevel where
  ppr :: TcLevel -> SDoc
ppr (TcLevel Arity
us) = forall a. Outputable a => a -> SDoc
ppr Arity
us

promoteSkolem :: TcLevel -> TcTyVar -> TcTyVar
promoteSkolem :: TcLevel -> Var -> Var
promoteSkolem TcLevel
tclvl Var
skol
  | TcLevel
tclvl forall a. Ord a => a -> a -> Bool
< Var -> TcLevel
tcTyVarLevel Var
skol
  = ASSERT( isTcTyVar skol && isSkolemTyVar skol )
    Var -> TcTyVarDetails -> Var
setTcTyVarDetails Var
skol (TcLevel -> Bool -> TcTyVarDetails
SkolemTv TcLevel
tclvl (Var -> Bool
isOverlappableTyVar Var
skol))

  | Bool
otherwise
  = Var
skol

-- | Change the TcLevel in a skolem, extending a substitution
promoteSkolemX :: TcLevel -> TCvSubst -> TcTyVar -> (TCvSubst, TcTyVar)
promoteSkolemX :: TcLevel -> TCvSubst -> Var -> (TCvSubst, Var)
promoteSkolemX TcLevel
tclvl TCvSubst
subst Var
skol
  = ASSERT( isTcTyVar skol && isSkolemTyVar skol )
    (TCvSubst
new_subst, Var
new_skol)
  where
    new_skol :: Var
new_skol
      | TcLevel
tclvl forall a. Ord a => a -> a -> Bool
< Var -> TcLevel
tcTyVarLevel Var
skol
      = Var -> TcTyVarDetails -> Var
setTcTyVarDetails ((Type -> Type) -> Var -> Var
updateTyVarKind (HasCallStack => TCvSubst -> Type -> Type
substTy TCvSubst
subst) Var
skol)
                          (TcLevel -> Bool -> TcTyVarDetails
SkolemTv TcLevel
tclvl (Var -> Bool
isOverlappableTyVar Var
skol))
      | Bool
otherwise
      = (Type -> Type) -> Var -> Var
updateTyVarKind (HasCallStack => TCvSubst -> Type -> Type
substTy TCvSubst
subst) Var
skol
    new_subst :: TCvSubst
new_subst = TCvSubst -> Var -> Var -> TCvSubst
extendTvSubstWithClone TCvSubst
subst Var
skol Var
new_skol

promoteSkolemsX :: TcLevel -> TCvSubst -> [TcTyVar] -> (TCvSubst, [TcTyVar])
promoteSkolemsX :: TcLevel -> TCvSubst -> [Var] -> (TCvSubst, [Var])
promoteSkolemsX TcLevel
tclvl = forall (t :: * -> *) s a b.
Traversable t =>
(s -> a -> (s, b)) -> s -> t a -> (s, t b)
mapAccumL (TcLevel -> TCvSubst -> Var -> (TCvSubst, Var)
promoteSkolemX TcLevel
tclvl)

{- *********************************************************************
*                                                                      *
    Finding type family instances
*                                                                      *
************************************************************************
-}

-- | Finds outermost type-family applications occurring in a type,
-- after expanding synonyms.  In the list (F, tys) that is returned
-- we guarantee that tys matches F's arity.  For example, given
--    type family F a :: * -> *    (arity 1)
-- calling tcTyFamInsts on (Maybe (F Int Bool) will return
--     (F, [Int]), not (F, [Int,Bool])
--
-- This is important for its use in deciding termination of type
-- instances (see #11581).  E.g.
--    type instance G [Int] = ...(F Int \<big type>)...
-- we don't need to take \<big type> into account when asking if
-- the calls on the RHS are smaller than the LHS
tcTyFamInsts :: Type -> [(TyCon, [Type])]
tcTyFamInsts :: Type -> [(TyCon, [Type])]
tcTyFamInsts = forall a b. (a -> b) -> [a] -> [b]
map (\(Bool
_,TyCon
b,[Type]
c) -> (TyCon
b,[Type]
c)) forall b c a. (b -> c) -> (a -> b) -> a -> c
. Type -> [(Bool, TyCon, [Type])]
tcTyFamInstsAndVis

-- | Like 'tcTyFamInsts', except that the output records whether the
-- type family and its arguments occur as an /invisible/ argument in
-- some type application. This information is useful because it helps GHC know
-- when to turn on @-fprint-explicit-kinds@ during error reporting so that
-- users can actually see the type family being mentioned.
--
-- As an example, consider:
--
-- @
-- class C a
-- data T (a :: k)
-- type family F a :: k
-- instance C (T @(F Int) (F Bool))
-- @
--
-- There are two occurrences of the type family `F` in that `C` instance, so
-- @'tcTyFamInstsAndVis' (C (T \@(F Int) (F Bool)))@ will return:
--
-- @
-- [ ('True',  F, [Int])
-- , ('False', F, [Bool]) ]
-- @
--
-- @F Int@ is paired with 'True' since it appears as an /invisible/ argument
-- to @C@, whereas @F Bool@ is paired with 'False' since it appears an a
-- /visible/ argument to @C@.
--
-- See also @Note [Kind arguments in error messages]@ in "GHC.Tc.Errors".
tcTyFamInstsAndVis :: Type -> [(Bool, TyCon, [Type])]
tcTyFamInstsAndVis :: Type -> [(Bool, TyCon, [Type])]
tcTyFamInstsAndVis = Bool -> Type -> [(Bool, TyCon, [Type])]
tcTyFamInstsAndVisX Bool
False

tcTyFamInstsAndVisX
  :: Bool -- ^ Is this an invisible argument to some type application?
  -> Type -> [(Bool, TyCon, [Type])]
tcTyFamInstsAndVisX :: Bool -> Type -> [(Bool, TyCon, [Type])]
tcTyFamInstsAndVisX = Bool -> Type -> [(Bool, TyCon, [Type])]
go
  where
    go :: Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg Type
ty
      | Just Type
exp_ty <- Type -> Maybe Type
tcView Type
ty       = Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg Type
exp_ty
    go Bool
_ (TyVarTy Var
_)                   = []
    go Bool
is_invis_arg (TyConApp TyCon
tc [Type]
tys)
      | TyCon -> Bool
isTypeFamilyTyCon TyCon
tc
      = [(Bool
is_invis_arg, TyCon
tc, forall a. Arity -> [a] -> [a]
take (TyCon -> Arity
tyConArity TyCon
tc) [Type]
tys)]
      | Bool
otherwise
      = Bool -> TyCon -> [Type] -> [(Bool, TyCon, [Type])]
tcTyConAppTyFamInstsAndVisX Bool
is_invis_arg TyCon
tc [Type]
tys
    go Bool
_            (LitTy {})         = []
    go Bool
is_invis_arg (ForAllTy TyCoVarBinder
bndr Type
ty) = Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg (forall argf. VarBndr Var argf -> Type
binderType TyCoVarBinder
bndr)
                                         forall a. [a] -> [a] -> [a]
++ Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg Type
ty
    go Bool
is_invis_arg (FunTy AnonArgFlag
_ Type
w Type
ty1 Type
ty2)  = Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg Type
w
                                         forall a. [a] -> [a] -> [a]
++ Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg Type
ty1
                                         forall a. [a] -> [a] -> [a]
++ Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg Type
ty2
    go Bool
is_invis_arg ty :: Type
ty@(AppTy Type
_ Type
_)     =
      let (Type
ty_head, [Type]
ty_args) = Type -> (Type, [Type])
splitAppTys Type
ty
          ty_arg_flags :: [ArgFlag]
ty_arg_flags       = Type -> [Type] -> [ArgFlag]
appTyArgFlags Type
ty_head [Type]
ty_args
      in Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg Type
ty_head
         forall a. [a] -> [a] -> [a]
++ forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat (forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
zipWith (\ArgFlag
flag -> Bool -> Type -> [(Bool, TyCon, [Type])]
go (ArgFlag -> Bool
isInvisibleArgFlag ArgFlag
flag))
                            [ArgFlag]
ty_arg_flags [Type]
ty_args)
    go Bool
is_invis_arg (CastTy Type
ty KindCoercion
_)      = Bool -> Type -> [(Bool, TyCon, [Type])]
go Bool
is_invis_arg Type
ty
    go Bool
_            (CoercionTy KindCoercion
_)     = [] -- don't count tyfams in coercions,
                                            -- as they never get normalized,
                                            -- anyway

-- | In an application of a 'TyCon' to some arguments, find the outermost
-- occurrences of type family applications within the arguments. This function
-- will not consider the 'TyCon' itself when checking for type family
-- applications.
--
-- See 'tcTyFamInstsAndVis' for more details on how this works (as this
-- function is called inside of 'tcTyFamInstsAndVis').
tcTyConAppTyFamInstsAndVis :: TyCon -> [Type] -> [(Bool, TyCon, [Type])]
tcTyConAppTyFamInstsAndVis :: TyCon -> [Type] -> [(Bool, TyCon, [Type])]
tcTyConAppTyFamInstsAndVis = Bool -> TyCon -> [Type] -> [(Bool, TyCon, [Type])]
tcTyConAppTyFamInstsAndVisX Bool
False

tcTyConAppTyFamInstsAndVisX
  :: Bool -- ^ Is this an invisible argument to some type application?
  -> TyCon -> [Type] -> [(Bool, TyCon, [Type])]
tcTyConAppTyFamInstsAndVisX :: Bool -> TyCon -> [Type] -> [(Bool, TyCon, [Type])]
tcTyConAppTyFamInstsAndVisX Bool
is_invis_arg TyCon
tc [Type]
tys =
  let ([Type]
invis_tys, [Type]
vis_tys) = TyCon -> [Type] -> ([Type], [Type])
partitionInvisibleTypes TyCon
tc [Type]
tys
  in forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat forall a b. (a -> b) -> a -> b
$ forall a b. (a -> b) -> [a] -> [b]
map (Bool -> Type -> [(Bool, TyCon, [Type])]
tcTyFamInstsAndVisX Bool
True)         [Type]
invis_tys
           forall a. [a] -> [a] -> [a]
++ forall a b. (a -> b) -> [a] -> [b]
map (Bool -> Type -> [(Bool, TyCon, [Type])]
tcTyFamInstsAndVisX Bool
is_invis_arg) [Type]
vis_tys

isTyFamFree :: Type -> Bool
-- ^ Check that a type does not contain any type family applications.
isTyFamFree :: Type -> Bool
isTyFamFree = forall (t :: * -> *) a. Foldable t => t a -> Bool
null forall b c a. (b -> c) -> (a -> b) -> a -> c
. Type -> [(TyCon, [Type])]
tcTyFamInsts

any_rewritable :: Bool    -- Ignore casts and coercions
               -> EqRel   -- Ambient role
               -> (EqRel -> TcTyVar -> Bool)           -- check tyvar
               -> (EqRel -> TyCon -> [TcType] -> Bool) -- check type family
               -> (TyCon -> Bool)                      -- expand type synonym?
               -> TcType -> Bool
-- Checks every tyvar and tyconapp (not including FunTys) within a type,
-- ORing the results of the predicates above together
-- Do not look inside casts and coercions if 'ignore_cos' is True
-- See Note [anyRewritableTyVar must be role-aware]
--
-- This looks like it should use foldTyCo, but that function is
-- role-agnostic, and this one must be role-aware. We could make
-- foldTyCon role-aware, but that may slow down more common usages.
--
-- See Note [Rewritable] in GHC.Tc.Solver.Monad for a specification for this function.
{-# INLINE any_rewritable #-} -- this allows specialization of predicates
any_rewritable :: Bool
-> EqRel
-> (EqRel -> Var -> Bool)
-> (EqRel -> TyCon -> [Type] -> Bool)
-> (TyCon -> Bool)
-> Type
-> Bool
any_rewritable Bool
ignore_cos EqRel
role EqRel -> Var -> Bool
tv_pred EqRel -> TyCon -> [Type] -> Bool
tc_pred TyCon -> Bool
should_expand
  = EqRel -> VarSet -> Type -> Bool
go EqRel
role VarSet
emptyVarSet
  where
    go_tv :: EqRel -> VarSet -> Var -> Bool
go_tv EqRel
rl VarSet
bvs Var
tv | Var
tv Var -> VarSet -> Bool
`elemVarSet` VarSet
bvs = Bool
False
                    | Bool
otherwise           = EqRel -> Var -> Bool
tv_pred EqRel
rl Var
tv

    go :: EqRel -> VarSet -> Type -> Bool
go EqRel
rl VarSet
bvs ty :: Type
ty@(TyConApp TyCon
tc [Type]
tys)
      | TyCon -> Bool
isTypeSynonymTyCon TyCon
tc
      , TyCon -> Bool
should_expand TyCon
tc
      , Just Type
ty' <- Type -> Maybe Type
tcView Type
ty   -- should always match
      = EqRel -> VarSet -> Type -> Bool
go EqRel
rl VarSet
bvs Type
ty'

      | EqRel -> TyCon -> [Type] -> Bool
tc_pred EqRel
rl TyCon
tc [Type]
tys
      = Bool
True

      | Bool
otherwise
      = EqRel -> VarSet -> TyCon -> [Type] -> Bool
go_tc EqRel
rl VarSet
bvs TyCon
tc [Type]
tys

    go EqRel
rl VarSet
bvs (TyVarTy Var
tv)       = EqRel -> VarSet -> Var -> Bool
go_tv EqRel
rl VarSet
bvs Var
tv
    go EqRel
_ VarSet
_     (LitTy {})        = Bool
False
    go EqRel
rl VarSet
bvs (AppTy Type
fun Type
arg)    = EqRel -> VarSet -> Type -> Bool
go EqRel
rl VarSet
bvs Type
fun Bool -> Bool -> Bool
|| EqRel -> VarSet -> Type -> Bool
go EqRel
NomEq VarSet
bvs Type
arg
    go EqRel
rl VarSet
bvs (FunTy AnonArgFlag
_ Type
w Type
arg Type
res)  = EqRel -> VarSet -> Type -> Bool
go EqRel
NomEq VarSet
bvs Type
arg_rep Bool -> Bool -> Bool
|| EqRel -> VarSet -> Type -> Bool
go EqRel
NomEq VarSet
bvs Type
res_rep Bool -> Bool -> Bool
||
                                     EqRel -> VarSet -> Type -> Bool
go EqRel
rl VarSet
bvs Type
arg Bool -> Bool -> Bool
|| EqRel -> VarSet -> Type -> Bool
go EqRel
rl VarSet
bvs Type
res Bool -> Bool -> Bool
|| EqRel -> VarSet -> Type -> Bool
go EqRel
NomEq VarSet
bvs Type
w
      where arg_rep :: Type
arg_rep = HasDebugCallStack => Type -> Type
getRuntimeRep Type
arg -- forgetting these causes #17024
            res_rep :: Type
res_rep = HasDebugCallStack => Type -> Type
getRuntimeRep Type
res
    go EqRel
rl VarSet
bvs (ForAllTy TyCoVarBinder
tv Type
ty)   = EqRel -> VarSet -> Type -> Bool
go EqRel
rl (VarSet
bvs VarSet -> Var -> VarSet
`extendVarSet` forall tv argf. VarBndr tv argf -> tv
binderVar TyCoVarBinder
tv) Type
ty
    go EqRel
rl VarSet
bvs (CastTy Type
ty KindCoercion
co)     = EqRel -> VarSet -> Type -> Bool
go EqRel
rl VarSet
bvs Type
ty Bool -> Bool -> Bool
|| EqRel -> VarSet -> KindCoercion -> Bool
go_co EqRel
rl VarSet
bvs KindCoercion
co
    go EqRel
rl VarSet
bvs (CoercionTy KindCoercion
co)    = EqRel -> VarSet -> KindCoercion -> Bool
go_co EqRel
rl VarSet
bvs KindCoercion
co  -- ToDo: check

    go_tc :: EqRel -> VarSet -> TyCon -> [Type] -> Bool
go_tc EqRel
NomEq  VarSet
bvs TyCon
_  [Type]
tys = forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any (EqRel -> VarSet -> Type -> Bool
go EqRel
NomEq VarSet
bvs) [Type]
tys
    go_tc EqRel
ReprEq VarSet
bvs TyCon
tc [Type]
tys = forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any (VarSet -> (Role, Type) -> Bool
go_arg VarSet
bvs)
                              (TyCon -> [Role]
tyConRolesRepresentational TyCon
tc forall a b. [a] -> [b] -> [(a, b)]
`zip` [Type]
tys)

    go_arg :: VarSet -> (Role, Type) -> Bool
go_arg VarSet
bvs (Role
Nominal,          Type
ty) = EqRel -> VarSet -> Type -> Bool
go EqRel
NomEq  VarSet
bvs Type
ty
    go_arg VarSet
bvs (Role
Representational, Type
ty) = EqRel -> VarSet -> Type -> Bool
go EqRel
ReprEq VarSet
bvs Type
ty
    go_arg VarSet
_   (Role
Phantom,          Type
_)  = Bool
False  -- We never rewrite with phantoms

    go_co :: EqRel -> VarSet -> KindCoercion -> Bool
go_co EqRel
rl VarSet
bvs KindCoercion
co
      | Bool
ignore_cos = Bool
False
      | Bool
otherwise  = (Var -> Bool) -> VarSet -> Bool
anyVarSet (EqRel -> VarSet -> Var -> Bool
go_tv EqRel
rl VarSet
bvs) (KindCoercion -> VarSet
tyCoVarsOfCo KindCoercion
co)
      -- We don't have an equivalent of anyRewritableTyVar for coercions
      -- (at least not yet) so take the free vars and test them

anyRewritableTyVar :: Bool     -- Ignore casts and coercions
                   -> EqRel    -- Ambient role
                   -> (EqRel -> TcTyVar -> Bool)  -- check tyvar
                   -> TcType -> Bool
-- See Note [Rewritable] in GHC.Tc.Solver.Monad for a specification for this function.
anyRewritableTyVar :: Bool -> EqRel -> (EqRel -> Var -> Bool) -> Type -> Bool
anyRewritableTyVar Bool
ignore_cos EqRel
role EqRel -> Var -> Bool
pred
  = Bool
-> EqRel
-> (EqRel -> Var -> Bool)
-> (EqRel -> TyCon -> [Type] -> Bool)
-> (TyCon -> Bool)
-> Type
-> Bool
any_rewritable Bool
ignore_cos EqRel
role EqRel -> Var -> Bool
pred
      (\ EqRel
_ TyCon
_ [Type]
_ -> Bool
False) -- no special check for tyconapps
                         -- (this False is ORed with other results, so it
                         --  really means "do nothing special"; the arguments
                         --   are still inspected)
      (\ TyCon
_ -> Bool
False)     -- don't expand synonyms
    -- NB: No need to expand synonyms, because we can find
    -- all free variables of a synonym by looking at its
    -- arguments

anyRewritableTyFamApp :: EqRel   -- Ambient role
                      -> (EqRel -> TyCon -> [TcType] -> Bool) -- check tyconapp
                          -- should return True only for type family applications
                      -> TcType -> Bool
  -- always ignores casts & coercions
-- See Note [Rewritable] in GHC.Tc.Solver.Monad for a specification for this function.
anyRewritableTyFamApp :: EqRel -> (EqRel -> TyCon -> [Type] -> Bool) -> Type -> Bool
anyRewritableTyFamApp EqRel
role EqRel -> TyCon -> [Type] -> Bool
check_tyconapp
  = Bool
-> EqRel
-> (EqRel -> Var -> Bool)
-> (EqRel -> TyCon -> [Type] -> Bool)
-> (TyCon -> Bool)
-> Type
-> Bool
any_rewritable Bool
True EqRel
role (\ EqRel
_ Var
_ -> Bool
False) EqRel -> TyCon -> [Type] -> Bool
check_tyconapp (Bool -> Bool
not forall b c a. (b -> c) -> (a -> b) -> a -> c
. TyCon -> Bool
isFamFreeTyCon)

-- This version is used by shouldSplitWD. It *does* look in casts
-- and coercions, and it always expands type synonyms whose RHSs mention
-- type families.
-- See Note [Rewritable] in GHC.Tc.Solver.Monad for a specification for this function.
anyRewritableCanEqLHS :: EqRel   -- Ambient role
                      -> (EqRel -> TcTyVar -> Bool)            -- check tyvar
                      -> (EqRel -> TyCon -> [TcType] -> Bool)  -- check type family
                      -> TcType -> Bool
anyRewritableCanEqLHS :: EqRel
-> (EqRel -> Var -> Bool)
-> (EqRel -> TyCon -> [Type] -> Bool)
-> Type
-> Bool
anyRewritableCanEqLHS EqRel
role EqRel -> Var -> Bool
check_tyvar EqRel -> TyCon -> [Type] -> Bool
check_tyconapp
  = Bool
-> EqRel
-> (EqRel -> Var -> Bool)
-> (EqRel -> TyCon -> [Type] -> Bool)
-> (TyCon -> Bool)
-> Type
-> Bool
any_rewritable Bool
False EqRel
role EqRel -> Var -> Bool
check_tyvar EqRel -> TyCon -> [Type] -> Bool
check_tyconapp (Bool -> Bool
not forall b c a. (b -> c) -> (a -> b) -> a -> c
. TyCon -> Bool
isFamFreeTyCon)

{- Note [anyRewritableTyVar must be role-aware]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
anyRewritableTyVar is used during kick-out from the inert set,
to decide if, given a new equality (a ~ ty), we should kick out
a constraint C.  Rather than gather free variables and see if 'a'
is among them, we instead pass in a predicate; this is just efficiency.

Moreover, consider
  work item:   [G] a ~R f b
  inert item:  [G] b ~R f a
We use anyRewritableTyVar to decide whether to kick out the inert item,
on the grounds that the work item might rewrite it. Well, 'a' is certainly
free in [G] b ~R f a.  But because the role of a type variable ('f' in
this case) is nominal, the work item can't actually rewrite the inert item.
Moreover, if we were to kick out the inert item the exact same situation
would re-occur and we end up with an infinite loop in which each kicks
out the other (#14363).

-}

{- *********************************************************************
*                                                                      *
          The "exact" free variables of a type
*                                                                      *
********************************************************************* -}

{- Note [Silly type synonym]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
  type T a = Int
What are the free tyvars of (T x)?  Empty, of course!

exactTyCoVarsOfType is used by the type checker to figure out exactly
which type variables are mentioned in a type.  It only matters
occasionally -- see the calls to exactTyCoVarsOfType.

We place this function here in GHC.Tc.Utils.TcType, not in GHC.Core.TyCo.FVs,
because we want to "see" tcView (efficiency issue only).
-}

exactTyCoVarsOfType  :: Type   -> TyCoVarSet
exactTyCoVarsOfTypes :: [Type] -> TyCoVarSet
-- Find the free type variables (of any kind)
-- but *expand* type synonyms.  See Note [Silly type synonym] above.

exactTyCoVarsOfType :: Type -> VarSet
exactTyCoVarsOfType  Type
ty  = Endo VarSet -> VarSet
runTyCoVars (Type -> Endo VarSet
exact_ty Type
ty)
exactTyCoVarsOfTypes :: [Type] -> VarSet
exactTyCoVarsOfTypes [Type]
tys = Endo VarSet -> VarSet
runTyCoVars ([Type] -> Endo VarSet
exact_tys [Type]
tys)

exact_ty  :: Type       -> Endo TyCoVarSet
exact_tys :: [Type]     -> Endo TyCoVarSet
(Type -> Endo VarSet
exact_ty, [Type] -> Endo VarSet
exact_tys, KindCoercion -> Endo VarSet
_, [KindCoercion] -> Endo VarSet
_) = forall a env.
Monoid a =>
TyCoFolder env a
-> env
-> (Type -> a, [Type] -> a, KindCoercion -> a, [KindCoercion] -> a)
foldTyCo TyCoFolder VarSet (Endo VarSet)
exactTcvFolder VarSet
emptyVarSet

exactTcvFolder :: TyCoFolder TyCoVarSet (Endo TyCoVarSet)
exactTcvFolder :: TyCoFolder VarSet (Endo VarSet)
exactTcvFolder = TyCoFolder VarSet (Endo VarSet)
deepTcvFolder { tcf_view :: Type -> Maybe Type
tcf_view = Type -> Maybe Type
tcView }
                 -- This is the key line

{-
************************************************************************
*                                                                      *
                Predicates
*                                                                      *
************************************************************************
-}

tcIsTcTyVar :: TcTyVar -> Bool
-- See Note [TcTyVars and TyVars in the typechecker]
tcIsTcTyVar :: Var -> Bool
tcIsTcTyVar Var
tv = Var -> Bool
isTyVar Var
tv

isPromotableMetaTyVar :: TcTyVar -> Bool
-- True is this is a meta-tyvar that can be
-- promoted to an outer level
isPromotableMetaTyVar :: Var -> Bool
isPromotableMetaTyVar Var
tv
  | Var -> Bool
isTyVar Var
tv -- See Note [Coercion variables in free variable lists]
  , MetaTv { mtv_info :: TcTyVarDetails -> MetaInfo
mtv_info = MetaInfo
info } <- Var -> TcTyVarDetails
tcTyVarDetails Var
tv
  = MetaInfo -> Bool
isTouchableInfo MetaInfo
info   -- Can't promote cycle breakers
  | Bool
otherwise
  = Bool
False

isTouchableMetaTyVar :: TcLevel -> TcTyVar -> Bool
isTouchableMetaTyVar :: TcLevel -> Var -> Bool
isTouchableMetaTyVar TcLevel
ctxt_tclvl Var
tv
  | Var -> Bool
isTyVar Var
tv -- See Note [Coercion variables in free variable lists]
  , MetaTv { mtv_tclvl :: TcTyVarDetails -> TcLevel
mtv_tclvl = TcLevel
tv_tclvl, mtv_info :: TcTyVarDetails -> MetaInfo
mtv_info = MetaInfo
info } <- Var -> TcTyVarDetails
tcTyVarDetails Var
tv
  , MetaInfo -> Bool
isTouchableInfo MetaInfo
info
  = ASSERT2( checkTcLevelInvariant ctxt_tclvl tv_tclvl,
             ppr tv $$ ppr tv_tclvl $$ ppr ctxt_tclvl )
    TcLevel
tv_tclvl TcLevel -> TcLevel -> Bool
`sameDepthAs` TcLevel
ctxt_tclvl

  | Bool
otherwise = Bool
False

isImmutableTyVar :: TyVar -> Bool
isImmutableTyVar :: Var -> Bool
isImmutableTyVar Var
tv = Var -> Bool
isSkolemTyVar Var
tv

isTyConableTyVar, isSkolemTyVar, isOverlappableTyVar,
  isMetaTyVar, isAmbiguousTyVar, isCycleBreakerTyVar :: TcTyVar -> Bool

isTyConableTyVar :: Var -> Bool
isTyConableTyVar Var
tv
        -- True of a meta-type variable that can be filled in
        -- with a type constructor application; in particular,
        -- not a TyVarTv
  | Var -> Bool
isTyVar Var
tv -- See Note [Coercion variables in free variable lists]
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
        MetaTv { mtv_info :: TcTyVarDetails -> MetaInfo
mtv_info = MetaInfo
TyVarTv } -> Bool
False
        TcTyVarDetails
_                             -> Bool
True
  | Bool
otherwise = Bool
True

isSkolemTyVar :: Var -> Bool
isSkolemTyVar Var
tv
  = ASSERT2( tcIsTcTyVar tv, ppr tv )
    case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
        MetaTv {} -> Bool
False
        TcTyVarDetails
_other    -> Bool
True

isOverlappableTyVar :: Var -> Bool
isOverlappableTyVar Var
tv
  | Var -> Bool
isTyVar Var
tv -- See Note [Coercion variables in free variable lists]
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
        SkolemTv TcLevel
_ Bool
overlappable -> Bool
overlappable
        TcTyVarDetails
_                       -> Bool
False
  | Bool
otherwise = Bool
False

isMetaTyVar :: Var -> Bool
isMetaTyVar Var
tv
  | Var -> Bool
isTyVar Var
tv -- See Note [Coercion variables in free variable lists]
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
        MetaTv {} -> Bool
True
        TcTyVarDetails
_         -> Bool
False
  | Bool
otherwise = Bool
False

-- isAmbiguousTyVar is used only when reporting type errors
-- It picks out variables that are unbound, namely meta
-- type variables and the RuntimUnk variables created by
-- GHC.Runtime.Heap.Inspect.zonkRTTIType.  These are "ambiguous" in
-- the sense that they stand for an as-yet-unknown type
isAmbiguousTyVar :: Var -> Bool
isAmbiguousTyVar Var
tv
  | Var -> Bool
isTyVar Var
tv -- See Note [Coercion variables in free variable lists]
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
        MetaTv {}     -> Bool
True
        RuntimeUnk {} -> Bool
True
        TcTyVarDetails
_             -> Bool
False
  | Bool
otherwise = Bool
False

isCycleBreakerTyVar :: Var -> Bool
isCycleBreakerTyVar Var
tv
  | Var -> Bool
isTyVar Var
tv -- See Note [Coercion variables in free variable lists]
  , MetaTv { mtv_info :: TcTyVarDetails -> MetaInfo
mtv_info = MetaInfo
CycleBreakerTv } <- Var -> TcTyVarDetails
tcTyVarDetails Var
tv
  = Bool
True

  | Bool
otherwise
  = Bool
False

isMetaTyVarTy :: TcType -> Bool
isMetaTyVarTy :: Type -> Bool
isMetaTyVarTy (TyVarTy Var
tv) = Var -> Bool
isMetaTyVar Var
tv
isMetaTyVarTy Type
_            = Bool
False

metaTyVarInfo :: TcTyVar -> MetaInfo
metaTyVarInfo :: Var -> MetaInfo
metaTyVarInfo Var
tv
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
      MetaTv { mtv_info :: TcTyVarDetails -> MetaInfo
mtv_info = MetaInfo
info } -> MetaInfo
info
      TcTyVarDetails
_ -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"metaTyVarInfo" (forall a. Outputable a => a -> SDoc
ppr Var
tv)

isTouchableInfo :: MetaInfo -> Bool
isTouchableInfo :: MetaInfo -> Bool
isTouchableInfo MetaInfo
info
  | MetaInfo
CycleBreakerTv <- MetaInfo
info = Bool
False
  | Bool
otherwise              = Bool
True

metaTyVarTcLevel :: TcTyVar -> TcLevel
metaTyVarTcLevel :: Var -> TcLevel
metaTyVarTcLevel Var
tv
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
      MetaTv { mtv_tclvl :: TcTyVarDetails -> TcLevel
mtv_tclvl = TcLevel
tclvl } -> TcLevel
tclvl
      TcTyVarDetails
_ -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"metaTyVarTcLevel" (forall a. Outputable a => a -> SDoc
ppr Var
tv)

metaTyVarTcLevel_maybe :: TcTyVar -> Maybe TcLevel
metaTyVarTcLevel_maybe :: Var -> Maybe TcLevel
metaTyVarTcLevel_maybe Var
tv
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
      MetaTv { mtv_tclvl :: TcTyVarDetails -> TcLevel
mtv_tclvl = TcLevel
tclvl } -> forall a. a -> Maybe a
Just TcLevel
tclvl
      TcTyVarDetails
_                            -> forall a. Maybe a
Nothing

metaTyVarRef :: TyVar -> IORef MetaDetails
metaTyVarRef :: Var -> IORef MetaDetails
metaTyVarRef Var
tv
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
        MetaTv { mtv_ref :: TcTyVarDetails -> IORef MetaDetails
mtv_ref = IORef MetaDetails
ref } -> IORef MetaDetails
ref
        TcTyVarDetails
_ -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"metaTyVarRef" (forall a. Outputable a => a -> SDoc
ppr Var
tv)

setMetaTyVarTcLevel :: TcTyVar -> TcLevel -> TcTyVar
setMetaTyVarTcLevel :: Var -> TcLevel -> Var
setMetaTyVarTcLevel Var
tv TcLevel
tclvl
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
      details :: TcTyVarDetails
details@(MetaTv {}) -> Var -> TcTyVarDetails -> Var
setTcTyVarDetails Var
tv (TcTyVarDetails
details { mtv_tclvl :: TcLevel
mtv_tclvl = TcLevel
tclvl })
      TcTyVarDetails
_ -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"metaTyVarTcLevel" (forall a. Outputable a => a -> SDoc
ppr Var
tv)

isTyVarTyVar :: Var -> Bool
isTyVarTyVar :: Var -> Bool
isTyVarTyVar Var
tv
  = case Var -> TcTyVarDetails
tcTyVarDetails Var
tv of
        MetaTv { mtv_info :: TcTyVarDetails -> MetaInfo
mtv_info = MetaInfo
TyVarTv } -> Bool
True
        TcTyVarDetails
_                             -> Bool
False

isFlexi, isIndirect :: MetaDetails -> Bool
isFlexi :: MetaDetails -> Bool
isFlexi MetaDetails
Flexi = Bool
True
isFlexi MetaDetails
_     = Bool
False

isIndirect :: MetaDetails -> Bool
isIndirect (Indirect Type
_) = Bool
True
isIndirect MetaDetails
_            = Bool
False

isRuntimeUnkSkol :: TyVar -> Bool
-- Called only in GHC.Tc.Errors; see Note [Runtime skolems] there
isRuntimeUnkSkol :: Var -> Bool
isRuntimeUnkSkol Var
x
  | TcTyVarDetails
RuntimeUnk <- Var -> TcTyVarDetails
tcTyVarDetails Var
x = Bool
True
  | Bool
otherwise                      = Bool
False

mkTyVarNamePairs :: [TyVar] -> [(Name,TyVar)]
-- Just pair each TyVar with its own name
mkTyVarNamePairs :: [Var] -> [(Name, Var)]
mkTyVarNamePairs [Var]
tvs = [(Var -> Name
tyVarName Var
tv, Var
tv) | Var
tv <- [Var]
tvs]

findDupTyVarTvs :: [(Name,TcTyVar)] -> [(Name,Name)]
-- If we have [...(x1,tv)...(x2,tv)...]
-- return (x1,x2) in the result list
findDupTyVarTvs :: [(Name, Var)] -> [(Name, Name)]
findDupTyVarTvs [(Name, Var)]
prs
  = forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap forall {b} {b}. NonEmpty (b, b) -> [(b, b)]
mk_result_prs forall a b. (a -> b) -> a -> b
$
    forall a. (a -> a -> Bool) -> [a] -> [NonEmpty a]
findDupsEq forall {a} {a} {a}. Eq a => (a, a) -> (a, a) -> Bool
eq_snd [(Name, Var)]
prs
  where
    eq_snd :: (a, a) -> (a, a) -> Bool
eq_snd (a
_,a
tv1) (a
_,a
tv2) = a
tv1 forall a. Eq a => a -> a -> Bool
== a
tv2
    mk_result_prs :: NonEmpty (b, b) -> [(b, b)]
mk_result_prs ((b
n1,b
_) :| [(b, b)]
xs) = forall a b. (a -> b) -> [a] -> [b]
map (\(b
n2,b
_) -> (b
n1,b
n2)) [(b, b)]
xs

{-
************************************************************************
*                                                                      *
   Tau, sigma and rho
*                                                                      *
************************************************************************
-}

mkSigmaTy :: [TyCoVarBinder] -> [PredType] -> Type -> Type
mkSigmaTy :: [TyCoVarBinder] -> [Type] -> Type -> Type
mkSigmaTy [TyCoVarBinder]
bndrs [Type]
theta Type
tau = [TyCoVarBinder] -> Type -> Type
mkForAllTys [TyCoVarBinder]
bndrs ([Type] -> Type -> Type
mkPhiTy [Type]
theta Type
tau)

-- | Make a sigma ty where all type variables are 'Inferred'. That is,
-- they cannot be used with visible type application.
mkInfSigmaTy :: [TyCoVar] -> [PredType] -> Type -> Type
mkInfSigmaTy :: [Var] -> [Type] -> Type -> Type
mkInfSigmaTy [Var]
tyvars [Type]
theta Type
ty = [TyCoVarBinder] -> [Type] -> Type -> Type
mkSigmaTy (forall vis. vis -> [Var] -> [VarBndr Var vis]
mkTyCoVarBinders ArgFlag
Inferred [Var]
tyvars) [Type]
theta Type
ty

-- | Make a sigma ty where all type variables are "specified". That is,
-- they can be used with visible type application
mkSpecSigmaTy :: [TyVar] -> [PredType] -> Type -> Type
mkSpecSigmaTy :: [Var] -> [Type] -> Type -> Type
mkSpecSigmaTy [Var]
tyvars [Type]
preds Type
ty = [TyCoVarBinder] -> [Type] -> Type -> Type
mkSigmaTy (forall vis. vis -> [Var] -> [VarBndr Var vis]
mkTyCoVarBinders ArgFlag
Specified [Var]
tyvars) [Type]
preds Type
ty

mkPhiTy :: [PredType] -> Type -> Type
mkPhiTy :: [Type] -> Type -> Type
mkPhiTy = [Type] -> Type -> Type
mkInvisFunTysMany

---------------
getDFunTyKey :: Type -> OccName -- Get some string from a type, to be used to
                                -- construct a dictionary function name
getDFunTyKey :: Type -> OccName
getDFunTyKey Type
ty | Just Type
ty' <- Type -> Maybe Type
coreView Type
ty = Type -> OccName
getDFunTyKey Type
ty'
getDFunTyKey (TyVarTy Var
tv)            = forall a. NamedThing a => a -> OccName
getOccName Var
tv
getDFunTyKey (TyConApp TyCon
tc [Type]
_)         = forall a. NamedThing a => a -> OccName
getOccName TyCon
tc
getDFunTyKey (LitTy TyLit
x)               = TyLit -> OccName
getDFunTyLitKey TyLit
x
getDFunTyKey (AppTy Type
fun Type
_)           = Type -> OccName
getDFunTyKey Type
fun
getDFunTyKey (FunTy {})              = forall a. NamedThing a => a -> OccName
getOccName TyCon
funTyCon
getDFunTyKey (ForAllTy TyCoVarBinder
_ Type
t)          = Type -> OccName
getDFunTyKey Type
t
getDFunTyKey (CastTy Type
ty KindCoercion
_)           = Type -> OccName
getDFunTyKey Type
ty
getDFunTyKey t :: Type
t@(CoercionTy KindCoercion
_)        = forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"getDFunTyKey" (forall a. Outputable a => a -> SDoc
ppr Type
t)

getDFunTyLitKey :: TyLit -> OccName
getDFunTyLitKey :: TyLit -> OccName
getDFunTyLitKey (NumTyLit Integer
n) = NameSpace -> String -> OccName
mkOccName NameSpace
Name.varName (forall a. Show a => a -> String
show Integer
n)
getDFunTyLitKey (StrTyLit FastString
n) = NameSpace -> String -> OccName
mkOccName NameSpace
Name.varName (forall a. Show a => a -> String
show FastString
n)  -- hm
getDFunTyLitKey (CharTyLit Char
n) = NameSpace -> String -> OccName
mkOccName NameSpace
Name.varName (forall a. Show a => a -> String
show Char
n)

{- *********************************************************************
*                                                                      *
           Building types
*                                                                      *
********************************************************************* -}

-- ToDo: I think we need Tc versions of these
-- Reason: mkCastTy checks isReflexiveCastTy, which checks
--         for equality; and that has a different answer
--         depending on whether or not Type = Constraint

mkTcAppTys :: Type -> [Type] -> Type
mkTcAppTys :: Type -> [Type] -> Type
mkTcAppTys = Type -> [Type] -> Type
mkAppTys

mkTcAppTy :: Type -> Type -> Type
mkTcAppTy :: Type -> Type -> Type
mkTcAppTy = Type -> Type -> Type
mkAppTy

mkTcCastTy :: Type -> Coercion -> Type
mkTcCastTy :: Type -> KindCoercion -> Type
mkTcCastTy = Type -> KindCoercion -> Type
mkCastTy   -- Do we need a tc version of mkCastTy?

{-
************************************************************************
*                                                                      *
   Expanding and splitting
*                                                                      *
************************************************************************

These tcSplit functions are like their non-Tc analogues, but
        *) they do not look through newtypes

However, they are non-monadic and do not follow through mutable type
variables.  It's up to you to make sure this doesn't matter.
-}

-- | Splits a forall type into a list of 'TyBinder's and the inner type.
-- Always succeeds, even if it returns an empty list.
tcSplitPiTys :: Type -> ([TyBinder], Type)
tcSplitPiTys :: Type -> ([TyBinder], Type)
tcSplitPiTys Type
ty
  = ASSERT( all isTyBinder (fst sty) ) sty
  where sty :: ([TyBinder], Type)
sty = Type -> ([TyBinder], Type)
splitPiTys Type
ty

-- | Splits a type into a TyBinder and a body, if possible. Panics otherwise
tcSplitPiTy_maybe :: Type -> Maybe (TyBinder, Type)
tcSplitPiTy_maybe :: Type -> Maybe (TyBinder, Type)
tcSplitPiTy_maybe Type
ty
  = ASSERT( isMaybeTyBinder sty ) sty
  where
    sty :: Maybe (TyBinder, Type)
sty = Type -> Maybe (TyBinder, Type)
splitPiTy_maybe Type
ty
    isMaybeTyBinder :: Maybe (TyBinder, b) -> Bool
isMaybeTyBinder (Just (TyBinder
t,b
_)) = TyBinder -> Bool
isTyBinder TyBinder
t
    isMaybeTyBinder Maybe (TyBinder, b)
_            = Bool
True

tcSplitForAllTyVarBinder_maybe :: Type -> Maybe (TyVarBinder, Type)
tcSplitForAllTyVarBinder_maybe :: Type -> Maybe (TyCoVarBinder, Type)
tcSplitForAllTyVarBinder_maybe Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Maybe (TyCoVarBinder, Type)
tcSplitForAllTyVarBinder_maybe Type
ty'
tcSplitForAllTyVarBinder_maybe (ForAllTy TyCoVarBinder
tv Type
ty) = ASSERT( isTyVarBinder tv ) Just (tv, ty)
tcSplitForAllTyVarBinder_maybe Type
_                = forall a. Maybe a
Nothing

-- | Like 'tcSplitPiTys', but splits off only named binders,
-- returning just the tyvars.
tcSplitForAllTyVars :: Type -> ([TyVar], Type)
tcSplitForAllTyVars :: Type -> ([Var], Type)
tcSplitForAllTyVars Type
ty
  = ASSERT( all isTyVar (fst sty) ) sty
  where sty :: ([Var], Type)
sty = Type -> ([Var], Type)
splitForAllTyCoVars Type
ty

-- | Like 'tcSplitForAllTyVars', but only splits 'ForAllTy's with 'Invisible'
-- type variable binders.
tcSplitForAllInvisTyVars :: Type -> ([TyVar], Type)
tcSplitForAllInvisTyVars :: Type -> ([Var], Type)
tcSplitForAllInvisTyVars Type
ty = (ArgFlag -> Bool) -> Type -> ([Var], Type)
tcSplitSomeForAllTyVars ArgFlag -> Bool
isInvisibleArgFlag Type
ty

-- | Like 'tcSplitForAllTyVars', but only splits a 'ForAllTy' if @argf_pred argf@
-- is 'True', where @argf@ is the visibility of the @ForAllTy@'s binder and
-- @argf_pred@ is a predicate over visibilities provided as an argument to this
-- function.
tcSplitSomeForAllTyVars :: (ArgFlag -> Bool) -> Type -> ([TyVar], Type)
tcSplitSomeForAllTyVars :: (ArgFlag -> Bool) -> Type -> ([Var], Type)
tcSplitSomeForAllTyVars ArgFlag -> Bool
argf_pred Type
ty
  = Type -> Type -> [Var] -> ([Var], Type)
split Type
ty Type
ty []
  where
    split :: Type -> Type -> [Var] -> ([Var], Type)
split Type
_ (ForAllTy (Bndr Var
tv ArgFlag
argf) Type
ty) [Var]
tvs
      | ArgFlag -> Bool
argf_pred ArgFlag
argf                             = Type -> Type -> [Var] -> ([Var], Type)
split Type
ty Type
ty (Var
tvforall a. a -> [a] -> [a]
:[Var]
tvs)
    split Type
orig_ty Type
ty [Var]
tvs | Just Type
ty' <- Type -> Maybe Type
coreView Type
ty = Type -> Type -> [Var] -> ([Var], Type)
split Type
orig_ty Type
ty' [Var]
tvs
    split Type
orig_ty Type
_                            [Var]
tvs = (forall a. [a] -> [a]
reverse [Var]
tvs, Type
orig_ty)

-- | Like 'tcSplitForAllTyVars', but only splits 'ForAllTy's with 'Required' type
-- variable binders. All split tyvars are annotated with '()'.
tcSplitForAllReqTVBinders :: Type -> ([TcReqTVBinder], Type)
tcSplitForAllReqTVBinders :: Type -> ([TcReqTVBinder], Type)
tcSplitForAllReqTVBinders Type
ty = ASSERT( all (isTyVar . binderVar) (fst sty) ) sty
  where sty :: ([TcReqTVBinder], Type)
sty = Type -> ([TcReqTVBinder], Type)
splitForAllReqTVBinders Type
ty

-- | Like 'tcSplitForAllTyVars', but only splits 'ForAllTy's with 'Invisible' type
-- variable binders. All split tyvars are annotated with their 'Specificity'.
tcSplitForAllInvisTVBinders :: Type -> ([TcInvisTVBinder], Type)
tcSplitForAllInvisTVBinders :: Type -> ([TcInvisTVBinder], Type)
tcSplitForAllInvisTVBinders Type
ty = ASSERT( all (isTyVar . binderVar) (fst sty) ) sty
  where sty :: ([TcInvisTVBinder], Type)
sty = Type -> ([TcInvisTVBinder], Type)
splitForAllInvisTVBinders Type
ty

-- | Like 'tcSplitForAllTyVars', but splits off only named binders.
tcSplitForAllTyVarBinders :: Type -> ([TyVarBinder], Type)
tcSplitForAllTyVarBinders :: Type -> ([TyCoVarBinder], Type)
tcSplitForAllTyVarBinders Type
ty = ASSERT( all isTyVarBinder (fst sty)) sty
  where sty :: ([TyCoVarBinder], Type)
sty = Type -> ([TyCoVarBinder], Type)
splitForAllTyCoVarBinders Type
ty

-- | Is this a ForAllTy with a named binder?
tcIsForAllTy :: Type -> Bool
tcIsForAllTy :: Type -> Bool
tcIsForAllTy Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Bool
tcIsForAllTy Type
ty'
tcIsForAllTy (ForAllTy {}) = Bool
True
tcIsForAllTy Type
_             = Bool
False

tcSplitPredFunTy_maybe :: Type -> Maybe (PredType, Type)
-- Split off the first predicate argument from a type
tcSplitPredFunTy_maybe :: Type -> Maybe (Type, Type)
tcSplitPredFunTy_maybe Type
ty
  | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Maybe (Type, Type)
tcSplitPredFunTy_maybe Type
ty'
tcSplitPredFunTy_maybe (FunTy { ft_af :: Type -> AnonArgFlag
ft_af = AnonArgFlag
InvisArg
                              , ft_arg :: Type -> Type
ft_arg = Type
arg, ft_res :: Type -> Type
ft_res = Type
res })
  = forall a. a -> Maybe a
Just (Type
arg, Type
res)
tcSplitPredFunTy_maybe Type
_
  = forall a. Maybe a
Nothing

tcSplitPhiTy :: Type -> (ThetaType, Type)
tcSplitPhiTy :: Type -> ([Type], Type)
tcSplitPhiTy Type
ty
  = Type -> [Type] -> ([Type], Type)
split Type
ty []
  where
    split :: Type -> [Type] -> ([Type], Type)
split Type
ty [Type]
ts
      = case Type -> Maybe (Type, Type)
tcSplitPredFunTy_maybe Type
ty of
          Just (Type
pred, Type
ty) -> Type -> [Type] -> ([Type], Type)
split Type
ty (Type
predforall a. a -> [a] -> [a]
:[Type]
ts)
          Maybe (Type, Type)
Nothing         -> (forall a. [a] -> [a]
reverse [Type]
ts, Type
ty)

-- | Split a sigma type into its parts. This only splits /invisible/ type
-- variable binders, as these are the only forms of binder that the typechecker
-- will implicitly instantiate.
tcSplitSigmaTy :: Type -> ([TyVar], ThetaType, Type)
tcSplitSigmaTy :: Type -> ([Var], [Type], Type)
tcSplitSigmaTy Type
ty = case Type -> ([Var], Type)
tcSplitForAllInvisTyVars Type
ty of
                        ([Var]
tvs, Type
rho) -> case Type -> ([Type], Type)
tcSplitPhiTy Type
rho of
                                        ([Type]
theta, Type
tau) -> ([Var]
tvs, [Type]
theta, Type
tau)

-- | Split a sigma type into its parts, going underneath as many arrows
-- and foralls as possible. See Note [tcSplitNestedSigmaTys]
tcSplitNestedSigmaTys :: Type -> ([TyVar], ThetaType, Type)
-- See Note [tcSplitNestedSigmaTys]
-- NB: This is basically a pure version of deeplyInstantiate (from Unify) that
--     doesn't compute an HsWrapper.
tcSplitNestedSigmaTys :: Type -> ([Var], [Type], Type)
tcSplitNestedSigmaTys Type
ty
    -- If there's a forall, split it apart and try splitting the rho type
    -- underneath it.
  | ([Scaled Type]
arg_tys, Type
body_ty)   <- Type -> ([Scaled Type], Type)
tcSplitFunTys Type
ty
  , ([Var]
tvs1, [Type]
theta1, Type
rho1) <- Type -> ([Var], [Type], Type)
tcSplitSigmaTy Type
body_ty
  , Bool -> Bool
not (forall (t :: * -> *) a. Foldable t => t a -> Bool
null [Var]
tvs1 Bool -> Bool -> Bool
&& forall (t :: * -> *) a. Foldable t => t a -> Bool
null [Type]
theta1)
  = let ([Var]
tvs2, [Type]
theta2, Type
rho2) = Type -> ([Var], [Type], Type)
tcSplitNestedSigmaTys Type
rho1
    in ([Var]
tvs1 forall a. [a] -> [a] -> [a]
++ [Var]
tvs2, [Type]
theta1 forall a. [a] -> [a] -> [a]
++ [Type]
theta2, [Scaled Type] -> Type -> Type
mkVisFunTys [Scaled Type]
arg_tys Type
rho2)

    -- If there's no forall, we're done.
  | Bool
otherwise = ([], [], Type
ty)

{- Note [tcSplitNestedSigmaTys]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tcSplitNestedSigmaTys splits out all the /nested/ foralls and constraints,
including under function arrows.  E.g. given this type synonym:
  type Traversal s t a b = forall f. Applicative f => (a -> f b) -> s -> f t

then
  tcSplitNestedSigmaTys (forall s t a b. C s t a b => Int -> Traversal s t a b)

will return
  ( [s,t,a,b,f]
  , [C s t a b, Applicative f]
  , Int -> (a -> f b) -> s -> f t)@.

This function is used in these places:
* Improving error messages in GHC.Tc.Gen.Head.addFunResCtxt
* Validity checking for default methods: GHC.Tc.TyCl.checkValidClass
* A couple of calls in the GHCi debugger: GHC.Runtime.Heap.Inspect

In other words, just in validity checking and error messages; hence
no wrappers or evidence generation.

Notice that tcSplitNestedSigmaTys even looks under function arrows;
doing so is the Right Thing even with simple subsumption, not just
with deep subsumption.
-}

-----------------------
tcTyConAppTyCon :: Type -> TyCon
tcTyConAppTyCon :: Type -> TyCon
tcTyConAppTyCon Type
ty
  = case Type -> Maybe TyCon
tcTyConAppTyCon_maybe Type
ty of
      Just TyCon
tc -> TyCon
tc
      Maybe TyCon
Nothing -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"tcTyConAppTyCon" (Type -> SDoc
pprType Type
ty)

-- | Like 'tcRepSplitTyConApp_maybe', but only returns the 'TyCon'.
tcTyConAppTyCon_maybe :: Type -> Maybe TyCon
tcTyConAppTyCon_maybe :: Type -> Maybe TyCon
tcTyConAppTyCon_maybe Type
ty
  | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Maybe TyCon
tcTyConAppTyCon_maybe Type
ty'
tcTyConAppTyCon_maybe (TyConApp TyCon
tc [Type]
_)
  = forall a. a -> Maybe a
Just TyCon
tc
tcTyConAppTyCon_maybe (FunTy { ft_af :: Type -> AnonArgFlag
ft_af = AnonArgFlag
VisArg })
  = forall a. a -> Maybe a
Just TyCon
funTyCon  -- (=>) is /not/ a TyCon in its own right
                   -- C.f. tcRepSplitAppTy_maybe
tcTyConAppTyCon_maybe Type
_
  = forall a. Maybe a
Nothing

tcTyConAppArgs :: Type -> [Type]
tcTyConAppArgs :: Type -> [Type]
tcTyConAppArgs Type
ty = case HasCallStack => Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty of
                        Just (TyCon
_, [Type]
args) -> [Type]
args
                        Maybe (TyCon, [Type])
Nothing        -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"tcTyConAppArgs" (Type -> SDoc
pprType Type
ty)

tcSplitTyConApp :: Type -> (TyCon, [Type])
tcSplitTyConApp :: Type -> (TyCon, [Type])
tcSplitTyConApp Type
ty = case HasCallStack => Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty of
                        Just (TyCon, [Type])
stuff -> (TyCon, [Type])
stuff
                        Maybe (TyCon, [Type])
Nothing    -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"tcSplitTyConApp" (Type -> SDoc
pprType Type
ty)

-----------------------
tcSplitFunTys :: Type -> ([Scaled Type], Type)
tcSplitFunTys :: Type -> ([Scaled Type], Type)
tcSplitFunTys Type
ty = case Type -> Maybe (Scaled Type, Type)
tcSplitFunTy_maybe Type
ty of
                        Maybe (Scaled Type, Type)
Nothing        -> ([], Type
ty)
                        Just (Scaled Type
arg,Type
res) -> (Scaled Type
argforall a. a -> [a] -> [a]
:[Scaled Type]
args, Type
res')
                                       where
                                          ([Scaled Type]
args,Type
res') = Type -> ([Scaled Type], Type)
tcSplitFunTys Type
res

tcSplitFunTy_maybe :: Type -> Maybe (Scaled Type, Type)
tcSplitFunTy_maybe :: Type -> Maybe (Scaled Type, Type)
tcSplitFunTy_maybe Type
ty
  | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Maybe (Scaled Type, Type)
tcSplitFunTy_maybe Type
ty'
tcSplitFunTy_maybe (FunTy { ft_af :: Type -> AnonArgFlag
ft_af = AnonArgFlag
af, ft_mult :: Type -> Type
ft_mult = Type
w, ft_arg :: Type -> Type
ft_arg = Type
arg, ft_res :: Type -> Type
ft_res = Type
res })
  | AnonArgFlag
VisArg <- AnonArgFlag
af = forall a. a -> Maybe a
Just (forall a. Type -> a -> Scaled a
Scaled Type
w Type
arg, Type
res)
tcSplitFunTy_maybe Type
_ = forall a. Maybe a
Nothing
        -- Note the VisArg guard
        -- Consider     (?x::Int) => Bool
        -- We don't want to treat this as a function type!
        -- A concrete example is test tc230:
        --      f :: () -> (?p :: ()) => () -> ()
        --
        --      g = f () ()

tcSplitFunTysN :: Arity                      -- n: Number of desired args
               -> TcRhoType
               -> Either Arity               -- Number of missing arrows
                        ([Scaled TcSigmaType],-- Arg types (always N types)
                         TcSigmaType)        -- The rest of the type
-- ^ Split off exactly the specified number argument types
-- Returns
--  (Left m) if there are 'm' missing arrows in the type
--  (Right (tys,res)) if the type looks like t1 -> ... -> tn -> res
tcSplitFunTysN :: Arity -> Type -> Either Arity ([Scaled Type], Type)
tcSplitFunTysN Arity
n Type
ty
 | Arity
n forall a. Eq a => a -> a -> Bool
== Arity
0
 = forall a b. b -> Either a b
Right ([], Type
ty)
 | Just (Scaled Type
arg,Type
res) <- Type -> Maybe (Scaled Type, Type)
tcSplitFunTy_maybe Type
ty
 = case Arity -> Type -> Either Arity ([Scaled Type], Type)
tcSplitFunTysN (Arity
nforall a. Num a => a -> a -> a
-Arity
1) Type
res of
     Left Arity
m            -> forall a b. a -> Either a b
Left Arity
m
     Right ([Scaled Type]
args,Type
body) -> forall a b. b -> Either a b
Right (Scaled Type
argforall a. a -> [a] -> [a]
:[Scaled Type]
args, Type
body)
 | Bool
otherwise
 = forall a b. a -> Either a b
Left Arity
n

tcSplitFunTy :: Type -> (Scaled Type, Type)
tcSplitFunTy :: Type -> (Scaled Type, Type)
tcSplitFunTy  Type
ty = forall a. HasCallStack => String -> Maybe a -> a
expectJust String
"tcSplitFunTy" (Type -> Maybe (Scaled Type, Type)
tcSplitFunTy_maybe Type
ty)

tcFunArgTy :: Type -> Scaled Type
tcFunArgTy :: Type -> Scaled Type
tcFunArgTy    Type
ty = forall a b. (a, b) -> a
fst (Type -> (Scaled Type, Type)
tcSplitFunTy Type
ty)

tcFunResultTy :: Type -> Type
tcFunResultTy :: Type -> Type
tcFunResultTy Type
ty = forall a b. (a, b) -> b
snd (Type -> (Scaled Type, Type)
tcSplitFunTy Type
ty)

-- | Strips off n *visible* arguments and returns the resulting type
tcFunResultTyN :: HasDebugCallStack => Arity -> Type -> Type
tcFunResultTyN :: HasDebugCallStack => Arity -> Type -> Type
tcFunResultTyN Arity
n Type
ty
  | Right ([Scaled Type]
_, Type
res_ty) <- Arity -> Type -> Either Arity ([Scaled Type], Type)
tcSplitFunTysN Arity
n Type
ty
  = Type
res_ty
  | Bool
otherwise
  = forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"tcFunResultTyN" (forall a. Outputable a => a -> SDoc
ppr Arity
n SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr Type
ty)

-----------------------
tcSplitAppTy_maybe :: Type -> Maybe (Type, Type)
tcSplitAppTy_maybe :: Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty'
tcSplitAppTy_maybe Type
ty = Type -> Maybe (Type, Type)
tcRepSplitAppTy_maybe Type
ty

tcSplitAppTy :: Type -> (Type, Type)
tcSplitAppTy :: Type -> (Type, Type)
tcSplitAppTy Type
ty = case Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty of
                    Just (Type, Type)
stuff -> (Type, Type)
stuff
                    Maybe (Type, Type)
Nothing    -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"tcSplitAppTy" (Type -> SDoc
pprType Type
ty)

tcSplitAppTys :: Type -> (Type, [Type])
tcSplitAppTys :: Type -> (Type, [Type])
tcSplitAppTys Type
ty
  = Type -> [Type] -> (Type, [Type])
go Type
ty []
  where
    go :: Type -> [Type] -> (Type, [Type])
go Type
ty [Type]
args = case Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty of
                   Just (Type
ty', Type
arg) -> Type -> [Type] -> (Type, [Type])
go Type
ty' (Type
argforall a. a -> [a] -> [a]
:[Type]
args)
                   Maybe (Type, Type)
Nothing         -> (Type
ty,[Type]
args)

-- | Returns the number of arguments in the given type, without
-- looking through synonyms. This is used only for error reporting.
-- We don't look through synonyms because of #11313.
tcRepGetNumAppTys :: Type -> Arity
tcRepGetNumAppTys :: Type -> Arity
tcRepGetNumAppTys = forall (t :: * -> *) a. Foldable t => t a -> Arity
length forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a b. (a, b) -> b
snd forall b c a. (b -> c) -> (a -> b) -> a -> c
. HasDebugCallStack => Type -> (Type, [Type])
repSplitAppTys

-----------------------
-- | If the type is a tyvar, possibly under a cast, returns it, along
-- with the coercion. Thus, the co is :: kind tv ~N kind type
tcGetCastedTyVar_maybe :: Type -> Maybe (TyVar, CoercionN)
tcGetCastedTyVar_maybe :: Type -> Maybe (Var, KindCoercion)
tcGetCastedTyVar_maybe Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Maybe (Var, KindCoercion)
tcGetCastedTyVar_maybe Type
ty'
tcGetCastedTyVar_maybe (CastTy (TyVarTy Var
tv) KindCoercion
co) = forall a. a -> Maybe a
Just (Var
tv, KindCoercion
co)
tcGetCastedTyVar_maybe (TyVarTy Var
tv)             = forall a. a -> Maybe a
Just (Var
tv, Type -> KindCoercion
mkNomReflCo (Var -> Type
tyVarKind Var
tv))
tcGetCastedTyVar_maybe Type
_                        = forall a. Maybe a
Nothing

tcGetTyVar_maybe :: Type -> Maybe TyVar
tcGetTyVar_maybe :: Type -> Maybe Var
tcGetTyVar_maybe Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Maybe Var
tcGetTyVar_maybe Type
ty'
tcGetTyVar_maybe (TyVarTy Var
tv)   = forall a. a -> Maybe a
Just Var
tv
tcGetTyVar_maybe Type
_              = forall a. Maybe a
Nothing

tcGetTyVar :: String -> Type -> TyVar
tcGetTyVar :: String -> Type -> Var
tcGetTyVar String
msg Type
ty
  = case Type -> Maybe Var
tcGetTyVar_maybe Type
ty of
     Just Var
tv -> Var
tv
     Maybe Var
Nothing -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
msg (forall a. Outputable a => a -> SDoc
ppr Type
ty)

tcIsTyVarTy :: Type -> Bool
tcIsTyVarTy :: Type -> Bool
tcIsTyVarTy Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Bool
tcIsTyVarTy Type
ty'
tcIsTyVarTy (CastTy Type
ty KindCoercion
_) = Type -> Bool
tcIsTyVarTy Type
ty  -- look through casts, as
                                            -- this is only used for
                                            -- e.g., FlexibleContexts
tcIsTyVarTy (TyVarTy Var
_)   = Bool
True
tcIsTyVarTy Type
_             = Bool
False

-----------------------
tcSplitDFunTy :: Type -> ([TyVar], [Type], Class, [Type])
-- Split the type of a dictionary function
-- We don't use tcSplitSigmaTy,  because a DFun may (with NDP)
-- have non-Pred arguments, such as
--     df :: forall m. (forall b. Eq b => Eq (m b)) -> C m
--
-- Also NB splitFunTys, not tcSplitFunTys;
-- the latter specifically stops at PredTy arguments,
-- and we don't want to do that here
tcSplitDFunTy :: Type -> ([Var], [Type], Class, [Type])
tcSplitDFunTy Type
ty
  = case Type -> ([Var], Type)
tcSplitForAllInvisTyVars Type
ty of { ([Var]
tvs, Type
rho)    ->
    case Type -> ([Scaled Type], Type)
splitFunTys Type
rho             of { ([Scaled Type]
theta, Type
tau)  ->
    case Type -> (Class, [Type])
tcSplitDFunHead Type
tau         of { (Class
clas, [Type]
tys)   ->
    ([Var]
tvs, forall a b. (a -> b) -> [a] -> [b]
map forall a. Scaled a -> a
scaledThing [Scaled Type]
theta, Class
clas, [Type]
tys) }}}

tcSplitDFunHead :: Type -> (Class, [Type])
tcSplitDFunHead :: Type -> (Class, [Type])
tcSplitDFunHead = HasDebugCallStack => Type -> (Class, [Type])
getClassPredTys

tcSplitMethodTy :: Type -> ([TyVar], PredType, Type)
-- A class method (selector) always has a type like
--   forall as. C as => blah
-- So if the class looks like
--   class C a where
--     op :: forall b. (Eq a, Ix b) => a -> b
-- the class method type looks like
--  op :: forall a. C a => forall b. (Eq a, Ix b) => a -> b
--
-- tcSplitMethodTy just peels off the outer forall and
-- that first predicate
tcSplitMethodTy :: Type -> ([Var], Type, Type)
tcSplitMethodTy Type
ty
  | ([Var]
sel_tyvars,Type
sel_rho) <- Type -> ([Var], Type)
tcSplitForAllInvisTyVars Type
ty
  , Just (Type
first_pred, Type
local_meth_ty) <- Type -> Maybe (Type, Type)
tcSplitPredFunTy_maybe Type
sel_rho
  = ([Var]
sel_tyvars, Type
first_pred, Type
local_meth_ty)
  | Bool
otherwise
  = forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"tcSplitMethodTy" (forall a. Outputable a => a -> SDoc
ppr Type
ty)


{- *********************************************************************
*                                                                      *
            Type equalities
*                                                                      *
********************************************************************* -}

tcEqKind :: HasDebugCallStack => TcKind -> TcKind -> Bool
tcEqKind :: HasDebugCallStack => Type -> Type -> Bool
tcEqKind = HasDebugCallStack => Type -> Type -> Bool
tcEqType

tcEqType :: HasDebugCallStack => TcType -> TcType -> Bool
-- ^ tcEqType implements typechecker equality, as described in
-- @Note [Typechecker equality vs definitional equality]@.
tcEqType :: HasDebugCallStack => Type -> Type -> Bool
tcEqType Type
ty1 Type
ty2
  =  Type -> Type -> Bool
tcEqTypeNoSyns Type
ki1 Type
ki2
  Bool -> Bool -> Bool
&& Type -> Type -> Bool
tcEqTypeNoSyns Type
ty1 Type
ty2
  where
    ki1 :: Type
ki1 = HasDebugCallStack => Type -> Type
tcTypeKind Type
ty1
    ki2 :: Type
ki2 = HasDebugCallStack => Type -> Type
tcTypeKind Type
ty2

-- | Just like 'tcEqType', but will return True for types of different kinds
-- as long as their non-coercion structure is identical.
tcEqTypeNoKindCheck :: TcType -> TcType -> Bool
tcEqTypeNoKindCheck :: Type -> Type -> Bool
tcEqTypeNoKindCheck Type
ty1 Type
ty2
  = Type -> Type -> Bool
tcEqTypeNoSyns Type
ty1 Type
ty2

-- | Check whether two TyConApps are the same; if the number of arguments
-- are different, just checks the common prefix of arguments.
tcEqTyConApps :: TyCon -> [Type] -> TyCon -> [Type] -> Bool
tcEqTyConApps :: TyCon -> [Type] -> TyCon -> [Type] -> Bool
tcEqTyConApps TyCon
tc1 [Type]
args1 TyCon
tc2 [Type]
args2
  = TyCon
tc1 forall a. Eq a => a -> a -> Bool
== TyCon
tc2 Bool -> Bool -> Bool
&&
    forall (t :: * -> *). Foldable t => t Bool -> Bool
and (forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
zipWith Type -> Type -> Bool
tcEqTypeNoKindCheck [Type]
args1 [Type]
args2)
    -- No kind check necessary: if both arguments are well typed, then
    -- any difference in the kinds of later arguments would show up
    -- as differences in earlier (dependent) arguments

{-
Note [Specialising tc_eq_type]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The type equality predicates in TcType are hit pretty hard during typechecking.
Consequently we take pains to ensure that these paths are compiled to
efficient, minimally-allocating code.

To this end we place an INLINE on tc_eq_type, ensuring that it is inlined into
its publicly-visible interfaces (e.g. tcEqType). In addition to eliminating
some dynamic branches, this allows the simplifier to eliminate the closure
allocations that would otherwise be necessary to capture the two boolean "mode"
flags. This reduces allocations by a good fraction of a percent when compiling
Cabal.

See #19226.
-}

-- | Type equality comparing both visible and invisible arguments and expanding
-- type synonyms.
tcEqTypeNoSyns :: TcType -> TcType -> Bool
tcEqTypeNoSyns :: Type -> Type -> Bool
tcEqTypeNoSyns Type
ta Type
tb = Bool -> Bool -> Type -> Type -> Bool
tc_eq_type Bool
False Bool
False Type
ta Type
tb

-- | Like 'tcEqType', but returns True if the /visible/ part of the types
-- are equal, even if they are really unequal (in the invisible bits)
tcEqTypeVis :: TcType -> TcType -> Bool
tcEqTypeVis :: Type -> Type -> Bool
tcEqTypeVis Type
ty1 Type
ty2 = Bool -> Bool -> Type -> Type -> Bool
tc_eq_type Bool
False Bool
True Type
ty1 Type
ty2

-- | Like 'pickyEqTypeVis', but returns a Bool for convenience
pickyEqType :: TcType -> TcType -> Bool
-- Check when two types _look_ the same, _including_ synonyms.
-- So (pickyEqType String [Char]) returns False
-- This ignores kinds and coercions, because this is used only for printing.
pickyEqType :: Type -> Type -> Bool
pickyEqType Type
ty1 Type
ty2 = Bool -> Bool -> Type -> Type -> Bool
tc_eq_type Bool
True Bool
False Type
ty1 Type
ty2

-- | Real worker for 'tcEqType'. No kind check!
tc_eq_type :: Bool          -- ^ True <=> do not expand type synonyms
           -> Bool          -- ^ True <=> compare visible args only
           -> Type -> Type
           -> Bool
-- Flags False, False is the usual setting for tc_eq_type
-- See Note [Computing equality on types] in Type
tc_eq_type :: Bool -> Bool -> Type -> Type -> Bool
tc_eq_type Bool
keep_syns Bool
vis_only Type
orig_ty1 Type
orig_ty2
  = RnEnv2 -> Type -> Type -> Bool
go RnEnv2
orig_env Type
orig_ty1 Type
orig_ty2
  where
    go :: RnEnv2 -> Type -> Type -> Bool
    -- See Note [Comparing nullary type synonyms] in GHC.Core.Type.
    go :: RnEnv2 -> Type -> Type -> Bool
go RnEnv2
_   (TyConApp TyCon
tc1 []) (TyConApp TyCon
tc2 [])
      | TyCon
tc1 forall a. Eq a => a -> a -> Bool
== TyCon
tc2
      = Bool
True

    go RnEnv2
env Type
t1 Type
t2 | Bool -> Bool
not Bool
keep_syns, Just Type
t1' <- Type -> Maybe Type
tcView Type
t1 = RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
t1' Type
t2
    go RnEnv2
env Type
t1 Type
t2 | Bool -> Bool
not Bool
keep_syns, Just Type
t2' <- Type -> Maybe Type
tcView Type
t2 = RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
t1 Type
t2'

    go RnEnv2
env (TyVarTy Var
tv1) (TyVarTy Var
tv2)
      = RnEnv2 -> Var -> Var
rnOccL RnEnv2
env Var
tv1 forall a. Eq a => a -> a -> Bool
== RnEnv2 -> Var -> Var
rnOccR RnEnv2
env Var
tv2

    go RnEnv2
_   (LitTy TyLit
lit1) (LitTy TyLit
lit2)
      = TyLit
lit1 forall a. Eq a => a -> a -> Bool
== TyLit
lit2

    go RnEnv2
env (ForAllTy (Bndr Var
tv1 ArgFlag
vis1) Type
ty1)
           (ForAllTy (Bndr Var
tv2 ArgFlag
vis2) Type
ty2)
      =  ArgFlag
vis1 ArgFlag -> ArgFlag -> Bool
`sameVis` ArgFlag
vis2
           -- See Note [ForAllTy and typechecker equality] in
           -- GHC.Tc.Solver.Canonical for why we use `sameVis` here
      Bool -> Bool -> Bool
&& (Bool
vis_only Bool -> Bool -> Bool
|| RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env (Var -> Type
varType Var
tv1) (Var -> Type
varType Var
tv2))
      Bool -> Bool -> Bool
&& RnEnv2 -> Type -> Type -> Bool
go (RnEnv2 -> Var -> Var -> RnEnv2
rnBndr2 RnEnv2
env Var
tv1 Var
tv2) Type
ty1 Type
ty2

    -- Make sure we handle all FunTy cases since falling through to the
    -- AppTy case means that tcRepSplitAppTy_maybe may see an unzonked
    -- kind variable, which causes things to blow up.
    -- See Note [Equality on FunTys] in GHC.Core.TyCo.Rep: we must check
    -- kinds here
    go RnEnv2
env (FunTy AnonArgFlag
_ Type
w1 Type
arg1 Type
res1) (FunTy AnonArgFlag
_ Type
w2 Type
arg2 Type
res2)
      = Bool
kinds_eq Bool -> Bool -> Bool
&& RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
arg1 Type
arg2 Bool -> Bool -> Bool
&& RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
res1 Type
res2 Bool -> Bool -> Bool
&& RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
w1 Type
w2
      where
        kinds_eq :: Bool
kinds_eq | Bool
vis_only  = Bool
True
                 | Bool
otherwise = RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env (HasDebugCallStack => Type -> Type
typeKind Type
arg1) (HasDebugCallStack => Type -> Type
typeKind Type
arg2) Bool -> Bool -> Bool
&&
                               RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env (HasDebugCallStack => Type -> Type
typeKind Type
res1) (HasDebugCallStack => Type -> Type
typeKind Type
res2)

      -- See Note [Equality on AppTys] in GHC.Core.Type
    go RnEnv2
env (AppTy Type
s1 Type
t1)        Type
ty2
      | Just (Type
s2, Type
t2) <- Type -> Maybe (Type, Type)
tcRepSplitAppTy_maybe Type
ty2
      = RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
s1 Type
s2 Bool -> Bool -> Bool
&& RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
t1 Type
t2
    go RnEnv2
env Type
ty1                  (AppTy Type
s2 Type
t2)
      | Just (Type
s1, Type
t1) <- Type -> Maybe (Type, Type)
tcRepSplitAppTy_maybe Type
ty1
      = RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
s1 Type
s2 Bool -> Bool -> Bool
&& RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
t1 Type
t2

    go RnEnv2
env (TyConApp TyCon
tc1 [Type]
ts1)   (TyConApp TyCon
tc2 [Type]
ts2)
      = TyCon
tc1 forall a. Eq a => a -> a -> Bool
== TyCon
tc2 Bool -> Bool -> Bool
&& RnEnv2 -> [Bool] -> [Type] -> [Type] -> Bool
gos RnEnv2
env (TyCon -> [Bool]
tc_vis TyCon
tc1) [Type]
ts1 [Type]
ts2

    go RnEnv2
env (CastTy Type
t1 KindCoercion
_)   Type
t2              = RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
t1 Type
t2
    go RnEnv2
env Type
t1              (CastTy Type
t2 KindCoercion
_)   = RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
t1 Type
t2
    go RnEnv2
_   (CoercionTy {}) (CoercionTy {}) = Bool
True

    go RnEnv2
_ Type
_ Type
_ = Bool
False

    gos :: RnEnv2 -> [Bool] -> [Type] -> [Type] -> Bool
gos RnEnv2
_   [Bool]
_         []       []      = Bool
True
    gos RnEnv2
env (Bool
ig:[Bool]
igs) (Type
t1:[Type]
ts1) (Type
t2:[Type]
ts2) = (Bool
ig Bool -> Bool -> Bool
|| RnEnv2 -> Type -> Type -> Bool
go RnEnv2
env Type
t1 Type
t2)
                                      Bool -> Bool -> Bool
&& RnEnv2 -> [Bool] -> [Type] -> [Type] -> Bool
gos RnEnv2
env [Bool]
igs [Type]
ts1 [Type]
ts2
    gos RnEnv2
_ [Bool]
_ [Type]
_ [Type]
_ = Bool
False

    tc_vis :: TyCon -> [Bool]  -- True for the fields we should ignore
    tc_vis :: TyCon -> [Bool]
tc_vis TyCon
tc | Bool
vis_only  = [Bool]
inviss forall a. [a] -> [a] -> [a]
++ forall a. a -> [a]
repeat Bool
False    -- Ignore invisibles
              | Bool
otherwise = forall a. a -> [a]
repeat Bool
False              -- Ignore nothing
       -- The repeat False is necessary because tycons
       -- can legitimately be oversaturated
      where
        bndrs :: [TyConBinder]
bndrs = TyCon -> [TyConBinder]
tyConBinders TyCon
tc
        inviss :: [Bool]
inviss  = forall a b. (a -> b) -> [a] -> [b]
map forall tv. VarBndr tv TyConBndrVis -> Bool
isInvisibleTyConBinder [TyConBinder]
bndrs

    orig_env :: RnEnv2
orig_env = InScopeSet -> RnEnv2
mkRnEnv2 forall a b. (a -> b) -> a -> b
$ VarSet -> InScopeSet
mkInScopeSet forall a b. (a -> b) -> a -> b
$ [Type] -> VarSet
tyCoVarsOfTypes [Type
orig_ty1, Type
orig_ty2]

{-# INLINE tc_eq_type #-} -- See Note [Specialising tc_eq_type].

{- Note [Typechecker equality vs definitional equality]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GHC has two notions of equality over Core types:

* Definitional equality, as implemented by GHC.Core.Type.eqType.
  See Note [Non-trivial definitional equality] in GHC.Core.TyCo.Rep.
* Typechecker equality, as implemented by tcEqType (in GHC.Tc.Utils.TcType).
  GHC.Tc.Solver.Canonical.canEqNC also respects typechecker equality.

Typechecker equality implies definitional equality: if two types are equal
according to typechecker equality, then they are also equal according to
definitional equality. The converse is not always true, as typechecker equality
is more finer-grained than definitional equality in two places:

* Unlike definitional equality, which equates Type and Constraint, typechecker
  treats them as distinct types. See Note [Kind Constraint and kind Type] in
  GHC.Core.Type.
* Unlike definitional equality, which does not care about the ArgFlag of a
  ForAllTy, typechecker equality treats Required type variable binders as
  distinct from Invisible type variable binders.
  See Note [ForAllTy and typechecker equality] in GHC.Tc.Solver.Canonical.
-}

{- *********************************************************************
*                                                                      *
                       Predicate types
*                                                                      *
************************************************************************

Deconstructors and tests on predicate types

Note [Kind polymorphic type classes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    class C f where...   -- C :: forall k. k -> Constraint
    g :: forall (f::*). C f => f -> f

Here the (C f) in the signature is really (C * f), and we
don't want to complain that the * isn't a type variable!
-}

isTyVarClassPred :: PredType -> Bool
isTyVarClassPred :: Type -> Bool
isTyVarClassPred Type
ty = case Type -> Maybe (Class, [Type])
getClassPredTys_maybe Type
ty of
    Just (Class
_, [Type]
tys) -> forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all Type -> Bool
isTyVarTy [Type]
tys
    Maybe (Class, [Type])
_             -> Bool
False

-------------------------
checkValidClsArgs :: Bool -> Class -> [KindOrType] -> Bool
-- If the Bool is True (flexible contexts), return True (i.e. ok)
-- Otherwise, check that the type (not kind) args are all headed by a tyvar
--   E.g. (Eq a) accepted, (Eq (f a)) accepted, but (Eq Int) rejected
-- This function is here rather than in GHC.Tc.Validity because it is
-- called from GHC.Tc.Solver, which itself is imported by GHC.Tc.Validity
checkValidClsArgs :: Bool -> Class -> [Type] -> Bool
checkValidClsArgs Bool
flexible_contexts Class
cls [Type]
kts
  | Bool
flexible_contexts = Bool
True
  | Bool
otherwise         = forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all Type -> Bool
hasTyVarHead [Type]
tys
  where
    tys :: [Type]
tys = TyCon -> [Type] -> [Type]
filterOutInvisibleTypes (Class -> TyCon
classTyCon Class
cls) [Type]
kts

hasTyVarHead :: Type -> Bool
-- Returns true of (a t1 .. tn), where 'a' is a type variable
hasTyVarHead :: Type -> Bool
hasTyVarHead Type
ty                 -- Haskell 98 allows predicates of form
  | Type -> Bool
tcIsTyVarTy Type
ty = Bool
True       --      C (a ty1 .. tyn)
  | Bool
otherwise                   -- where a is a type variable
  = case Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty of
       Just (Type
ty, Type
_) -> Type -> Bool
hasTyVarHead Type
ty
       Maybe (Type, Type)
Nothing      -> Bool
False

evVarPred :: EvVar -> PredType
evVarPred :: Var -> Type
evVarPred Var
var = Var -> Type
varType Var
var
  -- Historical note: I used to have an ASSERT here,
  -- checking (isEvVarType (varType var)).  But with something like
  --   f :: c => _ -> _
  -- we end up with (c :: kappa), and (kappa ~ Constraint).  Until
  -- we solve and zonk (which there is no particular reason to do for
  -- partial signatures, (isEvVarType kappa) will return False. But
  -- nothing is wrong.  So I just removed the ASSERT.

------------------
-- | When inferring types, should we quantify over a given predicate?
-- Generally true of classes; generally false of equality constraints.
-- Equality constraints that mention quantified type variables and
-- implicit variables complicate the story. See Notes
-- [Inheriting implicit parameters] and [Quantifying over equality constraints]
pickQuantifiablePreds
  :: TyVarSet           -- Quantifying over these
  -> TcThetaType        -- Proposed constraints to quantify
  -> TcThetaType        -- A subset that we can actually quantify
-- This function decides whether a particular constraint should be
-- quantified over, given the type variables that are being quantified
pickQuantifiablePreds :: VarSet -> [Type] -> [Type]
pickQuantifiablePreds VarSet
qtvs [Type]
theta
  = let flex_ctxt :: Bool
flex_ctxt = Bool
True in  -- Quantify over non-tyvar constraints, even without
                             -- -XFlexibleContexts: see #10608, #10351
         -- flex_ctxt <- xoptM Opt_FlexibleContexts
    forall a b. (a -> Maybe b) -> [a] -> [b]
mapMaybe (Bool -> Type -> Maybe Type
pick_me Bool
flex_ctxt) [Type]
theta
  where
    pick_me :: Bool -> Type -> Maybe Type
pick_me Bool
flex_ctxt Type
pred
      = case Type -> Pred
classifyPredType Type
pred of

          ClassPred Class
cls [Type]
tys
            | Just {} <- Class -> [Type] -> Maybe FastString
isCallStackPred Class
cls [Type]
tys
              -- NEVER infer a CallStack constraint.  Otherwise we let
              -- the constraints bubble up to be solved from the outer
              -- context, or be defaulted when we reach the top-level.
              -- See Note [Overview of implicit CallStacks]
            -> forall a. Maybe a
Nothing

            | Class -> Bool
isIPClass Class
cls
            -> forall a. a -> Maybe a
Just Type
pred -- See note [Inheriting implicit parameters]

            | Bool -> Class -> [Type] -> Bool
pick_cls_pred Bool
flex_ctxt Class
cls [Type]
tys
            -> forall a. a -> Maybe a
Just Type
pred

          EqPred EqRel
eq_rel Type
ty1 Type
ty2
            | EqRel -> Type -> Type -> Bool
quantify_equality EqRel
eq_rel Type
ty1 Type
ty2
            , Just (Class
cls, [Type]
tys) <- EqRel -> Type -> Type -> Maybe (Class, [Type])
boxEqPred EqRel
eq_rel Type
ty1 Type
ty2
              -- boxEqPred: See Note [Lift equality constraints when quantifying]
            , Bool -> Class -> [Type] -> Bool
pick_cls_pred Bool
flex_ctxt Class
cls [Type]
tys
            -> forall a. a -> Maybe a
Just (Class -> [Type] -> Type
mkClassPred Class
cls [Type]
tys)

          IrredPred Type
ty
            | Type -> VarSet
tyCoVarsOfType Type
ty VarSet -> VarSet -> Bool
`intersectsVarSet` VarSet
qtvs
            -> forall a. a -> Maybe a
Just Type
pred

          Pred
_ -> forall a. Maybe a
Nothing


    pick_cls_pred :: Bool -> Class -> [Type] -> Bool
pick_cls_pred Bool
flex_ctxt Class
cls [Type]
tys
      = [Type] -> VarSet
tyCoVarsOfTypes [Type]
tys VarSet -> VarSet -> Bool
`intersectsVarSet` VarSet
qtvs
        Bool -> Bool -> Bool
&& (Bool -> Class -> [Type] -> Bool
checkValidClsArgs Bool
flex_ctxt Class
cls [Type]
tys)
           -- Only quantify over predicates that checkValidType
           -- will pass!  See #10351.

    -- See Note [Quantifying over equality constraints]
    quantify_equality :: EqRel -> Type -> Type -> Bool
quantify_equality EqRel
NomEq  Type
ty1 Type
ty2 = Type -> Bool
quant_fun Type
ty1 Bool -> Bool -> Bool
|| Type -> Bool
quant_fun Type
ty2
    quantify_equality EqRel
ReprEq Type
_   Type
_   = Bool
True

    quant_fun :: Type -> Bool
quant_fun Type
ty
      = case HasCallStack => Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty of
          Just (TyCon
tc, [Type]
tys) | TyCon -> Bool
isTypeFamilyTyCon TyCon
tc
                         -> [Type] -> VarSet
tyCoVarsOfTypes [Type]
tys VarSet -> VarSet -> Bool
`intersectsVarSet` VarSet
qtvs
          Maybe (TyCon, [Type])
_ -> Bool
False

boxEqPred :: EqRel -> Type -> Type -> Maybe (Class, [Type])
-- Given (t1 ~# t2) or (t1 ~R# t2) return the boxed version
--       (t1 ~ t2)  or (t1 `Coercible` t2)
boxEqPred :: EqRel -> Type -> Type -> Maybe (Class, [Type])
boxEqPred EqRel
eq_rel Type
ty1 Type
ty2
  = case EqRel
eq_rel of
      EqRel
NomEq  | Bool
homo_kind -> forall a. a -> Maybe a
Just (Class
eqClass,        [Type
k1,     Type
ty1, Type
ty2])
             | Bool
otherwise -> forall a. a -> Maybe a
Just (Class
heqClass,       [Type
k1, Type
k2, Type
ty1, Type
ty2])
      EqRel
ReprEq | Bool
homo_kind -> forall a. a -> Maybe a
Just (Class
coercibleClass, [Type
k1,     Type
ty1, Type
ty2])
             | Bool
otherwise -> forall a. Maybe a
Nothing -- Sigh: we do not have hererogeneous Coercible
                                    --       so we can't abstract over it
                                    -- Nothing fundamental: we could add it
 where
   k1 :: Type
k1 = HasDebugCallStack => Type -> Type
tcTypeKind Type
ty1
   k2 :: Type
k2 = HasDebugCallStack => Type -> Type
tcTypeKind Type
ty2
   homo_kind :: Bool
homo_kind = Type
k1 HasDebugCallStack => Type -> Type -> Bool
`tcEqType` Type
k2

pickCapturedPreds
  :: TyVarSet           -- Quantifying over these
  -> TcThetaType        -- Proposed constraints to quantify
  -> TcThetaType        -- A subset that we can actually quantify
-- A simpler version of pickQuantifiablePreds, used to winnow down
-- the inferred constraints of a group of bindings, into those for
-- one particular identifier
pickCapturedPreds :: VarSet -> [Type] -> [Type]
pickCapturedPreds VarSet
qtvs [Type]
theta
  = forall a. (a -> Bool) -> [a] -> [a]
filter Type -> Bool
captured [Type]
theta
  where
    captured :: Type -> Bool
captured Type
pred = Type -> Bool
isIPLikePred Type
pred Bool -> Bool -> Bool
|| (Type -> VarSet
tyCoVarsOfType Type
pred VarSet -> VarSet -> Bool
`intersectsVarSet` VarSet
qtvs)


-- Superclasses

type PredWithSCs a = (PredType, [PredType], a)

mkMinimalBySCs :: forall a. (a -> PredType) -> [a] -> [a]
-- Remove predicates that
--
--   - are the same as another predicate
--
--   - can be deduced from another by superclasses,
--
--   - are a reflexive equality (e.g  * ~ *)
--     (see Note [Remove redundant provided dicts] in GHC.Tc.TyCl.PatSyn)
--
-- The result is a subset of the input.
-- The 'a' is just paired up with the PredType;
--   typically it might be a dictionary Id
mkMinimalBySCs :: forall a. (a -> Type) -> [a] -> [a]
mkMinimalBySCs a -> Type
get_pred [a]
xs = [PredWithSCs a] -> [PredWithSCs a] -> [a]
go [PredWithSCs a]
preds_with_scs []
 where
   preds_with_scs :: [PredWithSCs a]
   preds_with_scs :: [PredWithSCs a]
preds_with_scs = [ (Type
pred, Type -> [Type]
implicants Type
pred, a
x)
                    | a
x <- [a]
xs
                    , let pred :: Type
pred = a -> Type
get_pred a
x ]

   go :: [PredWithSCs a]   -- Work list
      -> [PredWithSCs a]   -- Accumulating result
      -> [a]
   go :: [PredWithSCs a] -> [PredWithSCs a] -> [a]
go [] [PredWithSCs a]
min_preds
     = forall a. [a] -> [a]
reverse (forall a b. (a -> b) -> [a] -> [b]
map forall a b c. (a, b, c) -> c
thdOf3 [PredWithSCs a]
min_preds)
       -- The 'reverse' isn't strictly necessary, but it
       -- means that the results are returned in the same
       -- order as the input, which is generally saner
   go (work_item :: PredWithSCs a
work_item@(Type
p,[Type]
_,a
_) : [PredWithSCs a]
work_list) [PredWithSCs a]
min_preds
     | EqPred EqRel
_ Type
t1 Type
t2 <- Type -> Pred
classifyPredType Type
p
     , Type
t1 HasDebugCallStack => Type -> Type -> Bool
`tcEqType` Type
t2   -- See GHC.Tc.TyCl.PatSyn
                          -- Note [Remove redundant provided dicts]
     = [PredWithSCs a] -> [PredWithSCs a] -> [a]
go [PredWithSCs a]
work_list [PredWithSCs a]
min_preds
     | Type
p Type -> [PredWithSCs a] -> Bool
`in_cloud` [PredWithSCs a]
work_list Bool -> Bool -> Bool
|| Type
p Type -> [PredWithSCs a] -> Bool
`in_cloud` [PredWithSCs a]
min_preds
       -- Why look at work-list too?  Suppose work_item is Eq a,
       -- and work-list contains Ord a
     = [PredWithSCs a] -> [PredWithSCs a] -> [a]
go [PredWithSCs a]
work_list [PredWithSCs a]
min_preds
     | Bool
otherwise
     = [PredWithSCs a] -> [PredWithSCs a] -> [a]
go [PredWithSCs a]
work_list (PredWithSCs a
work_item forall a. a -> [a] -> [a]
: [PredWithSCs a]
min_preds)

   in_cloud :: PredType -> [PredWithSCs a] -> Bool
   in_cloud :: Type -> [PredWithSCs a] -> Bool
in_cloud Type
p [PredWithSCs a]
ps = forall (t :: * -> *). Foldable t => t Bool -> Bool
or [ Type
p HasDebugCallStack => Type -> Type -> Bool
`tcEqType` Type
p' | (Type
_, [Type]
scs, a
_) <- [PredWithSCs a]
ps, Type
p' <- [Type]
scs ]

   implicants :: Type -> [Type]
implicants Type
pred
     = Type
pred forall a. a -> [a] -> [a]
: Type -> [Type]
eq_extras Type
pred forall a. [a] -> [a] -> [a]
++ Type -> [Type]
transSuperClasses Type
pred

   -- Combine (a ~ b) and (b ~ a); no need to have both in one context
   -- These can arise when dealing with partial type signatures (e.g. T14715)
   eq_extras :: Type -> [Type]
eq_extras Type
pred
     = case Type -> Pred
classifyPredType Type
pred of
         EqPred EqRel
r Type
t1 Type
t2               -> [Role -> Type -> Type -> Type
mkPrimEqPredRole (EqRel -> Role
eqRelRole EqRel
r) Type
t2 Type
t1]
         ClassPred Class
cls [Type
k1,Type
k2,Type
t1,Type
t2]
           | Class
cls forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
heqTyConKey -> [Class -> [Type] -> Type
mkClassPred Class
cls [Type
k2, Type
k1, Type
t2, Type
t1]]
         ClassPred Class
cls [Type
k,Type
t1,Type
t2]
           | Class
cls forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
eqTyConKey  -> [Class -> [Type] -> Type
mkClassPred Class
cls [Type
k, Type
t2, Type
t1]]
         Pred
_ -> []

transSuperClasses :: PredType -> [PredType]
-- (transSuperClasses p) returns (p's superclasses) not including p
-- Stop if you encounter the same class again
-- See Note [Expanding superclasses]
transSuperClasses :: Type -> [Type]
transSuperClasses Type
p
  = NameSet -> Type -> [Type]
go NameSet
emptyNameSet Type
p
  where
    go :: NameSet -> PredType -> [PredType]
    go :: NameSet -> Type -> [Type]
go NameSet
rec_clss Type
p
       | ClassPred Class
cls [Type]
tys <- Type -> Pred
classifyPredType Type
p
       , let cls_nm :: Name
cls_nm = Class -> Name
className Class
cls
       , Bool -> Bool
not (Name
cls_nm Name -> NameSet -> Bool
`elemNameSet` NameSet
rec_clss)
       , let rec_clss' :: NameSet
rec_clss' | Class -> Bool
isCTupleClass Class
cls = NameSet
rec_clss
                       | Bool
otherwise         = NameSet
rec_clss NameSet -> Name -> NameSet
`extendNameSet` Name
cls_nm
       = [ Type
p' | Type
sc <- Class -> [Type] -> [Type]
immSuperClasses Class
cls [Type]
tys
              , Type
p'  <- Type
sc forall a. a -> [a] -> [a]
: NameSet -> Type -> [Type]
go NameSet
rec_clss' Type
sc ]
       | Bool
otherwise
       = []

immSuperClasses :: Class -> [Type] -> [PredType]
immSuperClasses :: Class -> [Type] -> [Type]
immSuperClasses Class
cls [Type]
tys
  = HasCallStack => TCvSubst -> [Type] -> [Type]
substTheta (HasDebugCallStack => [Var] -> [Type] -> TCvSubst
zipTvSubst [Var]
tyvars [Type]
tys) [Type]
sc_theta
  where
    ([Var]
tyvars,[Type]
sc_theta,[Var]
_,[ClassOpItem]
_) = Class -> ([Var], [Type], [Var], [ClassOpItem])
classBigSig Class
cls

isImprovementPred :: PredType -> Bool
-- Either it's an equality, or has some functional dependency
isImprovementPred :: Type -> Bool
isImprovementPred Type
ty
  = case Type -> Pred
classifyPredType Type
ty of
      EqPred EqRel
NomEq Type
t1 Type
t2 -> Bool -> Bool
not (Type
t1 HasDebugCallStack => Type -> Type -> Bool
`tcEqType` Type
t2)
      EqPred EqRel
ReprEq Type
_ Type
_  -> Bool
False
      ClassPred Class
cls [Type]
_    -> Class -> Bool
classHasFds Class
cls
      IrredPred {}       -> Bool
True -- Might have equalities after reduction?
      ForAllPred {}      -> Bool
False

{- Note [Expanding superclasses]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When we expand superclasses, we use the following algorithm:

transSuperClasses( C tys ) returns the transitive superclasses
                           of (C tys), not including C itself

For example
  class C a b => D a b
  class D b a => C a b

Then
  transSuperClasses( Ord ty )  = [Eq ty]
  transSuperClasses( C ta tb ) = [D tb ta, C tb ta]

Notice that in the recursive-superclass case we include C again at
the end of the chain.  One could exclude C in this case, but
the code is more awkward and there seems no good reason to do so.
(However C.f. GHC.Tc.Solver.Canonical.mk_strict_superclasses, which /does/
appear to do so.)

The algorithm is expand( so_far, pred ):

 1. If pred is not a class constraint, return empty set
       Otherwise pred = C ts
 2. If C is in so_far, return empty set (breaks loops)
 3. Find the immediate superclasses constraints of (C ts)
 4. For each such sc_pred, return (sc_pred : expand( so_far+C, D ss )

Notice that

 * With normal Haskell-98 classes, the loop-detector will never bite,
   so we'll get all the superclasses.

 * We need the loop-breaker in case we have UndecidableSuperClasses on

 * Since there is only a finite number of distinct classes, expansion
   must terminate.

 * The loop breaking is a bit conservative. Notably, a tuple class
   could contain many times without threatening termination:
      (Eq a, (Ord a, Ix a))
   And this is try of any class that we can statically guarantee
   as non-recursive (in some sense).  For now, we just make a special
   case for tuples.  Something better would be cool.

See also GHC.Tc.TyCl.Utils.checkClassCycles.

Note [Lift equality constraints when quantifying]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We can't quantify over a constraint (t1 ~# t2) because that isn't a
predicate type; see Note [Types for coercions, predicates, and evidence]
in GHC.Core.TyCo.Rep.

So we have to 'lift' it to (t1 ~ t2).  Similarly (~R#) must be lifted
to Coercible.

This tiresome lifting is the reason that pick_me (in
pickQuantifiablePreds) returns a Maybe rather than a Bool.

Note [Quantifying over equality constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Should we quantify over an equality constraint (s ~ t)?  In general, we don't.
Doing so may simply postpone a type error from the function definition site to
its call site.  (At worst, imagine (Int ~ Bool)).

However, consider this
         forall a. (F [a] ~ Int) => blah
Should we quantify over the (F [a] ~ Int)?  Perhaps yes, because at the call
site we will know 'a', and perhaps we have instance  F [Bool] = Int.
So we *do* quantify over a type-family equality where the arguments mention
the quantified variables.

Note [Inheriting implicit parameters]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this:

        f x = (x::Int) + ?y

where f is *not* a top-level binding.
From the RHS of f we'll get the constraint (?y::Int).
There are two types we might infer for f:

        f :: Int -> Int

(so we get ?y from the context of f's definition), or

        f :: (?y::Int) => Int -> Int

At first you might think the first was better, because then
?y behaves like a free variable of the definition, rather than
having to be passed at each call site.  But of course, the WHOLE
IDEA is that ?y should be passed at each call site (that's what
dynamic binding means) so we'd better infer the second.

BOTTOM LINE: when *inferring types* you must quantify over implicit
parameters, *even if* they don't mention the bound type variables.
Reason: because implicit parameters, uniquely, have local instance
declarations. See pickQuantifiablePreds.

Note [Quantifying over equality constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Should we quantify over an equality constraint (s ~ t)?  In general, we don't.
Doing so may simply postpone a type error from the function definition site to
its call site.  (At worst, imagine (Int ~ Bool)).

However, consider this
         forall a. (F [a] ~ Int) => blah
Should we quantify over the (F [a] ~ Int).  Perhaps yes, because at the call
site we will know 'a', and perhaps we have instance  F [Bool] = Int.
So we *do* quantify over a type-family equality where the arguments mention
the quantified variables.

************************************************************************
*                                                                      *
      Classifying types
*                                                                      *
************************************************************************
-}

isSigmaTy :: TcType -> Bool
-- isSigmaTy returns true of any qualified type.  It doesn't
-- *necessarily* have any foralls.  E.g
--        f :: (?x::Int) => Int -> Int
isSigmaTy :: Type -> Bool
isSigmaTy Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Bool
isSigmaTy Type
ty'
isSigmaTy (ForAllTy {})                = Bool
True
isSigmaTy (FunTy { ft_af :: Type -> AnonArgFlag
ft_af = AnonArgFlag
InvisArg }) = Bool
True
isSigmaTy Type
_                            = Bool
False

isRhoTy :: TcType -> Bool   -- True of TcRhoTypes; see Note [TcRhoType]
isRhoTy :: Type -> Bool
isRhoTy Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Bool
isRhoTy Type
ty'
isRhoTy (ForAllTy {})                = Bool
False
isRhoTy (FunTy { ft_af :: Type -> AnonArgFlag
ft_af = AnonArgFlag
InvisArg }) = Bool
False
isRhoTy Type
_                            = Bool
True

-- | Like 'isRhoTy', but also says 'True' for 'Infer' types
isRhoExpTy :: ExpType -> Bool
isRhoExpTy :: ExpType -> Bool
isRhoExpTy (Check Type
ty) = Type -> Bool
isRhoTy Type
ty
isRhoExpTy (Infer {}) = Bool
True

isOverloadedTy :: Type -> Bool
-- Yes for a type of a function that might require evidence-passing
-- Used only by bindLocalMethods
isOverloadedTy :: Type -> Bool
isOverloadedTy Type
ty | Just Type
ty' <- Type -> Maybe Type
tcView Type
ty = Type -> Bool
isOverloadedTy Type
ty'
isOverloadedTy (ForAllTy TyCoVarBinder
_  Type
ty)             = Type -> Bool
isOverloadedTy Type
ty
isOverloadedTy (FunTy { ft_af :: Type -> AnonArgFlag
ft_af = AnonArgFlag
InvisArg }) = Bool
True
isOverloadedTy Type
_                            = Bool
False

isFloatTy, isDoubleTy, isIntegerTy, isNaturalTy,
    isIntTy, isWordTy, isBoolTy,
    isUnitTy, isCharTy, isAnyTy :: Type -> Bool
isFloatTy :: Type -> Bool
isFloatTy      = Unique -> Type -> Bool
is_tc Unique
floatTyConKey
isDoubleTy :: Type -> Bool
isDoubleTy     = Unique -> Type -> Bool
is_tc Unique
doubleTyConKey
isIntegerTy :: Type -> Bool
isIntegerTy    = Unique -> Type -> Bool
is_tc Unique
integerTyConKey
isNaturalTy :: Type -> Bool
isNaturalTy    = Unique -> Type -> Bool
is_tc Unique
naturalTyConKey
isIntTy :: Type -> Bool
isIntTy        = Unique -> Type -> Bool
is_tc Unique
intTyConKey
isWordTy :: Type -> Bool
isWordTy       = Unique -> Type -> Bool
is_tc Unique
wordTyConKey
isBoolTy :: Type -> Bool
isBoolTy       = Unique -> Type -> Bool
is_tc Unique
boolTyConKey
isUnitTy :: Type -> Bool
isUnitTy       = Unique -> Type -> Bool
is_tc Unique
unitTyConKey
isCharTy :: Type -> Bool
isCharTy       = Unique -> Type -> Bool
is_tc Unique
charTyConKey
isAnyTy :: Type -> Bool
isAnyTy        = Unique -> Type -> Bool
is_tc Unique
anyTyConKey

-- | Does a type represent a floating-point number?
isFloatingTy :: Type -> Bool
isFloatingTy :: Type -> Bool
isFloatingTy Type
ty = Type -> Bool
isFloatTy Type
ty Bool -> Bool -> Bool
|| Type -> Bool
isDoubleTy Type
ty

-- | Is a type 'String'?
isStringTy :: Type -> Bool
isStringTy :: Type -> Bool
isStringTy Type
ty
  = case HasCallStack => Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty of
      Just (TyCon
tc, [Type
arg_ty]) -> TyCon
tc forall a. Eq a => a -> a -> Bool
== TyCon
listTyCon Bool -> Bool -> Bool
&& Type -> Bool
isCharTy Type
arg_ty
      Maybe (TyCon, [Type])
_                   -> Bool
False

-- | Is a type a 'CallStack'?
isCallStackTy :: Type -> Bool
isCallStackTy :: Type -> Bool
isCallStackTy Type
ty
  | Just TyCon
tc <- Type -> Maybe TyCon
tyConAppTyCon_maybe Type
ty
  = TyCon
tc forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
callStackTyConKey
  | Bool
otherwise
  = Bool
False

-- | Is a 'PredType' a 'CallStack' implicit parameter?
--
-- If so, return the name of the parameter.
isCallStackPred :: Class -> [Type] -> Maybe FastString
isCallStackPred :: Class -> [Type] -> Maybe FastString
isCallStackPred Class
cls [Type]
tys
  | [Type
ty1, Type
ty2] <- [Type]
tys
  , Class -> Bool
isIPClass Class
cls
  , Type -> Bool
isCallStackTy Type
ty2
  = Type -> Maybe FastString
isStrLitTy Type
ty1
  | Bool
otherwise
  = forall a. Maybe a
Nothing

is_tc :: Unique -> Type -> Bool
-- Newtypes are opaque to this
is_tc :: Unique -> Type -> Bool
is_tc Unique
uniq Type
ty = case HasCallStack => Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty of
                        Just (TyCon
tc, [Type]
_) -> Unique
uniq forall a. Eq a => a -> a -> Bool
== forall a. Uniquable a => a -> Unique
getUnique TyCon
tc
                        Maybe (TyCon, [Type])
Nothing      -> Bool
False

isRigidTy :: TcType -> Bool
isRigidTy :: Type -> Bool
isRigidTy Type
ty
  | Just (TyCon
tc,[Type]
_) <- HasCallStack => Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty = TyCon -> Role -> Bool
isGenerativeTyCon TyCon
tc Role
Nominal
  | Just {} <- Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty        = Bool
True
  | Type -> Bool
isForAllTy Type
ty                           = Bool
True
  | Bool
otherwise                               = Bool
False


{-
************************************************************************
*                                                                      *
   Misc
*                                                                      *
************************************************************************

Note [Visible type application]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GHC implements a generalisation of the algorithm described in the
"Visible Type Application" paper (available from
http://www.cis.upenn.edu/~sweirich/publications.html). A key part
of that algorithm is to distinguish user-specified variables from inferred
variables. For example, the following should typecheck:

  f :: forall a b. a -> b -> b
  f = const id

  g = const id

  x = f @Int @Bool 5 False
  y = g 5 @Bool False

The idea is that we wish to allow visible type application when we are
instantiating a specified, fixed variable. In practice, specified, fixed
variables are either written in a type signature (or
annotation), OR are imported from another module. (We could do better here,
for example by doing SCC analysis on parts of a module and considering any
type from outside one's SCC to be fully specified, but this is very confusing to
users. The simple rule above is much more straightforward and predictable.)

So, both of f's quantified variables are specified and may be instantiated.
But g has no type signature, so only id's variable is specified (because id
is imported). We write the type of g as forall {a}. a -> forall b. b -> b.
Note that the a is in braces, meaning it cannot be instantiated with
visible type application.

Tracking specified vs. inferred variables is done conveniently by a field
in TyBinder.

-}

deNoteType :: Type -> Type
-- Remove all *outermost* type synonyms and other notes
deNoteType :: Type -> Type
deNoteType Type
ty | Just Type
ty' <- Type -> Maybe Type
coreView Type
ty = Type -> Type
deNoteType Type
ty'
deNoteType Type
ty = Type
ty

{-
Find the free tycons and classes of a type.  This is used in the front
end of the compiler.
-}

{-
************************************************************************
*                                                                      *
   External types
*                                                                      *
************************************************************************

The compiler's foreign function interface supports the passing of a
restricted set of types as arguments and results (the restricting factor
being the )
-}

tcSplitIOType_maybe :: Type -> Maybe (TyCon, Type)
-- (tcSplitIOType_maybe t) returns Just (IO,t',co)
--              if co : t ~ IO t'
--              returns Nothing otherwise
tcSplitIOType_maybe :: Type -> Maybe (TyCon, Type)
tcSplitIOType_maybe Type
ty
  = case HasCallStack => Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty of
        Just (TyCon
io_tycon, [Type
io_res_ty])
         | TyCon
io_tycon forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
ioTyConKey ->
            forall a. a -> Maybe a
Just (TyCon
io_tycon, Type
io_res_ty)
        Maybe (TyCon, [Type])
_ ->
            forall a. Maybe a
Nothing

isFFITy :: Type -> Bool
-- True for any TyCon that can possibly be an arg or result of an FFI call
isFFITy :: Type -> Bool
isFFITy Type
ty = Validity -> Bool
isValid ((TyCon -> Validity) -> Type -> Validity
checkRepTyCon TyCon -> Validity
legalFFITyCon Type
ty)

isFFIArgumentTy :: DynFlags -> Safety -> Type -> Validity
-- Checks for valid argument type for a 'foreign import'
isFFIArgumentTy :: DynFlags -> Safety -> Type -> Validity
isFFIArgumentTy DynFlags
dflags Safety
safety Type
ty
   = (TyCon -> Validity) -> Type -> Validity
checkRepTyCon (DynFlags -> Safety -> TyCon -> Validity
legalOutgoingTyCon DynFlags
dflags Safety
safety) Type
ty

isFFIExternalTy :: Type -> Validity
-- Types that are allowed as arguments of a 'foreign export'
isFFIExternalTy :: Type -> Validity
isFFIExternalTy Type
ty = (TyCon -> Validity) -> Type -> Validity
checkRepTyCon TyCon -> Validity
legalFEArgTyCon Type
ty

isFFIImportResultTy :: DynFlags -> Type -> Validity
isFFIImportResultTy :: DynFlags -> Type -> Validity
isFFIImportResultTy DynFlags
dflags Type
ty
  = (TyCon -> Validity) -> Type -> Validity
checkRepTyCon (DynFlags -> TyCon -> Validity
legalFIResultTyCon DynFlags
dflags) Type
ty

isFFIExportResultTy :: Type -> Validity
isFFIExportResultTy :: Type -> Validity
isFFIExportResultTy Type
ty = (TyCon -> Validity) -> Type -> Validity
checkRepTyCon TyCon -> Validity
legalFEResultTyCon Type
ty

isFFIDynTy :: Type -> Type -> Validity
-- The type in a foreign import dynamic must be Ptr, FunPtr, or a newtype of
-- either, and the wrapped function type must be equal to the given type.
-- We assume that all types have been run through normaliseFfiType, so we don't
-- need to worry about expanding newtypes here.
isFFIDynTy :: Type -> Type -> Validity
isFFIDynTy Type
expected Type
ty
    -- Note [Foreign import dynamic]
    -- In the example below, expected would be 'CInt -> IO ()', while ty would
    -- be 'FunPtr (CDouble -> IO ())'.
    | Just (TyCon
tc, [Type
ty']) <- HasDebugCallStack => Type -> Maybe (TyCon, [Type])
splitTyConApp_maybe Type
ty
    , TyCon -> Unique
tyConUnique TyCon
tc forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Unique
ptrTyConKey, Unique
funPtrTyConKey]
    , Type -> Type -> Bool
eqType Type
ty' Type
expected
    = Validity
IsValid
    | Bool
otherwise
    = SDoc -> Validity
NotValid ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"Expected: Ptr/FunPtr" SDoc -> SDoc -> SDoc
<+> Type -> SDoc
pprParendType Type
expected SDoc -> SDoc -> SDoc
<> SDoc
comma
                     , String -> SDoc
text String
"  Actual:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr Type
ty ])

isFFILabelTy :: Type -> Validity
-- The type of a foreign label must be Ptr, FunPtr, or a newtype of either.
isFFILabelTy :: Type -> Validity
isFFILabelTy Type
ty = (TyCon -> Validity) -> Type -> Validity
checkRepTyCon forall {a}. Uniquable a => a -> Validity
ok Type
ty
  where
    ok :: a -> Validity
ok a
tc | a
tc forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
funPtrTyConKey Bool -> Bool -> Bool
|| a
tc forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
ptrTyConKey
          = Validity
IsValid
          | Bool
otherwise
          = SDoc -> Validity
NotValid (String -> SDoc
text String
"A foreign-imported address (via &foo) must have type (Ptr a) or (FunPtr a)")

isFFIPrimArgumentTy :: DynFlags -> Type -> Validity
-- Checks for valid argument type for a 'foreign import prim'
-- Currently they must all be simple unlifted types, or the well-known type
-- Any, which can be used to pass the address to a Haskell object on the heap to
-- the foreign function.
isFFIPrimArgumentTy :: DynFlags -> Type -> Validity
isFFIPrimArgumentTy DynFlags
dflags Type
ty
  | Type -> Bool
isAnyTy Type
ty = Validity
IsValid
  | Bool
otherwise  = (TyCon -> Validity) -> Type -> Validity
checkRepTyCon (DynFlags -> TyCon -> Validity
legalFIPrimArgTyCon DynFlags
dflags) Type
ty

isFFIPrimResultTy :: DynFlags -> Type -> Validity
-- Checks for valid result type for a 'foreign import prim' Currently
-- it must be an unlifted type, including unboxed tuples, unboxed
-- sums, or the well-known type Any.
isFFIPrimResultTy :: DynFlags -> Type -> Validity
isFFIPrimResultTy DynFlags
dflags Type
ty
  | Type -> Bool
isAnyTy Type
ty = Validity
IsValid
  | Bool
otherwise = (TyCon -> Validity) -> Type -> Validity
checkRepTyCon (DynFlags -> TyCon -> Validity
legalFIPrimResultTyCon DynFlags
dflags) Type
ty

isFunPtrTy :: Type -> Bool
isFunPtrTy :: Type -> Bool
isFunPtrTy Type
ty
  | Just (TyCon
tc, [Type
_]) <- HasDebugCallStack => Type -> Maybe (TyCon, [Type])
splitTyConApp_maybe Type
ty
  = TyCon
tc forall a. Uniquable a => a -> Unique -> Bool
`hasKey` Unique
funPtrTyConKey
  | Bool
otherwise
  = Bool
False

-- normaliseFfiType gets run before checkRepTyCon, so we don't
-- need to worry about looking through newtypes or type functions
-- here; that's already been taken care of.
checkRepTyCon :: (TyCon -> Validity) -> Type -> Validity
checkRepTyCon :: (TyCon -> Validity) -> Type -> Validity
checkRepTyCon TyCon -> Validity
check_tc Type
ty
  = case HasDebugCallStack => Type -> Maybe (TyCon, [Type])
splitTyConApp_maybe Type
ty of
      Just (TyCon
tc, [Type]
tys)
        | TyCon -> Bool
isNewTyCon TyCon
tc -> SDoc -> Validity
NotValid (SDoc -> Arity -> SDoc -> SDoc
hang SDoc
msg Arity
2 (forall {t :: * -> *} {a} {a}.
(Foldable t, Outputable a) =>
a -> t a -> SDoc
mk_nt_reason TyCon
tc [Type]
tys SDoc -> SDoc -> SDoc
$$ SDoc
nt_fix))
        | Bool
otherwise     -> case TyCon -> Validity
check_tc TyCon
tc of
                             Validity
IsValid        -> Validity
IsValid
                             NotValid SDoc
extra -> SDoc -> Validity
NotValid (SDoc
msg SDoc -> SDoc -> SDoc
$$ SDoc
extra)
      Maybe (TyCon, [Type])
Nothing -> SDoc -> Validity
NotValid (SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr Type
ty) SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"is not a data type")
  where
    msg :: SDoc
msg = SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr Type
ty) SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"cannot be marshalled in a foreign call"
    mk_nt_reason :: a -> t a -> SDoc
mk_nt_reason a
tc t a
tys
      | forall (t :: * -> *) a. Foldable t => t a -> Bool
null t a
tys  = String -> SDoc
text String
"because its data constructor is not in scope"
      | Bool
otherwise = String -> SDoc
text String
"because the data constructor for"
                    SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr a
tc) SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"is not in scope"
    nt_fix :: SDoc
nt_fix = String -> SDoc
text String
"Possible fix: import the data constructor to bring it into scope"

{-
Note [Foreign import dynamic]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A dynamic stub must be of the form 'FunPtr ft -> ft' where ft is any foreign
type.  Similarly, a wrapper stub must be of the form 'ft -> IO (FunPtr ft)'.

We use isFFIDynTy to check whether a signature is well-formed. For example,
given a (illegal) declaration like:

foreign import ccall "dynamic"
  foo :: FunPtr (CDouble -> IO ()) -> CInt -> IO ()

isFFIDynTy will compare the 'FunPtr' type 'CDouble -> IO ()' with the curried
result type 'CInt -> IO ()', and return False, as they are not equal.


----------------------------------------------
These chaps do the work; they are not exported
----------------------------------------------
-}

legalFEArgTyCon :: TyCon -> Validity
legalFEArgTyCon :: TyCon -> Validity
legalFEArgTyCon TyCon
tc
  -- It's illegal to make foreign exports that take unboxed
  -- arguments.  The RTS API currently can't invoke such things.  --SDM 7/2000
  = TyCon -> Validity
boxedMarshalableTyCon TyCon
tc

legalFIResultTyCon :: DynFlags -> TyCon -> Validity
legalFIResultTyCon :: DynFlags -> TyCon -> Validity
legalFIResultTyCon DynFlags
dflags TyCon
tc
  | TyCon
tc forall a. Eq a => a -> a -> Bool
== TyCon
unitTyCon         = Validity
IsValid
  | Bool
otherwise               = DynFlags -> TyCon -> Validity
marshalableTyCon DynFlags
dflags TyCon
tc

legalFEResultTyCon :: TyCon -> Validity
legalFEResultTyCon :: TyCon -> Validity
legalFEResultTyCon TyCon
tc
  | TyCon
tc forall a. Eq a => a -> a -> Bool
== TyCon
unitTyCon         = Validity
IsValid
  | Bool
otherwise               = TyCon -> Validity
boxedMarshalableTyCon TyCon
tc

legalOutgoingTyCon :: DynFlags -> Safety -> TyCon -> Validity
-- Checks validity of types going from Haskell -> external world
legalOutgoingTyCon :: DynFlags -> Safety -> TyCon -> Validity
legalOutgoingTyCon DynFlags
dflags Safety
_ TyCon
tc
  = DynFlags -> TyCon -> Validity
marshalableTyCon DynFlags
dflags TyCon
tc

legalFFITyCon :: TyCon -> Validity
-- True for any TyCon that can possibly be an arg or result of an FFI call
legalFFITyCon :: TyCon -> Validity
legalFFITyCon TyCon
tc
  | TyCon -> Bool
isUnliftedTyCon TyCon
tc = Validity
IsValid
  | TyCon
tc forall a. Eq a => a -> a -> Bool
== TyCon
unitTyCon    = Validity
IsValid
  | Bool
otherwise          = TyCon -> Validity
boxedMarshalableTyCon TyCon
tc

marshalableTyCon :: DynFlags -> TyCon -> Validity
marshalableTyCon :: DynFlags -> TyCon -> Validity
marshalableTyCon DynFlags
dflags TyCon
tc
  | TyCon -> Bool
isUnliftedTyCon TyCon
tc
  , Bool -> Bool
not (TyCon -> Bool
isUnboxedTupleTyCon TyCon
tc Bool -> Bool -> Bool
|| TyCon -> Bool
isUnboxedSumTyCon TyCon
tc)
  , Bool -> Bool
not (forall (t :: * -> *) a. Foldable t => t a -> Bool
null (HasDebugCallStack => TyCon -> [PrimRep]
tyConPrimRep TyCon
tc)) -- Note [Marshalling void]
  = DynFlags -> Validity
validIfUnliftedFFITypes DynFlags
dflags
  | Bool
otherwise
  = TyCon -> Validity
boxedMarshalableTyCon TyCon
tc

boxedMarshalableTyCon :: TyCon -> Validity
boxedMarshalableTyCon :: TyCon -> Validity
boxedMarshalableTyCon TyCon
tc
   | forall a. Uniquable a => a -> Unique
getUnique TyCon
tc forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [ Unique
intTyConKey, Unique
int8TyConKey, Unique
int16TyConKey
                         , Unique
int32TyConKey, Unique
int64TyConKey
                         , Unique
wordTyConKey, Unique
word8TyConKey, Unique
word16TyConKey
                         , Unique
word32TyConKey, Unique
word64TyConKey
                         , Unique
floatTyConKey, Unique
doubleTyConKey
                         , Unique
ptrTyConKey, Unique
funPtrTyConKey
                         , Unique
charTyConKey
                         , Unique
stablePtrTyConKey
                         , Unique
boolTyConKey
                         ]
  = Validity
IsValid

  | Bool
otherwise = SDoc -> Validity
NotValid SDoc
empty

legalFIPrimArgTyCon :: DynFlags -> TyCon -> Validity
-- Check args of 'foreign import prim', only allow simple unlifted types.
-- Strictly speaking it is unnecessary to ban unboxed tuples and sums here since
-- currently they're of the wrong kind to use in function args anyway.
legalFIPrimArgTyCon :: DynFlags -> TyCon -> Validity
legalFIPrimArgTyCon DynFlags
dflags TyCon
tc
  | TyCon -> Bool
isUnliftedTyCon TyCon
tc
  , Bool -> Bool
not (TyCon -> Bool
isUnboxedTupleTyCon TyCon
tc Bool -> Bool -> Bool
|| TyCon -> Bool
isUnboxedSumTyCon TyCon
tc)
  = DynFlags -> Validity
validIfUnliftedFFITypes DynFlags
dflags
  | Bool
otherwise
  = SDoc -> Validity
NotValid SDoc
unlifted_only

legalFIPrimResultTyCon :: DynFlags -> TyCon -> Validity
-- Check result type of 'foreign import prim'. Allow simple unlifted
-- types and also unboxed tuple and sum result types.
legalFIPrimResultTyCon :: DynFlags -> TyCon -> Validity
legalFIPrimResultTyCon DynFlags
dflags TyCon
tc
  | TyCon -> Bool
isUnliftedTyCon TyCon
tc
  , TyCon -> Bool
isUnboxedTupleTyCon TyCon
tc Bool -> Bool -> Bool
|| TyCon -> Bool
isUnboxedSumTyCon TyCon
tc
     Bool -> Bool -> Bool
|| Bool -> Bool
not (forall (t :: * -> *) a. Foldable t => t a -> Bool
null (HasDebugCallStack => TyCon -> [PrimRep]
tyConPrimRep TyCon
tc))   -- Note [Marshalling void]
  = DynFlags -> Validity
validIfUnliftedFFITypes DynFlags
dflags

  | Bool
otherwise
  = SDoc -> Validity
NotValid SDoc
unlifted_only

unlifted_only :: SDoc
unlifted_only :: SDoc
unlifted_only = String -> SDoc
text String
"foreign import prim only accepts simple unlifted types"

validIfUnliftedFFITypes :: DynFlags -> Validity
validIfUnliftedFFITypes :: DynFlags -> Validity
validIfUnliftedFFITypes DynFlags
dflags
  | Extension -> DynFlags -> Bool
xopt Extension
LangExt.UnliftedFFITypes DynFlags
dflags =  Validity
IsValid
  | Bool
otherwise = SDoc -> Validity
NotValid (String -> SDoc
text String
"To marshal unlifted types, use UnliftedFFITypes")

{-
Note [Marshalling void]
~~~~~~~~~~~~~~~~~~~~~~~
We don't treat State# (whose PrimRep is VoidRep) as marshalable.
In turn that means you can't write
        foreign import foo :: Int -> State# RealWorld

Reason: the back end falls over with panic "primRepHint:VoidRep";
        and there is no compelling reason to permit it
-}

{-
************************************************************************
*                                                                      *
        The "Paterson size" of a type
*                                                                      *
************************************************************************
-}

{-
Note [Paterson conditions on PredTypes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We are considering whether *class* constraints terminate
(see Note [Paterson conditions]). Precisely, the Paterson conditions
would have us check that "the constraint has fewer constructors and variables
(taken together and counting repetitions) than the head.".

However, we can be a bit more refined by looking at which kind of constraint
this actually is. There are two main tricks:

 1. It seems like it should be OK not to count the tuple type constructor
    for a PredType like (Show a, Eq a) :: Constraint, since we don't
    count the "implicit" tuple in the ThetaType itself.

    In fact, the Paterson test just checks *each component* of the top level
    ThetaType against the size bound, one at a time. By analogy, it should be
    OK to return the size of the *largest* tuple component as the size of the
    whole tuple.

 2. Once we get into an implicit parameter or equality we
    can't get back to a class constraint, so it's safe
    to say "size 0".  See #4200.

NB: we don't want to detect PredTypes in sizeType (and then call
sizePred on them), or we might get an infinite loop if that PredType
is irreducible. See #5581.
-}

type TypeSize = IntWithInf

sizeType :: Type -> TypeSize
-- Size of a type: the number of variables and constructors
-- Ignore kinds altogether
sizeType :: Type -> TypeSize
sizeType = Type -> TypeSize
go
  where
    go :: Type -> TypeSize
go Type
ty | Just Type
exp_ty <- Type -> Maybe Type
tcView Type
ty = Type -> TypeSize
go Type
exp_ty
    go (TyVarTy {})              = TypeSize
1
    go (TyConApp TyCon
tc [Type]
tys)
      | TyCon -> Bool
isTypeFamilyTyCon TyCon
tc     = TypeSize
infinity  -- Type-family applications can
                                             -- expand to any arbitrary size
      | Bool
otherwise                = [Type] -> TypeSize
sizeTypes (TyCon -> [Type] -> [Type]
filterOutInvisibleTypes TyCon
tc [Type]
tys) forall a. Num a => a -> a -> a
+ TypeSize
1
                                   -- Why filter out invisible args?  I suppose any
                                   -- size ordering is sound, but why is this better?
                                   -- I came across this when investigating #14010.
    go (LitTy {})                = TypeSize
1
    go (FunTy AnonArgFlag
_ Type
w Type
arg Type
res)       = Type -> TypeSize
go Type
w forall a. Num a => a -> a -> a
+ Type -> TypeSize
go Type
arg forall a. Num a => a -> a -> a
+ Type -> TypeSize
go Type
res forall a. Num a => a -> a -> a
+ TypeSize
1
    go (AppTy Type
fun Type
arg)           = Type -> TypeSize
go Type
fun forall a. Num a => a -> a -> a
+ Type -> TypeSize
go Type
arg
    go (ForAllTy (Bndr Var
tv ArgFlag
vis) Type
ty)
        | ArgFlag -> Bool
isVisibleArgFlag ArgFlag
vis   = Type -> TypeSize
go (Var -> Type
tyVarKind Var
tv) forall a. Num a => a -> a -> a
+ Type -> TypeSize
go Type
ty forall a. Num a => a -> a -> a
+ TypeSize
1
        | Bool
otherwise              = Type -> TypeSize
go Type
ty forall a. Num a => a -> a -> a
+ TypeSize
1
    go (CastTy Type
ty KindCoercion
_)             = Type -> TypeSize
go Type
ty
    go (CoercionTy {})           = TypeSize
0

sizeTypes :: [Type] -> TypeSize
sizeTypes :: [Type] -> TypeSize
sizeTypes [Type]
tys = forall (t :: * -> *) a. (Foldable t, Num a) => t a -> a
sum (forall a b. (a -> b) -> [a] -> [b]
map Type -> TypeSize
sizeType [Type]
tys)

-----------------------------------------------------------------------------------
-----------------------------------------------------------------------------------
-----------------------
-- | For every arg a tycon can take, the returned list says True if the argument
-- is taken visibly, and False otherwise. Ends with an infinite tail of Trues to
-- allow for oversaturation.
tcTyConVisibilities :: TyCon -> [Bool]
tcTyConVisibilities :: TyCon -> [Bool]
tcTyConVisibilities TyCon
tc = [Bool]
tc_binder_viss forall a. [a] -> [a] -> [a]
++ [Bool]
tc_return_kind_viss forall a. [a] -> [a] -> [a]
++ forall a. a -> [a]
repeat Bool
True
  where
    tc_binder_viss :: [Bool]
tc_binder_viss      = forall a b. (a -> b) -> [a] -> [b]
map forall tv. VarBndr tv TyConBndrVis -> Bool
isVisibleTyConBinder (TyCon -> [TyConBinder]
tyConBinders TyCon
tc)
    tc_return_kind_viss :: [Bool]
tc_return_kind_viss = forall a b. (a -> b) -> [a] -> [b]
map TyBinder -> Bool
isVisibleBinder (forall a b. (a, b) -> a
fst forall a b. (a -> b) -> a -> b
$ Type -> ([TyBinder], Type)
tcSplitPiTys (TyCon -> Type
tyConResKind TyCon
tc))

-- | If the tycon is applied to the types, is the next argument visible?
isNextTyConArgVisible :: TyCon -> [Type] -> Bool
isNextTyConArgVisible :: TyCon -> [Type] -> Bool
isNextTyConArgVisible TyCon
tc [Type]
tys
  = TyCon -> [Bool]
tcTyConVisibilities TyCon
tc forall a. Outputable a => [a] -> Arity -> a
`getNth` forall (t :: * -> *) a. Foldable t => t a -> Arity
length [Type]
tys

-- | Should this type be applied to a visible argument?
isNextArgVisible :: TcType -> Bool
isNextArgVisible :: Type -> Bool
isNextArgVisible Type
ty
  | Just (TyBinder
bndr, Type
_) <- Type -> Maybe (TyBinder, Type)
tcSplitPiTy_maybe Type
ty = TyBinder -> Bool
isVisibleBinder TyBinder
bndr
  | Bool
otherwise                              = Bool
True
    -- this second case might happen if, say, we have an unzonked TauTv.
    -- But TauTvs can't range over types that take invisible arguments