    {-# 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 (Type -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Type
    ty)
      ppr (Infer InferResult
    ir) = InferResult -> SDoc
    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 (Unique -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Unique
    u SDoc -> SDoc -> SDoc
    <> SDoc
    comma SDoc -> SDoc -> SDoc
    <> TcLevel -> 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 (ExpType -> SyntaxOpType)
    -> (Type -> ExpType) -> Type -> SyntaxOpType
    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 = (SyntaxOpType -> SyntaxOpType -> SyntaxOpType)
    -> SyntaxOpType -> [SyntaxOpType] -> SyntaxOpType
    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
    <> TcLevel -> 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
    <> TcLevel -> 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 })
      = MetaInfo -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr MetaInfo
    info SDoc -> SDoc -> SDoc
    <> SDoc
    colon SDoc -> SDoc -> SDoc
    <> TcLevel -> 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 variable 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
    <+> Type -> 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
    (TcLevel -> TcLevel -> Bool)
    -> (TcLevel -> TcLevel -> Bool) -> Eq TcLevel
    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
    Eq TcLevel
    -> (TcLevel -> TcLevel -> Ordering)
    -> (TcLevel -> TcLevel -> Bool)
    -> (TcLevel -> TcLevel -> Bool)
    -> (TcLevel -> TcLevel -> Bool)
    -> (TcLevel -> TcLevel -> Bool)
    -> (TcLevel -> TcLevel -> TcLevel)
    -> (TcLevel -> TcLevel -> TcLevel)
    -> Ord 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.

    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 Arity -> Arity -> Arity
    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 Arity -> Arity -> Arity
    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 Arity -> Arity -> Bool
    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 Arity -> Arity -> Bool
    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 Arity -> Arity -> Bool
    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 Arity -> Arity -> Bool
    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
      = (Var -> TcLevel -> TcLevel) -> TcLevel -> DVarSet -> TcLevel
    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) = Arity -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Arity
    us

    promoteSkolem :: TcLevel -> TcTyVar -> TcTyVar
    promoteSkolem :: TcLevel -> Var -> Var
    promoteSkolem TcLevel
    tclvl Var
    skol
      | TcLevel
    tclvl TcLevel -> TcLevel -> Bool
    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 TcLevel -> TcLevel -> Bool
    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
    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
    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 = (TCvSubst -> Var -> (TCvSubst, Var))
    -> TCvSubst -> [Var] -> (TCvSubst, [Var])
    forall (t :: * -> *) a b c.
    Traversable t =>
    (a -> b -> (a, c)) -> a -> t b -> (a, t c)
    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 = ((Bool, TyCon, [Type]) -> (TyCon, [Type]))
    -> [(Bool, TyCon, [Type])] -> [(TyCon, [Type])]
    forall a b. (a -> b) -> [a] -> [b]
    map (\(Bool
    _,TyCon
    b,[Type]
    c) -> (TyCon
    b,[Type]
    c)) ([(Bool, TyCon, [Type])] -> [(TyCon, [Type])])
    -> (Type -> [(Bool, TyCon, [Type])]) -> Type -> [(TyCon, [Type])]
    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, Arity -> [Type] -> [Type]
    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 (TyCoVarBinder -> Type
    forall argf. VarBndr Var argf -> Type
    binderType TyCoVarBinder
    bndr)
                                             [(Bool, TyCon, [Type])]
    -> [(Bool, TyCon, [Type])] -> [(Bool, TyCon, [Type])]
    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
                                             [(Bool, TyCon, [Type])]
    -> [(Bool, TyCon, [Type])] -> [(Bool, TyCon, [Type])]
    forall a. [a] -> [a] -> [a]
    ++ Bool -> Type -> [(Bool, TyCon, [Type])]
    go Bool
    is_invis_arg Type
    ty1
                                             [(Bool, TyCon, [Type])]
    -> [(Bool, TyCon, [Type])] -> [(Bool, TyCon, [Type])]
    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
             [(Bool, TyCon, [Type])]
    -> [(Bool, TyCon, [Type])] -> [(Bool, TyCon, [Type])]
    forall a. [a] -> [a] -> [a]
    ++ [[(Bool, TyCon, [Type])]] -> [(Bool, TyCon, [Type])]
    forall (t :: * -> *) a. Foldable t => t [a] -> [a]
    concat ((ArgFlag -> Type -> [(Bool, TyCon, [Type])])
    -> [ArgFlag] -> [Type] -> [[(Bool, TyCon, [Type])]]
    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 [[(Bool, TyCon, [Type])]] -> [(Bool, TyCon, [Type])]
    forall (t :: * -> *) a. Foldable t => t [a] -> [a]
    concat ([[(Bool, TyCon, [Type])]] -> [(Bool, TyCon, [Type])])
    -> [[(Bool, TyCon, [Type])]] -> [(Bool, TyCon, [Type])]
    forall a b. (a -> b) -> a -> b
    $ (Type -> [(Bool, TyCon, [Type])])
    -> [Type] -> [[(Bool, TyCon, [Type])]]
    forall a b. (a -> b) -> [a] -> [b]
    map (Bool -> Type -> [(Bool, TyCon, [Type])]
    tcTyFamInstsAndVisX Bool
    True)         [Type]
    invis_tys
               [[(Bool, TyCon, [Type])]]
    -> [[(Bool, TyCon, [Type])]] -> [[(Bool, TyCon, [Type])]]
    forall a. [a] -> [a] -> [a]
    ++ (Type -> [(Bool, TyCon, [Type])])
    -> [Type] -> [[(Bool, TyCon, [Type])]]
    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 = [(TyCon, [Type])] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null ([(TyCon, [Type])] -> Bool)
    -> (Type -> [(TyCon, [Type])]) -> Type -> Bool
    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
    Type -> Type
    getRuntimeRep Type
    arg -- forgetting these causes #17024
                res_rep :: Type
    res_rep = HasDebugCallStack => Type -> Type
    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` TyCoVarBinder -> Var
    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 = (Type -> Bool) -> [Type] -> Bool
    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 = ((Role, Type) -> Bool) -> [(Role, Type)] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any (VarSet -> (Role, Type) -> Bool
    go_arg VarSet
    bvs)
                                  (TyCon -> [Role]
    tyConRolesRepresentational TyCon
    tc [Role] -> [Type] -> [(Role, Type)]
    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 (Bool -> Bool) -> (TyCon -> Bool) -> TyCon -> Bool
    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 (Bool -> Bool) -> (TyCon -> Bool) -> TyCon -> Bool
    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
    _) = TyCoFolder VarSet (Endo VarSet)
    -> VarSet
    -> (Type -> Endo VarSet, [Type] -> Endo VarSet,
        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
    _ -> String -> SDoc -> MetaInfo
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "metaTyVarInfo" (Var -> SDoc
    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
    _ -> String -> SDoc -> TcLevel
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "metaTyVarTcLevel" (Var -> SDoc
    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 } -> TcLevel -> Maybe TcLevel
    forall a. a -> Maybe a
    Just TcLevel
    tclvl
          TcTyVarDetails
    _                            -> Maybe TcLevel
    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
    _ -> String -> SDoc -> IORef MetaDetails
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "metaTyVarRef" (Var -> SDoc
    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
    _ -> String -> SDoc -> Var
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "metaTyVarTcLevel" (Var -> SDoc
    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
      = (NonEmpty (Name, Var) -> [(Name, Name)])
    -> [NonEmpty (Name, Var)] -> [(Name, Name)]
    forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
    concatMap NonEmpty (Name, Var) -> [(Name, Name)]
    forall {b} {b}. NonEmpty (b, b) -> [(b, b)]
    mk_result_prs ([NonEmpty (Name, Var)] -> [(Name, Name)])
    -> [NonEmpty (Name, Var)] -> [(Name, Name)]
    forall a b. (a -> b) -> a -> b
    $
        ((Name, Var) -> (Name, Var) -> Bool)
    -> [(Name, Var)] -> [NonEmpty (Name, Var)]
    forall a. (a -> a -> Bool) -> [a] -> [NonEmpty a]
    findDupsEq (Name, Var) -> (Name, Var) -> Bool
    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 a -> a -> Bool
    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) = ((b, b) -> (b, b)) -> [(b, b)] -> [(b, b)]
    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 (ArgFlag -> [Var] -> [TyCoVarBinder]
    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 (ArgFlag -> [Var] -> [TyCoVarBinder]
    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)            = Var -> OccName
    forall a. NamedThing a => a -> OccName
    getOccName Var
    tv
    getDFunTyKey (TyConApp TyCon
    tc [Type]
    _)         = TyCon -> OccName
    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 {})              = TyCon -> OccName
    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
    _)        = String -> SDoc -> OccName
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "getDFunTyKey" (Type -> SDoc
    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 (Integer -> String
    forall a. Show a => a -> String
    show Integer
    n)
    getDFunTyLitKey (StrTyLit FastString
    n) = NameSpace -> String -> OccName
    mkOccName NameSpace
    Name.varName (FastString -> String
    forall a. Show a => a -> String
    show FastString
    n)  -- hm
    getDFunTyLitKey (CharTyLit Char
    n) = NameSpace -> String -> OccName
    mkOccName NameSpace
    Name.varName (Char -> String
    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
    _                = Maybe (TyCoVarBinder, 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
    tvVar -> [Var] -> [Var]
    forall 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 = ([Var] -> [Var]
    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 })
      = (Type, Type) -> Maybe (Type, Type)
    forall a. a -> Maybe a
    Just (Type
    arg, Type
    res)
    tcSplitPredFunTy_maybe Type
    _
      = Maybe (Type, 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
    predType -> [Type] -> [Type]
    forall a. a -> [a] -> [a]
    :[Type]
    ts)
              Maybe (Type, Type)
    Nothing         -> ([Type] -> [Type]
    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 @ForAllTy@s
    -- as possible. For example, given this type synonym:
    --
    -- @
    -- type Traversal s t a b = forall f. Applicative f => (a -> f b) -> s -> f t
    -- @
    --
    -- if you called @tcSplitSigmaTy@ on this type:
    --
    -- @
    -- forall s t a b. Each s t a b => Traversal s t a b
    -- @
    --
    -- then it would return @([s,t,a,b], [Each s t a b], Traversal s t a b)@. But
    -- if you instead called @tcSplitNestedSigmaTys@ on the type, it would return
    -- @([s,t,a,b,f], [Each s t a b, Applicative f], (a -> f b) -> s -> f t)@.
    tcSplitNestedSigmaTys :: Type -> ([TyVar], ThetaType, Type)
    -- NB: This is basically a pure version of topInstantiate (from Inst) 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.
      | ([Var]
    tvs1, [Type]
    theta1, Type
    rho1) <- Type -> ([Var], [Type], Type)
    tcSplitSigmaTy Type
    ty
      , Bool -> Bool
    not ([Var] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Var]
    tvs1 Bool -> Bool -> Bool
    && [Type] -> 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 [Var] -> [Var] -> [Var]
    forall a. [a] -> [a] -> [a]
    ++ [Var]
    tvs2, [Type]
    theta1 [Type] -> [Type] -> [Type]
    forall a. [a] -> [a] -> [a]
    ++ [Type]
    theta2, Type
    rho2)
        -- If there's no forall, we're done.
      | Bool
    otherwise = ([], [], Type
    ty)

    -----------------------
    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 -> String -> SDoc -> TyCon
    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]
    _)
      = TyCon -> Maybe TyCon
    forall a. a -> Maybe a
    Just TyCon
    tc
    tcTyConAppTyCon_maybe (FunTy { ft_af :: Type -> AnonArgFlag
    ft_af = AnonArgFlag
    VisArg })
      = TyCon -> Maybe TyCon
    forall a. a -> Maybe a
    Just TyCon
    funTyCon  -- (=>) is /not/ a TyCon in its own right
                       -- C.f. tcRepSplitAppTy_maybe
    tcTyConAppTyCon_maybe Type
    _
      = Maybe TyCon
    forall a. Maybe a
    Nothing

    tcTyConAppArgs :: Type -> [Type]
    tcTyConAppArgs :: Type -> [Type]
    tcTyConAppArgs Type
    ty = case HasCallStack => Type -> Maybe (TyCon, [Type])
    Type -> Maybe (TyCon, [Type])
    tcSplitTyConApp_maybe Type
    ty of
                            Just (TyCon
    _, [Type]
    args) -> [Type]
    args
                            Maybe (TyCon, [Type])
    Nothing        -> String -> SDoc -> [Type]
    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])
    Type -> Maybe (TyCon, [Type])
    tcSplitTyConApp_maybe Type
    ty of
                            Just (TyCon, [Type])
    stuff -> (TyCon, [Type])
    stuff
                            Maybe (TyCon, [Type])
    Nothing    -> String -> SDoc -> (TyCon, [Type])
    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
    argScaled Type -> [Scaled Type] -> [Scaled Type]
    forall 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 = (Scaled Type, Type) -> Maybe (Scaled Type, Type)
    forall a. a -> Maybe a
    Just (Type -> Type -> Scaled Type
    forall a. Type -> a -> Scaled a
    Scaled Type
    w Type
    arg, Type
    res)
    tcSplitFunTy_maybe Type
    _ = Maybe (Scaled Type, 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 Arity -> Arity -> Bool
    forall a. Eq a => a -> a -> Bool
    == Arity
    0
     = ([Scaled Type], Type) -> Either Arity ([Scaled Type], Type)
    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
    nArity -> Arity -> Arity
    forall a. Num a => a -> a -> a
    -Arity
    1) Type
    res of
         Left Arity
    m            -> Arity -> Either Arity ([Scaled Type], Type)
    forall a b. a -> Either a b
    Left Arity
    m
         Right ([Scaled Type]
    args,Type
    body) -> ([Scaled Type], Type) -> Either Arity ([Scaled Type], Type)
    forall a b. b -> Either a b
    Right (Scaled Type
    argScaled Type -> [Scaled Type] -> [Scaled Type]
    forall a. a -> [a] -> [a]
    :[Scaled Type]
    args, Type
    body)
     | Bool
    otherwise
     = Arity -> Either Arity ([Scaled Type], Type)
    forall a b. a -> Either a b
    Left Arity
    n

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

    tcFunResultTy :: Type -> Type
    tcFunResultTy :: Type -> Type
    tcFunResultTy Type
    ty = (Scaled Type, Type) -> Type
    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
      = String -> SDoc -> Type
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "tcFunResultTyN" (Arity -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Arity
    n SDoc -> SDoc -> SDoc
    <+> Type -> 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    -> String -> SDoc -> (Type, Type)
    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
    argType -> [Type] -> [Type]
    forall 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 = [Type] -> Arity
    forall (t :: * -> *) a. Foldable t => t a -> Arity
    length ([Type] -> Arity) -> (Type -> [Type]) -> Type -> Arity
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (Type, [Type]) -> [Type]
    forall a b. (a, b) -> b
    snd ((Type, [Type]) -> [Type])
    -> (Type -> (Type, [Type])) -> Type -> [Type]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . HasDebugCallStack => Type -> (Type, [Type])
    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) = (Var, KindCoercion) -> Maybe (Var, KindCoercion)
    forall a. a -> Maybe a
    Just (Var
    tv, KindCoercion
    co)
    tcGetCastedTyVar_maybe (TyVarTy Var
    tv)             = (Var, KindCoercion) -> Maybe (Var, KindCoercion)
    forall a. a -> Maybe a
    Just (Var
    tv, Type -> KindCoercion
    mkNomReflCo (Var -> Type
    tyVarKind Var
    tv))
    tcGetCastedTyVar_maybe Type
    _                        = Maybe (Var, KindCoercion)
    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)   = Var -> Maybe Var
    forall a. a -> Maybe a
    Just Var
    tv
    tcGetTyVar_maybe Type
    _              = Maybe Var
    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 -> String -> SDoc -> Var
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    msg (Type -> SDoc
    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, (Scaled Type -> Type) -> [Scaled Type] -> [Type]
    forall a b. (a -> b) -> [a] -> [b]
    map Scaled Type -> Type
    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])
    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
      = String -> SDoc -> ([Var], Type, Type)
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "tcSplitMethodTy" (Type -> SDoc
    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
    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
    Type -> Type
    tcTypeKind Type
    ty1
        ki2 :: Type
    ki2 = HasDebugCallStack => Type -> Type
    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 TyCon -> TyCon -> Bool
    forall a. Eq a => a -> a -> Bool
    == TyCon
    tc2 Bool -> Bool -> Bool
    &&
        [Bool] -> Bool
    forall (t :: * -> *). Foldable t => t Bool -> Bool
    and ((Type -> Type -> Bool) -> [Type] -> [Type] -> [Bool]
    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
    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 TyCon -> TyCon -> Bool
    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 Var -> Var -> Bool
    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 TyLit -> TyLit -> Bool
    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.
        go RnEnv2
    env (FunTy AnonArgFlag
    _ Type
    w1 Type
    arg1 Type
    res1) (FunTy AnonArgFlag
    _ Type
    w2 Type
    arg2 Type
    res2)
          = RnEnv2 -> Type -> Type -> Bool
    go RnEnv2
    env Type
    w1 Type
    w2 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
        go RnEnv2
    env Type
    ty (FunTy AnonArgFlag
    _ Type
    w Type
    arg Type
    res) = RnEnv2 -> Type -> Type -> Type -> Type -> Bool
    eqFunTy RnEnv2
    env Type
    w Type
    arg Type
    res Type
    ty
        go RnEnv2
    env (FunTy AnonArgFlag
    _ Type
    w Type
    arg Type
    res) Type
    ty = RnEnv2 -> Type -> Type -> Type -> Type -> Bool
    eqFunTy RnEnv2
    env Type
    w Type
    arg Type
    res Type
    ty

          -- 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 TyCon -> TyCon -> Bool
    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 [Bool] -> [Bool] -> [Bool]
    forall a. [a] -> [a] -> [a]
    ++ Bool -> [Bool]
    forall a. a -> [a]
    repeat Bool
    False    -- Ignore invisibles
                  | Bool
    otherwise = Bool -> [Bool]
    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  = (TyConBinder -> Bool) -> [TyConBinder] -> [Bool]
    forall a b. (a -> b) -> [a] -> [b]
    map TyConBinder -> Bool
    forall tv. VarBndr tv TyConBndrVis -> Bool
    isInvisibleTyConBinder [TyConBinder]
    bndrs

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

        -- @eqFunTy w arg res ty@ is True when @ty@ equals @FunTy w arg res@. This is
        -- sometimes hard to know directly because @ty@ might have some casts
        -- obscuring the FunTy. And 'splitAppTy' is difficult because we can't
        -- always extract a RuntimeRep (see Note [xyz]) if the kind of the arg or
        -- res is unzonked. Thus this function, which handles this
        -- corner case.
        eqFunTy :: RnEnv2 -> Mult -> Type -> Type -> Type -> Bool
                   -- Last arg is /not/ FunTy
        eqFunTy :: RnEnv2 -> Type -> Type -> Type -> Type -> Bool
    eqFunTy RnEnv2
    env Type
    w Type
    arg Type
    res ty :: Type
    ty@(AppTy{}) = Type -> [Type] -> Bool
    get_args Type
    ty []
          where
            get_args :: Type -> [Type] -> Bool
            get_args :: Type -> [Type] -> Bool
    get_args (AppTy Type
    f Type
    x)       [Type]
    args = Type -> [Type] -> Bool
    get_args Type
    f (Type
    xType -> [Type] -> [Type]
    forall a. a -> [a] -> [a]
    :[Type]
    args)
            get_args (CastTy Type
    t KindCoercion
    _)      [Type]
    args = Type -> [Type] -> Bool
    get_args Type
    t [Type]
    args
            get_args (TyConApp TyCon
    tc [Type]
    tys) [Type]
    args
              | TyCon
    tc TyCon -> TyCon -> Bool
    forall a. Eq a => a -> a -> Bool
    == TyCon
    funTyCon
              , [Type
    w', Type
    _, Type
    _, Type
    arg', Type
    res'] <- [Type]
    tys [Type] -> [Type] -> [Type]
    forall a. [a] -> [a] -> [a]
    ++ [Type]
    args
              = RnEnv2 -> Type -> Type -> Bool
    go RnEnv2
    env Type
    w Type
    w' Bool -> Bool -> Bool
    && RnEnv2 -> Type -> Type -> Bool
    go RnEnv2
    env Type
    arg Type
    arg' Bool -> Bool -> Bool
    && RnEnv2 -> Type -> Type -> Bool
    go RnEnv2
    env Type
    res Type
    res'
            get_args Type
    _ [Type]
    _    = Bool
    False
        eqFunTy RnEnv2
    _ Type
    _ Type
    _ Type
    _ Type
    _   = Bool
    False
    {-# 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) -> (Type -> Bool) -> [Type] -> Bool
    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         = (Type -> Bool) -> [Type] -> Bool
    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
        (Type -> Maybe Type) -> [Type] -> [Type]
    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]
                -> Maybe Type
    forall a. Maybe a
    Nothing

                | Class -> Bool
    isIPClass Class
    cls
                -> Type -> Maybe Type
    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
                -> Type -> Maybe Type
    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
                -> Type -> Maybe Type
    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
                -> Type -> Maybe Type
    forall a. a -> Maybe a
    Just Type
    pred

              Pred
    _ -> Maybe Type
    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])
    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 -> (Class, [Type]) -> Maybe (Class, [Type])
    forall a. a -> Maybe a
    Just (Class
    eqClass,        [Type
    k1,     Type
    ty1, Type
    ty2])
                 | Bool
    otherwise -> (Class, [Type]) -> Maybe (Class, [Type])
    forall a. a -> Maybe a
    Just (Class
    heqClass,       [Type
    k1, Type
    k2, Type
    ty1, Type
    ty2])
          EqRel
    ReprEq | Bool
    homo_kind -> (Class, [Type]) -> Maybe (Class, [Type])
    forall a. a -> Maybe a
    Just (Class
    coercibleClass, [Type
    k1,     Type
    ty1, Type
    ty2])
                 | Bool
    otherwise -> Maybe (Class, [Type])
    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
    Type -> Type
    tcTypeKind Type
    ty1
       k2 :: Type
    k2 = HasDebugCallStack => Type -> Type
    Type -> Type
    tcTypeKind Type
    ty2
       homo_kind :: Bool
    homo_kind = Type
    k1 HasDebugCallStack => Type -> Type -> Bool
    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
      = (Type -> Bool) -> [Type] -> [Type]
    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
         = [a] -> [a]
    forall a. [a] -> [a]
    reverse ((PredWithSCs a -> a) -> [PredWithSCs a] -> [a]
    forall a b. (a -> b) -> [a] -> [b]
    map PredWithSCs a -> a
    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
    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 PredWithSCs a -> [PredWithSCs a] -> [PredWithSCs a]
    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 = [Bool] -> Bool
    forall (t :: * -> *). Foldable t => t Bool -> Bool
    or [ Type
    p HasDebugCallStack => Type -> Type -> Bool
    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 Type -> [Type] -> [Type]
    forall a. a -> [a] -> [a]
    : Type -> [Type]
    eq_extras Type
    pred [Type] -> [Type] -> [Type]
    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 Class -> Unique -> Bool
    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 Class -> Unique -> Bool
    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 Type -> [Type] -> [Type]
    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]
    TCvSubst -> [Type] -> [Type]
    substTheta ([Var] -> [Type] -> TCvSubst
    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
    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])
    Type -> Maybe (TyCon, [Type])
    tcSplitTyConApp_maybe Type
    ty of
          Just (TyCon
    tc, [Type
    arg_ty]) -> TyCon
    tc TyCon -> TyCon -> Bool
    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 TyCon -> Unique -> Bool
    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
      = Maybe FastString
    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])
    Type -> Maybe (TyCon, [Type])
    tcSplitTyConApp_maybe Type
    ty of
                            Just (TyCon
    tc, [Type]
    _) -> Unique
    uniq Unique -> Unique -> Bool
    forall a. Eq a => a -> a -> Bool
    == TyCon -> Unique
    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])
    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])
    Type -> Maybe (TyCon, [Type])
    tcSplitTyConApp_maybe Type
    ty of
            Just (TyCon
    io_tycon, [Type
    io_res_ty])
             | TyCon
    io_tycon TyCon -> Unique -> Bool
    forall a. Uniquable a => a -> Unique -> Bool
    `hasKey` Unique
    ioTyConKey ->
                (TyCon, Type) -> Maybe (TyCon, Type)
    forall a. a -> Maybe a
    Just (TyCon
    io_tycon, Type
    io_res_ty)
            Maybe (TyCon, [Type])
    _ ->
                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])
    Type -> Maybe (TyCon, [Type])
    splitTyConApp_maybe Type
    ty
        , TyCon -> Unique
    tyConUnique TyCon
    tc Unique -> [Unique] -> Bool
    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
    <+> Type -> 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 TyCon -> Validity
    forall {a}. Uniquable a => a -> Validity
    ok Type
    ty
      where
        ok :: a -> Validity
    ok a
    tc | a
    tc a -> Unique -> Bool
    forall a. Uniquable a => a -> Unique -> Bool
    `hasKey` Unique
    funPtrTyConKey Bool -> Bool -> Bool
    || a
    tc a -> Unique -> Bool
    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])
    Type -> Maybe (TyCon, [Type])
    splitTyConApp_maybe Type
    ty
      = TyCon
    tc TyCon -> Unique -> Bool
    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])
    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 (TyCon -> [Type] -> SDoc
    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 (Type -> SDoc
    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 (Type -> SDoc
    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
          | t a -> Bool
    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 (a -> SDoc
    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 TyCon -> TyCon -> Bool
    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 TyCon -> TyCon -> Bool
    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 TyCon -> TyCon -> Bool
    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 ([PrimRep] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null (HasDebugCallStack => TyCon -> [PrimRep]
    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
       | TyCon -> Unique
    forall a. Uniquable a => a -> Unique
    getUnique TyCon
    tc Unique -> [Unique] -> Bool
    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 ([PrimRep] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null (HasDebugCallStack => TyCon -> [PrimRep]
    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) TypeSize -> TypeSize -> TypeSize
    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 TypeSize -> TypeSize -> TypeSize
    forall a. Num a => a -> a -> a
    + Type -> TypeSize
    go Type
    arg TypeSize -> TypeSize -> TypeSize
    forall a. Num a => a -> a -> a
    + Type -> TypeSize
    go Type
    res TypeSize -> TypeSize -> TypeSize
    forall a. Num a => a -> a -> a
    + TypeSize
    1
        go (AppTy Type
    fun Type
    arg)           = Type -> TypeSize
    go Type
    fun TypeSize -> TypeSize -> TypeSize
    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) TypeSize -> TypeSize -> TypeSize
    forall a. Num a => a -> a -> a
    + Type -> TypeSize
    go Type
    ty TypeSize -> TypeSize -> TypeSize
    forall a. Num a => a -> a -> a
    + TypeSize
    1
            | Bool
    otherwise              = Type -> TypeSize
    go Type
    ty TypeSize -> TypeSize -> TypeSize
    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 = [TypeSize] -> TypeSize
    forall (t :: * -> *) a. (Foldable t, Num a) => t a -> a
    sum ((Type -> TypeSize) -> [Type] -> [TypeSize]
    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 [Bool] -> [Bool] -> [Bool]
    forall a. [a] -> [a] -> [a]
    ++ [Bool]
    tc_return_kind_viss [Bool] -> [Bool] -> [Bool]
    forall a. [a] -> [a] -> [a]
    ++ Bool -> [Bool]
    forall a. a -> [a]
    repeat Bool
    True
      where
        tc_binder_viss :: [Bool]
    tc_binder_viss      = (TyConBinder -> Bool) -> [TyConBinder] -> [Bool]
    forall a b. (a -> b) -> [a] -> [b]
    map TyConBinder -> Bool
    forall tv. VarBndr tv TyConBndrVis -> Bool
    isVisibleTyConBinder (TyCon -> [TyConBinder]
    tyConBinders TyCon
    tc)
        tc_return_kind_viss :: [Bool]
    tc_return_kind_viss = (TyBinder -> Bool) -> [TyBinder] -> [Bool]
    forall a b. (a -> b) -> [a] -> [b]
    map TyBinder -> Bool
    isVisibleBinder (([TyBinder], Type) -> [TyBinder]
    forall a b. (a, b) -> a
    fst (([TyBinder], Type) -> [TyBinder])
    -> ([TyBinder], Type) -> [TyBinder]
    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 [Bool] -> Arity -> Bool
    forall a. Outputable a => [a] -> Arity -> a
    `getNth` [Type] -> Arity
    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