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

    -}

    {-# LANGUAGE ViewPatterns #-}
    {-# LANGUAGE TypeFamilies #-}

    -- | 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.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 = (LRuleDecls GhcRn
     -> IOEnv (Env TcGblEnv TcLclEnv) (LRuleDecls GhcTc))
    -> [LRuleDecls GhcRn] -> TcM [LRuleDecls GhcTc]
    forall (t :: * -> *) (m :: * -> *) a b.
    (Traversable t, Monad m) =>
    (a -> m b) -> t a -> m (t b)
    mapM ((RuleDecls GhcRn -> TcM (RuleDecls GhcTc))
    -> LRuleDecls GhcRn
    -> IOEnv (Env TcGblEnv TcLclEnv) (LRuleDecls GhcTc)
    forall a b. (a -> TcM b) -> Located a -> TcM (Located b)
    wrapLocM RuleDecls GhcRn -> TcM (RuleDecls GhcTc)
    tcRuleDecls) [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 { [Located (RuleDecl GhcTc)]
    tc_decls <- (LRuleDecl GhcRn
     -> IOEnv (Env TcGblEnv TcLclEnv) (Located (RuleDecl GhcTc)))
    -> [LRuleDecl GhcRn]
    -> IOEnv (Env TcGblEnv TcLclEnv) [Located (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))
    -> LRuleDecl GhcRn
    -> IOEnv (Env TcGblEnv TcLclEnv) (Located (RuleDecl GhcTc))
    forall a b. (a -> TcM b) -> Located a -> TcM (Located b)
    wrapLocM RuleDecl GhcRn -> TcM (RuleDecl GhcTc)
    tcRule) [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 :: forall pass.
    XCRuleDecls pass
    -> SourceText -> [LRuleDecl pass] -> RuleDecls pass
    HsRules { rds_ext :: XCRuleDecls GhcTc
    rds_ext   = NoExtField
    XCRuleDecls GhcTc
    noExtField
                               , rds_src :: SourceText
    rds_src   = SourceText
    src
                               , rds_rules :: [Located (RuleDecl GhcTc)]
    rds_rules = [Located (RuleDecl 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 -> Located (SourceText, RuleName)
    rd_name = rname :: Located (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 -> Located (HsExpr pass)
    rd_lhs  = Located (HsExpr GhcRn)
    lhs
                   , rd_rhs :: forall pass. RuleDecl pass -> Located (HsExpr pass)
    rd_rhs  = Located (HsExpr GhcRn)
    rhs })
      = MsgDoc -> TcM (RuleDecl GhcTc) -> TcM (RuleDecl GhcTc)
    forall a. MsgDoc -> TcM a -> TcM a
    addErrCtxt (RuleName -> MsgDoc
    ruleCtxt RuleName
    name)  (TcM (RuleDecl GhcTc) -> TcM (RuleDecl GhcTc))
    -> TcM (RuleDecl GhcTc) -> TcM (RuleDecl GhcTc)
    forall a b. (a -> b) -> a -> b
    $
        do { String -> MsgDoc -> TcRn ()
    traceTc String
    "---- Rule ------" (Located (SourceText, RuleName) -> MsgDoc
    pprFullRuleName Located (SourceText, RuleName)
    rname)

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

           ; let ([TcTyVar]
    id_bndrs, LHsExpr GhcTc
    lhs', WantedConstraints
    lhs_wanted
                          , LHsExpr GhcTc
    rhs', WantedConstraints
    rhs_wanted, TcType
    rule_ty) = ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
     WantedConstraints, TcType)
    stuff

           ; String -> MsgDoc -> TcRn ()
    traceTc String
    "tcRule 1" ([MsgDoc] -> MsgDoc
    vcat [ Located (SourceText, RuleName) -> MsgDoc
    pprFullRuleName Located (SourceText, RuleName)
    rname
                                      , WantedConstraints -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr WantedConstraints
    lhs_wanted
                                      , WantedConstraints -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    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

           -- SimplfyRule 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 <- [TcType] -> TcM CandidatesQTvs
    candidateQTyVarsOfTypes (TcType
    rule_ty TcType -> [TcType] -> [TcType]
    forall a. a -> [a] -> [a]
    : (TcTyVar -> TcType) -> [TcTyVar] -> [TcType]
    forall a b. (a -> b) -> [a] -> [b]
    map TcTyVar -> TcType
    idType [TcTyVar]
    tpl_ids)
           ; [TcTyVar]
    qtkvs <- CandidatesQTvs -> TcM [TcTyVar]
    quantifyTyVars CandidatesQTvs
    forall_tkvs
           ; String -> MsgDoc -> TcRn ()
    traceTc String
    "tcRule" ([MsgDoc] -> MsgDoc
    vcat [ Located (SourceText, RuleName) -> MsgDoc
    pprFullRuleName Located (SourceText, RuleName)
    rname
                                    , CandidatesQTvs -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr CandidatesQTvs
    forall_tkvs
                                    , [TcTyVar] -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr [TcTyVar]
    qtkvs
                                    , TcType -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr TcType
    rule_ty
                                    , [MsgDoc] -> MsgDoc
    vcat [ TcTyVar -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr TcTyVar
    id MsgDoc -> MsgDoc -> MsgDoc
    <+> MsgDoc
    dcolon MsgDoc -> MsgDoc -> MsgDoc
    <+> TcType -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr (TcTyVar -> TcType
    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 :: forall pass.
    XHsRule pass
    -> Located (SourceText, RuleName)
    -> Activation
    -> Maybe [LHsTyVarBndr () (NoGhcTc pass)]
    -> [LRuleBndr pass]
    -> Located (HsExpr pass)
    -> Located (HsExpr pass)
    -> RuleDecl pass
    HsRule { rd_ext :: XHsRule GhcTc
    rd_ext = XHsRule GhcRn
    XHsRule GhcTc
    ext
                             , rd_name :: Located (SourceText, RuleName)
    rd_name = Located (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 -> LRuleBndr GhcTc) -> [TcTyVar] -> [LRuleBndr GhcTc]
    forall a b. (a -> b) -> [a] -> [b]
    map (RuleBndr GhcTc -> LRuleBndr GhcTc
    forall e. e -> Located e
    noLoc (RuleBndr GhcTc -> LRuleBndr GhcTc)
    -> (TcTyVar -> RuleBndr GhcTc) -> TcTyVar -> LRuleBndr GhcTc
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . XCRuleBndr GhcTc -> Located (IdP GhcTc) -> RuleBndr GhcTc
    forall pass. XCRuleBndr pass -> Located (IdP pass) -> RuleBndr pass
    RuleBndr NoExtField
    XCRuleBndr GhcTc
    noExtField (GenLocated SrcSpan TcTyVar -> RuleBndr GhcTc)
    -> (TcTyVar -> GenLocated SrcSpan TcTyVar)
    -> TcTyVar
    -> RuleBndr GhcTc
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcTyVar -> GenLocated SrcSpan TcTyVar
    forall e. e -> Located e
    noLoc)
                                             ([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 LHsExpr GhcTc
    lhs'
                             , rd_rhs :: LHsExpr GhcTc
    rd_rhs  = TcEvBinds -> LHsExpr GhcTc -> LHsExpr GhcTc
    mkHsDictLet TcEvBinds
    rhs_binds 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]
    -> Located (HsExpr GhcRn)
    -> Located (HsExpr GhcRn)
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    generateRuleConstraints Maybe [LHsTyVarBndr () GhcRn]
    ty_bndrs [LRuleBndr GhcRn]
    tm_bndrs Located (HsExpr GhcRn)
    lhs Located (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], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    forall r. [TcTyVar] -> TcM r -> TcM r
    tcExtendTyVarEnv [TcTyVar]
    tv_bndrs (TcM
       ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
        WantedConstraints, TcType)
     -> TcM
          ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
           WantedConstraints, TcType))
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    forall a b. (a -> b) -> a -> b
    $
             [TcTyVar]
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    forall r. [TcTyVar] -> TcM r -> TcM r
    tcExtendIdEnv    [TcTyVar]
    id_bndrs (TcM
       ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
        WantedConstraints, TcType)
     -> TcM
          ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
           WantedConstraints, TcType))
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    forall a b. (a -> b) -> a -> b
    $
        do { -- See Note [Solve order for RULES]
             ((LHsExpr GhcTc
    lhs', TcType
    rule_ty), WantedConstraints
    lhs_wanted) <- TcM (LHsExpr GhcTc, TcType)
    -> TcM ((LHsExpr GhcTc, TcType), WantedConstraints)
    forall a. TcM a -> TcM (a, WantedConstraints)
    captureConstraints (Located (HsExpr GhcRn) -> TcM (LHsExpr GhcTc, TcType)
    tcInferRho Located (HsExpr GhcRn)
    lhs)
           ; (LHsExpr 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
    $
                                              Located (HsExpr GhcRn) -> TcType -> TcM (LHsExpr GhcTc)
    tcCheckMonoExpr Located (HsExpr GhcRn)
    rhs TcType
    rule_ty
           ; let all_lhs_wanted :: WantedConstraints
    all_lhs_wanted = WantedConstraints
    bndr_wanted WantedConstraints -> WantedConstraints -> WantedConstraints
    `andWC` WantedConstraints
    lhs_wanted
           ; ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
     WantedConstraints, TcType)
    -> TcM
         ([TcTyVar], LHsExpr GhcTc, WantedConstraints, LHsExpr GhcTc,
          WantedConstraints, TcType)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([TcTyVar]
    id_bndrs, LHsExpr GhcTc
    lhs', WantedConstraints
    all_lhs_wanted, LHsExpr GhcTc
    rhs', WantedConstraints
    rhs_wanted, TcType
    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 =>
    [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 SrcSpan
    _ IdP GhcRn
    name)) : [LRuleBndr GhcRn]
    rule_bndrs)
      = do  { TcType
    ty <- TcM TcType
    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 -> TcType -> TcType -> TcTyVar
    Name -> TcType -> TcType -> TcTyVar
    mkLocalId Name
    IdP GhcRn
    name TcType
    Many TcType
    ty TcTyVar -> [TcTyVar] -> [TcTyVar]
    forall a. a -> [a] -> [a]
    : [TcTyVar]
    tmvars) }
    tcRuleTmBndrs (L SrcSpan
    _ (RuleBndrSig XRuleBndrSig GhcRn
    _ (L SrcSpan
    _ IdP GhcRn
    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
    IdP GhcRn
    name
            ; ([(Name, TcTyVar)]
    _ , [(Name, TcTyVar)]
    tvs, TcType
    id_ty) <- UserTypeCtxt
    -> HsPatSigType GhcRn
    -> TcM ([(Name, TcTyVar)], [(Name, TcTyVar)], TcType)
    tcHsPatSigType UserTypeCtxt
    ctxt HsPatSigType GhcRn
    rn_ty
            ; let id :: TcTyVar
    id  = HasDebugCallStack => Name -> TcType -> TcType -> TcTyVar
    Name -> TcType -> TcType -> TcTyVar
    mkLocalId Name
    IdP GhcRn
    name TcType
    Many TcType
    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 -> MsgDoc
    ruleCtxt RuleName
    name = String -> MsgDoc
    text String
    "When checking the rewrite rule" MsgDoc -> MsgDoc -> MsgDoc
    <+>
                    MsgDoc -> MsgDoc
    doubleQuotes (RuleName -> MsgDoc
    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
              We do this 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 -> MsgDoc -> TcRn ()
    traceTc String
    "simplifyRule" (MsgDoc -> TcRn ()) -> MsgDoc -> TcRn ()
    forall a b. (a -> b) -> a -> b
    $
             [MsgDoc] -> MsgDoc
    vcat [ String -> MsgDoc
    text String
    "LHS of rule" MsgDoc -> MsgDoc -> MsgDoc
    <+> MsgDoc -> MsgDoc
    doubleQuotes (RuleName -> MsgDoc
    ftext RuleName
    name)
                  , String -> MsgDoc
    text String
    "lhs_wanted" MsgDoc -> MsgDoc -> MsgDoc
    <+> WantedConstraints -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr WantedConstraints
    lhs_wanted
                  , String -> MsgDoc
    text String
    "rhs_wanted" MsgDoc -> MsgDoc -> MsgDoc
    <+> WantedConstraints -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr WantedConstraints
    rhs_wanted
                  , String -> MsgDoc
    text String
    "quant_cts" MsgDoc -> MsgDoc -> MsgDoc
    <+> Cts -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    ppr Cts
    quant_cts
                  , String -> MsgDoc
    text String
    "residual_lhs_wanted" MsgDoc -> MsgDoc -> MsgDoc
    <+> WantedConstraints -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    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 -> TcType
    ctev_pred = TcType
    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 <- TcType -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar
    forall gbl lcl. TcType -> TcRnIf gbl lcl TcTyVar
    newEvVar TcType
    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 -> MsgDoc -> IOEnv (Env TcGblEnv TcLclEnv) TcTyVar
    forall a. HasCallStack => String -> MsgDoc -> a
    pprPanic String
    "mk_quant_ev" (Ct -> MsgDoc
    forall a. Outputable a => a -> MsgDoc
    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
    _ TcType
    t1 TcType
    t2 <- TcType -> Pred
    classifyPredType (Ct -> TcType
    ctPred Ct
    ct)
          , Bool -> Bool
    not (TcType -> TcType -> Bool
    ok_eq TcType
    t1 TcType
    t2)
           = Bool
    False        -- Note [RULE quantification over equalities]
          | Bool
    otherwise
          = Ct -> TcTyCoVarSet
    tyCoVarsOfCt Ct
    ct TcTyCoVarSet -> TcTyCoVarSet -> Bool
    `disjointVarSet` TcTyCoVarSet
    skol_tvs

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

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