{-

This module defines types and simple operations over constraints,
as used in the type-checker and constraint solver.

-}

{-# LANGUAGE CPP, GeneralizedNewtypeDeriving #-}

module Constraint (
        -- QCInst
        QCInst(..), isPendingScInst,

        -- Canonical constraints
        Xi, Ct(..), Cts, emptyCts, andCts, andManyCts, pprCts,
        singleCt, listToCts, ctsElts, consCts, snocCts, extendCtsList,
        isEmptyCts, isCTyEqCan, isCFunEqCan,
        isPendingScDict, superClassesMightHelp, getPendingWantedScs,
        isCDictCan_Maybe, isCFunEqCan_maybe,
        isCNonCanonical, isWantedCt, isDerivedCt,
        isGivenCt, isHoleCt, isOutOfScopeCt, isExprHoleCt, isTypeHoleCt,
        isUserTypeErrorCt, getUserTypeErrorMsg,
        ctEvidence, ctLoc, setCtLoc, ctPred, ctFlavour, ctEqRel, ctOrigin,
        ctEvId, mkTcEqPredLikeEv,
        mkNonCanonical, mkNonCanonicalCt, mkGivens,
        mkIrredCt, mkInsolubleCt,
        ctEvPred, ctEvLoc, ctEvOrigin, ctEvEqRel,
        ctEvExpr, ctEvTerm, ctEvCoercion, ctEvEvId,
        tyCoVarsOfCt, tyCoVarsOfCts,
        tyCoVarsOfCtList, tyCoVarsOfCtsList,

        WantedConstraints(..), insolubleWC, emptyWC, isEmptyWC,
        isSolvedWC, andWC, unionsWC, mkSimpleWC, mkImplicWC,
        addInsols, insolublesOnly, addSimples, addImplics,
        tyCoVarsOfWC, dropDerivedWC, dropDerivedSimples,
        tyCoVarsOfWCList, insolubleCt, insolubleEqCt,
        isDroppableCt, insolubleImplic,
        arisesFromGivens,

        Implication(..), implicationPrototype,
        ImplicStatus(..), isInsolubleStatus, isSolvedStatus,
        SubGoalDepth, initialSubGoalDepth, maxSubGoalDepth,
        bumpSubGoalDepth, subGoalDepthExceeded,
        CtLoc(..), ctLocSpan, ctLocEnv, ctLocLevel, ctLocOrigin,
        ctLocTypeOrKind_maybe,
        ctLocDepth, bumpCtLocDepth, isGivenLoc,
        setCtLocOrigin, updateCtLocOrigin, setCtLocEnv, setCtLocSpan,
        pprCtLoc,

        -- CtEvidence
        CtEvidence(..), TcEvDest(..),
        mkKindLoc, toKindLoc, mkGivenLoc,
        isWanted, isGiven, isDerived, isGivenOrWDeriv,
        ctEvRole,

        wrapType, wrapTypeWithImplication,

        CtFlavour(..), ShadowInfo(..), ctEvFlavour,
        CtFlavourRole, ctEvFlavourRole, ctFlavourRole,
        eqCanRewrite, eqCanRewriteFR, eqMayRewriteFR,
        eqCanDischargeFR,
        funEqCanDischarge, funEqCanDischargeF,

        -- Pretty printing
        pprEvVarTheta,
        pprEvVars, pprEvVarWithType,

        -- holes
        Hole(..), holeOcc,

  )
  where

#include "GhclibHsVersions.h"

import GhcPrelude

import {-# SOURCE #-} TcRnTypes ( TcLclEnv, setLclEnvTcLevel, getLclEnvTcLevel
                                , setLclEnvLoc, getLclEnvLoc )

import GHC.Hs.Expr ( UnboundVar(..), unboundVarOcc )
import Predicate
import Type
import Coercion
import Class
import TyCon
import Var
import Id

import TcType
import TcEvidence
import TcOrigin

import CoreSyn

import TyCoPpr
import OccName
import FV
import VarSet
import DynFlags
import BasicTypes

import Outputable
import SrcLoc
import Bag
import Util

import Control.Monad ( msum )

{-
************************************************************************
*                                                                      *
*                       Canonical constraints                          *
*                                                                      *
*   These are the constraints the low-level simplifier works with      *
*                                                                      *
************************************************************************
-}

-- The syntax of xi (ξ) types:
-- xi ::= a | T xis | xis -> xis | ... | forall a. tau
-- Two important notes:
--      (i) No type families, unless we are under a ForAll
--      (ii) Note that xi types can contain unexpanded type synonyms;
--           however, the (transitive) expansions of those type synonyms
--           will not contain any type functions, unless we are under a ForAll.
-- We enforce the structure of Xi types when we flatten (TcCanonical)

type Xi = Type       -- In many comments, "xi" ranges over Xi

type Cts = Bag Ct

data Ct
  -- Atomic canonical constraints
  = CDictCan {  -- e.g.  Num xi
      Ct -> CtEvidence
cc_ev     :: CtEvidence, -- See Note [Ct/evidence invariant]

      Ct -> Class
cc_class  :: Class,
      Ct -> [Xi]
cc_tyargs :: [Xi],   -- cc_tyargs are function-free, hence Xi

      Ct -> Bool
cc_pend_sc :: Bool   -- See Note [The superclass story] in TcCanonical
                           -- True <=> (a) cc_class has superclasses
                           --          (b) we have not (yet) added those
                           --              superclasses as Givens
    }

  | CIrredCan {  -- These stand for yet-unusable predicates
      cc_ev    :: CtEvidence,   -- See Note [Ct/evidence invariant]
      Ct -> Bool
cc_insol :: Bool   -- True  <=> definitely an error, can never be solved
                         -- False <=> might be soluble

        -- For the might-be-soluble case, the ctev_pred of the evidence is
        -- of form   (tv xi1 xi2 ... xin)   with a tyvar at the head
        --      or   (tv1 ~ ty2)   where the CTyEqCan  kind invariant fails
        --      or   (F tys ~ ty)  where the CFunEqCan kind invariant fails
        -- See Note [CIrredCan constraints]

        -- The definitely-insoluble case is for things like
        --    Int ~ Bool      tycons don't match
        --    a ~ [a]         occurs check
    }

  | CTyEqCan {  -- tv ~ rhs
       -- Invariants:
       --   * See Note [inert_eqs: the inert equalities] in TcSMonad
       --   * tv not in tvs(rhs)   (occurs check)
       --   * If tv is a TauTv, then rhs has no foralls
       --       (this avoids substituting a forall for the tyvar in other types)
       --   * tcTypeKind ty `tcEqKind` tcTypeKind tv; Note [Ct kind invariant]
       --   * rhs may have at most one top-level cast
       --   * rhs (perhaps under the one cast) is *almost function-free*,
       --       See Note [Almost function-free]
       --   * If the equality is representational, rhs has no top-level newtype
       --     See Note [No top-level newtypes on RHS of representational
       --     equalities] in TcCanonical
       --   * If rhs (perhaps under the cast) is also a tv, then it is oriented
       --     to give best chance of
       --     unification happening; eg if rhs is touchable then lhs is too
      cc_ev     :: CtEvidence, -- See Note [Ct/evidence invariant]
      Ct -> TcTyVar
cc_tyvar  :: TcTyVar,
      Ct -> Xi
cc_rhs    :: TcType,     -- Not necessarily function-free (hence not Xi)
                               -- See invariants above

      Ct -> EqRel
cc_eq_rel :: EqRel       -- INVARIANT: cc_eq_rel = ctEvEqRel cc_ev
    }

  | CFunEqCan {  -- F xis ~ fsk
       -- Invariants:
       --   * isTypeFamilyTyCon cc_fun
       --   * tcTypeKind (F xis) = tyVarKind fsk; Note [Ct kind invariant]
       --   * always Nominal role
      cc_ev     :: CtEvidence,  -- See Note [Ct/evidence invariant]
      Ct -> TyCon
cc_fun    :: TyCon,       -- A type function

      cc_tyargs :: [Xi],        -- cc_tyargs are function-free (hence Xi)
        -- Either under-saturated or exactly saturated
        --    *never* over-saturated (because if so
        --    we should have decomposed)

      Ct -> TcTyVar
cc_fsk    :: TcTyVar  -- [G]  always a FlatSkolTv
                            -- [W], [WD], or [D] always a FlatMetaTv
        -- See Note [The flattening story] in TcFlatten
    }

  | CNonCanonical {        -- See Note [NonCanonical Semantics] in TcSMonad
      cc_ev  :: CtEvidence
    }

  | CHoleCan {             -- See Note [Hole constraints]
       -- Treated as an "insoluble" constraint
       -- See Note [Insoluble constraints]
      cc_ev   :: CtEvidence,
      Ct -> Hole
cc_hole :: Hole
    }

  | CQuantCan QCInst       -- A quantified constraint
      -- NB: I expect to make more of the cases in Ct
      --     look like this, with the payload in an
      --     auxiliary type

------------
data QCInst  -- A much simplified version of ClsInst
             -- See Note [Quantified constraints] in TcCanonical
  = QCI { QCInst -> CtEvidence
qci_ev   :: CtEvidence -- Always of type forall tvs. context => ty
                                 -- Always Given
        , QCInst -> [TcTyVar]
qci_tvs  :: [TcTyVar]  -- The tvs
        , QCInst -> Xi
qci_pred :: TcPredType -- The ty
        , QCInst -> Bool
qci_pend_sc :: Bool    -- Same as cc_pend_sc flag in CDictCan
                                 -- Invariant: True => qci_pred is a ClassPred
    }

instance Outputable QCInst where
  ppr :: QCInst -> SDoc
ppr (QCI { qci_ev :: QCInst -> CtEvidence
qci_ev = CtEvidence
ev }) = CtEvidence -> SDoc
forall a. Outputable a => a -> SDoc
ppr CtEvidence
ev

------------
-- | An expression or type hole
data Hole = ExprHole UnboundVar
            -- ^ Either an out-of-scope variable or a "true" hole in an
            -- expression (TypedHoles)
          | TypeHole OccName
            -- ^ A hole in a type (PartialTypeSignatures)

instance Outputable Hole where
  ppr :: Hole -> SDoc
ppr (ExprHole UnboundVar
ub)  = UnboundVar -> SDoc
forall a. Outputable a => a -> SDoc
ppr UnboundVar
ub
  ppr (TypeHole OccName
occ) = String -> SDoc
text String
"TypeHole" SDoc -> SDoc -> SDoc
<> SDoc -> SDoc
parens (OccName -> SDoc
forall a. Outputable a => a -> SDoc
ppr OccName
occ)

holeOcc :: Hole -> OccName
holeOcc :: Hole -> OccName
holeOcc (ExprHole UnboundVar
uv)  = UnboundVar -> OccName
unboundVarOcc UnboundVar
uv
holeOcc (TypeHole OccName
occ) = OccName
occ

{- Note [Hole constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~
CHoleCan constraints are used for two kinds of holes,
distinguished by cc_hole:

  * For holes in expressions (includings variables not in scope)
    e.g.   f x = g _ x

  * For holes in type signatures
    e.g.   f :: _ -> _
           f x = [x,True]

Note [CIrredCan constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CIrredCan constraints are used for constraints that are "stuck"
   - we can't solve them (yet)
   - we can't use them to solve other constraints
   - but they may become soluble if we substitute for some
     of the type variables in the constraint

Example 1:  (c Int), where c :: * -> Constraint.  We can't do anything
            with this yet, but if later c := Num, *then* we can solve it

Example 2:  a ~ b, where a :: *, b :: k, where k is a kind variable
            We don't want to use this to substitute 'b' for 'a', in case
            'k' is subsequently unifed with (say) *->*, because then
            we'd have ill-kinded types floating about.  Rather we want
            to defer using the equality altogether until 'k' get resolved.

Note [Ct/evidence invariant]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If  ct :: Ct, then extra fields of 'ct' cache precisely the ctev_pred field
of (cc_ev ct), and is fully rewritten wrt the substitution.   Eg for CDictCan,
   ctev_pred (cc_ev ct) = (cc_class ct) (cc_tyargs ct)
This holds by construction; look at the unique place where CDictCan is
built (in TcCanonical).

In contrast, the type of the evidence *term* (ctev_dest / ctev_evar) in
the evidence may *not* be fully zonked; we are careful not to look at it
during constraint solving. See Note [Evidence field of CtEvidence].

Note [Ct kind invariant]
~~~~~~~~~~~~~~~~~~~~~~~~
CTyEqCan and CFunEqCan both require that the kind of the lhs matches the kind
of the rhs. This is necessary because both constraints are used for substitutions
during solving. If the kinds differed, then the substitution would take a well-kinded
type to an ill-kinded one.

Note [Almost function-free]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
A type is *almost function-free* if it has no type functions (something that
responds True to isTypeFamilyTyCon), except (possibly)
 * under a forall, or
 * in a coercion (either in a CastTy or a CercionTy)

The RHS of a CTyEqCan must be almost function-free. This is for two reasons:

1. There cannot be a top-level function. If there were, the equality should
   really be a CFunEqCan, not a CTyEqCan.

2. Nested functions aren't too bad, on the other hand. However, consider this
   scenario:

     type family F a = r | r -> a

     [D] F ty1 ~ fsk1
     [D] F ty2 ~ fsk2
     [D] fsk1 ~ [G Int]
     [D] fsk2 ~ [G Bool]

     type instance G Int = Char
     type instance G Bool = Char

   If it was the case that fsk1 = fsk2, then we could unifty ty1 and ty2 --
   good! They don't look equal -- but if we aggressively reduce that G Int and
   G Bool they would become equal. The "almost function free" makes sure that
   these redexes are exposed.

   Note that this equality does *not* depend on casts or coercions, and so
   skipping these forms is OK. In addition, the result of a type family cannot
   be a polytype, so skipping foralls is OK, too. We skip foralls because we
   want the output of the flattener to be almost function-free. See Note
   [Flattening under a forall] in TcFlatten.

   As I (Richard E) write this, it is unclear if the scenario pictured above
   can happen -- I would expect the G Int and G Bool to be reduced. But
   perhaps it can arise somehow, and maintaining almost function-free is cheap.

Historical note: CTyEqCans used to require only condition (1) above: that no
type family was at the top of an RHS. But work on #16512 suggested that the
injectivity checks were not complete, and adding the requirement that functions
do not appear even in a nested fashion was easy (it was already true, but
unenforced).

The almost-function-free property is checked by isAlmostFunctionFree in TcType.
The flattener (in TcFlatten) produces types that are almost function-free.

-}

mkNonCanonical :: CtEvidence -> Ct
mkNonCanonical :: CtEvidence -> Ct
mkNonCanonical CtEvidence
ev = CNonCanonical :: CtEvidence -> Ct
CNonCanonical { cc_ev :: CtEvidence
cc_ev = CtEvidence
ev }

mkNonCanonicalCt :: Ct -> Ct
mkNonCanonicalCt :: Ct -> Ct
mkNonCanonicalCt Ct
ct = CNonCanonical :: CtEvidence -> Ct
CNonCanonical { cc_ev :: CtEvidence
cc_ev = Ct -> CtEvidence
cc_ev Ct
ct }

mkIrredCt :: CtEvidence -> Ct
mkIrredCt :: CtEvidence -> Ct
mkIrredCt CtEvidence
ev = CIrredCan :: CtEvidence -> Bool -> Ct
CIrredCan { cc_ev :: CtEvidence
cc_ev = CtEvidence
ev, cc_insol :: Bool
cc_insol = Bool
False }

mkInsolubleCt :: CtEvidence -> Ct
mkInsolubleCt :: CtEvidence -> Ct
mkInsolubleCt CtEvidence
ev = CIrredCan :: CtEvidence -> Bool -> Ct
CIrredCan { cc_ev :: CtEvidence
cc_ev = CtEvidence
ev, cc_insol :: Bool
cc_insol = Bool
True }

mkGivens :: CtLoc -> [EvId] -> [Ct]
mkGivens :: CtLoc -> [TcTyVar] -> [Ct]
mkGivens CtLoc
loc [TcTyVar]
ev_ids
  = (TcTyVar -> Ct) -> [TcTyVar] -> [Ct]
forall a b. (a -> b) -> [a] -> [b]
map TcTyVar -> Ct
mk [TcTyVar]
ev_ids
  where
    mk :: TcTyVar -> Ct
mk TcTyVar
ev_id = CtEvidence -> Ct
mkNonCanonical (CtGiven :: Xi -> TcTyVar -> CtLoc -> CtEvidence
CtGiven { ctev_evar :: TcTyVar
ctev_evar = TcTyVar
ev_id
                                       , ctev_pred :: Xi
ctev_pred = TcTyVar -> Xi
evVarPred TcTyVar
ev_id
                                       , ctev_loc :: CtLoc
ctev_loc = CtLoc
loc })

ctEvidence :: Ct -> CtEvidence
ctEvidence :: Ct -> CtEvidence
ctEvidence (CQuantCan (QCI { qci_ev :: QCInst -> CtEvidence
qci_ev = CtEvidence
ev })) = CtEvidence
ev
ctEvidence Ct
ct = Ct -> CtEvidence
cc_ev Ct
ct

ctLoc :: Ct -> CtLoc
ctLoc :: Ct -> CtLoc
ctLoc = CtEvidence -> CtLoc
ctEvLoc (CtEvidence -> CtLoc) -> (Ct -> CtEvidence) -> Ct -> CtLoc
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> CtEvidence
ctEvidence

setCtLoc :: Ct -> CtLoc -> Ct
setCtLoc :: Ct -> CtLoc -> Ct
setCtLoc Ct
ct CtLoc
loc = Ct
ct { cc_ev :: CtEvidence
cc_ev = (Ct -> CtEvidence
cc_ev Ct
ct) { ctev_loc :: CtLoc
ctev_loc = CtLoc
loc } }

ctOrigin :: Ct -> CtOrigin
ctOrigin :: Ct -> CtOrigin
ctOrigin = CtLoc -> CtOrigin
ctLocOrigin (CtLoc -> CtOrigin) -> (Ct -> CtLoc) -> Ct -> CtOrigin
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> CtLoc
ctLoc

ctPred :: Ct -> PredType
-- See Note [Ct/evidence invariant]
ctPred :: Ct -> Xi
ctPred Ct
ct = CtEvidence -> Xi
ctEvPred (Ct -> CtEvidence
ctEvidence Ct
ct)

ctEvId :: Ct -> EvVar
-- The evidence Id for this Ct
ctEvId :: Ct -> TcTyVar
ctEvId Ct
ct = CtEvidence -> TcTyVar
ctEvEvId (Ct -> CtEvidence
ctEvidence Ct
ct)

-- | Makes a new equality predicate with the same role as the given
-- evidence.
mkTcEqPredLikeEv :: CtEvidence -> TcType -> TcType -> TcType
mkTcEqPredLikeEv :: CtEvidence -> Xi -> Xi -> Xi
mkTcEqPredLikeEv CtEvidence
ev
  = case Xi -> EqRel
predTypeEqRel Xi
pred of
      EqRel
NomEq  -> Xi -> Xi -> Xi
mkPrimEqPred
      EqRel
ReprEq -> Xi -> Xi -> Xi
mkReprPrimEqPred
  where
    pred :: Xi
pred = CtEvidence -> Xi
ctEvPred CtEvidence
ev

-- | Get the flavour of the given 'Ct'
ctFlavour :: Ct -> CtFlavour
ctFlavour :: Ct -> CtFlavour
ctFlavour = CtEvidence -> CtFlavour
ctEvFlavour (CtEvidence -> CtFlavour) -> (Ct -> CtEvidence) -> Ct -> CtFlavour
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> CtEvidence
ctEvidence

-- | Get the equality relation for the given 'Ct'
ctEqRel :: Ct -> EqRel
ctEqRel :: Ct -> EqRel
ctEqRel = CtEvidence -> EqRel
ctEvEqRel (CtEvidence -> EqRel) -> (Ct -> CtEvidence) -> Ct -> EqRel
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> CtEvidence
ctEvidence

instance Outputable Ct where
  ppr :: Ct -> SDoc
ppr Ct
ct = CtEvidence -> SDoc
forall a. Outputable a => a -> SDoc
ppr (Ct -> CtEvidence
ctEvidence Ct
ct) SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
parens SDoc
pp_sort
    where
      pp_sort :: SDoc
pp_sort = case Ct
ct of
         CTyEqCan {}      -> String -> SDoc
text String
"CTyEqCan"
         CFunEqCan {}     -> String -> SDoc
text String
"CFunEqCan"
         CNonCanonical {} -> String -> SDoc
text String
"CNonCanonical"
         CDictCan { cc_pend_sc :: Ct -> Bool
cc_pend_sc = Bool
pend_sc }
            | Bool
pend_sc   -> String -> SDoc
text String
"CDictCan(psc)"
            | Bool
otherwise -> String -> SDoc
text String
"CDictCan"
         CIrredCan { cc_insol :: Ct -> Bool
cc_insol = Bool
insol }
            | Bool
insol     -> String -> SDoc
text String
"CIrredCan(insol)"
            | Bool
otherwise -> String -> SDoc
text String
"CIrredCan(sol)"
         CHoleCan { cc_hole :: Ct -> Hole
cc_hole = Hole
hole } -> String -> SDoc
text String
"CHoleCan:" SDoc -> SDoc -> SDoc
<+> Hole -> SDoc
forall a. Outputable a => a -> SDoc
ppr Hole
hole
         CQuantCan (QCI { qci_pend_sc :: QCInst -> Bool
qci_pend_sc = Bool
pend_sc })
            | Bool
pend_sc   -> String -> SDoc
text String
"CQuantCan(psc)"
            | Bool
otherwise -> String -> SDoc
text String
"CQuantCan"

{-
************************************************************************
*                                                                      *
        Simple functions over evidence variables
*                                                                      *
************************************************************************
-}

---------------- Getting free tyvars -------------------------

-- | Returns free variables of constraints as a non-deterministic set
tyCoVarsOfCt :: Ct -> TcTyCoVarSet
tyCoVarsOfCt :: Ct -> TcTyCoVarSet
tyCoVarsOfCt = FV -> TcTyCoVarSet
fvVarSet (FV -> TcTyCoVarSet) -> (Ct -> FV) -> Ct -> TcTyCoVarSet
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> FV
tyCoFVsOfCt

-- | Returns free variables of constraints as a deterministically ordered.
-- list. See Note [Deterministic FV] in FV.
tyCoVarsOfCtList :: Ct -> [TcTyCoVar]
tyCoVarsOfCtList :: Ct -> [TcTyVar]
tyCoVarsOfCtList = FV -> [TcTyVar]
fvVarList (FV -> [TcTyVar]) -> (Ct -> FV) -> Ct -> [TcTyVar]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> FV
tyCoFVsOfCt

-- | Returns free variables of constraints as a composable FV computation.
-- See Note [Deterministic FV] in FV.
tyCoFVsOfCt :: Ct -> FV
tyCoFVsOfCt :: Ct -> FV
tyCoFVsOfCt (CTyEqCan { cc_tyvar :: Ct -> TcTyVar
cc_tyvar = TcTyVar
tv, cc_rhs :: Ct -> Xi
cc_rhs = Xi
xi })
  = Xi -> FV
tyCoFVsOfType Xi
xi FV -> FV -> FV
`unionFV` TcTyVar -> FV
FV.unitFV TcTyVar
tv
                     FV -> FV -> FV
`unionFV` Xi -> FV
tyCoFVsOfType (TcTyVar -> Xi
tyVarKind TcTyVar
tv)
tyCoFVsOfCt (CFunEqCan { cc_tyargs :: Ct -> [Xi]
cc_tyargs = [Xi]
tys, cc_fsk :: Ct -> TcTyVar
cc_fsk = TcTyVar
fsk })
  = [Xi] -> FV
tyCoFVsOfTypes [Xi]
tys FV -> FV -> FV
`unionFV` TcTyVar -> FV
FV.unitFV TcTyVar
fsk
                       FV -> FV -> FV
`unionFV` Xi -> FV
tyCoFVsOfType (TcTyVar -> Xi
tyVarKind TcTyVar
fsk)
tyCoFVsOfCt (CDictCan { cc_tyargs :: Ct -> [Xi]
cc_tyargs = [Xi]
tys }) = [Xi] -> FV
tyCoFVsOfTypes [Xi]
tys
tyCoFVsOfCt Ct
ct = Xi -> FV
tyCoFVsOfType (Ct -> Xi
ctPred Ct
ct)

-- | Returns free variables of a bag of constraints as a non-deterministic
-- set. See Note [Deterministic FV] in FV.
tyCoVarsOfCts :: Cts -> TcTyCoVarSet
tyCoVarsOfCts :: Cts -> TcTyCoVarSet
tyCoVarsOfCts = FV -> TcTyCoVarSet
fvVarSet (FV -> TcTyCoVarSet) -> (Cts -> FV) -> Cts -> TcTyCoVarSet
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Cts -> FV
tyCoFVsOfCts

-- | Returns free variables of a bag of constraints as a deterministically
-- odered list. See Note [Deterministic FV] in FV.
tyCoVarsOfCtsList :: Cts -> [TcTyCoVar]
tyCoVarsOfCtsList :: Cts -> [TcTyVar]
tyCoVarsOfCtsList = FV -> [TcTyVar]
fvVarList (FV -> [TcTyVar]) -> (Cts -> FV) -> Cts -> [TcTyVar]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Cts -> FV
tyCoFVsOfCts

-- | Returns free variables of a bag of constraints as a composable FV
-- computation. See Note [Deterministic FV] in FV.
tyCoFVsOfCts :: Cts -> FV
tyCoFVsOfCts :: Cts -> FV
tyCoFVsOfCts = (Ct -> FV -> FV) -> FV -> Cts -> FV
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr (FV -> FV -> FV
unionFV (FV -> FV -> FV) -> (Ct -> FV) -> Ct -> FV -> FV
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> FV
tyCoFVsOfCt) FV
emptyFV

-- | Returns free variables of WantedConstraints as a non-deterministic
-- set. See Note [Deterministic FV] in FV.
tyCoVarsOfWC :: WantedConstraints -> TyCoVarSet
-- Only called on *zonked* things, hence no need to worry about flatten-skolems
tyCoVarsOfWC :: WantedConstraints -> TcTyCoVarSet
tyCoVarsOfWC = FV -> TcTyCoVarSet
fvVarSet (FV -> TcTyCoVarSet)
-> (WantedConstraints -> FV) -> WantedConstraints -> TcTyCoVarSet
forall b c a. (b -> c) -> (a -> b) -> a -> c
. WantedConstraints -> FV
tyCoFVsOfWC

-- | Returns free variables of WantedConstraints as a deterministically
-- ordered list. See Note [Deterministic FV] in FV.
tyCoVarsOfWCList :: WantedConstraints -> [TyCoVar]
-- Only called on *zonked* things, hence no need to worry about flatten-skolems
tyCoVarsOfWCList :: WantedConstraints -> [TcTyVar]
tyCoVarsOfWCList = FV -> [TcTyVar]
fvVarList (FV -> [TcTyVar])
-> (WantedConstraints -> FV) -> WantedConstraints -> [TcTyVar]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. WantedConstraints -> FV
tyCoFVsOfWC

-- | Returns free variables of WantedConstraints as a composable FV
-- computation. See Note [Deterministic FV] in FV.
tyCoFVsOfWC :: WantedConstraints -> FV
-- Only called on *zonked* things, hence no need to worry about flatten-skolems
tyCoFVsOfWC :: WantedConstraints -> FV
tyCoFVsOfWC (WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
simple, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
implic })
  = Cts -> FV
tyCoFVsOfCts Cts
simple FV -> FV -> FV
`unionFV`
    (Implication -> FV) -> Bag Implication -> FV
forall a. (a -> FV) -> Bag a -> FV
tyCoFVsOfBag Implication -> FV
tyCoFVsOfImplic Bag Implication
implic

-- | Returns free variables of Implication as a composable FV computation.
-- See Note [Deterministic FV] in FV.
tyCoFVsOfImplic :: Implication -> FV
-- Only called on *zonked* things, hence no need to worry about flatten-skolems
tyCoFVsOfImplic :: Implication -> FV
tyCoFVsOfImplic (Implic { ic_skols :: Implication -> [TcTyVar]
ic_skols = [TcTyVar]
skols
                        , ic_given :: Implication -> [TcTyVar]
ic_given = [TcTyVar]
givens
                        , ic_wanted :: Implication -> WantedConstraints
ic_wanted = WantedConstraints
wanted })
  | WantedConstraints -> Bool
isEmptyWC WantedConstraints
wanted
  = FV
emptyFV
  | Bool
otherwise
  = [TcTyVar] -> FV -> FV
tyCoFVsVarBndrs [TcTyVar]
skols  (FV -> FV) -> FV -> FV
forall a b. (a -> b) -> a -> b
$
    [TcTyVar] -> FV -> FV
tyCoFVsVarBndrs [TcTyVar]
givens (FV -> FV) -> FV -> FV
forall a b. (a -> b) -> a -> b
$
    WantedConstraints -> FV
tyCoFVsOfWC WantedConstraints
wanted

tyCoFVsOfBag :: (a -> FV) -> Bag a -> FV
tyCoFVsOfBag :: (a -> FV) -> Bag a -> FV
tyCoFVsOfBag a -> FV
tvs_of = (a -> FV -> FV) -> FV -> Bag a -> FV
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr (FV -> FV -> FV
unionFV (FV -> FV -> FV) -> (a -> FV) -> a -> FV -> FV
forall b c a. (b -> c) -> (a -> b) -> a -> c
. a -> FV
tvs_of) FV
emptyFV

---------------------------
dropDerivedWC :: WantedConstraints -> WantedConstraints
-- See Note [Dropping derived constraints]
dropDerivedWC :: WantedConstraints -> WantedConstraints
dropDerivedWC wc :: WantedConstraints
wc@(WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
simples })
  = WantedConstraints
wc { wc_simple :: Cts
wc_simple = Cts -> Cts
dropDerivedSimples Cts
simples }
    -- The wc_impl implications are already (recursively) filtered

--------------------------
dropDerivedSimples :: Cts -> Cts
-- Drop all Derived constraints, but make [W] back into [WD],
-- so that if we re-simplify these constraints we will get all
-- the right derived constraints re-generated.  Forgetting this
-- step led to #12936
dropDerivedSimples :: Cts -> Cts
dropDerivedSimples Cts
simples = (Ct -> Maybe Ct) -> Cts -> Cts
forall a b. (a -> Maybe b) -> Bag a -> Bag b
mapMaybeBag Ct -> Maybe Ct
dropDerivedCt Cts
simples

dropDerivedCt :: Ct -> Maybe Ct
dropDerivedCt :: Ct -> Maybe Ct
dropDerivedCt Ct
ct
  = case CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev of
      Wanted ShadowInfo
WOnly -> Ct -> Maybe Ct
forall a. a -> Maybe a
Just (Ct
ct' { cc_ev :: CtEvidence
cc_ev = CtEvidence
ev_wd })
      Wanted ShadowInfo
_     -> Ct -> Maybe Ct
forall a. a -> Maybe a
Just Ct
ct'
      CtFlavour
_ | Ct -> Bool
isDroppableCt Ct
ct -> Maybe Ct
forall a. Maybe a
Nothing
        | Bool
otherwise        -> Ct -> Maybe Ct
forall a. a -> Maybe a
Just Ct
ct
  where
    ev :: CtEvidence
ev    = Ct -> CtEvidence
ctEvidence Ct
ct
    ev_wd :: CtEvidence
ev_wd = CtEvidence
ev { ctev_nosh :: ShadowInfo
ctev_nosh = ShadowInfo
WDeriv }
    ct' :: Ct
ct'   = Ct -> Ct
setPendingScDict Ct
ct -- See Note [Resetting cc_pend_sc]

{- Note [Resetting cc_pend_sc]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
When we discard Derived constraints, in dropDerivedSimples, we must
set the cc_pend_sc flag to True, so that if we re-process this
CDictCan we will re-generate its derived superclasses. Otherwise
we might miss some fundeps.  #13662 showed this up.

See Note [The superclass story] in TcCanonical.
-}

isDroppableCt :: Ct -> Bool
isDroppableCt :: Ct -> Bool
isDroppableCt Ct
ct
  = CtEvidence -> Bool
isDerived CtEvidence
ev Bool -> Bool -> Bool
&& Bool -> Bool
not Bool
keep_deriv
    -- Drop only derived constraints, and then only if they
    -- obey Note [Dropping derived constraints]
  where
    ev :: CtEvidence
ev   = Ct -> CtEvidence
ctEvidence Ct
ct
    loc :: CtLoc
loc  = CtEvidence -> CtLoc
ctEvLoc CtEvidence
ev
    orig :: CtOrigin
orig = CtLoc -> CtOrigin
ctLocOrigin CtLoc
loc

    keep_deriv :: Bool
keep_deriv
      = case Ct
ct of
          CHoleCan {} -> Bool
True
          CIrredCan { cc_insol :: Ct -> Bool
cc_insol = Bool
insoluble }
                      -> Bool -> Bool
keep_eq Bool
insoluble
          Ct
_           -> Bool -> Bool
keep_eq Bool
False

    keep_eq :: Bool -> Bool
keep_eq Bool
definitely_insoluble
       | CtOrigin -> Bool
isGivenOrigin CtOrigin
orig    -- Arising only from givens
       = Bool
definitely_insoluble  -- Keep only definitely insoluble
       | Bool
otherwise
       = case CtOrigin
orig of
           KindEqOrigin {} -> Bool
True    -- See Note [Dropping derived constraints]

           -- See Note [Dropping derived constraints]
           -- For fundeps, drop wanted/wanted interactions
           FunDepOrigin2 {} -> Bool
True   -- Top-level/Wanted
           FunDepOrigin1 Xi
_ CtOrigin
orig1 RealSrcSpan
_ Xi
_ CtOrigin
orig2 RealSrcSpan
_
             | Bool
g1 Bool -> Bool -> Bool
|| Bool
g2  -> Bool
True  -- Given/Wanted errors: keep all
             | Bool
otherwise -> Bool
False -- Wanted/Wanted errors: discard
             where
               g1 :: Bool
g1 = CtOrigin -> Bool
isGivenOrigin CtOrigin
orig1
               g2 :: Bool
g2 = CtOrigin -> Bool
isGivenOrigin CtOrigin
orig2

           CtOrigin
_ -> Bool
False

arisesFromGivens :: Ct -> Bool
arisesFromGivens :: Ct -> Bool
arisesFromGivens Ct
ct
  = case Ct -> CtEvidence
ctEvidence Ct
ct of
      CtGiven {}                   -> Bool
True
      CtWanted {}                  -> Bool
False
      CtDerived { ctev_loc :: CtEvidence -> CtLoc
ctev_loc = CtLoc
loc } -> CtLoc -> Bool
isGivenLoc CtLoc
loc

isGivenLoc :: CtLoc -> Bool
isGivenLoc :: CtLoc -> Bool
isGivenLoc CtLoc
loc = CtOrigin -> Bool
isGivenOrigin (CtLoc -> CtOrigin
ctLocOrigin CtLoc
loc)

{- Note [Dropping derived constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In general we discard derived constraints at the end of constraint solving;
see dropDerivedWC.  For example

 * Superclasses: if we have an unsolved [W] (Ord a), we don't want to
   complain about an unsolved [D] (Eq a) as well.

 * If we have [W] a ~ Int, [W] a ~ Bool, improvement will generate
   [D] Int ~ Bool, and we don't want to report that because it's
   incomprehensible. That is why we don't rewrite wanteds with wanteds!

 * We might float out some Wanteds from an implication, leaving behind
   their insoluble Deriveds. For example:

   forall a[2]. [W] alpha[1] ~ Int
                [W] alpha[1] ~ Bool
                [D] Int ~ Bool

   The Derived is insoluble, but we very much want to drop it when floating
   out.

But (tiresomely) we do keep *some* Derived constraints:

 * Type holes are derived constraints, because they have no evidence
   and we want to keep them, so we get the error report

 * Insoluble kind equalities (e.g. [D] * ~ (* -> *)), with
   KindEqOrigin, may arise from a type equality a ~ Int#, say.  See
   Note [Equalities with incompatible kinds] in TcCanonical.
   Keeping these around produces better error messages, in practice.
   E.g., test case dependent/should_fail/T11471

 * We keep most derived equalities arising from functional dependencies
      - Given/Given interactions (subset of FunDepOrigin1):
        The definitely-insoluble ones reflect unreachable code.

        Others not-definitely-insoluble ones like [D] a ~ Int do not
        reflect unreachable code; indeed if fundeps generated proofs, it'd
        be a useful equality.  See #14763.   So we discard them.

      - Given/Wanted interacGiven or Wanted interacting with an
        instance declaration (FunDepOrigin2)

      - Given/Wanted interactions (FunDepOrigin1); see #9612

      - But for Wanted/Wanted interactions we do /not/ want to report an
        error (#13506).  Consider [W] C Int Int, [W] C Int Bool, with
        a fundep on class C.  We don't want to report an insoluble Int~Bool;
        c.f. "wanteds do not rewrite wanteds".

To distinguish these cases we use the CtOrigin.

NB: we keep *all* derived insolubles under some circumstances:

  * They are looked at by simplifyInfer, to decide whether to
    generalise.  Example: [W] a ~ Int, [W] a ~ Bool
    We get [D] Int ~ Bool, and indeed the constraints are insoluble,
    and we want simplifyInfer to see that, even though we don't
    ultimately want to generate an (inexplicable) error message from it


************************************************************************
*                                                                      *
                    CtEvidence
         The "flavor" of a canonical constraint
*                                                                      *
************************************************************************
-}

isWantedCt :: Ct -> Bool
isWantedCt :: Ct -> Bool
isWantedCt = CtEvidence -> Bool
isWanted (CtEvidence -> Bool) -> (Ct -> CtEvidence) -> Ct -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> CtEvidence
ctEvidence

isGivenCt :: Ct -> Bool
isGivenCt :: Ct -> Bool
isGivenCt = CtEvidence -> Bool
isGiven (CtEvidence -> Bool) -> (Ct -> CtEvidence) -> Ct -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> CtEvidence
ctEvidence

isDerivedCt :: Ct -> Bool
isDerivedCt :: Ct -> Bool
isDerivedCt = CtEvidence -> Bool
isDerived (CtEvidence -> Bool) -> (Ct -> CtEvidence) -> Ct -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> CtEvidence
ctEvidence

isCTyEqCan :: Ct -> Bool
isCTyEqCan :: Ct -> Bool
isCTyEqCan (CTyEqCan {})  = Bool
True
isCTyEqCan (CFunEqCan {}) = Bool
False
isCTyEqCan Ct
_              = Bool
False

isCDictCan_Maybe :: Ct -> Maybe Class
isCDictCan_Maybe :: Ct -> Maybe Class
isCDictCan_Maybe (CDictCan {cc_class :: Ct -> Class
cc_class = Class
cls })  = Class -> Maybe Class
forall a. a -> Maybe a
Just Class
cls
isCDictCan_Maybe Ct
_              = Maybe Class
forall a. Maybe a
Nothing

isCFunEqCan_maybe :: Ct -> Maybe (TyCon, [Type])
isCFunEqCan_maybe :: Ct -> Maybe (TyCon, [Xi])
isCFunEqCan_maybe (CFunEqCan { cc_fun :: Ct -> TyCon
cc_fun = TyCon
tc, cc_tyargs :: Ct -> [Xi]
cc_tyargs = [Xi]
xis }) = (TyCon, [Xi]) -> Maybe (TyCon, [Xi])
forall a. a -> Maybe a
Just (TyCon
tc, [Xi]
xis)
isCFunEqCan_maybe Ct
_ = Maybe (TyCon, [Xi])
forall a. Maybe a
Nothing

isCFunEqCan :: Ct -> Bool
isCFunEqCan :: Ct -> Bool
isCFunEqCan (CFunEqCan {}) = Bool
True
isCFunEqCan Ct
_ = Bool
False

isCNonCanonical :: Ct -> Bool
isCNonCanonical :: Ct -> Bool
isCNonCanonical (CNonCanonical {}) = Bool
True
isCNonCanonical Ct
_ = Bool
False

isHoleCt:: Ct -> Bool
isHoleCt :: Ct -> Bool
isHoleCt (CHoleCan {}) = Bool
True
isHoleCt Ct
_ = Bool
False

isOutOfScopeCt :: Ct -> Bool
-- We treat expression holes representing out-of-scope variables a bit
-- differently when it comes to error reporting
isOutOfScopeCt :: Ct -> Bool
isOutOfScopeCt (CHoleCan { cc_hole :: Ct -> Hole
cc_hole = ExprHole (OutOfScope {}) }) = Bool
True
isOutOfScopeCt Ct
_ = Bool
False

isExprHoleCt :: Ct -> Bool
isExprHoleCt :: Ct -> Bool
isExprHoleCt (CHoleCan { cc_hole :: Ct -> Hole
cc_hole = ExprHole {} }) = Bool
True
isExprHoleCt Ct
_ = Bool
False

isTypeHoleCt :: Ct -> Bool
isTypeHoleCt :: Ct -> Bool
isTypeHoleCt (CHoleCan { cc_hole :: Ct -> Hole
cc_hole = TypeHole {} }) = Bool
True
isTypeHoleCt Ct
_ = Bool
False


{- Note [Custom type errors in constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When GHC reports a type-error about an unsolved-constraint, we check
to see if the constraint contains any custom-type errors, and if so
we report them.  Here are some examples of constraints containing type
errors:

TypeError msg           -- The actual constraint is a type error

TypError msg ~ Int      -- Some type was supposed to be Int, but ended up
                        -- being a type error instead

Eq (TypeError msg)      -- A class constraint is stuck due to a type error

F (TypeError msg) ~ a   -- A type function failed to evaluate due to a type err

It is also possible to have constraints where the type error is nested deeper,
for example see #11990, and also:

Eq (F (TypeError msg))  -- Here the type error is nested under a type-function
                        -- call, which failed to evaluate because of it,
                        -- and so the `Eq` constraint was unsolved.
                        -- This may happen when one function calls another
                        -- and the called function produced a custom type error.
-}

-- | A constraint is considered to be a custom type error, if it contains
-- custom type errors anywhere in it.
-- See Note [Custom type errors in constraints]
getUserTypeErrorMsg :: Ct -> Maybe Type
getUserTypeErrorMsg :: Ct -> Maybe Xi
getUserTypeErrorMsg Ct
ct = Xi -> Maybe Xi
findUserTypeError (Ct -> Xi
ctPred Ct
ct)
  where
  findUserTypeError :: Xi -> Maybe Xi
findUserTypeError Xi
t = [Maybe Xi] -> Maybe Xi
forall (t :: * -> *) (m :: * -> *) a.
(Foldable t, MonadPlus m) =>
t (m a) -> m a
msum ( Xi -> Maybe Xi
userTypeError_maybe Xi
t
                             Maybe Xi -> [Maybe Xi] -> [Maybe Xi]
forall a. a -> [a] -> [a]
: (Xi -> Maybe Xi) -> [Xi] -> [Maybe Xi]
forall a b. (a -> b) -> [a] -> [b]
map Xi -> Maybe Xi
findUserTypeError (Xi -> [Xi]
subTys Xi
t)
                             )

  subTys :: Xi -> [Xi]
subTys Xi
t            = case Xi -> (Xi, [Xi])
splitAppTys Xi
t of
                          (Xi
t,[]) ->
                            case HasDebugCallStack => Xi -> Maybe (TyCon, [Xi])
Xi -> Maybe (TyCon, [Xi])
splitTyConApp_maybe Xi
t of
                              Maybe (TyCon, [Xi])
Nothing     -> []
                              Just (TyCon
_,[Xi]
ts) -> [Xi]
ts
                          (Xi
t,[Xi]
ts) -> Xi
t Xi -> [Xi] -> [Xi]
forall a. a -> [a] -> [a]
: [Xi]
ts




isUserTypeErrorCt :: Ct -> Bool
isUserTypeErrorCt :: Ct -> Bool
isUserTypeErrorCt Ct
ct = case Ct -> Maybe Xi
getUserTypeErrorMsg Ct
ct of
                         Just Xi
_ -> Bool
True
                         Maybe Xi
_      -> Bool
False

isPendingScDict :: Ct -> Maybe Ct
-- Says whether this is a CDictCan with cc_pend_sc is True,
-- AND if so flips the flag
isPendingScDict :: Ct -> Maybe Ct
isPendingScDict ct :: Ct
ct@(CDictCan { cc_pend_sc :: Ct -> Bool
cc_pend_sc = Bool
True })
                  = Ct -> Maybe Ct
forall a. a -> Maybe a
Just (Ct
ct { cc_pend_sc :: Bool
cc_pend_sc = Bool
False })
isPendingScDict Ct
_ = Maybe Ct
forall a. Maybe a
Nothing

isPendingScInst :: QCInst -> Maybe QCInst
-- Same as isPrendinScDict, but for QCInsts
isPendingScInst :: QCInst -> Maybe QCInst
isPendingScInst qci :: QCInst
qci@(QCI { qci_pend_sc :: QCInst -> Bool
qci_pend_sc = Bool
True })
                  = QCInst -> Maybe QCInst
forall a. a -> Maybe a
Just (QCInst
qci { qci_pend_sc :: Bool
qci_pend_sc = Bool
False })
isPendingScInst QCInst
_ = Maybe QCInst
forall a. Maybe a
Nothing

setPendingScDict :: Ct -> Ct
-- Set the cc_pend_sc flag to True
setPendingScDict :: Ct -> Ct
setPendingScDict ct :: Ct
ct@(CDictCan { cc_pend_sc :: Ct -> Bool
cc_pend_sc = Bool
False })
                    = Ct
ct { cc_pend_sc :: Bool
cc_pend_sc = Bool
True }
setPendingScDict Ct
ct = Ct
ct

superClassesMightHelp :: WantedConstraints -> Bool
-- ^ True if taking superclasses of givens, or of wanteds (to perhaps
-- expose more equalities or functional dependencies) might help to
-- solve this constraint.  See Note [When superclasses help]
superClassesMightHelp :: WantedConstraints -> Bool
superClassesMightHelp (WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
simples, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
implics })
  = (Ct -> Bool) -> Cts -> Bool
forall a. (a -> Bool) -> Bag a -> Bool
anyBag Ct -> Bool
might_help_ct Cts
simples Bool -> Bool -> Bool
|| (Implication -> Bool) -> Bag Implication -> Bool
forall a. (a -> Bool) -> Bag a -> Bool
anyBag Implication -> Bool
might_help_implic Bag Implication
implics
  where
    might_help_implic :: Implication -> Bool
might_help_implic Implication
ic
       | ImplicStatus
IC_Unsolved <- Implication -> ImplicStatus
ic_status Implication
ic = WantedConstraints -> Bool
superClassesMightHelp (Implication -> WantedConstraints
ic_wanted Implication
ic)
       | Bool
otherwise                   = Bool
False

    might_help_ct :: Ct -> Bool
might_help_ct Ct
ct = Ct -> Bool
isWantedCt Ct
ct Bool -> Bool -> Bool
&& Bool -> Bool
not (Ct -> Bool
is_ip Ct
ct)

    is_ip :: Ct -> Bool
is_ip (CDictCan { cc_class :: Ct -> Class
cc_class = Class
cls }) = Class -> Bool
isIPClass Class
cls
    is_ip Ct
_                             = Bool
False

getPendingWantedScs :: Cts -> ([Ct], Cts)
getPendingWantedScs :: Cts -> ([Ct], Cts)
getPendingWantedScs Cts
simples
  = ([Ct] -> Ct -> ([Ct], Ct)) -> [Ct] -> Cts -> ([Ct], Cts)
forall acc x y.
(acc -> x -> (acc, y)) -> acc -> Bag x -> (acc, Bag y)
mapAccumBagL [Ct] -> Ct -> ([Ct], Ct)
get [] Cts
simples
  where
    get :: [Ct] -> Ct -> ([Ct], Ct)
get [Ct]
acc Ct
ct | Just Ct
ct' <- Ct -> Maybe Ct
isPendingScDict Ct
ct
               = (Ct
ct'Ct -> [Ct] -> [Ct]
forall a. a -> [a] -> [a]
:[Ct]
acc, Ct
ct')
               | Bool
otherwise
               = ([Ct]
acc,     Ct
ct)

{- Note [When superclasses help]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
First read Note [The superclass story] in TcCanonical.

We expand superclasses and iterate only if there is at unsolved wanted
for which expansion of superclasses (e.g. from given constraints)
might actually help. The function superClassesMightHelp tells if
doing this superclass expansion might help solve this constraint.
Note that

  * We look inside implications; maybe it'll help to expand the Givens
    at level 2 to help solve an unsolved Wanted buried inside an
    implication.  E.g.
        forall a. Ord a => forall b. [W] Eq a

  * Superclasses help only for Wanted constraints.  Derived constraints
    are not really "unsolved" and we certainly don't want them to
    trigger superclass expansion. This was a good part of the loop
    in  #11523

  * Even for Wanted constraints, we say "no" for implicit parameters.
    we have [W] ?x::ty, expanding superclasses won't help:
      - Superclasses can't be implicit parameters
      - If we have a [G] ?x:ty2, then we'll have another unsolved
        [D] ty ~ ty2 (from the functional dependency)
        which will trigger superclass expansion.

    It's a bit of a special case, but it's easy to do.  The runtime cost
    is low because the unsolved set is usually empty anyway (errors
    aside), and the first non-imlicit-parameter will terminate the search.

    The special case is worth it (#11480, comment:2) because it
    applies to CallStack constraints, which aren't type errors. If we have
       f :: (C a) => blah
       f x = ...undefined...
    we'll get a CallStack constraint.  If that's the only unsolved
    constraint it'll eventually be solved by defaulting.  So we don't
    want to emit warnings about hitting the simplifier's iteration
    limit.  A CallStack constraint really isn't an unsolved
    constraint; it can always be solved by defaulting.
-}

singleCt :: Ct -> Cts
singleCt :: Ct -> Cts
singleCt = Ct -> Cts
forall a. a -> Bag a
unitBag

andCts :: Cts -> Cts -> Cts
andCts :: Cts -> Cts -> Cts
andCts = Cts -> Cts -> Cts
forall a. Bag a -> Bag a -> Bag a
unionBags

listToCts :: [Ct] -> Cts
listToCts :: [Ct] -> Cts
listToCts = [Ct] -> Cts
forall a. [a] -> Bag a
listToBag

ctsElts :: Cts -> [Ct]
ctsElts :: Cts -> [Ct]
ctsElts = Cts -> [Ct]
forall a. Bag a -> [a]
bagToList

consCts :: Ct -> Cts -> Cts
consCts :: Ct -> Cts -> Cts
consCts = Ct -> Cts -> Cts
forall a. a -> Bag a -> Bag a
consBag

snocCts :: Cts -> Ct -> Cts
snocCts :: Cts -> Ct -> Cts
snocCts = Cts -> Ct -> Cts
forall a. Bag a -> a -> Bag a
snocBag

extendCtsList :: Cts -> [Ct] -> Cts
extendCtsList :: Cts -> [Ct] -> Cts
extendCtsList Cts
cts [Ct]
xs | [Ct] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [Ct]
xs   = Cts
cts
                     | Bool
otherwise = Cts
cts Cts -> Cts -> Cts
forall a. Bag a -> Bag a -> Bag a
`unionBags` [Ct] -> Cts
forall a. [a] -> Bag a
listToBag [Ct]
xs

andManyCts :: [Cts] -> Cts
andManyCts :: [Cts] -> Cts
andManyCts = [Cts] -> Cts
forall a. [Bag a] -> Bag a
unionManyBags

emptyCts :: Cts
emptyCts :: Cts
emptyCts = Cts
forall a. Bag a
emptyBag

isEmptyCts :: Cts -> Bool
isEmptyCts :: Cts -> Bool
isEmptyCts = Cts -> Bool
forall a. Bag a -> Bool
isEmptyBag

pprCts :: Cts -> SDoc
pprCts :: Cts -> SDoc
pprCts Cts
cts = [SDoc] -> SDoc
vcat ((Ct -> SDoc) -> [Ct] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map Ct -> SDoc
forall a. Outputable a => a -> SDoc
ppr (Cts -> [Ct]
forall a. Bag a -> [a]
bagToList Cts
cts))

{-
************************************************************************
*                                                                      *
                Wanted constraints
     These are forced to be in TcRnTypes because
           TcLclEnv mentions WantedConstraints
           WantedConstraint mentions CtLoc
           CtLoc mentions ErrCtxt
           ErrCtxt mentions TcM
*                                                                      *
v%************************************************************************
-}

data WantedConstraints
  = WC { WantedConstraints -> Cts
wc_simple :: Cts              -- Unsolved constraints, all wanted
       , WantedConstraints -> Bag Implication
wc_impl   :: Bag Implication
    }

emptyWC :: WantedConstraints
emptyWC :: WantedConstraints
emptyWC = WC :: Cts -> Bag Implication -> WantedConstraints
WC { wc_simple :: Cts
wc_simple = Cts
forall a. Bag a
emptyBag, wc_impl :: Bag Implication
wc_impl = Bag Implication
forall a. Bag a
emptyBag }

mkSimpleWC :: [CtEvidence] -> WantedConstraints
mkSimpleWC :: [CtEvidence] -> WantedConstraints
mkSimpleWC [CtEvidence]
cts
  = WC :: Cts -> Bag Implication -> WantedConstraints
WC { wc_simple :: Cts
wc_simple = [Ct] -> Cts
forall a. [a] -> Bag a
listToBag ((CtEvidence -> Ct) -> [CtEvidence] -> [Ct]
forall a b. (a -> b) -> [a] -> [b]
map CtEvidence -> Ct
mkNonCanonical [CtEvidence]
cts)
       , wc_impl :: Bag Implication
wc_impl = Bag Implication
forall a. Bag a
emptyBag }

mkImplicWC :: Bag Implication -> WantedConstraints
mkImplicWC :: Bag Implication -> WantedConstraints
mkImplicWC Bag Implication
implic
  = WC :: Cts -> Bag Implication -> WantedConstraints
WC { wc_simple :: Cts
wc_simple = Cts
forall a. Bag a
emptyBag, wc_impl :: Bag Implication
wc_impl = Bag Implication
implic }

isEmptyWC :: WantedConstraints -> Bool
isEmptyWC :: WantedConstraints -> Bool
isEmptyWC (WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
f, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
i })
  = Cts -> Bool
forall a. Bag a -> Bool
isEmptyBag Cts
f Bool -> Bool -> Bool
&& Bag Implication -> Bool
forall a. Bag a -> Bool
isEmptyBag Bag Implication
i


-- | Checks whether a the given wanted constraints are solved, i.e.
-- that there are no simple constraints left and all the implications
-- are solved.
isSolvedWC :: WantedConstraints -> Bool
isSolvedWC :: WantedConstraints -> Bool
isSolvedWC WC {wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
wc_simple, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
wc_impl} =
  Cts -> Bool
forall a. Bag a -> Bool
isEmptyBag Cts
wc_simple Bool -> Bool -> Bool
&& (Implication -> Bool) -> Bag Implication -> Bool
forall a. (a -> Bool) -> Bag a -> Bool
allBag (ImplicStatus -> Bool
isSolvedStatus (ImplicStatus -> Bool)
-> (Implication -> ImplicStatus) -> Implication -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Implication -> ImplicStatus
ic_status) Bag Implication
wc_impl

andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints
andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints
andWC (WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
f1, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
i1 })
      (WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
f2, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
i2 })
  = WC :: Cts -> Bag Implication -> WantedConstraints
WC { wc_simple :: Cts
wc_simple = Cts
f1 Cts -> Cts -> Cts
forall a. Bag a -> Bag a -> Bag a
`unionBags` Cts
f2
       , wc_impl :: Bag Implication
wc_impl   = Bag Implication
i1 Bag Implication -> Bag Implication -> Bag Implication
forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag Implication
i2 }

unionsWC :: [WantedConstraints] -> WantedConstraints
unionsWC :: [WantedConstraints] -> WantedConstraints
unionsWC = (WantedConstraints -> WantedConstraints -> WantedConstraints)
-> WantedConstraints -> [WantedConstraints] -> WantedConstraints
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr WantedConstraints -> WantedConstraints -> WantedConstraints
andWC WantedConstraints
emptyWC

addSimples :: WantedConstraints -> Bag Ct -> WantedConstraints
addSimples :: WantedConstraints -> Cts -> WantedConstraints
addSimples WantedConstraints
wc Cts
cts
  = WantedConstraints
wc { wc_simple :: Cts
wc_simple = WantedConstraints -> Cts
wc_simple WantedConstraints
wc Cts -> Cts -> Cts
forall a. Bag a -> Bag a -> Bag a
`unionBags` Cts
cts }
    -- Consider: Put the new constraints at the front, so they get solved first

addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints
addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints
addImplics WantedConstraints
wc Bag Implication
implic = WantedConstraints
wc { wc_impl :: Bag Implication
wc_impl = WantedConstraints -> Bag Implication
wc_impl WantedConstraints
wc Bag Implication -> Bag Implication -> Bag Implication
forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag Implication
implic }

addInsols :: WantedConstraints -> Bag Ct -> WantedConstraints
addInsols :: WantedConstraints -> Cts -> WantedConstraints
addInsols WantedConstraints
wc Cts
cts
  = WantedConstraints
wc { wc_simple :: Cts
wc_simple = WantedConstraints -> Cts
wc_simple WantedConstraints
wc Cts -> Cts -> Cts
forall a. Bag a -> Bag a -> Bag a
`unionBags` Cts
cts }

insolublesOnly :: WantedConstraints -> WantedConstraints
-- Keep only the definitely-insoluble constraints
insolublesOnly :: WantedConstraints -> WantedConstraints
insolublesOnly (WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
simples, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
implics })
  = WC :: Cts -> Bag Implication -> WantedConstraints
WC { wc_simple :: Cts
wc_simple = (Ct -> Bool) -> Cts -> Cts
forall a. (a -> Bool) -> Bag a -> Bag a
filterBag Ct -> Bool
insolubleCt Cts
simples
       , wc_impl :: Bag Implication
wc_impl   = (Implication -> Implication) -> Bag Implication -> Bag Implication
forall a b. (a -> b) -> Bag a -> Bag b
mapBag Implication -> Implication
implic_insols_only Bag Implication
implics }
  where
    implic_insols_only :: Implication -> Implication
implic_insols_only Implication
implic
      = Implication
implic { ic_wanted :: WantedConstraints
ic_wanted = WantedConstraints -> WantedConstraints
insolublesOnly (Implication -> WantedConstraints
ic_wanted Implication
implic) }

isSolvedStatus :: ImplicStatus -> Bool
isSolvedStatus :: ImplicStatus -> Bool
isSolvedStatus (IC_Solved {}) = Bool
True
isSolvedStatus ImplicStatus
_              = Bool
False

isInsolubleStatus :: ImplicStatus -> Bool
isInsolubleStatus :: ImplicStatus -> Bool
isInsolubleStatus ImplicStatus
IC_Insoluble    = Bool
True
isInsolubleStatus ImplicStatus
IC_BadTelescope = Bool
True
isInsolubleStatus ImplicStatus
_               = Bool
False

insolubleImplic :: Implication -> Bool
insolubleImplic :: Implication -> Bool
insolubleImplic Implication
ic = ImplicStatus -> Bool
isInsolubleStatus (Implication -> ImplicStatus
ic_status Implication
ic)

insolubleWC :: WantedConstraints -> Bool
insolubleWC :: WantedConstraints -> Bool
insolubleWC (WC { wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
implics, wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
simples })
  =  (Ct -> Bool) -> Cts -> Bool
forall a. (a -> Bool) -> Bag a -> Bool
anyBag Ct -> Bool
insolubleCt Cts
simples
  Bool -> Bool -> Bool
|| (Implication -> Bool) -> Bag Implication -> Bool
forall a. (a -> Bool) -> Bag a -> Bool
anyBag Implication -> Bool
insolubleImplic Bag Implication
implics

insolubleCt :: Ct -> Bool
-- Definitely insoluble, in particular /excluding/ type-hole constraints
-- Namely: a) an equality constraint
--         b) that is insoluble
--         c) and does not arise from a Given
insolubleCt :: Ct -> Bool
insolubleCt Ct
ct
  | Ct -> Bool
isHoleCt Ct
ct            = Ct -> Bool
isOutOfScopeCt Ct
ct  -- See Note [Insoluble holes]
  | Bool -> Bool
not (Ct -> Bool
insolubleEqCt Ct
ct) = Bool
False
  | Ct -> Bool
arisesFromGivens Ct
ct    = Bool
False              -- See Note [Given insolubles]
  | Bool
otherwise              = Bool
True

insolubleEqCt :: Ct -> Bool
-- Returns True of /equality/ constraints
-- that are /definitely/ insoluble
-- It won't detect some definite errors like
--       F a ~ T (F a)
-- where F is a type family, which actually has an occurs check
--
-- The function is tuned for application /after/ constraint solving
--       i.e. assuming canonicalisation has been done
-- E.g.  It'll reply True  for     a ~ [a]
--               but False for   [a] ~ a
-- and
--                   True for  Int ~ F a Int
--               but False for  Maybe Int ~ F a Int Int
--               (where F is an arity-1 type function)
insolubleEqCt :: Ct -> Bool
insolubleEqCt (CIrredCan { cc_insol :: Ct -> Bool
cc_insol = Bool
insol }) = Bool
insol
insolubleEqCt Ct
_                                = Bool
False

instance Outputable WantedConstraints where
  ppr :: WantedConstraints -> SDoc
ppr (WC {wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
s, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
i})
   = String -> SDoc
text String
"WC" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
braces ([SDoc] -> SDoc
vcat
        [ SDoc -> Cts -> SDoc
forall a. Outputable a => SDoc -> Bag a -> SDoc
ppr_bag (String -> SDoc
text String
"wc_simple") Cts
s
        , SDoc -> Bag Implication -> SDoc
forall a. Outputable a => SDoc -> Bag a -> SDoc
ppr_bag (String -> SDoc
text String
"wc_impl") Bag Implication
i ])

ppr_bag :: Outputable a => SDoc -> Bag a -> SDoc
ppr_bag :: SDoc -> Bag a -> SDoc
ppr_bag SDoc
doc Bag a
bag
 | Bag a -> Bool
forall a. Bag a -> Bool
isEmptyBag Bag a
bag = SDoc
empty
 | Bool
otherwise      = SDoc -> Int -> SDoc -> SDoc
hang (SDoc
doc SDoc -> SDoc -> SDoc
<+> SDoc
equals)
                       Int
2 ((a -> SDoc -> SDoc) -> SDoc -> Bag a -> SDoc
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr (SDoc -> SDoc -> SDoc
($$) (SDoc -> SDoc -> SDoc) -> (a -> SDoc) -> a -> SDoc -> SDoc
forall b c a. (b -> c) -> (a -> b) -> a -> c
. a -> SDoc
forall a. Outputable a => a -> SDoc
ppr) SDoc
empty Bag a
bag)

{- Note [Given insolubles]
~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider (#14325, comment:)
    class (a~b) => C a b

    foo :: C a c => a -> c
    foo x = x

    hm3 :: C (f b) b => b -> f b
    hm3 x = foo x

In the RHS of hm3, from the [G] C (f b) b we get the insoluble
[G] f b ~# b.  Then we also get an unsolved [W] C b (f b).
Residual implication looks like
    forall b. C (f b) b => [G] f b ~# b
                           [W] C f (f b)

We do /not/ want to set the implication status to IC_Insoluble,
because that'll suppress reports of [W] C b (f b).  But we
may not report the insoluble [G] f b ~# b either (see Note [Given errors]
in TcErrors), so we may fail to report anything at all!  Yikes.

The same applies to Derived constraints that /arise from/ Givens.
E.g.   f :: (C Int [a]) => blah
where a fundep means we get
       [D] Int ~ [a]
By the same reasoning we must not suppress other errors (#15767)

Bottom line: insolubleWC (called in TcSimplify.setImplicationStatus)
             should ignore givens even if they are insoluble.

Note [Insoluble holes]
~~~~~~~~~~~~~~~~~~~~~~
Hole constraints that ARE NOT treated as truly insoluble:
  a) type holes, arising from PartialTypeSignatures,
  b) "true" expression holes arising from TypedHoles

An "expression hole" or "type hole" constraint isn't really an error
at all; it's a report saying "_ :: Int" here.  But an out-of-scope
variable masquerading as expression holes IS treated as truly
insoluble, so that it trumps other errors during error reporting.
Yuk!

************************************************************************
*                                                                      *
                Implication constraints
*                                                                      *
************************************************************************
-}

data Implication
  = Implic {   -- Invariants for a tree of implications:
               -- see TcType Note [TcLevel and untouchable type variables]

      Implication -> TcLevel
ic_tclvl :: TcLevel,       -- TcLevel of unification variables
                                 -- allocated /inside/ this implication

      Implication -> [TcTyVar]
ic_skols :: [TcTyVar],     -- Introduced skolems
      Implication -> SkolemInfo
ic_info  :: SkolemInfo,    -- See Note [Skolems in an implication]
                                 -- See Note [Shadowing in a constraint]

      Implication -> Maybe SDoc
ic_telescope :: Maybe SDoc,  -- User-written telescope, if there is one
                                   -- See Note [Checking telescopes]

      Implication -> [TcTyVar]
ic_given  :: [EvVar],      -- Given evidence variables
                                 --   (order does not matter)
                                 -- See Invariant (GivenInv) in TcType

      Implication -> Bool
ic_no_eqs :: Bool,         -- True  <=> ic_givens have no equalities, for sure
                                 -- False <=> ic_givens might have equalities

      Implication -> Bool
ic_warn_inaccessible :: Bool,
                                 -- True  <=> -Winaccessible-code is enabled
                                 -- at construction. See
                                 -- Note [Avoid -Winaccessible-code when deriving]
                                 -- in TcInstDcls

      Implication -> TcLclEnv
ic_env   :: TcLclEnv,
                                 -- Records the TcLClEnv at the time of creation.
                                 --
                                 -- The TcLclEnv gives the source location
                                 -- and error context for the implication, and
                                 -- hence for all the given evidence variables.

      Implication -> WantedConstraints
ic_wanted :: WantedConstraints,  -- The wanteds
                                       -- See Invariang (WantedInf) in TcType

      Implication -> EvBindsVar
ic_binds  :: EvBindsVar,    -- Points to the place to fill in the
                                  -- abstraction and bindings.

      -- The ic_need fields keep track of which Given evidence
      -- is used by this implication or its children
      -- NB: including stuff used by nested implications that have since
      --     been discarded
      -- See Note [Needed evidence variables]
      Implication -> TcTyCoVarSet
ic_need_inner :: VarSet,    -- Includes all used Given evidence
      Implication -> TcTyCoVarSet
ic_need_outer :: VarSet,    -- Includes only the free Given evidence
                                  --  i.e. ic_need_inner after deleting
                                  --       (a) givens (b) binders of ic_binds

      Implication -> ImplicStatus
ic_status   :: ImplicStatus
    }

implicationPrototype :: Implication
implicationPrototype :: Implication
implicationPrototype
   = Implic :: TcLevel
-> [TcTyVar]
-> SkolemInfo
-> Maybe SDoc
-> [TcTyVar]
-> Bool
-> Bool
-> TcLclEnv
-> WantedConstraints
-> EvBindsVar
-> TcTyCoVarSet
-> TcTyCoVarSet
-> ImplicStatus
-> Implication
Implic { -- These fields must be initialised
              ic_tclvl :: TcLevel
ic_tclvl      = String -> TcLevel
forall a. String -> a
panic String
"newImplic:tclvl"
            , ic_binds :: EvBindsVar
ic_binds      = String -> EvBindsVar
forall a. String -> a
panic String
"newImplic:binds"
            , ic_info :: SkolemInfo
ic_info       = String -> SkolemInfo
forall a. String -> a
panic String
"newImplic:info"
            , ic_env :: TcLclEnv
ic_env        = String -> TcLclEnv
forall a. String -> a
panic String
"newImplic:env"
            , ic_warn_inaccessible :: Bool
ic_warn_inaccessible = String -> Bool
forall a. String -> a
panic String
"newImplic:warn_inaccessible"

              -- The rest have sensible default values
            , ic_skols :: [TcTyVar]
ic_skols      = []
            , ic_telescope :: Maybe SDoc
ic_telescope  = Maybe SDoc
forall a. Maybe a
Nothing
            , ic_given :: [TcTyVar]
ic_given      = []
            , ic_wanted :: WantedConstraints
ic_wanted     = WantedConstraints
emptyWC
            , ic_no_eqs :: Bool
ic_no_eqs     = Bool
False
            , ic_status :: ImplicStatus
ic_status     = ImplicStatus
IC_Unsolved
            , ic_need_inner :: TcTyCoVarSet
ic_need_inner = TcTyCoVarSet
emptyVarSet
            , ic_need_outer :: TcTyCoVarSet
ic_need_outer = TcTyCoVarSet
emptyVarSet }

data ImplicStatus
  = IC_Solved     -- All wanteds in the tree are solved, all the way down
       { ImplicStatus -> [TcTyVar]
ics_dead :: [EvVar] }  -- Subset of ic_given that are not needed
         -- See Note [Tracking redundant constraints] in TcSimplify

  | IC_Insoluble  -- At least one insoluble constraint in the tree

  | IC_BadTelescope  -- solved, but the skolems in the telescope are out of
                     -- dependency order

  | IC_Unsolved   -- Neither of the above; might go either way

instance Outputable Implication where
  ppr :: Implication -> SDoc
ppr (Implic { ic_tclvl :: Implication -> TcLevel
ic_tclvl = TcLevel
tclvl, ic_skols :: Implication -> [TcTyVar]
ic_skols = [TcTyVar]
skols
              , ic_given :: Implication -> [TcTyVar]
ic_given = [TcTyVar]
given, ic_no_eqs :: Implication -> Bool
ic_no_eqs = Bool
no_eqs
              , ic_wanted :: Implication -> WantedConstraints
ic_wanted = WantedConstraints
wanted, ic_status :: Implication -> ImplicStatus
ic_status = ImplicStatus
status
              , ic_binds :: Implication -> EvBindsVar
ic_binds = EvBindsVar
binds
              , ic_need_inner :: Implication -> TcTyCoVarSet
ic_need_inner = TcTyCoVarSet
need_in, ic_need_outer :: Implication -> TcTyCoVarSet
ic_need_outer = TcTyCoVarSet
need_out
              , ic_info :: Implication -> SkolemInfo
ic_info = SkolemInfo
info })
   = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"Implic" SDoc -> SDoc -> SDoc
<+> SDoc
lbrace)
        Int
2 ([SDoc] -> SDoc
sep [ String -> SDoc
text String
"TcLevel =" SDoc -> SDoc -> SDoc
<+> TcLevel -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcLevel
tclvl
               , String -> SDoc
text String
"Skolems =" SDoc -> SDoc -> SDoc
<+> [TcTyVar] -> SDoc
pprTyVars [TcTyVar]
skols
               , String -> SDoc
text String
"No-eqs =" SDoc -> SDoc -> SDoc
<+> Bool -> SDoc
forall a. Outputable a => a -> SDoc
ppr Bool
no_eqs
               , String -> SDoc
text String
"Status =" SDoc -> SDoc -> SDoc
<+> ImplicStatus -> SDoc
forall a. Outputable a => a -> SDoc
ppr ImplicStatus
status
               , SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"Given =")  Int
2 ([TcTyVar] -> SDoc
pprEvVars [TcTyVar]
given)
               , SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"Wanted =") Int
2 (WantedConstraints -> SDoc
forall a. Outputable a => a -> SDoc
ppr WantedConstraints
wanted)
               , String -> SDoc
text String
"Binds =" SDoc -> SDoc -> SDoc
<+> EvBindsVar -> SDoc
forall a. Outputable a => a -> SDoc
ppr EvBindsVar
binds
               , SDoc -> SDoc
whenPprDebug (String -> SDoc
text String
"Needed inner =" SDoc -> SDoc -> SDoc
<+> TcTyCoVarSet -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcTyCoVarSet
need_in)
               , SDoc -> SDoc
whenPprDebug (String -> SDoc
text String
"Needed outer =" SDoc -> SDoc -> SDoc
<+> TcTyCoVarSet -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcTyCoVarSet
need_out)
               , SkolemInfo -> SDoc
pprSkolInfo SkolemInfo
info ] SDoc -> SDoc -> SDoc
<+> SDoc
rbrace)

instance Outputable ImplicStatus where
  ppr :: ImplicStatus -> SDoc
ppr ImplicStatus
IC_Insoluble    = String -> SDoc
text String
"Insoluble"
  ppr ImplicStatus
IC_BadTelescope = String -> SDoc
text String
"Bad telescope"
  ppr ImplicStatus
IC_Unsolved     = String -> SDoc
text String
"Unsolved"
  ppr (IC_Solved { ics_dead :: ImplicStatus -> [TcTyVar]
ics_dead = [TcTyVar]
dead })
    = String -> SDoc
text String
"Solved" SDoc -> SDoc -> SDoc
<+> (SDoc -> SDoc
braces (String -> SDoc
text String
"Dead givens =" SDoc -> SDoc -> SDoc
<+> [TcTyVar] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [TcTyVar]
dead))

{- Note [Checking telescopes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When kind-checking a /user-written/ type, we might have a "bad telescope"
like this one:
  data SameKind :: forall k. k -> k -> Type
  type Foo :: forall a k (b :: k). SameKind a b -> Type

The kind of 'a' mentions 'k' which is bound after 'a'.  Oops.

Knowing this means that unification etc must have happened, so it's
convenient to detect it in the constraint solver:

* We make a single implication constraint when kind-checking
  the 'forall' in Foo's kind, something like
      forall a k (b::k). { wanted constraints }

* Having solved {wanted}, before discarding the now-solved implication,
  the costraint solver checks the dependency order of the skolem
  variables (ic_skols).  This is done in setImplicationStatus.

* This check is only necessary if the implication was born from a
  user-written signature.  If, say, it comes from checking a pattern
  match that binds existentials, where the type of the data constructor
  is known to be valid (it in tcConPat), no need for the check.

  So the check is done if and only if ic_telescope is (Just blah).

* If ic_telesope is (Just d), the d::SDoc displays the original,
  user-written type variables.

* Be careful /NOT/ to discard an implication with non-Nothing
  ic_telescope, even if ic_wanted is empty.  We must give the
  constraint solver a chance to make that bad-telesope test!  Hence
  the extra guard in emitResidualTvConstraint; see #16247

See also TcHsType Note [Keeping scoped variables in order: Explicit]

Note [Needed evidence variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Th ic_need_evs field holds the free vars of ic_binds, and all the
ic_binds in nested implications.

  * Main purpose: if one of the ic_givens is not mentioned in here, it
    is redundant.

  * solveImplication may drop an implication altogether if it has no
    remaining 'wanteds'. But we still track the free vars of its
    evidence binds, even though it has now disappeared.

Note [Shadowing in a constraint]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We assume NO SHADOWING in a constraint.  Specifically
 * The unification variables are all implicitly quantified at top
   level, and are all unique
 * The skolem variables bound in ic_skols are all freah when the
   implication is created.
So we can safely substitute. For example, if we have
   forall a.  a~Int => ...(forall b. ...a...)...
we can push the (a~Int) constraint inwards in the "givens" without
worrying that 'b' might clash.

Note [Skolems in an implication]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The skolems in an implication are not there to perform a skolem escape
check.  That happens because all the environment variables are in the
untouchables, and therefore cannot be unified with anything at all,
let alone the skolems.

Instead, ic_skols is used only when considering floating a constraint
outside the implication in TcSimplify.floatEqualities or
TcSimplify.approximateImplications

Note [Insoluble constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Some of the errors that we get during canonicalization are best
reported when all constraints have been simplified as much as
possible. For instance, assume that during simplification the
following constraints arise:

 [Wanted]   F alpha ~  uf1
 [Wanted]   beta ~ uf1 beta

When canonicalizing the wanted (beta ~ uf1 beta), if we eagerly fail
we will simply see a message:
    'Can't construct the infinite type  beta ~ uf1 beta'
and the user has no idea what the uf1 variable is.

Instead our plan is that we will NOT fail immediately, but:
    (1) Record the "frozen" error in the ic_insols field
    (2) Isolate the offending constraint from the rest of the inerts
    (3) Keep on simplifying/canonicalizing

At the end, we will hopefully have substituted uf1 := F alpha, and we
will be able to report a more informative error:
    'Can't construct the infinite type beta ~ F alpha beta'

Insoluble constraints *do* include Derived constraints. For example,
a functional dependency might give rise to [D] Int ~ Bool, and we must
report that.  If insolubles did not contain Deriveds, reportErrors would
never see it.


************************************************************************
*                                                                      *
            Pretty printing
*                                                                      *
************************************************************************
-}

pprEvVars :: [EvVar] -> SDoc    -- Print with their types
pprEvVars :: [TcTyVar] -> SDoc
pprEvVars [TcTyVar]
ev_vars = [SDoc] -> SDoc
vcat ((TcTyVar -> SDoc) -> [TcTyVar] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map TcTyVar -> SDoc
pprEvVarWithType [TcTyVar]
ev_vars)

pprEvVarTheta :: [EvVar] -> SDoc
pprEvVarTheta :: [TcTyVar] -> SDoc
pprEvVarTheta [TcTyVar]
ev_vars = [Xi] -> SDoc
pprTheta ((TcTyVar -> Xi) -> [TcTyVar] -> [Xi]
forall a b. (a -> b) -> [a] -> [b]
map TcTyVar -> Xi
evVarPred [TcTyVar]
ev_vars)

pprEvVarWithType :: EvVar -> SDoc
pprEvVarWithType :: TcTyVar -> SDoc
pprEvVarWithType TcTyVar
v = TcTyVar -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcTyVar
v SDoc -> SDoc -> SDoc
<+> SDoc
dcolon SDoc -> SDoc -> SDoc
<+> Xi -> SDoc
pprType (TcTyVar -> Xi
evVarPred TcTyVar
v)



-- | Wraps the given type with the constraints (via ic_given) in the given
-- implication, according to the variables mentioned (via ic_skols)
-- in the implication, but taking care to only wrap those variables
-- that are mentioned in the type or the implication.
wrapTypeWithImplication :: Type -> Implication -> Type
wrapTypeWithImplication :: Xi -> Implication -> Xi
wrapTypeWithImplication Xi
ty Implication
impl = Xi -> [TcTyVar] -> [Xi] -> Xi
wrapType Xi
ty [TcTyVar]
mentioned_skols [Xi]
givens
    where givens :: [Xi]
givens = (TcTyVar -> Xi) -> [TcTyVar] -> [Xi]
forall a b. (a -> b) -> [a] -> [b]
map TcTyVar -> Xi
idType ([TcTyVar] -> [Xi]) -> [TcTyVar] -> [Xi]
forall a b. (a -> b) -> a -> b
$ Implication -> [TcTyVar]
ic_given Implication
impl
          skols :: [TcTyVar]
skols = Implication -> [TcTyVar]
ic_skols Implication
impl
          freeVars :: TcTyCoVarSet
freeVars = FV -> TcTyCoVarSet
fvVarSet (FV -> TcTyCoVarSet) -> FV -> TcTyCoVarSet
forall a b. (a -> b) -> a -> b
$ [Xi] -> FV
tyCoFVsOfTypes (Xi
tyXi -> [Xi] -> [Xi]
forall a. a -> [a] -> [a]
:[Xi]
givens)
          mentioned_skols :: [TcTyVar]
mentioned_skols = (TcTyVar -> Bool) -> [TcTyVar] -> [TcTyVar]
forall a. (a -> Bool) -> [a] -> [a]
filter (TcTyVar -> TcTyCoVarSet -> Bool
`elemVarSet` TcTyCoVarSet
freeVars) [TcTyVar]
skols

wrapType :: Type -> [TyVar] -> [PredType] -> Type
wrapType :: Xi -> [TcTyVar] -> [Xi] -> Xi
wrapType Xi
ty [TcTyVar]
skols [Xi]
givens = [TcTyVar] -> Xi -> Xi
mkSpecForAllTys [TcTyVar]
skols (Xi -> Xi) -> Xi -> Xi
forall a b. (a -> b) -> a -> b
$ [Xi] -> Xi -> Xi
mkPhiTy [Xi]
givens Xi
ty


{-
************************************************************************
*                                                                      *
            CtEvidence
*                                                                      *
************************************************************************

Note [Evidence field of CtEvidence]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
During constraint solving we never look at the type of ctev_evar/ctev_dest;
instead we look at the ctev_pred field.  The evtm/evar field
may be un-zonked.

Note [Bind new Givens immediately]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For Givens we make new EvVars and bind them immediately. Two main reasons:
  * Gain sharing.  E.g. suppose we start with g :: C a b, where
       class D a => C a b
       class (E a, F a) => D a
    If we generate all g's superclasses as separate EvTerms we might
    get    selD1 (selC1 g) :: E a
           selD2 (selC1 g) :: F a
           selC1 g :: D a
    which we could do more economically as:
           g1 :: D a = selC1 g
           g2 :: E a = selD1 g1
           g3 :: F a = selD2 g1

  * For *coercion* evidence we *must* bind each given:
      class (a~b) => C a b where ....
      f :: C a b => ....
    Then in f's Givens we have g:(C a b) and the superclass sc(g,0):a~b.
    But that superclass selector can't (yet) appear in a coercion
    (see evTermCoercion), so the easy thing is to bind it to an Id.

So a Given has EvVar inside it rather than (as previously) an EvTerm.

-}

-- | A place for type-checking evidence to go after it is generated.
-- Wanted equalities are always HoleDest; other wanteds are always
-- EvVarDest.
data TcEvDest
  = EvVarDest EvVar         -- ^ bind this var to the evidence
              -- EvVarDest is always used for non-type-equalities
              -- e.g. class constraints

  | HoleDest  CoercionHole  -- ^ fill in this hole with the evidence
              -- HoleDest is always used for type-equalities
              -- See Note [Coercion holes] in TyCoRep

data CtEvidence
  = CtGiven    -- Truly given, not depending on subgoals
      { CtEvidence -> Xi
ctev_pred :: TcPredType      -- See Note [Ct/evidence invariant]
      , CtEvidence -> TcTyVar
ctev_evar :: EvVar           -- See Note [Evidence field of CtEvidence]
      , CtEvidence -> CtLoc
ctev_loc  :: CtLoc }


  | CtWanted   -- Wanted goal
      { ctev_pred :: TcPredType     -- See Note [Ct/evidence invariant]
      , CtEvidence -> TcEvDest
ctev_dest :: TcEvDest
      , CtEvidence -> ShadowInfo
ctev_nosh :: ShadowInfo     -- See Note [Constraint flavours]
      , ctev_loc  :: CtLoc }

  | CtDerived  -- A goal that we don't really have to solve and can't
               -- immediately rewrite anything other than a derived
               -- (there's no evidence!) but if we do manage to solve
               -- it may help in solving other goals.
      { ctev_pred :: TcPredType
      , ctev_loc  :: CtLoc }

ctEvPred :: CtEvidence -> TcPredType
-- The predicate of a flavor
ctEvPred :: CtEvidence -> Xi
ctEvPred = CtEvidence -> Xi
ctev_pred

ctEvLoc :: CtEvidence -> CtLoc
ctEvLoc :: CtEvidence -> CtLoc
ctEvLoc = CtEvidence -> CtLoc
ctev_loc

ctEvOrigin :: CtEvidence -> CtOrigin
ctEvOrigin :: CtEvidence -> CtOrigin
ctEvOrigin = CtLoc -> CtOrigin
ctLocOrigin (CtLoc -> CtOrigin)
-> (CtEvidence -> CtLoc) -> CtEvidence -> CtOrigin
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CtEvidence -> CtLoc
ctEvLoc

-- | Get the equality relation relevant for a 'CtEvidence'
ctEvEqRel :: CtEvidence -> EqRel
ctEvEqRel :: CtEvidence -> EqRel
ctEvEqRel = Xi -> EqRel
predTypeEqRel (Xi -> EqRel) -> (CtEvidence -> Xi) -> CtEvidence -> EqRel
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CtEvidence -> Xi
ctEvPred

-- | Get the role relevant for a 'CtEvidence'
ctEvRole :: CtEvidence -> Role
ctEvRole :: CtEvidence -> Role
ctEvRole = EqRel -> Role
eqRelRole (EqRel -> Role) -> (CtEvidence -> EqRel) -> CtEvidence -> Role
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CtEvidence -> EqRel
ctEvEqRel

ctEvTerm :: CtEvidence -> EvTerm
ctEvTerm :: CtEvidence -> EvTerm
ctEvTerm CtEvidence
ev = EvExpr -> EvTerm
EvExpr (CtEvidence -> EvExpr
ctEvExpr CtEvidence
ev)

ctEvExpr :: CtEvidence -> EvExpr
ctEvExpr :: CtEvidence -> EvExpr
ctEvExpr ev :: CtEvidence
ev@(CtWanted { ctev_dest :: CtEvidence -> TcEvDest
ctev_dest = HoleDest CoercionHole
_ })
            = Coercion -> EvExpr
forall b. Coercion -> Expr b
Coercion (Coercion -> EvExpr) -> Coercion -> EvExpr
forall a b. (a -> b) -> a -> b
$ HasDebugCallStack => CtEvidence -> Coercion
CtEvidence -> Coercion
ctEvCoercion CtEvidence
ev
ctEvExpr CtEvidence
ev = TcTyVar -> EvExpr
evId (CtEvidence -> TcTyVar
ctEvEvId CtEvidence
ev)

ctEvCoercion :: HasDebugCallStack => CtEvidence -> TcCoercion
ctEvCoercion :: CtEvidence -> Coercion
ctEvCoercion (CtGiven { ctev_evar :: CtEvidence -> TcTyVar
ctev_evar = TcTyVar
ev_id })
  = TcTyVar -> Coercion
mkTcCoVarCo TcTyVar
ev_id
ctEvCoercion (CtWanted { ctev_dest :: CtEvidence -> TcEvDest
ctev_dest = TcEvDest
dest })
  | HoleDest CoercionHole
hole <- TcEvDest
dest
  = -- ctEvCoercion is only called on type equalities
    -- and they always have HoleDests
    CoercionHole -> Coercion
mkHoleCo CoercionHole
hole
ctEvCoercion CtEvidence
ev
  = String -> SDoc -> Coercion
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"ctEvCoercion" (CtEvidence -> SDoc
forall a. Outputable a => a -> SDoc
ppr CtEvidence
ev)

ctEvEvId :: CtEvidence -> EvVar
ctEvEvId :: CtEvidence -> TcTyVar
ctEvEvId (CtWanted { ctev_dest :: CtEvidence -> TcEvDest
ctev_dest = EvVarDest TcTyVar
ev }) = TcTyVar
ev
ctEvEvId (CtWanted { ctev_dest :: CtEvidence -> TcEvDest
ctev_dest = HoleDest CoercionHole
h })   = CoercionHole -> TcTyVar
coHoleCoVar CoercionHole
h
ctEvEvId (CtGiven  { ctev_evar :: CtEvidence -> TcTyVar
ctev_evar = TcTyVar
ev })           = TcTyVar
ev
ctEvEvId ctev :: CtEvidence
ctev@(CtDerived {}) = String -> SDoc -> TcTyVar
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"ctEvId:" (CtEvidence -> SDoc
forall a. Outputable a => a -> SDoc
ppr CtEvidence
ctev)

instance Outputable TcEvDest where
  ppr :: TcEvDest -> SDoc
ppr (HoleDest CoercionHole
h)   = String -> SDoc
text String
"hole" SDoc -> SDoc -> SDoc
<> CoercionHole -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoercionHole
h
  ppr (EvVarDest TcTyVar
ev) = TcTyVar -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcTyVar
ev

instance Outputable CtEvidence where
  ppr :: CtEvidence -> SDoc
ppr CtEvidence
ev = CtFlavour -> SDoc
forall a. Outputable a => a -> SDoc
ppr (CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev)
           SDoc -> SDoc -> SDoc
<+> SDoc
pp_ev
           SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
braces (SubGoalDepth -> SDoc
forall a. Outputable a => a -> SDoc
ppr (CtLoc -> SubGoalDepth
ctl_depth (CtEvidence -> CtLoc
ctEvLoc CtEvidence
ev))) SDoc -> SDoc -> SDoc
<> SDoc
dcolon
                  -- Show the sub-goal depth too
           SDoc -> SDoc -> SDoc
<+> Xi -> SDoc
forall a. Outputable a => a -> SDoc
ppr (CtEvidence -> Xi
ctEvPred CtEvidence
ev)
    where
      pp_ev :: SDoc
pp_ev = case CtEvidence
ev of
             CtGiven { ctev_evar :: CtEvidence -> TcTyVar
ctev_evar = TcTyVar
v } -> TcTyVar -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcTyVar
v
             CtWanted {ctev_dest :: CtEvidence -> TcEvDest
ctev_dest = TcEvDest
d } -> TcEvDest -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcEvDest
d
             CtDerived {}              -> String -> SDoc
text String
"_"

isWanted :: CtEvidence -> Bool
isWanted :: CtEvidence -> Bool
isWanted (CtWanted {}) = Bool
True
isWanted CtEvidence
_ = Bool
False

isGiven :: CtEvidence -> Bool
isGiven :: CtEvidence -> Bool
isGiven (CtGiven {})  = Bool
True
isGiven CtEvidence
_ = Bool
False

isDerived :: CtEvidence -> Bool
isDerived :: CtEvidence -> Bool
isDerived (CtDerived {}) = Bool
True
isDerived CtEvidence
_              = Bool
False

{-
%************************************************************************
%*                                                                      *
            CtFlavour
%*                                                                      *
%************************************************************************

Note [Constraint flavours]
~~~~~~~~~~~~~~~~~~~~~~~~~~
Constraints come in four flavours:

* [G] Given: we have evidence

* [W] Wanted WOnly: we want evidence

* [D] Derived: any solution must satisfy this constraint, but
      we don't need evidence for it.  Examples include:
        - superclasses of [W] class constraints
        - equalities arising from functional dependencies
          or injectivity

* [WD] Wanted WDeriv: a single constraint that represents
                      both [W] and [D]
  We keep them paired as one both for efficiency, and because
  when we have a finite map  F tys -> CFunEqCan, it's inconvenient
  to have two CFunEqCans in the range

The ctev_nosh field of a Wanted distinguishes between [W] and [WD]

Wanted constraints are born as [WD], but are split into [W] and its
"shadow" [D] in TcSMonad.maybeEmitShadow.

See Note [The improvement story and derived shadows] in TcSMonad
-}

data CtFlavour  -- See Note [Constraint flavours]
  = Given
  | Wanted ShadowInfo
  | Derived
  deriving CtFlavour -> CtFlavour -> Bool
(CtFlavour -> CtFlavour -> Bool)
-> (CtFlavour -> CtFlavour -> Bool) -> Eq CtFlavour
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: CtFlavour -> CtFlavour -> Bool
$c/= :: CtFlavour -> CtFlavour -> Bool
== :: CtFlavour -> CtFlavour -> Bool
$c== :: CtFlavour -> CtFlavour -> Bool
Eq

data ShadowInfo
  = WDeriv   -- [WD] This Wanted constraint has no Derived shadow,
             -- so it behaves like a pair of a Wanted and a Derived
  | WOnly    -- [W] It has a separate derived shadow
             -- See Note [The improvement story and derived shadows] in TcSMonad
  deriving( ShadowInfo -> ShadowInfo -> Bool
(ShadowInfo -> ShadowInfo -> Bool)
-> (ShadowInfo -> ShadowInfo -> Bool) -> Eq ShadowInfo
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: ShadowInfo -> ShadowInfo -> Bool
$c/= :: ShadowInfo -> ShadowInfo -> Bool
== :: ShadowInfo -> ShadowInfo -> Bool
$c== :: ShadowInfo -> ShadowInfo -> Bool
Eq )

isGivenOrWDeriv :: CtFlavour -> Bool
isGivenOrWDeriv :: CtFlavour -> Bool
isGivenOrWDeriv CtFlavour
Given           = Bool
True
isGivenOrWDeriv (Wanted ShadowInfo
WDeriv) = Bool
True
isGivenOrWDeriv CtFlavour
_               = Bool
False

instance Outputable CtFlavour where
  ppr :: CtFlavour -> SDoc
ppr CtFlavour
Given           = String -> SDoc
text String
"[G]"
  ppr (Wanted ShadowInfo
WDeriv) = String -> SDoc
text String
"[WD]"
  ppr (Wanted ShadowInfo
WOnly)  = String -> SDoc
text String
"[W]"
  ppr CtFlavour
Derived         = String -> SDoc
text String
"[D]"

ctEvFlavour :: CtEvidence -> CtFlavour
ctEvFlavour :: CtEvidence -> CtFlavour
ctEvFlavour (CtWanted { ctev_nosh :: CtEvidence -> ShadowInfo
ctev_nosh = ShadowInfo
nosh }) = ShadowInfo -> CtFlavour
Wanted ShadowInfo
nosh
ctEvFlavour (CtGiven {})                    = CtFlavour
Given
ctEvFlavour (CtDerived {})                  = CtFlavour
Derived

-- | Whether or not one 'Ct' can rewrite another is determined by its
-- flavour and its equality relation. See also
-- Note [Flavours with roles] in TcSMonad
type CtFlavourRole = (CtFlavour, EqRel)

-- | Extract the flavour, role, and boxity from a 'CtEvidence'
ctEvFlavourRole :: CtEvidence -> CtFlavourRole
ctEvFlavourRole :: CtEvidence -> CtFlavourRole
ctEvFlavourRole CtEvidence
ev = (CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev, CtEvidence -> EqRel
ctEvEqRel CtEvidence
ev)

-- | Extract the flavour and role from a 'Ct'
ctFlavourRole :: Ct -> CtFlavourRole
-- Uses short-cuts to role for special cases
ctFlavourRole :: Ct -> CtFlavourRole
ctFlavourRole (CDictCan { cc_ev :: Ct -> CtEvidence
cc_ev = CtEvidence
ev })
  = (CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev, EqRel
NomEq)
ctFlavourRole (CTyEqCan { cc_ev :: Ct -> CtEvidence
cc_ev = CtEvidence
ev, cc_eq_rel :: Ct -> EqRel
cc_eq_rel = EqRel
eq_rel })
  = (CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev, EqRel
eq_rel)
ctFlavourRole (CFunEqCan { cc_ev :: Ct -> CtEvidence
cc_ev = CtEvidence
ev })
  = (CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev, EqRel
NomEq)
ctFlavourRole (CHoleCan { cc_ev :: Ct -> CtEvidence
cc_ev = CtEvidence
ev })
  = (CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev, EqRel
NomEq)  -- NomEq: CHoleCans can be rewritten by
                             -- by nominal equalities but empahatically
                             -- not by representational equalities
ctFlavourRole Ct
ct
  = CtEvidence -> CtFlavourRole
ctEvFlavourRole (Ct -> CtEvidence
ctEvidence Ct
ct)

{- Note [eqCanRewrite]
~~~~~~~~~~~~~~~~~~~~~~
(eqCanRewrite ct1 ct2) holds if the constraint ct1 (a CTyEqCan of form
tv ~ ty) can be used to rewrite ct2.  It must satisfy the properties of
a can-rewrite relation, see Definition [Can-rewrite relation] in
TcSMonad.

With the solver handling Coercible constraints like equality constraints,
the rewrite conditions must take role into account, never allowing
a representational equality to rewrite a nominal one.

Note [Wanteds do not rewrite Wanteds]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We don't allow Wanteds to rewrite Wanteds, because that can give rise
to very confusing type error messages.  A good example is #8450.
Here's another
   f :: a -> Bool
   f x = ( [x,'c'], [x,True] ) `seq` True
Here we get
  [W] a ~ Char
  [W] a ~ Bool
but we do not want to complain about Bool ~ Char!

Note [Deriveds do rewrite Deriveds]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
However we DO allow Deriveds to rewrite Deriveds, because that's how
improvement works; see Note [The improvement story] in TcInteract.

However, for now at least I'm only letting (Derived,NomEq) rewrite
(Derived,NomEq) and not doing anything for ReprEq.  If we have
    eqCanRewriteFR (Derived, NomEq) (Derived, _)  = True
then we lose property R2 of Definition [Can-rewrite relation]
in TcSMonad
  R2.  If f1 >= f, and f2 >= f,
       then either f1 >= f2 or f2 >= f1
Consider f1 = (Given, ReprEq)
         f2 = (Derived, NomEq)
          f = (Derived, ReprEq)

I thought maybe we could never get Derived ReprEq constraints, but
we can; straight from the Wanteds during improvement. And from a Derived
ReprEq we could conceivably get a Derived NomEq improvement (by decomposing
a type constructor with Nomninal role), and hence unify.
-}

eqCanRewrite :: EqRel -> EqRel -> Bool
eqCanRewrite :: EqRel -> EqRel -> Bool
eqCanRewrite EqRel
NomEq  EqRel
_      = Bool
True
eqCanRewrite EqRel
ReprEq EqRel
ReprEq = Bool
True
eqCanRewrite EqRel
ReprEq EqRel
NomEq  = Bool
False

eqCanRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
-- Can fr1 actually rewrite fr2?
-- Very important function!
-- See Note [eqCanRewrite]
-- See Note [Wanteds do not rewrite Wanteds]
-- See Note [Deriveds do rewrite Deriveds]
eqCanRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
eqCanRewriteFR (CtFlavour
Given,         EqRel
r1)    (CtFlavour
_,       EqRel
r2)    = EqRel -> EqRel -> Bool
eqCanRewrite EqRel
r1 EqRel
r2
eqCanRewriteFR (Wanted ShadowInfo
WDeriv, EqRel
NomEq) (CtFlavour
Derived, EqRel
NomEq) = Bool
True
eqCanRewriteFR (CtFlavour
Derived,       EqRel
NomEq) (CtFlavour
Derived, EqRel
NomEq) = Bool
True
eqCanRewriteFR CtFlavourRole
_                      CtFlavourRole
_                = Bool
False

eqMayRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
-- Is it /possible/ that fr1 can rewrite fr2?
-- This is used when deciding which inerts to kick out,
-- at which time a [WD] inert may be split into [W] and [D]
eqMayRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
eqMayRewriteFR (Wanted ShadowInfo
WDeriv, EqRel
NomEq) (Wanted ShadowInfo
WDeriv, EqRel
NomEq) = Bool
True
eqMayRewriteFR (CtFlavour
Derived,       EqRel
NomEq) (Wanted ShadowInfo
WDeriv, EqRel
NomEq) = Bool
True
eqMayRewriteFR CtFlavourRole
fr1 CtFlavourRole
fr2 = CtFlavourRole -> CtFlavourRole -> Bool
eqCanRewriteFR CtFlavourRole
fr1 CtFlavourRole
fr2

-----------------
{- Note [funEqCanDischarge]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we have two CFunEqCans with the same LHS:
    (x1:F ts ~ f1) `funEqCanDischarge` (x2:F ts ~ f2)
Can we drop x2 in favour of x1, either unifying
f2 (if it's a flatten meta-var) or adding a new Given
(f1 ~ f2), if x2 is a Given?

Answer: yes if funEqCanDischarge is true.
-}

funEqCanDischarge
  :: CtEvidence -> CtEvidence
  -> ( SwapFlag   -- NotSwapped => lhs can discharge rhs
                  -- Swapped    => rhs can discharge lhs
     , Bool)      -- True <=> upgrade non-discharded one
                  --          from [W] to [WD]
-- See Note [funEqCanDischarge]
funEqCanDischarge :: CtEvidence -> CtEvidence -> (SwapFlag, Bool)
funEqCanDischarge CtEvidence
ev1 CtEvidence
ev2
  = ASSERT2( ctEvEqRel ev1 == NomEq, ppr ev1 )
    ASSERT2( ctEvEqRel ev2 == NomEq, ppr ev2 )
    -- CFunEqCans are all Nominal, hence asserts
    CtFlavour -> CtFlavour -> (SwapFlag, Bool)
funEqCanDischargeF (CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev1) (CtEvidence -> CtFlavour
ctEvFlavour CtEvidence
ev2)

funEqCanDischargeF :: CtFlavour -> CtFlavour -> (SwapFlag, Bool)
funEqCanDischargeF :: CtFlavour -> CtFlavour -> (SwapFlag, Bool)
funEqCanDischargeF CtFlavour
Given           CtFlavour
_               = (SwapFlag
NotSwapped, Bool
False)
funEqCanDischargeF CtFlavour
_               CtFlavour
Given           = (SwapFlag
IsSwapped,  Bool
False)
funEqCanDischargeF (Wanted ShadowInfo
WDeriv) CtFlavour
_               = (SwapFlag
NotSwapped, Bool
False)
funEqCanDischargeF CtFlavour
_               (Wanted ShadowInfo
WDeriv) = (SwapFlag
IsSwapped,  Bool
True)
funEqCanDischargeF (Wanted ShadowInfo
WOnly)  (Wanted ShadowInfo
WOnly)  = (SwapFlag
NotSwapped, Bool
False)
funEqCanDischargeF (Wanted ShadowInfo
WOnly)  CtFlavour
Derived         = (SwapFlag
NotSwapped, Bool
True)
funEqCanDischargeF CtFlavour
Derived         (Wanted ShadowInfo
WOnly)  = (SwapFlag
IsSwapped,  Bool
True)
funEqCanDischargeF CtFlavour
Derived         CtFlavour
Derived         = (SwapFlag
NotSwapped, Bool
False)


{- Note [eqCanDischarge]
~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we have two identical CTyEqCan equality constraints
(i.e. both LHS and RHS are the same)
      (x1:a~t) `eqCanDischarge` (xs:a~t)
Can we just drop x2 in favour of x1?

Answer: yes if eqCanDischarge is true.

Note that we do /not/ allow Wanted to discharge Derived.
We must keep both.  Why?  Because the Derived may rewrite
other Deriveds in the model whereas the Wanted cannot.

However a Wanted can certainly discharge an identical Wanted.  So
eqCanDischarge does /not/ define a can-rewrite relation in the
sense of Definition [Can-rewrite relation] in TcSMonad.

We /do/ say that a [W] can discharge a [WD].  In evidence terms it
certainly can, and the /caller/ arranges that the otherwise-lost [D]
is spat out as a new Derived.  -}

eqCanDischargeFR :: CtFlavourRole -> CtFlavourRole -> Bool
-- See Note [eqCanDischarge]
eqCanDischargeFR :: CtFlavourRole -> CtFlavourRole -> Bool
eqCanDischargeFR (CtFlavour
f1,EqRel
r1) (CtFlavour
f2, EqRel
r2) =  EqRel -> EqRel -> Bool
eqCanRewrite EqRel
r1 EqRel
r2
                                  Bool -> Bool -> Bool
&& CtFlavour -> CtFlavour -> Bool
eqCanDischargeF CtFlavour
f1 CtFlavour
f2

eqCanDischargeF :: CtFlavour -> CtFlavour -> Bool
eqCanDischargeF :: CtFlavour -> CtFlavour -> Bool
eqCanDischargeF CtFlavour
Given   CtFlavour
_                  = Bool
True
eqCanDischargeF (Wanted ShadowInfo
_)      (Wanted ShadowInfo
_) = Bool
True
eqCanDischargeF (Wanted ShadowInfo
WDeriv) CtFlavour
Derived    = Bool
True
eqCanDischargeF CtFlavour
Derived         CtFlavour
Derived    = Bool
True
eqCanDischargeF CtFlavour
_               CtFlavour
_          = Bool
False


{-
************************************************************************
*                                                                      *
            SubGoalDepth
*                                                                      *
************************************************************************

Note [SubGoalDepth]
~~~~~~~~~~~~~~~~~~~
The 'SubGoalDepth' takes care of stopping the constraint solver from looping.

The counter starts at zero and increases. It includes dictionary constraints,
equality simplification, and type family reduction. (Why combine these? Because
it's actually quite easy to mistake one for another, in sufficiently involved
scenarios, like ConstraintKinds.)

The flag -freduction-depth=n fixes the maximium level.

* The counter includes the depth of type class instance declarations.  Example:
     [W] d{7} : Eq [Int]
  That is d's dictionary-constraint depth is 7.  If we use the instance
     $dfEqList :: Eq a => Eq [a]
  to simplify it, we get
     d{7} = $dfEqList d'{8}
  where d'{8} : Eq Int, and d' has depth 8.

  For civilised (decidable) instance declarations, each increase of
  depth removes a type constructor from the type, so the depth never
  gets big; i.e. is bounded by the structural depth of the type.

* The counter also increments when resolving
equalities involving type functions. Example:
  Assume we have a wanted at depth 7:
    [W] d{7} : F () ~ a
  If there is a type function equation "F () = Int", this would be rewritten to
    [W] d{8} : Int ~ a
  and remembered as having depth 8.

  Again, without UndecidableInstances, this counter is bounded, but without it
  can resolve things ad infinitum. Hence there is a maximum level.

* Lastly, every time an equality is rewritten, the counter increases. Again,
  rewriting an equality constraint normally makes progress, but it's possible
  the "progress" is just the reduction of an infinitely-reducing type family.
  Hence we need to track the rewrites.

When compiling a program requires a greater depth, then GHC recommends turning
off this check entirely by setting -freduction-depth=0. This is because the
exact number that works is highly variable, and is likely to change even between
minor releases. Because this check is solely to prevent infinite compilation
times, it seems safe to disable it when a user has ascertained that their program
doesn't loop at the type level.

-}

-- | See Note [SubGoalDepth]
newtype SubGoalDepth = SubGoalDepth Int
  deriving (SubGoalDepth -> SubGoalDepth -> Bool
(SubGoalDepth -> SubGoalDepth -> Bool)
-> (SubGoalDepth -> SubGoalDepth -> Bool) -> Eq SubGoalDepth
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: SubGoalDepth -> SubGoalDepth -> Bool
$c/= :: SubGoalDepth -> SubGoalDepth -> Bool
== :: SubGoalDepth -> SubGoalDepth -> Bool
$c== :: SubGoalDepth -> SubGoalDepth -> Bool
Eq, Eq SubGoalDepth
Eq SubGoalDepth
-> (SubGoalDepth -> SubGoalDepth -> Ordering)
-> (SubGoalDepth -> SubGoalDepth -> Bool)
-> (SubGoalDepth -> SubGoalDepth -> Bool)
-> (SubGoalDepth -> SubGoalDepth -> Bool)
-> (SubGoalDepth -> SubGoalDepth -> Bool)
-> (SubGoalDepth -> SubGoalDepth -> SubGoalDepth)
-> (SubGoalDepth -> SubGoalDepth -> SubGoalDepth)
-> Ord SubGoalDepth
SubGoalDepth -> SubGoalDepth -> Bool
SubGoalDepth -> SubGoalDepth -> Ordering
SubGoalDepth -> SubGoalDepth -> SubGoalDepth
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 :: SubGoalDepth -> SubGoalDepth -> SubGoalDepth
$cmin :: SubGoalDepth -> SubGoalDepth -> SubGoalDepth
max :: SubGoalDepth -> SubGoalDepth -> SubGoalDepth
$cmax :: SubGoalDepth -> SubGoalDepth -> SubGoalDepth
>= :: SubGoalDepth -> SubGoalDepth -> Bool
$c>= :: SubGoalDepth -> SubGoalDepth -> Bool
> :: SubGoalDepth -> SubGoalDepth -> Bool
$c> :: SubGoalDepth -> SubGoalDepth -> Bool
<= :: SubGoalDepth -> SubGoalDepth -> Bool
$c<= :: SubGoalDepth -> SubGoalDepth -> Bool
< :: SubGoalDepth -> SubGoalDepth -> Bool
$c< :: SubGoalDepth -> SubGoalDepth -> Bool
compare :: SubGoalDepth -> SubGoalDepth -> Ordering
$ccompare :: SubGoalDepth -> SubGoalDepth -> Ordering
$cp1Ord :: Eq SubGoalDepth
Ord, Rational -> SubGoalDepth -> SDoc
SubGoalDepth -> SDoc
(SubGoalDepth -> SDoc)
-> (Rational -> SubGoalDepth -> SDoc) -> Outputable SubGoalDepth
forall a. (a -> SDoc) -> (Rational -> a -> SDoc) -> Outputable a
pprPrec :: Rational -> SubGoalDepth -> SDoc
$cpprPrec :: Rational -> SubGoalDepth -> SDoc
ppr :: SubGoalDepth -> SDoc
$cppr :: SubGoalDepth -> SDoc
Outputable)

initialSubGoalDepth :: SubGoalDepth
initialSubGoalDepth :: SubGoalDepth
initialSubGoalDepth = Int -> SubGoalDepth
SubGoalDepth Int
0

bumpSubGoalDepth :: SubGoalDepth -> SubGoalDepth
bumpSubGoalDepth :: SubGoalDepth -> SubGoalDepth
bumpSubGoalDepth (SubGoalDepth Int
n) = Int -> SubGoalDepth
SubGoalDepth (Int
n Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int
1)

maxSubGoalDepth :: SubGoalDepth -> SubGoalDepth -> SubGoalDepth
maxSubGoalDepth :: SubGoalDepth -> SubGoalDepth -> SubGoalDepth
maxSubGoalDepth (SubGoalDepth Int
n) (SubGoalDepth Int
m) = Int -> SubGoalDepth
SubGoalDepth (Int
n Int -> Int -> Int
forall a. Ord a => a -> a -> a
`max` Int
m)

subGoalDepthExceeded :: DynFlags -> SubGoalDepth -> Bool
subGoalDepthExceeded :: DynFlags -> SubGoalDepth -> Bool
subGoalDepthExceeded DynFlags
dflags (SubGoalDepth Int
d)
  = Int -> IntWithInf
mkIntWithInf Int
d IntWithInf -> IntWithInf -> Bool
forall a. Ord a => a -> a -> Bool
> DynFlags -> IntWithInf
reductionDepth DynFlags
dflags

{-
************************************************************************
*                                                                      *
            CtLoc
*                                                                      *
************************************************************************

The 'CtLoc' gives information about where a constraint came from.
This is important for decent error message reporting because
dictionaries don't appear in the original source code.
type will evolve...

-}

data CtLoc = CtLoc { CtLoc -> CtOrigin
ctl_origin :: CtOrigin
                   , CtLoc -> TcLclEnv
ctl_env    :: TcLclEnv
                   , CtLoc -> Maybe TypeOrKind
ctl_t_or_k :: Maybe TypeOrKind  -- OK if we're not sure
                   , CtLoc -> SubGoalDepth
ctl_depth  :: !SubGoalDepth }

  -- The TcLclEnv includes particularly
  --    source location:  tcl_loc   :: RealSrcSpan
  --    context:          tcl_ctxt  :: [ErrCtxt]
  --    binder stack:     tcl_bndrs :: TcBinderStack
  --    level:            tcl_tclvl :: TcLevel

mkKindLoc :: TcType -> TcType   -- original *types* being compared
          -> CtLoc -> CtLoc
mkKindLoc :: Xi -> Xi -> CtLoc -> CtLoc
mkKindLoc Xi
s1 Xi
s2 CtLoc
loc = CtLoc -> CtOrigin -> CtLoc
setCtLocOrigin (CtLoc -> CtLoc
toKindLoc CtLoc
loc)
                        (Xi -> Maybe Xi -> CtOrigin -> Maybe TypeOrKind -> CtOrigin
KindEqOrigin Xi
s1 (Xi -> Maybe Xi
forall a. a -> Maybe a
Just Xi
s2) (CtLoc -> CtOrigin
ctLocOrigin CtLoc
loc)
                                      (CtLoc -> Maybe TypeOrKind
ctLocTypeOrKind_maybe CtLoc
loc))

-- | Take a CtLoc and moves it to the kind level
toKindLoc :: CtLoc -> CtLoc
toKindLoc :: CtLoc -> CtLoc
toKindLoc CtLoc
loc = CtLoc
loc { ctl_t_or_k :: Maybe TypeOrKind
ctl_t_or_k = TypeOrKind -> Maybe TypeOrKind
forall a. a -> Maybe a
Just TypeOrKind
KindLevel }

mkGivenLoc :: TcLevel -> SkolemInfo -> TcLclEnv -> CtLoc
mkGivenLoc :: TcLevel -> SkolemInfo -> TcLclEnv -> CtLoc
mkGivenLoc TcLevel
tclvl SkolemInfo
skol_info TcLclEnv
env
  = CtLoc :: CtOrigin -> TcLclEnv -> Maybe TypeOrKind -> SubGoalDepth -> CtLoc
CtLoc { ctl_origin :: CtOrigin
ctl_origin = SkolemInfo -> CtOrigin
GivenOrigin SkolemInfo
skol_info
          , ctl_env :: TcLclEnv
ctl_env    = TcLclEnv -> TcLevel -> TcLclEnv
setLclEnvTcLevel TcLclEnv
env TcLevel
tclvl
          , ctl_t_or_k :: Maybe TypeOrKind
ctl_t_or_k = Maybe TypeOrKind
forall a. Maybe a
Nothing    -- this only matters for error msgs
          , ctl_depth :: SubGoalDepth
ctl_depth  = SubGoalDepth
initialSubGoalDepth }

ctLocEnv :: CtLoc -> TcLclEnv
ctLocEnv :: CtLoc -> TcLclEnv
ctLocEnv = CtLoc -> TcLclEnv
ctl_env

ctLocLevel :: CtLoc -> TcLevel
ctLocLevel :: CtLoc -> TcLevel
ctLocLevel CtLoc
loc = TcLclEnv -> TcLevel
getLclEnvTcLevel (CtLoc -> TcLclEnv
ctLocEnv CtLoc
loc)

ctLocDepth :: CtLoc -> SubGoalDepth
ctLocDepth :: CtLoc -> SubGoalDepth
ctLocDepth = CtLoc -> SubGoalDepth
ctl_depth

ctLocOrigin :: CtLoc -> CtOrigin
ctLocOrigin :: CtLoc -> CtOrigin
ctLocOrigin = CtLoc -> CtOrigin
ctl_origin

ctLocSpan :: CtLoc -> RealSrcSpan
ctLocSpan :: CtLoc -> RealSrcSpan
ctLocSpan (CtLoc { ctl_env :: CtLoc -> TcLclEnv
ctl_env = TcLclEnv
lcl}) = TcLclEnv -> RealSrcSpan
getLclEnvLoc TcLclEnv
lcl

ctLocTypeOrKind_maybe :: CtLoc -> Maybe TypeOrKind
ctLocTypeOrKind_maybe :: CtLoc -> Maybe TypeOrKind
ctLocTypeOrKind_maybe = CtLoc -> Maybe TypeOrKind
ctl_t_or_k

setCtLocSpan :: CtLoc -> RealSrcSpan -> CtLoc
setCtLocSpan :: CtLoc -> RealSrcSpan -> CtLoc
setCtLocSpan ctl :: CtLoc
ctl@(CtLoc { ctl_env :: CtLoc -> TcLclEnv
ctl_env = TcLclEnv
lcl }) RealSrcSpan
loc = CtLoc -> TcLclEnv -> CtLoc
setCtLocEnv CtLoc
ctl (TcLclEnv -> RealSrcSpan -> TcLclEnv
setLclEnvLoc TcLclEnv
lcl RealSrcSpan
loc)

bumpCtLocDepth :: CtLoc -> CtLoc
bumpCtLocDepth :: CtLoc -> CtLoc
bumpCtLocDepth loc :: CtLoc
loc@(CtLoc { ctl_depth :: CtLoc -> SubGoalDepth
ctl_depth = SubGoalDepth
d }) = CtLoc
loc { ctl_depth :: SubGoalDepth
ctl_depth = SubGoalDepth -> SubGoalDepth
bumpSubGoalDepth SubGoalDepth
d }

setCtLocOrigin :: CtLoc -> CtOrigin -> CtLoc
setCtLocOrigin :: CtLoc -> CtOrigin -> CtLoc
setCtLocOrigin CtLoc
ctl CtOrigin
orig = CtLoc
ctl { ctl_origin :: CtOrigin
ctl_origin = CtOrigin
orig }

updateCtLocOrigin :: CtLoc -> (CtOrigin -> CtOrigin) -> CtLoc
updateCtLocOrigin :: CtLoc -> (CtOrigin -> CtOrigin) -> CtLoc
updateCtLocOrigin ctl :: CtLoc
ctl@(CtLoc { ctl_origin :: CtLoc -> CtOrigin
ctl_origin = CtOrigin
orig }) CtOrigin -> CtOrigin
upd
  = CtLoc
ctl { ctl_origin :: CtOrigin
ctl_origin = CtOrigin -> CtOrigin
upd CtOrigin
orig }

setCtLocEnv :: CtLoc -> TcLclEnv -> CtLoc
setCtLocEnv :: CtLoc -> TcLclEnv -> CtLoc
setCtLocEnv CtLoc
ctl TcLclEnv
env = CtLoc
ctl { ctl_env :: TcLclEnv
ctl_env = TcLclEnv
env }

pprCtLoc :: CtLoc -> SDoc
-- "arising from ... at ..."
-- Not an instance of Outputable because of the "arising from" prefix
pprCtLoc :: CtLoc -> SDoc
pprCtLoc (CtLoc { ctl_origin :: CtLoc -> CtOrigin
ctl_origin = CtOrigin
o, ctl_env :: CtLoc -> TcLclEnv
ctl_env = TcLclEnv
lcl})
  = [SDoc] -> SDoc
sep [ CtOrigin -> SDoc
pprCtOrigin CtOrigin
o
        , String -> SDoc
text String
"at" SDoc -> SDoc -> SDoc
<+> RealSrcSpan -> SDoc
forall a. Outputable a => a -> SDoc
ppr (TcLclEnv -> RealSrcSpan
getLclEnvLoc TcLclEnv
lcl)]