{-# LANGUAGE TypeFamilies #-}

{-
(c) The University of Glasgow 2006
(c) The AQUA Project, Glasgow University, 1993-1998

-}

-- | Typechecking rewrite rules
module GHC.Tc.Gen.Rule ( tcRules ) where

import GHC.Prelude

import GHC.Hs
import GHC.Tc.Types
import GHC.Tc.Utils.Monad
import GHC.Tc.Solver
import GHC.Tc.Types.Constraint
import GHC.Core.Predicate
import GHC.Tc.Types.Origin
import GHC.Tc.Utils.TcMType
import GHC.Tc.Utils.TcType
import GHC.Tc.Gen.HsType
import GHC.Tc.Gen.Expr
import GHC.Tc.Utils.Env
import GHC.Tc.Utils.Unify( buildImplicationFor )
import GHC.Tc.Types.Evidence( mkTcCoVarCo )
import GHC.Core.Type
import GHC.Core.TyCon( isTypeFamilyTyCon )
import GHC.Types.Id
import GHC.Types.Var( EvVar )
import GHC.Types.Var.Set
import GHC.Types.Basic ( RuleName )
import GHC.Types.SrcLoc
import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Data.FastString
import GHC.Data.Bag

{-
Note [Typechecking rules]
~~~~~~~~~~~~~~~~~~~~~~~~~
We *infer* the typ of the LHS, and use that type to *check* the type of
the RHS.  That means that higher-rank rules work reasonably well. Here's
an example (test simplCore/should_compile/rule2.hs) produced by Roman:

   foo :: (forall m. m a -> m b) -> m a -> m b
   foo f = ...

   bar :: (forall m. m a -> m a) -> m a -> m a
   bar f = ...

   {-# RULES "foo/bar" foo = bar #-}

He wanted the rule to typecheck.

Note [TcLevel in type checking rules]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Bringing type variables into scope naturally bumps the TcLevel. Thus, we type
check the term-level binders in a bumped level, and we must accordingly bump
the level whenever these binders are in scope.

Note [Re-quantify type variables in rules]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this example from #17710:

  foo :: forall k (a :: k) (b :: k). Proxy a -> Proxy b
  foo x = Proxy
  {-# RULES "foo" forall (x :: Proxy (a :: k)). foo x = Proxy #-}

Written out in more detail, the "foo" rewrite rule looks like this:

  forall k (a :: k). forall (x :: Proxy (a :: k)). foo @k @a @b0 x = Proxy @k @b0

Where b0 is a unification variable. Where should b0 be quantified? We have to
quantify it after k, since (b0 :: k). But generalization usually puts inferred
type variables (such as b0) at the /front/ of the telescope! This creates a
conflict.

One option is to simply throw an error, per the principles of
Note [Naughty quantification candidates] in GHC.Tc.Utils.TcMType. This is what would happen
if we were generalising over a normal type signature. On the other hand, the
types in a rewrite rule aren't quite "normal", since the notions of specified
and inferred type variables aren't applicable.

A more permissive design (and the design that GHC uses) is to simply requantify
all of the type variables. That is, we would end up with this:

  forall k (a :: k) (b :: k). forall (x :: Proxy (a :: k)). foo @k @a @b x = Proxy @k @b

It's a bit strange putting the generalized variable `b` after the user-written
variables `k` and `a`. But again, the notion of specificity is not relevant to
rewrite rules, since one cannot "visibly apply" a rewrite rule. This design not
only makes "foo" typecheck, but it also makes the implementation simpler.

See also Note [Generalising in tcTyFamInstEqnGuts] in GHC.Tc.TyCl, which
explains a very similar design when generalising over a type family instance
equation.
-}

tcRules :: [LRuleDecls GhcRn] -> TcM [LRuleDecls GhcTc]
tcRules :: [LRuleDecls GhcRn] -> TcM [LRuleDecls GhcTc]
tcRules [LRuleDecls GhcRn]
decls = (GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecls GhcRn)
 -> IOEnv
      (Env TcGblEnv TcLclEnv)
      (GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecls GhcTc)))
-> [GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecls GhcRn)]
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     [GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecls GhcTc)]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM ((RuleDecls GhcRn -> TcM (RuleDecls GhcTc))
-> GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecls GhcRn)
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     (GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecls GhcTc))
forall a b ann.
(a -> TcM b)
-> GenLocated (SrcSpanAnn' ann) a
-> TcRn (GenLocated (SrcSpanAnn' ann) b)
wrapLocMA RuleDecls GhcRn -> TcM (RuleDecls GhcTc)
tcRuleDecls) [GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecls GhcRn)]
[LRuleDecls GhcRn]
decls

tcRuleDecls :: RuleDecls GhcRn -> TcM (RuleDecls GhcTc)
tcRuleDecls :: RuleDecls GhcRn -> TcM (RuleDecls GhcTc)
tcRuleDecls (HsRules { rds_src :: forall pass. RuleDecls pass -> SourceText
rds_src = SourceText
src
                     , rds_rules :: forall pass. RuleDecls pass -> [LRuleDecl pass]
rds_rules = [LRuleDecl GhcRn]
decls })
   = do { [GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcTc)]
tc_decls <- (GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcRn)
 -> IOEnv
      (Env TcGblEnv TcLclEnv)
      (GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcTc)))
-> [GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcRn)]
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     [GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcTc)]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM ((RuleDecl GhcRn -> TcM (RuleDecl GhcTc))
-> GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcRn)
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     (GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcTc))
forall a b ann.
(a -> TcM b)
-> GenLocated (SrcSpanAnn' ann) a
-> TcRn (GenLocated (SrcSpanAnn' ann) b)
wrapLocMA RuleDecl GhcRn -> TcM (RuleDecl GhcTc)
tcRule) [GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcRn)]
[LRuleDecl GhcRn]
decls
        ; RuleDecls GhcTc -> TcM (RuleDecls GhcTc)
forall (m :: * -> *) a. Monad m => a -> m a
return (RuleDecls GhcTc -> TcM (RuleDecls GhcTc))
-> RuleDecls GhcTc -> TcM (RuleDecls GhcTc)
forall a b. (a -> b) -> a -> b
$ HsRules { rds_ext :: XCRuleDecls GhcTc
rds_ext   = NoExtField
XCRuleDecls GhcTc
noExtField
                           , rds_src :: SourceText
rds_src   = SourceText
src
                           , rds_rules :: [LRuleDecl GhcTc]
rds_rules = [GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (RuleDecl GhcTc)]
[LRuleDecl GhcTc]
tc_decls } }

tcRule :: RuleDecl GhcRn -> TcM (RuleDecl GhcTc)
tcRule :: RuleDecl GhcRn -> TcM (RuleDecl GhcTc)
tcRule (HsRule { rd_ext :: forall pass. RuleDecl pass -> XHsRule pass
rd_ext  = XHsRule GhcRn
ext
               , rd_name :: forall pass. RuleDecl pass -> XRec pass (SourceText, RuleName)
rd_name = rname :: XRec GhcRn (SourceText, RuleName)
rname@(L SrcSpan
_ (SourceText
_,RuleName
name))
               , rd_act :: forall pass. RuleDecl pass -> Activation
rd_act  = Activation
act
               , rd_tyvs :: forall pass.
RuleDecl pass -> Maybe [LHsTyVarBndr () (NoGhcTc pass)]
rd_tyvs = Maybe [LHsTyVarBndr () (NoGhcTc GhcRn)]
ty_bndrs
               , rd_tmvs :: forall pass. RuleDecl pass -> [LRuleBndr pass]
rd_tmvs = [LRuleBndr GhcRn]
tm_bndrs
               , rd_lhs :: forall pass. RuleDecl pass -> XRec pass (HsExpr pass)
rd_lhs  = XRec GhcRn (HsExpr GhcRn)
lhs
               , rd_rhs :: forall pass. RuleDecl pass -> XRec pass (HsExpr pass)
rd_rhs  = XRec GhcRn (HsExpr GhcRn)
rhs })
  = SDoc -> TcM (RuleDecl GhcTc) -> TcM (RuleDecl GhcTc)
forall a. SDoc -> TcM a -> TcM a
addErrCtxt (RuleName -> SDoc
ruleCtxt RuleName
name)  (TcM (RuleDecl GhcTc) -> TcM (RuleDecl GhcTc))
-> TcM (RuleDecl GhcTc) -> TcM (RuleDecl GhcTc)
forall a b. (a -> b) -> a -> b
$
    do { String -> SDoc -> TcRn ()
traceTc String
"---- Rule ------" (GenLocated SrcSpan (SourceText, RuleName) -> SDoc
pprFullRuleName GenLocated SrcSpan (SourceText, RuleName)
XRec GhcRn (SourceText, RuleName)
rname)

        -- Note [Typechecking rules]
       ; (TcLevel
tc_lvl, ([TcTyVar],
 GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
 WantedConstraints,
 GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
 WantedConstraints, Type)
stuff) <- TcM
  ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
   WantedConstraints, Type)
-> TcM
     (TcLevel,
      ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
       WantedConstraints, Type))
forall a. TcM a -> TcM (TcLevel, a)
pushTcLevelM (TcM
   ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
    WantedConstraints, Type)
 -> TcM
      (TcLevel,
       ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
        WantedConstraints, Type)))
-> TcM
     ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
      WantedConstraints, Type)
-> TcM
     (TcLevel,
      ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
       WantedConstraints, Type))
forall a b. (a -> b) -> a -> b
$
                            Maybe [LHsTyVarBndr () GhcRn]
-> [LRuleBndr GhcRn]
-> XRec GhcRn (HsExpr GhcRn)
-> XRec GhcRn (HsExpr GhcRn)
-> TcM
     ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
      WantedConstraints, Type)
generateRuleConstraints Maybe [LHsTyVarBndr () (NoGhcTc GhcRn)]
Maybe [LHsTyVarBndr () GhcRn]
ty_bndrs [LRuleBndr GhcRn]
tm_bndrs XRec GhcRn (HsExpr GhcRn)
lhs XRec GhcRn (HsExpr GhcRn)
rhs

       ; let ([TcTyVar]
id_bndrs, GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc)
lhs', WantedConstraints
lhs_wanted
                      , GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc)
rhs', WantedConstraints
rhs_wanted, Type
rule_ty) = ([TcTyVar],
 GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
 WantedConstraints,
 GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
 WantedConstraints, Type)
stuff

       ; String -> SDoc -> TcRn ()
traceTc String
"tcRule 1" ([SDoc] -> SDoc
vcat [ GenLocated SrcSpan (SourceText, RuleName) -> SDoc
pprFullRuleName GenLocated SrcSpan (SourceText, RuleName)
XRec GhcRn (SourceText, RuleName)
rname
                                  , WantedConstraints -> SDoc
forall a. Outputable a => a -> SDoc
ppr WantedConstraints
lhs_wanted
                                  , WantedConstraints -> SDoc
forall a. Outputable a => a -> SDoc
ppr WantedConstraints
rhs_wanted ])

       ; ([TcTyVar]
lhs_evs, WantedConstraints
residual_lhs_wanted)
            <- RuleName
-> TcLevel
-> WantedConstraints
-> WantedConstraints
-> TcM ([TcTyVar], WantedConstraints)
simplifyRule RuleName
name TcLevel
tc_lvl WantedConstraints
lhs_wanted WantedConstraints
rhs_wanted

       -- SimplifyRule Plan, step 4
       -- Now figure out what to quantify over
       -- c.f. GHC.Tc.Solver.simplifyInfer
       -- We quantify over any tyvars free in *either* the rule
       --  *or* the bound variables.  The latter is important.  Consider
       --      ss (x,(y,z)) = (x,z)
       --      RULE:  forall v. fst (ss v) = fst v
       -- The type of the rhs of the rule is just a, but v::(a,(b,c))
       --
       -- We also need to get the completely-unconstrained tyvars of
       -- the LHS, lest they otherwise get defaulted to Any; but we do that
       -- during zonking (see GHC.Tc.Utils.Zonk.zonkRule)

       ; let tpl_ids :: [TcTyVar]
tpl_ids = [TcTyVar]
lhs_evs [TcTyVar] -> [TcTyVar] -> [TcTyVar]
forall a. [a] -> [a] -> [a]
++ [TcTyVar]
id_bndrs

       -- See Note [Re-quantify type variables in rules]
       ; CandidatesQTvs
forall_tkvs <- [Type] -> TcM CandidatesQTvs
candidateQTyVarsOfTypes (Type
rule_ty Type -> [Type] -> [Type]
forall a. a -> [a] -> [a]
: (TcTyVar -> Type) -> [TcTyVar] -> [Type]
forall a b. (a -> b) -> [a] -> [b]
map TcTyVar -> Type
idType [TcTyVar]
tpl_ids)
       ; [TcTyVar]
qtkvs <- CandidatesQTvs -> TcM [TcTyVar]
quantifyTyVars CandidatesQTvs
forall_tkvs
       ; String -> SDoc -> TcRn ()
traceTc String
"tcRule" ([SDoc] -> SDoc
vcat [ GenLocated SrcSpan (SourceText, RuleName) -> SDoc
pprFullRuleName GenLocated SrcSpan (SourceText, RuleName)
XRec GhcRn (SourceText, RuleName)
rname
                                , CandidatesQTvs -> SDoc
forall a. Outputable a => a -> SDoc
ppr CandidatesQTvs
forall_tkvs
                                , [TcTyVar] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [TcTyVar]
qtkvs
                                , Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
rule_ty
                                , [SDoc] -> SDoc
vcat [ TcTyVar -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcTyVar
id SDoc -> SDoc -> SDoc
<+> SDoc
dcolon SDoc -> SDoc -> SDoc
<+> Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr (TcTyVar -> Type
idType TcTyVar
id) | TcTyVar
id <- [TcTyVar]
tpl_ids ]
                  ])

       -- SimplfyRule Plan, step 5
       -- Simplify the LHS and RHS constraints:
       -- For the LHS constraints we must solve the remaining constraints
       -- (a) so that we report insoluble ones
       -- (b) so that we bind any soluble ones
       ; let skol_info :: SkolemInfo
skol_info = RuleName -> SkolemInfo
RuleSkol RuleName
name
       ; (Bag Implication
lhs_implic, TcEvBinds
lhs_binds) <- TcLevel
-> SkolemInfo
-> [TcTyVar]
-> [TcTyVar]
-> WantedConstraints
-> TcM (Bag Implication, TcEvBinds)
buildImplicationFor TcLevel
tc_lvl SkolemInfo
skol_info [TcTyVar]
qtkvs
                                         [TcTyVar]
lhs_evs WantedConstraints
residual_lhs_wanted
       ; (Bag Implication
rhs_implic, TcEvBinds
rhs_binds) <- TcLevel
-> SkolemInfo
-> [TcTyVar]
-> [TcTyVar]
-> WantedConstraints
-> TcM (Bag Implication, TcEvBinds)
buildImplicationFor TcLevel
tc_lvl SkolemInfo
skol_info [TcTyVar]
qtkvs
                                         [TcTyVar]
lhs_evs WantedConstraints
rhs_wanted

       ; Bag Implication -> TcRn ()
emitImplications (Bag Implication
lhs_implic Bag Implication -> Bag Implication -> Bag Implication
forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag Implication
rhs_implic)
       ; RuleDecl GhcTc -> TcM (RuleDecl GhcTc)
forall (m :: * -> *) a. Monad m => a -> m a
return (RuleDecl GhcTc -> TcM (RuleDecl GhcTc))
-> RuleDecl GhcTc -> TcM (RuleDecl GhcTc)
forall a b. (a -> b) -> a -> b
$ HsRule { rd_ext :: XHsRule GhcTc
rd_ext = XHsRule GhcRn
XHsRule GhcTc
ext
                         , rd_name :: XRec GhcTc (SourceText, RuleName)
rd_name = XRec GhcRn (SourceText, RuleName)
XRec GhcTc (SourceText, RuleName)
rname
                         , rd_act :: Activation
rd_act = Activation
act
                         , rd_tyvs :: Maybe [LHsTyVarBndr () (NoGhcTc GhcTc)]
rd_tyvs = Maybe [LHsTyVarBndr () (NoGhcTc GhcRn)]
Maybe [LHsTyVarBndr () (NoGhcTc GhcTc)]
ty_bndrs -- preserved for ppr-ing
                         , rd_tmvs :: [LRuleBndr GhcTc]
rd_tmvs = (TcTyVar -> Located (RuleBndr GhcTc))
-> [TcTyVar] -> [Located (RuleBndr GhcTc)]
forall a b. (a -> b) -> [a] -> [b]
map (RuleBndr GhcTc -> Located (RuleBndr GhcTc)
forall e. e -> Located e
noLoc (RuleBndr GhcTc -> Located (RuleBndr GhcTc))
-> (TcTyVar -> RuleBndr GhcTc)
-> TcTyVar
-> Located (RuleBndr GhcTc)
forall b c a. (b -> c) -> (a -> b) -> a -> c
. XCRuleBndr GhcTc -> LIdP GhcTc -> RuleBndr GhcTc
forall pass. XCRuleBndr pass -> LIdP pass -> RuleBndr pass
RuleBndr XCRuleBndr GhcTc
forall a. EpAnn a
noAnn (GenLocated SrcSpanAnnN TcTyVar -> RuleBndr GhcTc)
-> (TcTyVar -> GenLocated SrcSpanAnnN TcTyVar)
-> TcTyVar
-> RuleBndr GhcTc
forall b c a. (b -> c) -> (a -> b) -> a -> c
. TcTyVar -> GenLocated SrcSpanAnnN TcTyVar
forall a an. a -> LocatedAn an a
noLocA)
                                         ([TcTyVar]
qtkvs [TcTyVar] -> [TcTyVar] -> [TcTyVar]
forall a. [a] -> [a] -> [a]
++ [TcTyVar]
tpl_ids)
                         , rd_lhs :: LHsExpr GhcTc
rd_lhs  = TcEvBinds -> LHsExpr GhcTc -> LHsExpr GhcTc
mkHsDictLet TcEvBinds
lhs_binds GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc)
LHsExpr GhcTc
lhs'
                         , rd_rhs :: LHsExpr GhcTc
rd_rhs  = TcEvBinds -> LHsExpr GhcTc -> LHsExpr GhcTc
mkHsDictLet TcEvBinds
rhs_binds GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc)
LHsExpr GhcTc
rhs' } }

generateRuleConstraints :: Maybe [LHsTyVarBndr () GhcRn] -> [LRuleBndr GhcRn]
                        -> LHsExpr GhcRn -> LHsExpr GhcRn
                        -> TcM ( [TcId]
                               , LHsExpr GhcTc, WantedConstraints
                               , LHsExpr GhcTc, WantedConstraints
                               , TcType )
generateRuleConstraints :: Maybe [LHsTyVarBndr () GhcRn]
-> [LRuleBndr GhcRn]
-> XRec GhcRn (HsExpr GhcRn)
-> XRec GhcRn (HsExpr GhcRn)
-> TcM
     ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
      WantedConstraints, Type)
generateRuleConstraints Maybe [LHsTyVarBndr () GhcRn]
ty_bndrs [LRuleBndr GhcRn]
tm_bndrs XRec GhcRn (HsExpr GhcRn)
lhs XRec GhcRn (HsExpr GhcRn)
rhs
  = do { (([TcTyVar]
tv_bndrs, [TcTyVar]
id_bndrs), WantedConstraints
bndr_wanted) <- TcM ([TcTyVar], [TcTyVar])
-> TcM (([TcTyVar], [TcTyVar]), WantedConstraints)
forall a. TcM a -> TcM (a, WantedConstraints)
captureConstraints (TcM ([TcTyVar], [TcTyVar])
 -> TcM (([TcTyVar], [TcTyVar]), WantedConstraints))
-> TcM ([TcTyVar], [TcTyVar])
-> TcM (([TcTyVar], [TcTyVar]), WantedConstraints)
forall a b. (a -> b) -> a -> b
$
                                                Maybe [LHsTyVarBndr () GhcRn]
-> [LRuleBndr GhcRn] -> TcM ([TcTyVar], [TcTyVar])
tcRuleBndrs Maybe [LHsTyVarBndr () GhcRn]
ty_bndrs [LRuleBndr GhcRn]
tm_bndrs
              -- bndr_wanted constraints can include wildcard hole
              -- constraints, which we should not forget about.
              -- It may mention the skolem type variables bound by
              -- the RULE.  c.f. #10072

       ; [TcTyVar]
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
forall r. [TcTyVar] -> TcM r -> TcM r
tcExtendTyVarEnv [TcTyVar]
tv_bndrs (TcM
   ([TcTyVar],
    GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
    WantedConstraints,
    GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
    WantedConstraints, Type)
 -> TcM
      ([TcTyVar],
       GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
       WantedConstraints,
       GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
       WantedConstraints, Type))
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
forall a b. (a -> b) -> a -> b
$
         [TcTyVar]
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
forall r. [TcTyVar] -> TcM r -> TcM r
tcExtendIdEnv    [TcTyVar]
id_bndrs (TcM
   ([TcTyVar],
    GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
    WantedConstraints,
    GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
    WantedConstraints, Type)
 -> TcM
      ([TcTyVar],
       GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
       WantedConstraints,
       GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
       WantedConstraints, Type))
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
forall a b. (a -> b) -> a -> b
$
    do { -- See Note [Solve order for RULES]
         ((GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc)
lhs', Type
rule_ty), WantedConstraints
lhs_wanted) <- TcM
  (GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc), Type)
-> TcM
     ((GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
       Type),
      WantedConstraints)
forall a. TcM a -> TcM (a, WantedConstraints)
captureConstraints (XRec GhcRn (HsExpr GhcRn) -> TcM (LHsExpr GhcTc, Type)
tcInferRho XRec GhcRn (HsExpr GhcRn)
lhs)
       ; (GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc)
rhs',            WantedConstraints
rhs_wanted) <- TcM (LHsExpr GhcTc) -> TcM (LHsExpr GhcTc, WantedConstraints)
forall a. TcM a -> TcM (a, WantedConstraints)
captureConstraints (TcM (LHsExpr GhcTc) -> TcM (LHsExpr GhcTc, WantedConstraints))
-> TcM (LHsExpr GhcTc) -> TcM (LHsExpr GhcTc, WantedConstraints)
forall a b. (a -> b) -> a -> b
$
                                          XRec GhcRn (HsExpr GhcRn) -> Type -> TcM (LHsExpr GhcTc)
tcCheckMonoExpr XRec GhcRn (HsExpr GhcRn)
rhs Type
rule_ty
       ; let all_lhs_wanted :: WantedConstraints
all_lhs_wanted = WantedConstraints
bndr_wanted WantedConstraints -> WantedConstraints -> WantedConstraints
`andWC` WantedConstraints
lhs_wanted
       ; ([TcTyVar],
 GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
 WantedConstraints,
 GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
 WantedConstraints, Type)
-> TcM
     ([TcTyVar],
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints,
      GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc),
      WantedConstraints, Type)
forall (m :: * -> *) a. Monad m => a -> m a
return ([TcTyVar]
id_bndrs, GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc)
lhs', WantedConstraints
all_lhs_wanted, GenLocated (SrcSpanAnn' (EpAnn AnnListItem)) (HsExpr GhcTc)
rhs', WantedConstraints
rhs_wanted, Type
rule_ty) } }

-- See Note [TcLevel in type checking rules]
tcRuleBndrs :: Maybe [LHsTyVarBndr () GhcRn] -> [LRuleBndr GhcRn]
            -> TcM ([TcTyVar], [Id])
tcRuleBndrs :: Maybe [LHsTyVarBndr () GhcRn]
-> [LRuleBndr GhcRn] -> TcM ([TcTyVar], [TcTyVar])
tcRuleBndrs (Just [LHsTyVarBndr () GhcRn]
bndrs) [LRuleBndr GhcRn]
xs
  = do { ([VarBndr TcTyVar ()]
tybndrs1,([TcTyVar]
tys2,[TcTyVar]
tms)) <- [LHsTyVarBndr () GhcRn]
-> TcM ([TcTyVar], [TcTyVar])
-> TcM ([VarBndr TcTyVar ()], ([TcTyVar], [TcTyVar]))
forall flag a.
OutputableBndrFlag flag 'Renamed =>
[LHsTyVarBndr flag GhcRn]
-> TcM a -> TcM ([VarBndr TcTyVar flag], a)
bindExplicitTKBndrs_Skol [LHsTyVarBndr () GhcRn]
bndrs (TcM ([TcTyVar], [TcTyVar])
 -> TcM ([VarBndr TcTyVar ()], ([TcTyVar], [TcTyVar])))
-> TcM ([TcTyVar], [TcTyVar])
-> TcM ([VarBndr TcTyVar ()], ([TcTyVar], [TcTyVar]))
forall a b. (a -> b) -> a -> b
$
                                  [LRuleBndr GhcRn] -> TcM ([TcTyVar], [TcTyVar])
tcRuleTmBndrs [LRuleBndr GhcRn]
xs
       ; let tys1 :: [TcTyVar]
tys1 = [VarBndr TcTyVar ()] -> [TcTyVar]
forall tv argf. [VarBndr tv argf] -> [tv]
binderVars [VarBndr TcTyVar ()]
tybndrs1
       ; ([TcTyVar], [TcTyVar]) -> TcM ([TcTyVar], [TcTyVar])
forall (m :: * -> *) a. Monad m => a -> m a
return ([TcTyVar]
tys1 [TcTyVar] -> [TcTyVar] -> [TcTyVar]
forall a. [a] -> [a] -> [a]
++ [TcTyVar]
tys2, [TcTyVar]
tms) }

tcRuleBndrs Maybe [LHsTyVarBndr () GhcRn]
Nothing [LRuleBndr GhcRn]
xs
  = [LRuleBndr GhcRn] -> TcM ([TcTyVar], [TcTyVar])
tcRuleTmBndrs [LRuleBndr GhcRn]
xs

-- See Note [TcLevel in type checking rules]
tcRuleTmBndrs :: [LRuleBndr GhcRn] -> TcM ([TcTyVar],[Id])
tcRuleTmBndrs :: [LRuleBndr GhcRn] -> TcM ([TcTyVar], [TcTyVar])
tcRuleTmBndrs [] = ([TcTyVar], [TcTyVar]) -> TcM ([TcTyVar], [TcTyVar])
forall (m :: * -> *) a. Monad m => a -> m a
return ([],[])
tcRuleTmBndrs (L SrcSpan
_ (RuleBndr XCRuleBndr GhcRn
_ (L SrcSpanAnnN
_ Name
name)) : [LRuleBndr GhcRn]
rule_bndrs)
  = do  { Type
ty <- TcM Type
newOpenFlexiTyVarTy
        ; ([TcTyVar]
tyvars, [TcTyVar]
tmvars) <- [LRuleBndr GhcRn] -> TcM ([TcTyVar], [TcTyVar])
tcRuleTmBndrs [LRuleBndr GhcRn]
rule_bndrs
        ; ([TcTyVar], [TcTyVar]) -> TcM ([TcTyVar], [TcTyVar])
forall (m :: * -> *) a. Monad m => a -> m a
return ([TcTyVar]
tyvars, HasDebugCallStack => Name -> Type -> Type -> TcTyVar
Name -> Type -> Type -> TcTyVar
mkLocalId Name
name Type
Many Type
ty TcTyVar -> [TcTyVar] -> [TcTyVar]
forall a. a -> [a] -> [a]
: [TcTyVar]
tmvars) }
tcRuleTmBndrs (L SrcSpan
_ (RuleBndrSig XRuleBndrSig GhcRn
_ (L SrcSpanAnnN
_ Name
name) HsPatSigType GhcRn
rn_ty) : [LRuleBndr GhcRn]
rule_bndrs)
--  e.g         x :: a->a
--  The tyvar 'a' is brought into scope first, just as if you'd written
--              a::*, x :: a->a
--  If there's an explicit forall, the renamer would have already reported an
--   error for each out-of-scope type variable used
  = do  { let ctxt :: UserTypeCtxt
ctxt = Name -> UserTypeCtxt
RuleSigCtxt Name
name
        ; ([(Name, TcTyVar)]
_ , [(Name, TcTyVar)]
tvs, Type
id_ty) <- UserTypeCtxt
-> HoleMode
-> HsPatSigType GhcRn
-> ContextKind
-> TcM ([(Name, TcTyVar)], [(Name, TcTyVar)], Type)
tcHsPatSigType UserTypeCtxt
ctxt HoleMode
HM_Sig HsPatSigType GhcRn
rn_ty ContextKind
OpenKind
        ; let id :: TcTyVar
id  = HasDebugCallStack => Name -> Type -> Type -> TcTyVar
Name -> Type -> Type -> TcTyVar
mkLocalId Name
name Type
Many Type
id_ty
                    -- See Note [Typechecking pattern signature binders] in GHC.Tc.Gen.HsType

              -- The type variables scope over subsequent bindings; yuk
        ; ([TcTyVar]
tyvars, [TcTyVar]
tmvars) <- [(Name, TcTyVar)]
-> TcM ([TcTyVar], [TcTyVar]) -> TcM ([TcTyVar], [TcTyVar])
forall r. [(Name, TcTyVar)] -> TcM r -> TcM r
tcExtendNameTyVarEnv [(Name, TcTyVar)]
tvs (TcM ([TcTyVar], [TcTyVar]) -> TcM ([TcTyVar], [TcTyVar]))
-> TcM ([TcTyVar], [TcTyVar]) -> TcM ([TcTyVar], [TcTyVar])
forall a b. (a -> b) -> a -> b
$
                                   [LRuleBndr GhcRn] -> TcM ([TcTyVar], [TcTyVar])
tcRuleTmBndrs [LRuleBndr GhcRn]
rule_bndrs
        ; ([TcTyVar], [TcTyVar]) -> TcM ([TcTyVar], [TcTyVar])
forall (m :: * -> *) a. Monad m => a -> m a
return (((Name, TcTyVar) -> TcTyVar) -> [(Name, TcTyVar)] -> [TcTyVar]
forall a b. (a -> b) -> [a] -> [b]
map (Name, TcTyVar) -> TcTyVar
forall a b. (a, b) -> b
snd [(Name, TcTyVar)]
tvs [TcTyVar] -> [TcTyVar] -> [TcTyVar]
forall a. [a] -> [a] -> [a]
++ [TcTyVar]
tyvars, TcTyVar
id TcTyVar -> [TcTyVar] -> [TcTyVar]
forall a. a -> [a] -> [a]
: [TcTyVar]
tmvars) }

ruleCtxt :: FastString -> SDoc
ruleCtxt :: RuleName -> SDoc
ruleCtxt RuleName
name = String -> SDoc
text String
"When checking the rewrite rule" SDoc -> SDoc -> SDoc
<+>
                SDoc -> SDoc
doubleQuotes (RuleName -> SDoc
ftext RuleName
name)


{-
*********************************************************************************
*                                                                                 *
              Constraint simplification for rules
*                                                                                 *
***********************************************************************************

Note [The SimplifyRule Plan]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Example.  Consider the following left-hand side of a rule
        f (x == y) (y > z) = ...
If we typecheck this expression we get constraints
        d1 :: Ord a, d2 :: Eq a
We do NOT want to "simplify" to the LHS
        forall x::a, y::a, z::a, d1::Ord a.
          f ((==) (eqFromOrd d1) x y) ((>) d1 y z) = ...
Instead we want
        forall x::a, y::a, z::a, d1::Ord a, d2::Eq a.
          f ((==) d2 x y) ((>) d1 y z) = ...

Here is another example:
        fromIntegral :: (Integral a, Num b) => a -> b
        {-# RULES "foo"  fromIntegral = id :: Int -> Int #-}
In the rule, a=b=Int, and Num Int is a superclass of Integral Int. But
we *dont* want to get
        forall dIntegralInt.
           fromIntegral Int Int dIntegralInt (scsel dIntegralInt) = id Int
because the scsel will mess up RULE matching.  Instead we want
        forall dIntegralInt, dNumInt.
          fromIntegral Int Int dIntegralInt dNumInt = id Int

Even if we have
        g (x == y) (y == z) = ..
where the two dictionaries are *identical*, we do NOT WANT
        forall x::a, y::a, z::a, d1::Eq a
          f ((==) d1 x y) ((>) d1 y z) = ...
because that will only match if the dict args are (visibly) equal.
Instead we want to quantify over the dictionaries separately.

In short, simplifyRuleLhs must *only* squash equalities, leaving
all dicts unchanged, with absolutely no sharing.

Also note that we can't solve the LHS constraints in isolation:
Example   foo :: Ord a => a -> a
          foo_spec :: Int -> Int
          {-# RULE "foo"  foo = foo_spec #-}
Here, it's the RHS that fixes the type variable

HOWEVER, under a nested implication things are different
Consider
  f :: (forall a. Eq a => a->a) -> Bool -> ...
  {-# RULES "foo" forall (v::forall b. Eq b => b->b).
       f b True = ...
    #-}
Here we *must* solve the wanted (Eq a) from the given (Eq a)
resulting from skolemising the argument type of g.  So we
revert to SimplCheck when going under an implication.


--------- So the SimplifyRule Plan is this -----------------------

* Step 0: typecheck the LHS and RHS to get constraints from each

* Step 1: Simplify the LHS and RHS constraints all together in one bag,
          but /discarding/ the simplified constraints. We do this only
          to discover all unification equalities.

* Step 2: Zonk the ORIGINAL (unsimplified) LHS constraints, to take
          advantage of those unifications

* Setp 3: Partition the LHS constraints into the ones we will
          quantify over, and the others.
          See Note [RULE quantification over equalities]

* Step 4: Decide on the type variables to quantify over

* Step 5: Simplify the LHS and RHS constraints separately, using the
          quantified constraints as givens

Note [Solve order for RULES]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In step 1 above, we need to be a bit careful about solve order.
Consider
   f :: Int -> T Int
   type instance T Int = Bool

   RULE f 3 = True

From the RULE we get
   lhs-constraints:  T Int ~ alpha
   rhs-constraints:  Bool ~ alpha
where 'alpha' is the type that connects the two.  If we glom them
all together, and solve the RHS constraint first, we might solve
with alpha := Bool.  But then we'd end up with a RULE like

    RULE: f 3 |> (co :: T Int ~ Bool) = True

which is terrible.  We want

    RULE: f 3 = True |> (sym co :: Bool ~ T Int)

So we are careful to solve the LHS constraints first, and *then* the
RHS constraints.  Actually much of this is done by the on-the-fly
constraint solving, so the same order must be observed in
tcRule.


Note [RULE quantification over equalities]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Deciding which equalities to quantify over is tricky:
 * We do not want to quantify over insoluble equalities (Int ~ Bool)
    (a) because we prefer to report a LHS type error
    (b) because if such things end up in 'givens' we get a bogus
        "inaccessible code" error

 * But we do want to quantify over things like (a ~ F b), where
   F is a type function.

The difficulty is that it's hard to tell what is insoluble!
So we see whether the simplification step yielded any type errors,
and if so refrain from quantifying over *any* equalities.

Note [Quantifying over coercion holes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Equality constraints from the LHS will emit coercion hole Wanteds.
These don't have a name, so we can't quantify over them directly.
Instead, because we really do want to quantify here, invent a new
EvVar for the coercion, fill the hole with the invented EvVar, and
then quantify over the EvVar. Not too tricky -- just some
impedance matching, really.

Note [Simplify cloned constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
At this stage, we're simplifying constraints only for insolubility
and for unification. Note that all the evidence is quickly discarded.
We use a clone of the real constraint. If we don't do this,
then RHS coercion-hole constraints get filled in, only to get filled
in *again* when solving the implications emitted from tcRule. That's
terrible, so we avoid the problem by cloning the constraints.

-}

simplifyRule :: RuleName
             -> TcLevel                 -- Level at which to solve the constraints
             -> WantedConstraints       -- Constraints from LHS
             -> WantedConstraints       -- Constraints from RHS
             -> TcM ( [EvVar]               -- Quantify over these LHS vars
                    , WantedConstraints)    -- Residual un-quantified LHS constraints
-- See Note [The SimplifyRule Plan]
-- NB: This consumes all simple constraints on the LHS, but not
-- any LHS implication constraints.
simplifyRule :: RuleName
-> TcLevel
-> WantedConstraints
-> WantedConstraints
-> TcM ([TcTyVar], WantedConstraints)
simplifyRule RuleName
name TcLevel
tc_lvl WantedConstraints
lhs_wanted WantedConstraints
rhs_wanted
  = do {
       -- Note [The SimplifyRule Plan] step 1
       -- First solve the LHS and *then* solve the RHS
       -- Crucially, this performs unifications
       -- Why clone?  See Note [Simplify cloned constraints]
       ; WantedConstraints
lhs_clone <- WantedConstraints -> TcM WantedConstraints
cloneWC WantedConstraints
lhs_wanted
       ; WantedConstraints
rhs_clone <- WantedConstraints -> TcM WantedConstraints
cloneWC WantedConstraints
rhs_wanted
       ; TcLevel -> TcRn () -> TcRn ()
forall a. TcLevel -> TcM a -> TcM a
setTcLevel TcLevel
tc_lvl (TcRn () -> TcRn ()) -> TcRn () -> TcRn ()
forall a b. (a -> b) -> a -> b
$
         TcS () -> TcRn ()
forall a. TcS a -> TcM a
runTcSDeriveds    (TcS () -> TcRn ()) -> TcS () -> TcRn ()
forall a b. (a -> b) -> a -> b
$
         do { WantedConstraints
_ <- WantedConstraints -> TcS WantedConstraints
solveWanteds WantedConstraints
lhs_clone
            ; WantedConstraints
_ <- WantedConstraints -> TcS WantedConstraints
solveWanteds WantedConstraints
rhs_clone
                  -- Why do them separately?
                  -- See Note [Solve order for RULES]
            ; () -> TcS ()
forall (m :: * -> *) a. Monad m => a -> m a
return () }

       -- Note [The SimplifyRule Plan] step 2
       ; WantedConstraints
lhs_wanted <- WantedConstraints -> TcM WantedConstraints
zonkWC WantedConstraints
lhs_wanted
       ; let (Cts
quant_cts, WantedConstraints
residual_lhs_wanted) = WantedConstraints -> (Cts, WantedConstraints)
getRuleQuantCts WantedConstraints
lhs_wanted

       -- Note [The SimplifyRule Plan] step 3
       ; [TcTyVar]
quant_evs <- (Ct -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar)
-> [Ct] -> TcM [TcTyVar]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM Ct -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar
mk_quant_ev (Cts -> [Ct]
forall a. Bag a -> [a]
bagToList Cts
quant_cts)

       ; String -> SDoc -> TcRn ()
traceTc String
"simplifyRule" (SDoc -> TcRn ()) -> SDoc -> TcRn ()
forall a b. (a -> b) -> a -> b
$
         [SDoc] -> SDoc
vcat [ String -> SDoc
text String
"LHS of rule" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
doubleQuotes (RuleName -> SDoc
ftext RuleName
name)
              , String -> SDoc
text String
"lhs_wanted" SDoc -> SDoc -> SDoc
<+> WantedConstraints -> SDoc
forall a. Outputable a => a -> SDoc
ppr WantedConstraints
lhs_wanted
              , String -> SDoc
text String
"rhs_wanted" SDoc -> SDoc -> SDoc
<+> WantedConstraints -> SDoc
forall a. Outputable a => a -> SDoc
ppr WantedConstraints
rhs_wanted
              , String -> SDoc
text String
"quant_cts" SDoc -> SDoc -> SDoc
<+> Cts -> SDoc
forall a. Outputable a => a -> SDoc
ppr Cts
quant_cts
              , String -> SDoc
text String
"residual_lhs_wanted" SDoc -> SDoc -> SDoc
<+> WantedConstraints -> SDoc
forall a. Outputable a => a -> SDoc
ppr WantedConstraints
residual_lhs_wanted
              ]

       ; ([TcTyVar], WantedConstraints)
-> TcM ([TcTyVar], WantedConstraints)
forall (m :: * -> *) a. Monad m => a -> m a
return ([TcTyVar]
quant_evs, WantedConstraints
residual_lhs_wanted) }

  where
    mk_quant_ev :: Ct -> TcM EvVar
    mk_quant_ev :: Ct -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar
mk_quant_ev Ct
ct
      | CtWanted { ctev_dest :: CtEvidence -> TcEvDest
ctev_dest = TcEvDest
dest, ctev_pred :: CtEvidence -> Type
ctev_pred = Type
pred } <- Ct -> CtEvidence
ctEvidence Ct
ct
      = case TcEvDest
dest of
          EvVarDest TcTyVar
ev_id -> TcTyVar -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar
forall (m :: * -> *) a. Monad m => a -> m a
return TcTyVar
ev_id
          HoleDest CoercionHole
hole   -> -- See Note [Quantifying over coercion holes]
                             do { TcTyVar
ev_id <- Type -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar
forall gbl lcl. Type -> TcRnIf gbl lcl TcTyVar
newEvVar Type
pred
                                ; CoercionHole -> Coercion -> TcRn ()
fillCoercionHole CoercionHole
hole (TcTyVar -> Coercion
mkTcCoVarCo TcTyVar
ev_id)
                                ; TcTyVar -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar
forall (m :: * -> *) a. Monad m => a -> m a
return TcTyVar
ev_id }
    mk_quant_ev Ct
ct = String -> SDoc -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"mk_quant_ev" (Ct -> SDoc
forall a. Outputable a => a -> SDoc
ppr Ct
ct)


getRuleQuantCts :: WantedConstraints -> (Cts, WantedConstraints)
-- Extract all the constraints we can quantify over,
--   also returning the depleted WantedConstraints
--
-- NB: we must look inside implications, because with
--     -fdefer-type-errors we generate implications rather eagerly;
--     see GHC.Tc.Utils.Unify.implicationNeeded. Not doing so caused #14732.
--
-- Unlike simplifyInfer, we don't leave the WantedConstraints unchanged,
--   and attempt to solve them from the quantified constraints.  That
--   nearly works, but fails for a constraint like (d :: Eq Int).
--   We /do/ want to quantify over it, but the short-cut solver
--   (see GHC.Tc.Solver.Interact Note [Shortcut solving]) ignores the quantified
--   and instead solves from the top level.
--
--   So we must partition the WantedConstraints ourselves
--   Not hard, but tiresome.

getRuleQuantCts :: WantedConstraints -> (Cts, WantedConstraints)
getRuleQuantCts WantedConstraints
wc
  = TcTyCoVarSet -> WantedConstraints -> (Cts, WantedConstraints)
float_wc TcTyCoVarSet
emptyVarSet WantedConstraints
wc
  where
    float_wc :: TcTyCoVarSet -> WantedConstraints -> (Cts, WantedConstraints)
    float_wc :: TcTyCoVarSet -> WantedConstraints -> (Cts, WantedConstraints)
float_wc TcTyCoVarSet
skol_tvs (WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
simples, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
implics, wc_holes :: WantedConstraints -> Bag Hole
wc_holes = Bag Hole
holes })
      = ( Cts
simple_yes Cts -> Cts -> Cts
`andCts` Cts
implic_yes
        , WantedConstraints
emptyWC { wc_simple :: Cts
wc_simple = Cts
simple_no, wc_impl :: Bag Implication
wc_impl = Bag Implication
implics_no, wc_holes :: Bag Hole
wc_holes = Bag Hole
holes })
     where
        (Cts
simple_yes, Cts
simple_no) = (Ct -> Bool) -> Cts -> (Cts, Cts)
forall a. (a -> Bool) -> Bag a -> (Bag a, Bag a)
partitionBag (TcTyCoVarSet -> Ct -> Bool
rule_quant_ct TcTyCoVarSet
skol_tvs) Cts
simples
        (Cts
implic_yes, Bag Implication
implics_no) = (Cts -> Implication -> (Cts, Implication))
-> Cts -> Bag Implication -> (Cts, Bag Implication)
forall acc x y.
(acc -> x -> (acc, y)) -> acc -> Bag x -> (acc, Bag y)
mapAccumBagL (TcTyCoVarSet -> Cts -> Implication -> (Cts, Implication)
float_implic TcTyCoVarSet
skol_tvs)
                                                Cts
forall a. Bag a
emptyBag Bag Implication
implics

    float_implic :: TcTyCoVarSet -> Cts -> Implication -> (Cts, Implication)
    float_implic :: TcTyCoVarSet -> Cts -> Implication -> (Cts, Implication)
float_implic TcTyCoVarSet
skol_tvs Cts
yes1 Implication
imp
      = (Cts
yes1 Cts -> Cts -> Cts
`andCts` Cts
yes2, Implication
imp { ic_wanted :: WantedConstraints
ic_wanted = WantedConstraints
no })
      where
        (Cts
yes2, WantedConstraints
no) = TcTyCoVarSet -> WantedConstraints -> (Cts, WantedConstraints)
float_wc TcTyCoVarSet
new_skol_tvs (Implication -> WantedConstraints
ic_wanted Implication
imp)
        new_skol_tvs :: TcTyCoVarSet
new_skol_tvs = TcTyCoVarSet
skol_tvs TcTyCoVarSet -> [TcTyVar] -> TcTyCoVarSet
`extendVarSetList` Implication -> [TcTyVar]
ic_skols Implication
imp

    rule_quant_ct :: TcTyCoVarSet -> Ct -> Bool
    rule_quant_ct :: TcTyCoVarSet -> Ct -> Bool
rule_quant_ct TcTyCoVarSet
skol_tvs Ct
ct
      | EqPred EqRel
_ Type
t1 Type
t2 <- Type -> Pred
classifyPredType (Ct -> Type
ctPred Ct
ct)
      , Bool -> Bool
not (Type -> Type -> Bool
ok_eq Type
t1 Type
t2)
       = Bool
False        -- Note [RULE quantification over equalities]
      | Bool
otherwise
      = Ct -> TcTyCoVarSet
tyCoVarsOfCt Ct
ct TcTyCoVarSet -> TcTyCoVarSet -> Bool
`disjointVarSet` TcTyCoVarSet
skol_tvs

    ok_eq :: Type -> Type -> Bool
ok_eq Type
t1 Type
t2
       | Type
t1 HasDebugCallStack => Type -> Type -> Bool
Type -> Type -> Bool
`tcEqType` Type
t2 = Bool
False
       | Bool
otherwise        = Type -> Bool
is_fun_app Type
t1 Bool -> Bool -> Bool
|| Type -> Bool
is_fun_app Type
t2

    is_fun_app :: Type -> Bool
is_fun_app Type
ty   -- ty is of form (F tys) where F is a type function
      = case Type -> Maybe TyCon
tyConAppTyCon_maybe Type
ty of
          Just TyCon
tc -> TyCon -> Bool
isTypeFamilyTyCon TyCon
tc
          Maybe TyCon
Nothing -> Bool
False