nodeFuncs.c

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/*-------------------------------------------------------------------------
 *
 * nodeFuncs.c
 *      Various general-purpose manipulations of Node trees
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/nodes/nodeFuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_collation.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/relation.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"


static bool expression_returns_set_walker(Node *node, void *context);
static int  leftmostLoc(int loc1, int loc2);


/*
 *  exprType -
 *    returns the Oid of the type of the expression's result.
 */
Oid
exprType(const Node *expr)
{
    Oid         type;

    if (!expr)
        return InvalidOid;

    switch (nodeTag(expr))
    {
        case T_Var:
            type = ((const Var *) expr)->vartype;
            break;
        case T_Const:
            type = ((const Const *) expr)->consttype;
            break;
        case T_Param:
            type = ((const Param *) expr)->paramtype;
            break;
        case T_Aggref:
            type = ((const Aggref *) expr)->aggtype;
            break;
        case T_WindowFunc:
            type = ((const WindowFunc *) expr)->wintype;
            break;
        case T_ArrayRef:
            {
                const ArrayRef *arrayref = (const ArrayRef *) expr;

                /* slice and/or store operations yield the array type */
                if (arrayref->reflowerindexpr || arrayref->refassgnexpr)
                    type = arrayref->refarraytype;
                else
                    type = arrayref->refelemtype;
            }
            break;
        case T_FuncExpr:
            type = ((const FuncExpr *) expr)->funcresulttype;
            break;
        case T_NamedArgExpr:
            type = exprType((Node *) ((const NamedArgExpr *) expr)->arg);
            break;
        case T_OpExpr:
            type = ((const OpExpr *) expr)->opresulttype;
            break;
        case T_DistinctExpr:
            type = ((const DistinctExpr *) expr)->opresulttype;
            break;
        case T_NullIfExpr:
            type = ((const NullIfExpr *) expr)->opresulttype;
            break;
        case T_ScalarArrayOpExpr:
            type = BOOLOID;
            break;
        case T_BoolExpr:
            type = BOOLOID;
            break;
        case T_SubLink:
            {
                const SubLink *sublink = (const SubLink *) expr;

                if (sublink->subLinkType == EXPR_SUBLINK ||
                    sublink->subLinkType == ARRAY_SUBLINK)
                {
                    /* get the type of the subselect's first target column */
                    Query      *qtree = (Query *) sublink->subselect;
                    TargetEntry *tent;

                    if (!qtree || !IsA(qtree, Query))
                        elog(ERROR, "cannot get type for untransformed sublink");
                    tent = (TargetEntry *) linitial(qtree->targetList);
                    Assert(IsA(tent, TargetEntry));
                    Assert(!tent->resjunk);
                    type = exprType((Node *) tent->expr);
                    if (sublink->subLinkType == ARRAY_SUBLINK)
                    {
                        type = get_array_type(type);
                        if (!OidIsValid(type))
                            ereport(ERROR,
                                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                                     errmsg("could not find array type for data type %s",
                            format_type_be(exprType((Node *) tent->expr)))));
                    }
                }
                else
                {
                    /* for all other sublink types, result is boolean */
                    type = BOOLOID;
                }
            }
            break;
        case T_SubPlan:
            {
                const SubPlan *subplan = (const SubPlan *) expr;

                if (subplan->subLinkType == EXPR_SUBLINK ||
                    subplan->subLinkType == ARRAY_SUBLINK)
                {
                    /* get the type of the subselect's first target column */
                    type = subplan->firstColType;
                    if (subplan->subLinkType == ARRAY_SUBLINK)
                    {
                        type = get_array_type(type);
                        if (!OidIsValid(type))
                            ereport(ERROR,
                                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                                     errmsg("could not find array type for data type %s",
                                    format_type_be(subplan->firstColType))));
                    }
                }
                else
                {
                    /* for all other subplan types, result is boolean */
                    type = BOOLOID;
                }
            }
            break;
        case T_AlternativeSubPlan:
            {
                const AlternativeSubPlan *asplan = (const AlternativeSubPlan *) expr;

                /* subplans should all return the same thing */
                type = exprType((Node *) linitial(asplan->subplans));
            }
            break;
        case T_FieldSelect:
            type = ((const FieldSelect *) expr)->resulttype;
            break;
        case T_FieldStore:
            type = ((const FieldStore *) expr)->resulttype;
            break;
        case T_RelabelType:
            type = ((const RelabelType *) expr)->resulttype;
            break;
        case T_CoerceViaIO:
            type = ((const CoerceViaIO *) expr)->resulttype;
            break;
        case T_ArrayCoerceExpr:
            type = ((const ArrayCoerceExpr *) expr)->resulttype;
            break;
        case T_ConvertRowtypeExpr:
            type = ((const ConvertRowtypeExpr *) expr)->resulttype;
            break;
        case T_CollateExpr:
            type = exprType((Node *) ((const CollateExpr *) expr)->arg);
            break;
        case T_CaseExpr:
            type = ((const CaseExpr *) expr)->casetype;
            break;
        case T_CaseTestExpr:
            type = ((const CaseTestExpr *) expr)->typeId;
            break;
        case T_ArrayExpr:
            type = ((const ArrayExpr *) expr)->array_typeid;
            break;
        case T_RowExpr:
            type = ((const RowExpr *) expr)->row_typeid;
            break;
        case T_RowCompareExpr:
            type = BOOLOID;
            break;
        case T_CoalesceExpr:
            type = ((const CoalesceExpr *) expr)->coalescetype;
            break;
        case T_MinMaxExpr:
            type = ((const MinMaxExpr *) expr)->minmaxtype;
            break;
        case T_XmlExpr:
            if (((const XmlExpr *) expr)->op == IS_DOCUMENT)
                type = BOOLOID;
            else if (((const XmlExpr *) expr)->op == IS_XMLSERIALIZE)
                type = TEXTOID;
            else
                type = XMLOID;
            break;
        case T_NullTest:
            type = BOOLOID;
            break;
        case T_BooleanTest:
            type = BOOLOID;
            break;
        case T_CoerceToDomain:
            type = ((const CoerceToDomain *) expr)->resulttype;
            break;
        case T_CoerceToDomainValue:
            type = ((const CoerceToDomainValue *) expr)->typeId;
            break;
        case T_SetToDefault:
            type = ((const SetToDefault *) expr)->typeId;
            break;
        case T_CurrentOfExpr:
            type = BOOLOID;
            break;
        case T_PlaceHolderVar:
            type = exprType((Node *) ((const PlaceHolderVar *) expr)->phexpr);
            break;
        default:
            elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
            type = InvalidOid;  /* keep compiler quiet */
            break;
    }
    return type;
}

/*
 *  exprTypmod -
 *    returns the type-specific modifier of the expression's result type,
 *    if it can be determined.  In many cases, it can't and we return -1.
 */
int32
exprTypmod(const Node *expr)
{
    if (!expr)
        return -1;

    switch (nodeTag(expr))
    {
        case T_Var:
            return ((const Var *) expr)->vartypmod;
        case T_Const:
            return ((const Const *) expr)->consttypmod;
        case T_Param:
            return ((const Param *) expr)->paramtypmod;
        case T_ArrayRef:
            /* typmod is the same for array or element */
            return ((const ArrayRef *) expr)->reftypmod;
        case T_FuncExpr:
            {
                int32       coercedTypmod;

                /* Be smart about length-coercion functions... */
                if (exprIsLengthCoercion(expr, &coercedTypmod))
                    return coercedTypmod;
            }
            break;
        case T_NamedArgExpr:
            return exprTypmod((Node *) ((const NamedArgExpr *) expr)->arg);
        case T_NullIfExpr:
            {
                /*
                 * Result is either first argument or NULL, so we can report
                 * first argument's typmod if known.
                 */
                const NullIfExpr *nexpr = (const NullIfExpr *) expr;

                return exprTypmod((Node *) linitial(nexpr->args));
            }
            break;
        case T_SubLink:
            {
                const SubLink *sublink = (const SubLink *) expr;

                if (sublink->subLinkType == EXPR_SUBLINK ||
                    sublink->subLinkType == ARRAY_SUBLINK)
                {
                    /* get the typmod of the subselect's first target column */
                    Query      *qtree = (Query *) sublink->subselect;
                    TargetEntry *tent;

                    if (!qtree || !IsA(qtree, Query))
                        elog(ERROR, "cannot get type for untransformed sublink");
                    tent = (TargetEntry *) linitial(qtree->targetList);
                    Assert(IsA(tent, TargetEntry));
                    Assert(!tent->resjunk);
                    return exprTypmod((Node *) tent->expr);
                    /* note we don't need to care if it's an array */
                }
            }
            break;
        case T_SubPlan:
            {
                const SubPlan *subplan = (const SubPlan *) expr;

                if (subplan->subLinkType == EXPR_SUBLINK ||
                    subplan->subLinkType == ARRAY_SUBLINK)
                {
                    /* get the typmod of the subselect's first target column */
                    /* note we don't need to care if it's an array */
                    return subplan->firstColTypmod;
                }
                else
                {
                    /* for all other subplan types, result is boolean */
                    return -1;
                }
            }
            break;
        case T_AlternativeSubPlan:
            {
                const AlternativeSubPlan *asplan = (const AlternativeSubPlan *) expr;

                /* subplans should all return the same thing */
                return exprTypmod((Node *) linitial(asplan->subplans));
            }
            break;
        case T_FieldSelect:
            return ((const FieldSelect *) expr)->resulttypmod;
        case T_RelabelType:
            return ((const RelabelType *) expr)->resulttypmod;
        case T_ArrayCoerceExpr:
            return ((const ArrayCoerceExpr *) expr)->resulttypmod;
        case T_CollateExpr:
            return exprTypmod((Node *) ((const CollateExpr *) expr)->arg);
        case T_CaseExpr:
            {
                /*
                 * If all the alternatives agree on type/typmod, return that
                 * typmod, else use -1
                 */
                const CaseExpr *cexpr = (const CaseExpr *) expr;
                Oid         casetype = cexpr->casetype;
                int32       typmod;
                ListCell   *arg;

                if (!cexpr->defresult)
                    return -1;
                if (exprType((Node *) cexpr->defresult) != casetype)
                    return -1;
                typmod = exprTypmod((Node *) cexpr->defresult);
                if (typmod < 0)
                    return -1;  /* no point in trying harder */
                foreach(arg, cexpr->args)
                {
                    CaseWhen   *w = (CaseWhen *) lfirst(arg);

                    Assert(IsA(w, CaseWhen));
                    if (exprType((Node *) w->result) != casetype)
                        return -1;
                    if (exprTypmod((Node *) w->result) != typmod)
                        return -1;
                }
                return typmod;
            }
            break;
        case T_CaseTestExpr:
            return ((const CaseTestExpr *) expr)->typeMod;
        case T_ArrayExpr:
            {
                /*
                 * If all the elements agree on type/typmod, return that
                 * typmod, else use -1
                 */
                const ArrayExpr *arrayexpr = (const ArrayExpr *) expr;
                Oid         commontype;
                int32       typmod;
                ListCell   *elem;

                if (arrayexpr->elements == NIL)
                    return -1;
                typmod = exprTypmod((Node *) linitial(arrayexpr->elements));
                if (typmod < 0)
                    return -1;  /* no point in trying harder */
                if (arrayexpr->multidims)
                    commontype = arrayexpr->array_typeid;
                else
                    commontype = arrayexpr->element_typeid;
                foreach(elem, arrayexpr->elements)
                {
                    Node       *e = (Node *) lfirst(elem);

                    if (exprType(e) != commontype)
                        return -1;
                    if (exprTypmod(e) != typmod)
                        return -1;
                }
                return typmod;
            }
            break;
        case T_CoalesceExpr:
            {
                /*
                 * If all the alternatives agree on type/typmod, return that
                 * typmod, else use -1
                 */
                const CoalesceExpr *cexpr = (const CoalesceExpr *) expr;
                Oid         coalescetype = cexpr->coalescetype;
                int32       typmod;
                ListCell   *arg;

                if (exprType((Node *) linitial(cexpr->args)) != coalescetype)
                    return -1;
                typmod = exprTypmod((Node *) linitial(cexpr->args));
                if (typmod < 0)
                    return -1;  /* no point in trying harder */
                for_each_cell(arg, lnext(list_head(cexpr->args)))
                {
                    Node       *e = (Node *) lfirst(arg);

                    if (exprType(e) != coalescetype)
                        return -1;
                    if (exprTypmod(e) != typmod)
                        return -1;
                }
                return typmod;
            }
            break;
        case T_MinMaxExpr:
            {
                /*
                 * If all the alternatives agree on type/typmod, return that
                 * typmod, else use -1
                 */
                const MinMaxExpr *mexpr = (const MinMaxExpr *) expr;
                Oid         minmaxtype = mexpr->minmaxtype;
                int32       typmod;
                ListCell   *arg;

                if (exprType((Node *) linitial(mexpr->args)) != minmaxtype)
                    return -1;
                typmod = exprTypmod((Node *) linitial(mexpr->args));
                if (typmod < 0)
                    return -1;  /* no point in trying harder */
                for_each_cell(arg, lnext(list_head(mexpr->args)))
                {
                    Node       *e = (Node *) lfirst(arg);

                    if (exprType(e) != minmaxtype)
                        return -1;
                    if (exprTypmod(e) != typmod)
                        return -1;
                }
                return typmod;
            }
            break;
        case T_CoerceToDomain:
            return ((const CoerceToDomain *) expr)->resulttypmod;
        case T_CoerceToDomainValue:
            return ((const CoerceToDomainValue *) expr)->typeMod;
        case T_SetToDefault:
            return ((const SetToDefault *) expr)->typeMod;
        case T_PlaceHolderVar:
            return exprTypmod((Node *) ((const PlaceHolderVar *) expr)->phexpr);
        default:
            break;
    }
    return -1;
}

/*
 * exprIsLengthCoercion
 *      Detect whether an expression tree is an application of a datatype's
 *      typmod-coercion function.  Optionally extract the result's typmod.
 *
 * If coercedTypmod is not NULL, the typmod is stored there if the expression
 * is a length-coercion function, else -1 is stored there.
 *
 * Note that a combined type-and-length coercion will be treated as a
 * length coercion by this routine.
 */
bool
exprIsLengthCoercion(const Node *expr, int32 *coercedTypmod)
{
    if (coercedTypmod != NULL)
        *coercedTypmod = -1;    /* default result on failure */

    /*
     * Scalar-type length coercions are FuncExprs, array-type length coercions
     * are ArrayCoerceExprs
     */
    if (expr && IsA(expr, FuncExpr))
    {
        const FuncExpr *func = (const FuncExpr *) expr;
        int         nargs;
        Const      *second_arg;

        /*
         * If it didn't come from a coercion context, reject.
         */
        if (func->funcformat != COERCE_EXPLICIT_CAST &&
            func->funcformat != COERCE_IMPLICIT_CAST)
            return false;

        /*
         * If it's not a two-argument or three-argument function with the
         * second argument being an int4 constant, it can't have been created
         * from a length coercion (it must be a type coercion, instead).
         */
        nargs = list_length(func->args);
        if (nargs < 2 || nargs > 3)
            return false;

        second_arg = (Const *) lsecond(func->args);
        if (!IsA(second_arg, Const) ||
            second_arg->consttype != INT4OID ||
            second_arg->constisnull)
            return false;

        /*
         * OK, it is indeed a length-coercion function.
         */
        if (coercedTypmod != NULL)
            *coercedTypmod = DatumGetInt32(second_arg->constvalue);

        return true;
    }

    if (expr && IsA(expr, ArrayCoerceExpr))
    {
        const ArrayCoerceExpr *acoerce = (const ArrayCoerceExpr *) expr;

        /* It's not a length coercion unless there's a nondefault typmod */
        if (acoerce->resulttypmod < 0)
            return false;

        /*
         * OK, it is indeed a length-coercion expression.
         */
        if (coercedTypmod != NULL)
            *coercedTypmod = acoerce->resulttypmod;

        return true;
    }

    return false;
}

/*
 * relabel_to_typmod
 *      Add a RelabelType node that changes just the typmod of the expression.
 *
 * This is primarily intended to be used during planning.  Therefore, it
 * strips any existing RelabelType nodes to maintain the planner's invariant
 * that there are not adjacent RelabelTypes.
 */
Node *
relabel_to_typmod(Node *expr, int32 typmod)
{
    Oid         type = exprType(expr);
    Oid         coll = exprCollation(expr);

    /* Strip any existing RelabelType node(s) */
    while (expr && IsA(expr, RelabelType))
        expr = (Node *) ((RelabelType *) expr)->arg;

    /* Apply new typmod, preserving the previous exposed type and collation */
    return (Node *) makeRelabelType((Expr *) expr, type, typmod, coll,
                                    COERCE_EXPLICIT_CAST);
}

/*
 * expression_returns_set
 *    Test whether an expression returns a set result.
 *
 * Because we use expression_tree_walker(), this can also be applied to
 * whole targetlists; it'll produce TRUE if any one of the tlist items
 * returns a set.
 */
bool
expression_returns_set(Node *clause)
{
    return expression_returns_set_walker(clause, NULL);
}

static bool
expression_returns_set_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, FuncExpr))
    {
        FuncExpr   *expr = (FuncExpr *) node;

        if (expr->funcretset)
            return true;
        /* else fall through to check args */
    }
    if (IsA(node, OpExpr))
    {
        OpExpr     *expr = (OpExpr *) node;

        if (expr->opretset)
            return true;
        /* else fall through to check args */
    }

    /* Avoid recursion for some cases that can't return a set */
    if (IsA(node, Aggref))
        return false;
    if (IsA(node, WindowFunc))
        return false;
    if (IsA(node, DistinctExpr))
        return false;
    if (IsA(node, NullIfExpr))
        return false;
    if (IsA(node, ScalarArrayOpExpr))
        return false;
    if (IsA(node, BoolExpr))
        return false;
    if (IsA(node, SubLink))
        return false;
    if (IsA(node, SubPlan))
        return false;
    if (IsA(node, AlternativeSubPlan))
        return false;
    if (IsA(node, ArrayExpr))
        return false;
    if (IsA(node, RowExpr))
        return false;
    if (IsA(node, RowCompareExpr))
        return false;
    if (IsA(node, CoalesceExpr))
        return false;
    if (IsA(node, MinMaxExpr))
        return false;
    if (IsA(node, XmlExpr))
        return false;

    return expression_tree_walker(node, expression_returns_set_walker,
                                  context);
}


/*
 *  exprCollation -
 *    returns the Oid of the collation of the expression's result.
 *
 * Note: expression nodes that can invoke functions generally have an
 * "inputcollid" field, which is what the function should use as collation.
 * That is the resolved common collation of the node's inputs.  It is often
 * but not always the same as the result collation; in particular, if the
 * function produces a non-collatable result type from collatable inputs
 * or vice versa, the two are different.
 */
Oid
exprCollation(const Node *expr)
{
    Oid         coll;

    if (!expr)
        return InvalidOid;

    switch (nodeTag(expr))
    {
        case T_Var:
            coll = ((const Var *) expr)->varcollid;
            break;
        case T_Const:
            coll = ((const Const *) expr)->constcollid;
            break;
        case T_Param:
            coll = ((const Param *) expr)->paramcollid;
            break;
        case T_Aggref:
            coll = ((const Aggref *) expr)->aggcollid;
            break;
        case T_WindowFunc:
            coll = ((const WindowFunc *) expr)->wincollid;
            break;
        case T_ArrayRef:
            coll = ((const ArrayRef *) expr)->refcollid;
            break;
        case T_FuncExpr:
            coll = ((const FuncExpr *) expr)->funccollid;
            break;
        case T_NamedArgExpr:
            coll = exprCollation((Node *) ((const NamedArgExpr *) expr)->arg);
            break;
        case T_OpExpr:
            coll = ((const OpExpr *) expr)->opcollid;
            break;
        case T_DistinctExpr:
            coll = ((const DistinctExpr *) expr)->opcollid;
            break;
        case T_NullIfExpr:
            coll = ((const NullIfExpr *) expr)->opcollid;
            break;
        case T_ScalarArrayOpExpr:
            coll = InvalidOid;  /* result is always boolean */
            break;
        case T_BoolExpr:
            coll = InvalidOid;  /* result is always boolean */
            break;
        case T_SubLink:
            {
                const SubLink *sublink = (const SubLink *) expr;

                if (sublink->subLinkType == EXPR_SUBLINK ||
                    sublink->subLinkType == ARRAY_SUBLINK)
                {
                    /* get the collation of subselect's first target column */
                    Query      *qtree = (Query *) sublink->subselect;
                    TargetEntry *tent;

                    if (!qtree || !IsA(qtree, Query))
                        elog(ERROR, "cannot get collation for untransformed sublink");
                    tent = (TargetEntry *) linitial(qtree->targetList);
                    Assert(IsA(tent, TargetEntry));
                    Assert(!tent->resjunk);
                    coll = exprCollation((Node *) tent->expr);
                    /* collation doesn't change if it's converted to array */
                }
                else
                {
                    /* for all other sublink types, result is boolean */
                    coll = InvalidOid;
                }
            }
            break;
        case T_SubPlan:
            {
                const SubPlan *subplan = (const SubPlan *) expr;

                if (subplan->subLinkType == EXPR_SUBLINK ||
                    subplan->subLinkType == ARRAY_SUBLINK)
                {
                    /* get the collation of subselect's first target column */
                    coll = subplan->firstColCollation;
                    /* collation doesn't change if it's converted to array */
                }
                else
                {
                    /* for all other subplan types, result is boolean */
                    coll = InvalidOid;
                }
            }
            break;
        case T_AlternativeSubPlan:
            {
                const AlternativeSubPlan *asplan = (const AlternativeSubPlan *) expr;

                /* subplans should all return the same thing */
                coll = exprCollation((Node *) linitial(asplan->subplans));
            }
            break;
        case T_FieldSelect:
            coll = ((const FieldSelect *) expr)->resultcollid;
            break;
        case T_FieldStore:
            coll = InvalidOid;  /* result is always composite */
            break;
        case T_RelabelType:
            coll = ((const RelabelType *) expr)->resultcollid;
            break;
        case T_CoerceViaIO:
            coll = ((const CoerceViaIO *) expr)->resultcollid;
            break;
        case T_ArrayCoerceExpr:
            coll = ((const ArrayCoerceExpr *) expr)->resultcollid;
            break;
        case T_ConvertRowtypeExpr:
            coll = InvalidOid;  /* result is always composite */
            break;
        case T_CollateExpr:
            coll = ((const CollateExpr *) expr)->collOid;
            break;
        case T_CaseExpr:
            coll = ((const CaseExpr *) expr)->casecollid;
            break;
        case T_CaseTestExpr:
            coll = ((const CaseTestExpr *) expr)->collation;
            break;
        case T_ArrayExpr:
            coll = ((const ArrayExpr *) expr)->array_collid;
            break;
        case T_RowExpr:
            coll = InvalidOid;  /* result is always composite */
            break;
        case T_RowCompareExpr:
            coll = InvalidOid;  /* result is always boolean */
            break;
        case T_CoalesceExpr:
            coll = ((const CoalesceExpr *) expr)->coalescecollid;
            break;
        case T_MinMaxExpr:
            coll = ((const MinMaxExpr *) expr)->minmaxcollid;
            break;
        case T_XmlExpr:

            /*
             * XMLSERIALIZE returns text from non-collatable inputs, so its
             * collation is always default.  The other cases return boolean or
             * XML, which are non-collatable.
             */
            if (((const XmlExpr *) expr)->op == IS_XMLSERIALIZE)
                coll = DEFAULT_COLLATION_OID;
            else
                coll = InvalidOid;
            break;
        case T_NullTest:
            coll = InvalidOid;  /* result is always boolean */
            break;
        case T_BooleanTest:
            coll = InvalidOid;  /* result is always boolean */
            break;
        case T_CoerceToDomain:
            coll = ((const CoerceToDomain *) expr)->resultcollid;
            break;
        case T_CoerceToDomainValue:
            coll = ((const CoerceToDomainValue *) expr)->collation;
            break;
        case T_SetToDefault:
            coll = ((const SetToDefault *) expr)->collation;
            break;
        case T_CurrentOfExpr:
            coll = InvalidOid;  /* result is always boolean */
            break;
        case T_PlaceHolderVar:
            coll = exprCollation((Node *) ((const PlaceHolderVar *) expr)->phexpr);
            break;
        default:
            elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
            coll = InvalidOid;  /* keep compiler quiet */
            break;
    }
    return coll;
}

/*
 *  exprInputCollation -
 *    returns the Oid of the collation a function should use, if available.
 *
 * Result is InvalidOid if the node type doesn't store this information.
 */
Oid
exprInputCollation(const Node *expr)
{
    Oid         coll;

    if (!expr)
        return InvalidOid;

    switch (nodeTag(expr))
    {
        case T_Aggref:
            coll = ((const Aggref *) expr)->inputcollid;
            break;
        case T_WindowFunc:
            coll = ((const WindowFunc *) expr)->inputcollid;
            break;
        case T_FuncExpr:
            coll = ((const FuncExpr *) expr)->inputcollid;
            break;
        case T_OpExpr:
            coll = ((const OpExpr *) expr)->inputcollid;
            break;
        case T_DistinctExpr:
            coll = ((const DistinctExpr *) expr)->inputcollid;
            break;
        case T_NullIfExpr:
            coll = ((const NullIfExpr *) expr)->inputcollid;
            break;
        case T_ScalarArrayOpExpr:
            coll = ((const ScalarArrayOpExpr *) expr)->inputcollid;
            break;
        case T_MinMaxExpr:
            coll = ((const MinMaxExpr *) expr)->inputcollid;
            break;
        default:
            coll = InvalidOid;
            break;
    }
    return coll;
}

/*
 *  exprSetCollation -
 *    Assign collation information to an expression tree node.
 *
 * Note: since this is only used during parse analysis, we don't need to
 * worry about subplans or PlaceHolderVars.
 */
void
exprSetCollation(Node *expr, Oid collation)
{
    switch (nodeTag(expr))
    {
        case T_Var:
            ((Var *) expr)->varcollid = collation;
            break;
        case T_Const:
            ((Const *) expr)->constcollid = collation;
            break;
        case T_Param:
            ((Param *) expr)->paramcollid = collation;
            break;
        case T_Aggref:
            ((Aggref *) expr)->aggcollid = collation;
            break;
        case T_WindowFunc:
            ((WindowFunc *) expr)->wincollid = collation;
            break;
        case T_ArrayRef:
            ((ArrayRef *) expr)->refcollid = collation;
            break;
        case T_FuncExpr:
            ((FuncExpr *) expr)->funccollid = collation;
            break;
        case T_NamedArgExpr:
            Assert(collation == exprCollation((Node *) ((NamedArgExpr *) expr)->arg));
            break;
        case T_OpExpr:
            ((OpExpr *) expr)->opcollid = collation;
            break;
        case T_DistinctExpr:
            ((DistinctExpr *) expr)->opcollid = collation;
            break;
        case T_NullIfExpr:
            ((NullIfExpr *) expr)->opcollid = collation;
            break;
        case T_ScalarArrayOpExpr:
            Assert(!OidIsValid(collation));     /* result is always boolean */
            break;
        case T_BoolExpr:
            Assert(!OidIsValid(collation));     /* result is always boolean */
            break;
        case T_SubLink:
#ifdef USE_ASSERT_CHECKING
            {
                SubLink    *sublink = (SubLink *) expr;

                if (sublink->subLinkType == EXPR_SUBLINK ||
                    sublink->subLinkType == ARRAY_SUBLINK)
                {
                    /* get the collation of subselect's first target column */
                    Query      *qtree = (Query *) sublink->subselect;
                    TargetEntry *tent;

                    if (!qtree || !IsA(qtree, Query))
                        elog(ERROR, "cannot set collation for untransformed sublink");
                    tent = (TargetEntry *) linitial(qtree->targetList);
                    Assert(IsA(tent, TargetEntry));
                    Assert(!tent->resjunk);
                    Assert(collation == exprCollation((Node *) tent->expr));
                }
                else
                {
                    /* for all other sublink types, result is boolean */
                    Assert(!OidIsValid(collation));
                }
            }
#endif   /* USE_ASSERT_CHECKING */
            break;
        case T_FieldSelect:
            ((FieldSelect *) expr)->resultcollid = collation;
            break;
        case T_FieldStore:
            Assert(!OidIsValid(collation));     /* result is always composite */
            break;
        case T_RelabelType:
            ((RelabelType *) expr)->resultcollid = collation;
            break;
        case T_CoerceViaIO:
            ((CoerceViaIO *) expr)->resultcollid = collation;
            break;
        case T_ArrayCoerceExpr:
            ((ArrayCoerceExpr *) expr)->resultcollid = collation;
            break;
        case T_ConvertRowtypeExpr:
            Assert(!OidIsValid(collation));     /* result is always composite */
            break;
        case T_CaseExpr:
            ((CaseExpr *) expr)->casecollid = collation;
            break;
        case T_ArrayExpr:
            ((ArrayExpr *) expr)->array_collid = collation;
            break;
        case T_RowExpr:
            Assert(!OidIsValid(collation));     /* result is always composite */
            break;
        case T_RowCompareExpr:
            Assert(!OidIsValid(collation));     /* result is always boolean */
            break;
        case T_CoalesceExpr:
            ((CoalesceExpr *) expr)->coalescecollid = collation;
            break;
        case T_MinMaxExpr:
            ((MinMaxExpr *) expr)->minmaxcollid = collation;
            break;
        case T_XmlExpr:
            Assert((((XmlExpr *) expr)->op == IS_XMLSERIALIZE) ?
                   (collation == DEFAULT_COLLATION_OID) :
                   (collation == InvalidOid));
            break;
        case T_NullTest:
            Assert(!OidIsValid(collation));     /* result is always boolean */
            break;
        case T_BooleanTest:
            Assert(!OidIsValid(collation));     /* result is always boolean */
            break;
        case T_CoerceToDomain:
            ((CoerceToDomain *) expr)->resultcollid = collation;
            break;
        case T_CoerceToDomainValue:
            ((CoerceToDomainValue *) expr)->collation = collation;
            break;
        case T_SetToDefault:
            ((SetToDefault *) expr)->collation = collation;
            break;
        case T_CurrentOfExpr:
            Assert(!OidIsValid(collation));     /* result is always boolean */
            break;
        default:
            elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
            break;
    }
}

/*
 *  exprSetInputCollation -
 *    Assign input-collation information to an expression tree node.
 *
 * This is a no-op for node types that don't store their input collation.
 * Note we omit RowCompareExpr, which needs special treatment since it
 * contains multiple input collation OIDs.
 */
void
exprSetInputCollation(Node *expr, Oid inputcollation)
{
    switch (nodeTag(expr))
    {
        case T_Aggref:
            ((Aggref *) expr)->inputcollid = inputcollation;
            break;
        case T_WindowFunc:
            ((WindowFunc *) expr)->inputcollid = inputcollation;
            break;
        case T_FuncExpr:
            ((FuncExpr *) expr)->inputcollid = inputcollation;
            break;
        case T_OpExpr:
            ((OpExpr *) expr)->inputcollid = inputcollation;
            break;
        case T_DistinctExpr:
            ((DistinctExpr *) expr)->inputcollid = inputcollation;
            break;
        case T_NullIfExpr:
            ((NullIfExpr *) expr)->inputcollid = inputcollation;
            break;
        case T_ScalarArrayOpExpr:
            ((ScalarArrayOpExpr *) expr)->inputcollid = inputcollation;
            break;
        case T_MinMaxExpr:
            ((MinMaxExpr *) expr)->inputcollid = inputcollation;
            break;
        default:
            break;
    }
}


/*
 *  exprLocation -
 *    returns the parse location of an expression tree, for error reports
 *
 * -1 is returned if the location can't be determined.
 *
 * For expressions larger than a single token, the intent here is to
 * return the location of the expression's leftmost token, not necessarily
 * the topmost Node's location field.  For example, an OpExpr's location
 * field will point at the operator name, but if it is not a prefix operator
 * then we should return the location of the left-hand operand instead.
 * The reason is that we want to reference the entire expression not just
 * that operator, and pointing to its start seems to be the most natural way.
 *
 * The location is not perfect --- for example, since the grammar doesn't
 * explicitly represent parentheses in the parsetree, given something that
 * had been written "(a + b) * c" we are going to point at "a" not "(".
 * But it should be plenty good enough for error reporting purposes.
 *
 * You might think that this code is overly general, for instance why check
 * the operands of a FuncExpr node, when the function name can be expected
 * to be to the left of them?  There are a couple of reasons.  The grammar
 * sometimes builds expressions that aren't quite what the user wrote;
 * for instance x IS NOT BETWEEN ... becomes a NOT-expression whose keyword
 * pointer is to the right of its leftmost argument.  Also, nodes that were
 * inserted implicitly by parse analysis (such as FuncExprs for implicit
 * coercions) will have location -1, and so we can have odd combinations of
 * known and unknown locations in a tree.
 */
int
exprLocation(const Node *expr)
{
    int         loc;

    if (expr == NULL)
        return -1;
    switch (nodeTag(expr))
    {
        case T_RangeVar:
            loc = ((const RangeVar *) expr)->location;
            break;
        case T_Var:
            loc = ((const Var *) expr)->location;
            break;
        case T_Const:
            loc = ((const Const *) expr)->location;
            break;
        case T_Param:
            loc = ((const Param *) expr)->location;
            break;
        case T_Aggref:
            /* function name should always be the first thing */
            loc = ((const Aggref *) expr)->location;
            break;
        case T_WindowFunc:
            /* function name should always be the first thing */
            loc = ((const WindowFunc *) expr)->location;
            break;
        case T_ArrayRef:
            /* just use array argument's location */
            loc = exprLocation((Node *) ((const ArrayRef *) expr)->refexpr);
            break;
        case T_FuncExpr:
            {
                const FuncExpr *fexpr = (const FuncExpr *) expr;

                /* consider both function name and leftmost arg */
                loc = leftmostLoc(fexpr->location,
                                  exprLocation((Node *) fexpr->args));
            }
            break;
        case T_NamedArgExpr:
            {
                const NamedArgExpr *na = (const NamedArgExpr *) expr;

                /* consider both argument name and value */
                loc = leftmostLoc(na->location,
                                  exprLocation((Node *) na->arg));
            }
            break;
        case T_OpExpr:
        case T_DistinctExpr:    /* struct-equivalent to OpExpr */
        case T_NullIfExpr:      /* struct-equivalent to OpExpr */
            {
                const OpExpr *opexpr = (const OpExpr *) expr;

                /* consider both operator name and leftmost arg */
                loc = leftmostLoc(opexpr->location,
                                  exprLocation((Node *) opexpr->args));
            }
            break;
        case T_ScalarArrayOpExpr:
            {
                const ScalarArrayOpExpr *saopexpr = (const ScalarArrayOpExpr *) expr;

                /* consider both operator name and leftmost arg */
                loc = leftmostLoc(saopexpr->location,
                                  exprLocation((Node *) saopexpr->args));
            }
            break;
        case T_BoolExpr:
            {
                const BoolExpr *bexpr = (const BoolExpr *) expr;

                /*
                 * Same as above, to handle either NOT or AND/OR.  We can't
                 * special-case NOT because of the way that it's used for
                 * things like IS NOT BETWEEN.
                 */
                loc = leftmostLoc(bexpr->location,
                                  exprLocation((Node *) bexpr->args));
            }
            break;
        case T_SubLink:
            {
                const SubLink *sublink = (const SubLink *) expr;

                /* check the testexpr, if any, and the operator/keyword */
                loc = leftmostLoc(exprLocation(sublink->testexpr),
                                  sublink->location);
            }
            break;
        case T_FieldSelect:
            /* just use argument's location */
            loc = exprLocation((Node *) ((const FieldSelect *) expr)->arg);
            break;
        case T_FieldStore:
            /* just use argument's location */
            loc = exprLocation((Node *) ((const FieldStore *) expr)->arg);
            break;
        case T_RelabelType:
            {
                const RelabelType *rexpr = (const RelabelType *) expr;

                /* Much as above */
                loc = leftmostLoc(rexpr->location,
                                  exprLocation((Node *) rexpr->arg));
            }
            break;
        case T_CoerceViaIO:
            {
                const CoerceViaIO *cexpr = (const CoerceViaIO *) expr;

                /* Much as above */
                loc = leftmostLoc(cexpr->location,
                                  exprLocation((Node *) cexpr->arg));
            }
            break;
        case T_ArrayCoerceExpr:
            {
                const ArrayCoerceExpr *cexpr = (const ArrayCoerceExpr *) expr;

                /* Much as above */
                loc = leftmostLoc(cexpr->location,
                                  exprLocation((Node *) cexpr->arg));
            }
            break;
        case T_ConvertRowtypeExpr:
            {
                const ConvertRowtypeExpr *cexpr = (const ConvertRowtypeExpr *) expr;

                /* Much as above */
                loc = leftmostLoc(cexpr->location,
                                  exprLocation((Node *) cexpr->arg));
            }
            break;
        case T_CollateExpr:
            /* just use argument's location */
            loc = exprLocation((Node *) ((const CollateExpr *) expr)->arg);
            break;
        case T_CaseExpr:
            /* CASE keyword should always be the first thing */
            loc = ((const CaseExpr *) expr)->location;
            break;
        case T_CaseWhen:
            /* WHEN keyword should always be the first thing */
            loc = ((const CaseWhen *) expr)->location;
            break;
        case T_ArrayExpr:
            /* the location points at ARRAY or [, which must be leftmost */
            loc = ((const ArrayExpr *) expr)->location;
            break;
        case T_RowExpr:
            /* the location points at ROW or (, which must be leftmost */
            loc = ((const RowExpr *) expr)->location;
            break;
        case T_RowCompareExpr:
            /* just use leftmost argument's location */
            loc = exprLocation((Node *) ((const RowCompareExpr *) expr)->largs);
            break;
        case T_CoalesceExpr:
            /* COALESCE keyword should always be the first thing */
            loc = ((const CoalesceExpr *) expr)->location;
            break;
        case T_MinMaxExpr:
            /* GREATEST/LEAST keyword should always be the first thing */
            loc = ((const MinMaxExpr *) expr)->location;
            break;
        case T_XmlExpr:
            {
                const XmlExpr *xexpr = (const XmlExpr *) expr;

                /* consider both function name and leftmost arg */
                loc = leftmostLoc(xexpr->location,
                                  exprLocation((Node *) xexpr->args));
            }
            break;
        case T_NullTest:
            /* just use argument's location */
            loc = exprLocation((Node *) ((const NullTest *) expr)->arg);
            break;
        case T_BooleanTest:
            /* just use argument's location */
            loc = exprLocation((Node *) ((const BooleanTest *) expr)->arg);
            break;
        case T_CoerceToDomain:
            {
                const CoerceToDomain *cexpr = (const CoerceToDomain *) expr;

                /* Much as above */
                loc = leftmostLoc(cexpr->location,
                                  exprLocation((Node *) cexpr->arg));
            }
            break;
        case T_CoerceToDomainValue:
            loc = ((const CoerceToDomainValue *) expr)->location;
            break;
        case T_SetToDefault:
            loc = ((const SetToDefault *) expr)->location;
            break;
        case T_TargetEntry:
            /* just use argument's location */
            loc = exprLocation((Node *) ((const TargetEntry *) expr)->expr);
            break;
        case T_IntoClause:
            /* use the contained RangeVar's location --- close enough */
            loc = exprLocation((Node *) ((const IntoClause *) expr)->rel);
            break;
        case T_List:
            {
                /* report location of first list member that has a location */
                ListCell   *lc;

                loc = -1;       /* just to suppress compiler warning */
                foreach(lc, (const List *) expr)
                {
                    loc = exprLocation((Node *) lfirst(lc));
                    if (loc >= 0)
                        break;
                }
            }
            break;
        case T_A_Expr:
            {
                const A_Expr *aexpr = (const A_Expr *) expr;

                /* use leftmost of operator or left operand (if any) */
                /* we assume right operand can't be to left of operator */
                loc = leftmostLoc(aexpr->location,
                                  exprLocation(aexpr->lexpr));
            }
            break;
        case T_ColumnRef:
            loc = ((const ColumnRef *) expr)->location;
            break;
        case T_ParamRef:
            loc = ((const ParamRef *) expr)->location;
            break;
        case T_A_Const:
            loc = ((const A_Const *) expr)->location;
            break;
        case T_FuncCall:
            {
                const FuncCall *fc = (const FuncCall *) expr;

                /* consider both function name and leftmost arg */
                /* (we assume any ORDER BY nodes must be to right of name) */
                loc = leftmostLoc(fc->location,
                                  exprLocation((Node *) fc->args));
            }
            break;
        case T_A_ArrayExpr:
            /* the location points at ARRAY or [, which must be leftmost */
            loc = ((const A_ArrayExpr *) expr)->location;
            break;
        case T_ResTarget:
            /* we need not examine the contained expression (if any) */
            loc = ((const ResTarget *) expr)->location;
            break;
        case T_TypeCast:
            {
                const TypeCast *tc = (const TypeCast *) expr;

                /*
                 * This could represent CAST(), ::, or TypeName 'literal', so
                 * any of the components might be leftmost.
                 */
                loc = exprLocation(tc->arg);
                loc = leftmostLoc(loc, tc->typeName->location);
                loc = leftmostLoc(loc, tc->location);
            }
            break;
        case T_CollateClause:
            /* just use argument's location */
            loc = exprLocation(((const CollateClause *) expr)->arg);
            break;
        case T_SortBy:
            /* just use argument's location (ignore operator, if any) */
            loc = exprLocation(((const SortBy *) expr)->node);
            break;
        case T_WindowDef:
            loc = ((const WindowDef *) expr)->location;
            break;
        case T_TypeName:
            loc = ((const TypeName *) expr)->location;
            break;
        case T_Constraint:
            loc = ((const Constraint *) expr)->location;
            break;
        case T_XmlSerialize:
            /* XMLSERIALIZE keyword should always be the first thing */
            loc = ((const XmlSerialize *) expr)->location;
            break;
        case T_WithClause:
            loc = ((const WithClause *) expr)->location;
            break;
        case T_CommonTableExpr:
            loc = ((const CommonTableExpr *) expr)->location;
            break;
        case T_PlaceHolderVar:
            /* just use argument's location */
            loc = exprLocation((Node *) ((const PlaceHolderVar *) expr)->phexpr);
            break;
        default:
            /* for any other node type it's just unknown... */
            loc = -1;
            break;
    }
    return loc;
}

/*
 * leftmostLoc - support for exprLocation
 *
 * Take the minimum of two parse location values, but ignore unknowns
 */
static int
leftmostLoc(int loc1, int loc2)
{
    if (loc1 < 0)
        return loc2;
    else if (loc2 < 0)
        return loc1;
    else
        return Min(loc1, loc2);
}


/*
 * Standard expression-tree walking support
 *
 * We used to have near-duplicate code in many different routines that
 * understood how to recurse through an expression node tree.  That was
 * a pain to maintain, and we frequently had bugs due to some particular
 * routine neglecting to support a particular node type.  In most cases,
 * these routines only actually care about certain node types, and don't
 * care about other types except insofar as they have to recurse through
 * non-primitive node types.  Therefore, we now provide generic tree-walking
 * logic to consolidate the redundant "boilerplate" code.  There are
 * two versions: expression_tree_walker() and expression_tree_mutator().
 */

/*
 * expression_tree_walker() is designed to support routines that traverse
 * a tree in a read-only fashion (although it will also work for routines
 * that modify nodes in-place but never add/delete/replace nodes).
 * A walker routine should look like this:
 *
 * bool my_walker (Node *node, my_struct *context)
 * {
 *      if (node == NULL)
 *          return false;
 *      // check for nodes that special work is required for, eg:
 *      if (IsA(node, Var))
 *      {
 *          ... do special actions for Var nodes
 *      }
 *      else if (IsA(node, ...))
 *      {
 *          ... do special actions for other node types
 *      }
 *      // for any node type not specially processed, do:
 *      return expression_tree_walker(node, my_walker, (void *) context);
 * }
 *
 * The "context" argument points to a struct that holds whatever context
 * information the walker routine needs --- it can be used to return data
 * gathered by the walker, too.  This argument is not touched by
 * expression_tree_walker, but it is passed down to recursive sub-invocations
 * of my_walker.  The tree walk is started from a setup routine that
 * fills in the appropriate context struct, calls my_walker with the top-level
 * node of the tree, and then examines the results.
 *
 * The walker routine should return "false" to continue the tree walk, or
 * "true" to abort the walk and immediately return "true" to the top-level
 * caller.  This can be used to short-circuit the traversal if the walker
 * has found what it came for.  "false" is returned to the top-level caller
 * iff no invocation of the walker returned "true".
 *
 * The node types handled by expression_tree_walker include all those
 * normally found in target lists and qualifier clauses during the planning
 * stage.  In particular, it handles List nodes since a cnf-ified qual clause
 * will have List structure at the top level, and it handles TargetEntry nodes
 * so that a scan of a target list can be handled without additional code.
 * Also, RangeTblRef, FromExpr, JoinExpr, and SetOperationStmt nodes are
 * handled, so that query jointrees and setOperation trees can be processed
 * without additional code.
 *
 * expression_tree_walker will handle SubLink nodes by recursing normally
 * into the "testexpr" subtree (which is an expression belonging to the outer
 * plan).  It will also call the walker on the sub-Query node; however, when
 * expression_tree_walker itself is called on a Query node, it does nothing
 * and returns "false".  The net effect is that unless the walker does
 * something special at a Query node, sub-selects will not be visited during
 * an expression tree walk. This is exactly the behavior wanted in many cases
 * --- and for those walkers that do want to recurse into sub-selects, special
 * behavior is typically needed anyway at the entry to a sub-select (such as
 * incrementing a depth counter). A walker that wants to examine sub-selects
 * should include code along the lines of:
 *
 *      if (IsA(node, Query))
 *      {
 *          adjust context for subquery;
 *          result = query_tree_walker((Query *) node, my_walker, context,
 *                                     0); // adjust flags as needed
 *          restore context if needed;
 *          return result;
 *      }
 *
 * query_tree_walker is a convenience routine (see below) that calls the
 * walker on all the expression subtrees of the given Query node.
 *
 * expression_tree_walker will handle SubPlan nodes by recursing normally
 * into the "testexpr" and the "args" list (which are expressions belonging to
 * the outer plan).  It will not touch the completed subplan, however.  Since
 * there is no link to the original Query, it is not possible to recurse into
 * subselects of an already-planned expression tree.  This is OK for current
 * uses, but may need to be revisited in future.
 */

bool
expression_tree_walker(Node *node,
                       bool (*walker) (),
                       void *context)
{
    ListCell   *temp;

    /*
     * The walker has already visited the current node, and so we need only
     * recurse into any sub-nodes it has.
     *
     * We assume that the walker is not interested in List nodes per se, so
     * when we expect a List we just recurse directly to self without
     * bothering to call the walker.
     */
    if (node == NULL)
        return false;

    /* Guard against stack overflow due to overly complex expressions */
    check_stack_depth();

    switch (nodeTag(node))
    {
        case T_Var:
        case T_Const:
        case T_Param:
        case T_CoerceToDomainValue:
        case T_CaseTestExpr:
        case T_SetToDefault:
        case T_CurrentOfExpr:
        case T_RangeTblRef:
        case T_SortGroupClause:
            /* primitive node types with no expression subnodes */
            break;
        case T_Aggref:
            {
                Aggref     *expr = (Aggref *) node;

                /* recurse directly on List */
                if (expression_tree_walker((Node *) expr->args,
                                           walker, context))
                    return true;
                if (expression_tree_walker((Node *) expr->aggorder,
                                           walker, context))
                    return true;
                if (expression_tree_walker((Node *) expr->aggdistinct,
                                           walker, context))
                    return true;
            }
            break;
        case T_WindowFunc:
            {
                WindowFunc *expr = (WindowFunc *) node;

                /* recurse directly on List */
                if (expression_tree_walker((Node *) expr->args,
                                           walker, context))
                    return true;
            }
            break;
        case T_ArrayRef:
            {
                ArrayRef   *aref = (ArrayRef *) node;

                /* recurse directly for upper/lower array index lists */
                if (expression_tree_walker((Node *) aref->refupperindexpr,
                                           walker, context))
                    return true;
                if (expression_tree_walker((Node *) aref->reflowerindexpr,
                                           walker, context))
                    return true;
                /* walker must see the refexpr and refassgnexpr, however */
                if (walker(aref->refexpr, context))
                    return true;
                if (walker(aref->refassgnexpr, context))
                    return true;
            }
            break;
        case T_FuncExpr:
            {
                FuncExpr   *expr = (FuncExpr *) node;

                if (expression_tree_walker((Node *) expr->args,
                                           walker, context))
                    return true;
            }
            break;
        case T_NamedArgExpr:
            return walker(((NamedArgExpr *) node)->arg, context);
        case T_OpExpr:
        case T_DistinctExpr:    /* struct-equivalent to OpExpr */
        case T_NullIfExpr:      /* struct-equivalent to OpExpr */
            {
                OpExpr     *expr = (OpExpr *) node;

                if (expression_tree_walker((Node *) expr->args,
                                           walker, context))
                    return true;
            }
            break;
        case T_ScalarArrayOpExpr:
            {
                ScalarArrayOpExpr *expr = (ScalarArrayOpExpr *) node;

                if (expression_tree_walker((Node *) expr->args,
                                           walker, context))
                    return true;
            }
            break;
        case T_BoolExpr:
            {
                BoolExpr   *expr = (BoolExpr *) node;

                if (expression_tree_walker((Node *) expr->args,
                                           walker, context))
                    return true;
            }
            break;
        case T_SubLink:
            {
                SubLink    *sublink = (SubLink *) node;

                if (walker(sublink->testexpr, context))
                    return true;

                /*
                 * Also invoke the walker on the sublink's Query node, so it
                 * can recurse into the sub-query if it wants to.
                 */
                return walker(sublink->subselect, context);
            }
            break;
        case T_SubPlan:
            {
                SubPlan    *subplan = (SubPlan *) node;

                /* recurse into the testexpr, but not into the Plan */
                if (walker(subplan->testexpr, context))
                    return true;
                /* also examine args list */
                if (expression_tree_walker((Node *) subplan->args,
                                           walker, context))
                    return true;
            }
            break;
        case T_AlternativeSubPlan:
            return walker(((AlternativeSubPlan *) node)->subplans, context);
        case T_FieldSelect:
            return walker(((FieldSelect *) node)->arg, context);
        case T_FieldStore:
            {
                FieldStore *fstore = (FieldStore *) node;

                if (walker(fstore->arg, context))
                    return true;
                if (walker(fstore->newvals, context))
                    return true;
            }
            break;
        case T_RelabelType:
            return walker(((RelabelType *) node)->arg, context);
        case T_CoerceViaIO:
            return walker(((CoerceViaIO *) node)->arg, context);
        case T_ArrayCoerceExpr:
            return walker(((ArrayCoerceExpr *) node)->arg, context);
        case T_ConvertRowtypeExpr:
            return walker(((ConvertRowtypeExpr *) node)->arg, context);
        case T_CollateExpr:
            return walker(((CollateExpr *) node)->arg, context);
        case T_CaseExpr:
            {
                CaseExpr   *caseexpr = (CaseExpr *) node;

                if (walker(caseexpr->arg, context))
                    return true;
                /* we assume walker doesn't care about CaseWhens, either */
                foreach(temp, caseexpr->args)
                {
                    CaseWhen   *when = (CaseWhen *) lfirst(temp);

                    Assert(IsA(when, CaseWhen));
                    if (walker(when->expr, context))
                        return true;
                    if (walker(when->result, context))
                        return true;
                }
                if (walker(caseexpr->defresult, context))
                    return true;
            }
            break;
        case T_ArrayExpr:
            return walker(((ArrayExpr *) node)->elements, context);
        case T_RowExpr:
            /* Assume colnames isn't interesting */
            return walker(((RowExpr *) node)->args, context);
        case T_RowCompareExpr:
            {
                RowCompareExpr *rcexpr = (RowCompareExpr *) node;

                if (walker(rcexpr->largs, context))
                    return true;
                if (walker(rcexpr->rargs, context))
                    return true;
            }
            break;
        case T_CoalesceExpr:
            return walker(((CoalesceExpr *) node)->args, context);
        case T_MinMaxExpr:
            return walker(((MinMaxExpr *) node)->args, context);
        case T_XmlExpr:
            {
                XmlExpr    *xexpr = (XmlExpr *) node;

                if (walker(xexpr->named_args, context))
                    return true;
                /* we assume walker doesn't care about arg_names */
                if (walker(xexpr->args, context))
                    return true;
            }
            break;
        case T_NullTest:
            return walker(((NullTest *) node)->arg, context);
        case T_BooleanTest:
            return walker(((BooleanTest *) node)->arg, context);
        case T_CoerceToDomain:
            return walker(((CoerceToDomain *) node)->arg, context);
        case T_TargetEntry:
            return walker(((TargetEntry *) node)->expr, context);
        case T_Query:
            /* Do nothing with a sub-Query, per discussion above */
            break;
        case T_WindowClause:
            {
                WindowClause *wc = (WindowClause *) node;

                if (walker(wc->partitionClause, context))
                    return true;
                if (walker(wc->orderClause, context))
                    return true;
                if (walker(wc->startOffset, context))
                    return true;
                if (walker(wc->endOffset, context))
                    return true;
            }
            break;
        case T_CommonTableExpr:
            {
                CommonTableExpr *cte = (CommonTableExpr *) node;

                /*
                 * Invoke the walker on the CTE's Query node, so it can
                 * recurse into the sub-query if it wants to.
                 */
                return walker(cte->ctequery, context);
            }
            break;
        case T_List:
            foreach(temp, (List *) node)
            {
                if (walker((Node *) lfirst(temp), context))
                    return true;
            }
            break;
        case T_FromExpr:
            {
                FromExpr   *from = (FromExpr *) node;

                if (walker(from->fromlist, context))
                    return true;
                if (walker(from->quals, context))
                    return true;
            }
            break;
        case T_JoinExpr:
            {
                JoinExpr   *join = (JoinExpr *) node;

                if (walker(join->larg, context))
                    return true;
                if (walker(join->rarg, context))
                    return true;
                if (walker(join->quals, context))
                    return true;

                /*
                 * alias clause, using list are deemed uninteresting.
                 */
            }
            break;
        case T_SetOperationStmt:
            {
                SetOperationStmt *setop = (SetOperationStmt *) node;

                if (walker(setop->larg, context))
                    return true;
                if (walker(setop->rarg, context))
                    return true;

                /* groupClauses are deemed uninteresting */
            }
            break;
        case T_PlaceHolderVar:
            return walker(((PlaceHolderVar *) node)->phexpr, context);
        case T_AppendRelInfo:
            {
                AppendRelInfo *appinfo = (AppendRelInfo *) node;

                if (expression_tree_walker((Node *) appinfo->translated_vars,
                                           walker, context))
                    return true;
            }
            break;
        case T_PlaceHolderInfo:
            return walker(((PlaceHolderInfo *) node)->ph_var, context);
        default:
            elog(ERROR, "unrecognized node type: %d",
                 (int) nodeTag(node));
            break;
    }
    return false;
}

/*
 * query_tree_walker --- initiate a walk of a Query's expressions
 *
 * This routine exists just to reduce the number of places that need to know
 * where all the expression subtrees of a Query are.  Note it can be used
 * for starting a walk at top level of a Query regardless of whether the
 * walker intends to descend into subqueries.  It is also useful for
 * descending into subqueries within a walker.
 *
 * Some callers want to suppress visitation of certain items in the sub-Query,
 * typically because they need to process them specially, or don't actually
 * want to recurse into subqueries.  This is supported by the flags argument,
 * which is the bitwise OR of flag values to suppress visitation of
 * indicated items.  (More flag bits may be added as needed.)
 */
bool
query_tree_walker(Query *query,
                  bool (*walker) (),
                  void *context,
                  int flags)
{
    Assert(query != NULL && IsA(query, Query));

    if (walker((Node *) query->targetList, context))
        return true;
    if (walker((Node *) query->returningList, context))
        return true;
    if (walker((Node *) query->jointree, context))
        return true;
    if (walker(query->setOperations, context))
        return true;
    if (walker(query->havingQual, context))
        return true;
    if (walker(query->limitOffset, context))
        return true;
    if (walker(query->limitCount, context))
        return true;
    if (!(flags & QTW_IGNORE_CTE_SUBQUERIES))
    {
        if (walker((Node *) query->cteList, context))
            return true;
    }
    if (!(flags & QTW_IGNORE_RANGE_TABLE))
    {
        if (range_table_walker(query->rtable, walker, context, flags))
            return true;
    }
    return false;
}

/*
 * range_table_walker is just the part of query_tree_walker that scans
 * a query's rangetable.  This is split out since it can be useful on
 * its own.
 */
bool
range_table_walker(List *rtable,
                   bool (*walker) (),
                   void *context,
                   int flags)
{
    ListCell   *rt;

    foreach(rt, rtable)
    {
        RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);

        /* For historical reasons, visiting RTEs is not the default */
        if (flags & QTW_EXAMINE_RTES)
            if (walker(rte, context))
                return true;

        switch (rte->rtekind)
        {
            case RTE_RELATION:
            case RTE_CTE:
                /* nothing to do */
                break;
            case RTE_SUBQUERY:
                if (!(flags & QTW_IGNORE_RT_SUBQUERIES))
                    if (walker(rte->subquery, context))
                        return true;
                break;
            case RTE_JOIN:
                if (!(flags & QTW_IGNORE_JOINALIASES))
                    if (walker(rte->joinaliasvars, context))
                        return true;
                break;
            case RTE_FUNCTION:
                if (walker(rte->funcexpr, context))
                    return true;
                break;
            case RTE_VALUES:
                if (walker(rte->values_lists, context))
                    return true;
                break;
        }
    }
    return false;
}


/*
 * expression_tree_mutator() is designed to support routines that make a
 * modified copy of an expression tree, with some nodes being added,
 * removed, or replaced by new subtrees.  The original tree is (normally)
 * not changed.  Each recursion level is responsible for returning a copy of
 * (or appropriately modified substitute for) the subtree it is handed.
 * A mutator routine should look like this:
 *
 * Node * my_mutator (Node *node, my_struct *context)
 * {
 *      if (node == NULL)
 *          return NULL;
 *      // check for nodes that special work is required for, eg:
 *      if (IsA(node, Var))
 *      {
 *          ... create and return modified copy of Var node
 *      }
 *      else if (IsA(node, ...))
 *      {
 *          ... do special transformations of other node types
 *      }
 *      // for any node type not specially processed, do:
 *      return expression_tree_mutator(node, my_mutator, (void *) context);
 * }
 *
 * The "context" argument points to a struct that holds whatever context
 * information the mutator routine needs --- it can be used to return extra
 * data gathered by the mutator, too.  This argument is not touched by
 * expression_tree_mutator, but it is passed down to recursive sub-invocations
 * of my_mutator.  The tree walk is started from a setup routine that
 * fills in the appropriate context struct, calls my_mutator with the
 * top-level node of the tree, and does any required post-processing.
 *
 * Each level of recursion must return an appropriately modified Node.
 * If expression_tree_mutator() is called, it will make an exact copy
 * of the given Node, but invoke my_mutator() to copy the sub-node(s)
 * of that Node.  In this way, my_mutator() has full control over the
 * copying process but need not directly deal with expression trees
 * that it has no interest in.
 *
 * Just as for expression_tree_walker, the node types handled by
 * expression_tree_mutator include all those normally found in target lists
 * and qualifier clauses during the planning stage.
 *
 * expression_tree_mutator will handle SubLink nodes by recursing normally
 * into the "testexpr" subtree (which is an expression belonging to the outer
 * plan).  It will also call the mutator on the sub-Query node; however, when
 * expression_tree_mutator itself is called on a Query node, it does nothing
 * and returns the unmodified Query node.  The net effect is that unless the
 * mutator does something special at a Query node, sub-selects will not be
 * visited or modified; the original sub-select will be linked to by the new
 * SubLink node.  Mutators that want to descend into sub-selects will usually
 * do so by recognizing Query nodes and calling query_tree_mutator (below).
 *
 * expression_tree_mutator will handle a SubPlan node by recursing into the
 * "testexpr" and the "args" list (which belong to the outer plan), but it
 * will simply copy the link to the inner plan, since that's typically what
 * expression tree mutators want.  A mutator that wants to modify the subplan
 * can force appropriate behavior by recognizing SubPlan expression nodes
 * and doing the right thing.
 */

Node *
expression_tree_mutator(Node *node,
                        Node *(*mutator) (),
                        void *context)
{
    /*
     * The mutator has already decided not to modify the current node, but we
     * must call the mutator for any sub-nodes.
     */

#define FLATCOPY(newnode, node, nodetype)  \
    ( (newnode) = (nodetype *) palloc(sizeof(nodetype)), \
      memcpy((newnode), (node), sizeof(nodetype)) )

#define CHECKFLATCOPY(newnode, node, nodetype)  \
    ( AssertMacro(IsA((node), nodetype)), \
      (newnode) = (nodetype *) palloc(sizeof(nodetype)), \
      memcpy((newnode), (node), sizeof(nodetype)) )

#define MUTATE(newfield, oldfield, fieldtype)  \
        ( (newfield) = (fieldtype) mutator((Node *) (oldfield), context) )

    if (node == NULL)
        return NULL;

    /* Guard against stack overflow due to overly complex expressions */
    check_stack_depth();

    switch (nodeTag(node))
    {
            /*
             * Primitive node types with no expression subnodes.  Var and
             * Const are frequent enough to deserve special cases, the others
             * we just use copyObject for.
             */
        case T_Var:
            {
                Var        *var = (Var *) node;
                Var        *newnode;

                FLATCOPY(newnode, var, Var);
                return (Node *) newnode;
            }
            break;
        case T_Const:
            {
                Const      *oldnode = (Const *) node;
                Const      *newnode;

                FLATCOPY(newnode, oldnode, Const);
                /* XXX we don't bother with datumCopy; should we? */
                return (Node *) newnode;
            }
            break;
        case T_Param:
        case T_CoerceToDomainValue:
        case T_CaseTestExpr:
        case T_SetToDefault:
        case T_CurrentOfExpr:
        case T_RangeTblRef:
        case T_SortGroupClause:
            return (Node *) copyObject(node);
        case T_Aggref:
            {
                Aggref     *aggref = (Aggref *) node;
                Aggref     *newnode;

                FLATCOPY(newnode, aggref, Aggref);
                MUTATE(newnode->args, aggref->args, List *);
                MUTATE(newnode->aggorder, aggref->aggorder, List *);
                MUTATE(newnode->aggdistinct, aggref->aggdistinct, List *);
                return (Node *) newnode;
            }
            break;
        case T_WindowFunc:
            {
                WindowFunc *wfunc = (WindowFunc *) node;
                WindowFunc *newnode;

                FLATCOPY(newnode, wfunc, WindowFunc);
                MUTATE(newnode->args, wfunc->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_ArrayRef:
            {
                ArrayRef   *arrayref = (ArrayRef *) node;
                ArrayRef   *newnode;

                FLATCOPY(newnode, arrayref, ArrayRef);
                MUTATE(newnode->refupperindexpr, arrayref->refupperindexpr,
                       List *);
                MUTATE(newnode->reflowerindexpr, arrayref->reflowerindexpr,
                       List *);
                MUTATE(newnode->refexpr, arrayref->refexpr,
                       Expr *);
                MUTATE(newnode->refassgnexpr, arrayref->refassgnexpr,
                       Expr *);
                return (Node *) newnode;
            }
            break;
        case T_FuncExpr:
            {
                FuncExpr   *expr = (FuncExpr *) node;
                FuncExpr   *newnode;

                FLATCOPY(newnode, expr, FuncExpr);
                MUTATE(newnode->args, expr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_NamedArgExpr:
            {
                NamedArgExpr *nexpr = (NamedArgExpr *) node;
                NamedArgExpr *newnode;

                FLATCOPY(newnode, nexpr, NamedArgExpr);
                MUTATE(newnode->arg, nexpr->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_OpExpr:
            {
                OpExpr     *expr = (OpExpr *) node;
                OpExpr     *newnode;

                FLATCOPY(newnode, expr, OpExpr);
                MUTATE(newnode->args, expr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_DistinctExpr:
            {
                DistinctExpr *expr = (DistinctExpr *) node;
                DistinctExpr *newnode;

                FLATCOPY(newnode, expr, DistinctExpr);
                MUTATE(newnode->args, expr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_NullIfExpr:
            {
                NullIfExpr *expr = (NullIfExpr *) node;
                NullIfExpr *newnode;

                FLATCOPY(newnode, expr, NullIfExpr);
                MUTATE(newnode->args, expr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_ScalarArrayOpExpr:
            {
                ScalarArrayOpExpr *expr = (ScalarArrayOpExpr *) node;
                ScalarArrayOpExpr *newnode;

                FLATCOPY(newnode, expr, ScalarArrayOpExpr);
                MUTATE(newnode->args, expr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_BoolExpr:
            {
                BoolExpr   *expr = (BoolExpr *) node;
                BoolExpr   *newnode;

                FLATCOPY(newnode, expr, BoolExpr);
                MUTATE(newnode->args, expr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_SubLink:
            {
                SubLink    *sublink = (SubLink *) node;
                SubLink    *newnode;

                FLATCOPY(newnode, sublink, SubLink);
                MUTATE(newnode->testexpr, sublink->testexpr, Node *);

                /*
                 * Also invoke the mutator on the sublink's Query node, so it
                 * can recurse into the sub-query if it wants to.
                 */
                MUTATE(newnode->subselect, sublink->subselect, Node *);
                return (Node *) newnode;
            }
            break;
        case T_SubPlan:
            {
                SubPlan    *subplan = (SubPlan *) node;
                SubPlan    *newnode;

                FLATCOPY(newnode, subplan, SubPlan);
                /* transform testexpr */
                MUTATE(newnode->testexpr, subplan->testexpr, Node *);
                /* transform args list (params to be passed to subplan) */
                MUTATE(newnode->args, subplan->args, List *);
                /* but not the sub-Plan itself, which is referenced as-is */
                return (Node *) newnode;
            }
            break;
        case T_AlternativeSubPlan:
            {
                AlternativeSubPlan *asplan = (AlternativeSubPlan *) node;
                AlternativeSubPlan *newnode;

                FLATCOPY(newnode, asplan, AlternativeSubPlan);
                MUTATE(newnode->subplans, asplan->subplans, List *);
                return (Node *) newnode;
            }
            break;
        case T_FieldSelect:
            {
                FieldSelect *fselect = (FieldSelect *) node;
                FieldSelect *newnode;

                FLATCOPY(newnode, fselect, FieldSelect);
                MUTATE(newnode->arg, fselect->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_FieldStore:
            {
                FieldStore *fstore = (FieldStore *) node;
                FieldStore *newnode;

                FLATCOPY(newnode, fstore, FieldStore);
                MUTATE(newnode->arg, fstore->arg, Expr *);
                MUTATE(newnode->newvals, fstore->newvals, List *);
                newnode->fieldnums = list_copy(fstore->fieldnums);
                return (Node *) newnode;
            }
            break;
        case T_RelabelType:
            {
                RelabelType *relabel = (RelabelType *) node;
                RelabelType *newnode;

                FLATCOPY(newnode, relabel, RelabelType);
                MUTATE(newnode->arg, relabel->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_CoerceViaIO:
            {
                CoerceViaIO *iocoerce = (CoerceViaIO *) node;
                CoerceViaIO *newnode;

                FLATCOPY(newnode, iocoerce, CoerceViaIO);
                MUTATE(newnode->arg, iocoerce->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_ArrayCoerceExpr:
            {
                ArrayCoerceExpr *acoerce = (ArrayCoerceExpr *) node;
                ArrayCoerceExpr *newnode;

                FLATCOPY(newnode, acoerce, ArrayCoerceExpr);
                MUTATE(newnode->arg, acoerce->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_ConvertRowtypeExpr:
            {
                ConvertRowtypeExpr *convexpr = (ConvertRowtypeExpr *) node;
                ConvertRowtypeExpr *newnode;

                FLATCOPY(newnode, convexpr, ConvertRowtypeExpr);
                MUTATE(newnode->arg, convexpr->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_CollateExpr:
            {
                CollateExpr *collate = (CollateExpr *) node;
                CollateExpr *newnode;

                FLATCOPY(newnode, collate, CollateExpr);
                MUTATE(newnode->arg, collate->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_CaseExpr:
            {
                CaseExpr   *caseexpr = (CaseExpr *) node;
                CaseExpr   *newnode;

                FLATCOPY(newnode, caseexpr, CaseExpr);
                MUTATE(newnode->arg, caseexpr->arg, Expr *);
                MUTATE(newnode->args, caseexpr->args, List *);
                MUTATE(newnode->defresult, caseexpr->defresult, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_CaseWhen:
            {
                CaseWhen   *casewhen = (CaseWhen *) node;
                CaseWhen   *newnode;

                FLATCOPY(newnode, casewhen, CaseWhen);
                MUTATE(newnode->expr, casewhen->expr, Expr *);
                MUTATE(newnode->result, casewhen->result, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_ArrayExpr:
            {
                ArrayExpr  *arrayexpr = (ArrayExpr *) node;
                ArrayExpr  *newnode;

                FLATCOPY(newnode, arrayexpr, ArrayExpr);
                MUTATE(newnode->elements, arrayexpr->elements, List *);
                return (Node *) newnode;
            }
            break;
        case T_RowExpr:
            {
                RowExpr    *rowexpr = (RowExpr *) node;
                RowExpr    *newnode;

                FLATCOPY(newnode, rowexpr, RowExpr);
                MUTATE(newnode->args, rowexpr->args, List *);
                /* Assume colnames needn't be duplicated */
                return (Node *) newnode;
            }
            break;
        case T_RowCompareExpr:
            {
                RowCompareExpr *rcexpr = (RowCompareExpr *) node;
                RowCompareExpr *newnode;

                FLATCOPY(newnode, rcexpr, RowCompareExpr);
                MUTATE(newnode->largs, rcexpr->largs, List *);
                MUTATE(newnode->rargs, rcexpr->rargs, List *);
                return (Node *) newnode;
            }
            break;
        case T_CoalesceExpr:
            {
                CoalesceExpr *coalesceexpr = (CoalesceExpr *) node;
                CoalesceExpr *newnode;

                FLATCOPY(newnode, coalesceexpr, CoalesceExpr);
                MUTATE(newnode->args, coalesceexpr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_MinMaxExpr:
            {
                MinMaxExpr *minmaxexpr = (MinMaxExpr *) node;
                MinMaxExpr *newnode;

                FLATCOPY(newnode, minmaxexpr, MinMaxExpr);
                MUTATE(newnode->args, minmaxexpr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_XmlExpr:
            {
                XmlExpr    *xexpr = (XmlExpr *) node;
                XmlExpr    *newnode;

                FLATCOPY(newnode, xexpr, XmlExpr);
                MUTATE(newnode->named_args, xexpr->named_args, List *);
                /* assume mutator does not care about arg_names */
                MUTATE(newnode->args, xexpr->args, List *);
                return (Node *) newnode;
            }
            break;
        case T_NullTest:
            {
                NullTest   *ntest = (NullTest *) node;
                NullTest   *newnode;

                FLATCOPY(newnode, ntest, NullTest);
                MUTATE(newnode->arg, ntest->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_BooleanTest:
            {
                BooleanTest *btest = (BooleanTest *) node;
                BooleanTest *newnode;

                FLATCOPY(newnode, btest, BooleanTest);
                MUTATE(newnode->arg, btest->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_CoerceToDomain:
            {
                CoerceToDomain *ctest = (CoerceToDomain *) node;
                CoerceToDomain *newnode;

                FLATCOPY(newnode, ctest, CoerceToDomain);
                MUTATE(newnode->arg, ctest->arg, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_TargetEntry:
            {
                TargetEntry *targetentry = (TargetEntry *) node;
                TargetEntry *newnode;

                FLATCOPY(newnode, targetentry, TargetEntry);
                MUTATE(newnode->expr, targetentry->expr, Expr *);
                return (Node *) newnode;
            }
            break;
        case T_Query:
            /* Do nothing with a sub-Query, per discussion above */
            return node;
        case T_WindowClause:
            {
                WindowClause *wc = (WindowClause *) node;
                WindowClause *newnode;

                FLATCOPY(newnode, wc, WindowClause);
                MUTATE(newnode->partitionClause, wc->partitionClause, List *);
                MUTATE(newnode->orderClause, wc->orderClause, List *);
                MUTATE(newnode->startOffset, wc->startOffset, Node *);
                MUTATE(newnode->endOffset, wc->endOffset, Node *);
                return (Node *) newnode;
            }
            break;
        case T_CommonTableExpr:
            {
                CommonTableExpr *cte = (CommonTableExpr *) node;
                CommonTableExpr *newnode;

                FLATCOPY(newnode, cte, CommonTableExpr);

                /*
                 * Also invoke the mutator on the CTE's Query node, so it can
                 * recurse into the sub-query if it wants to.
                 */
                MUTATE(newnode->ctequery, cte->ctequery, Node *);
                return (Node *) newnode;
            }
            break;
        case T_List:
            {
                /*
                 * We assume the mutator isn't interested in the list nodes
                 * per se, so just invoke it on each list element. NOTE: this
                 * would fail badly on a list with integer elements!
                 */
                List       *resultlist;
                ListCell   *temp;

                resultlist = NIL;
                foreach(temp, (List *) node)
                {
                    resultlist = lappend(resultlist,
                                         mutator((Node *) lfirst(temp),
                                                 context));
                }
                return (Node *) resultlist;
            }
            break;
        case T_FromExpr:
            {
                FromExpr   *from = (FromExpr *) node;
                FromExpr   *newnode;

                FLATCOPY(newnode, from, FromExpr);
                MUTATE(newnode->fromlist, from->fromlist, List *);
                MUTATE(newnode->quals, from->quals, Node *);
                return (Node *) newnode;
            }
            break;
        case T_JoinExpr:
            {
                JoinExpr   *join = (JoinExpr *) node;
                JoinExpr   *newnode;

                FLATCOPY(newnode, join, JoinExpr);
                MUTATE(newnode->larg, join->larg, Node *);
                MUTATE(newnode->rarg, join->rarg, Node *);
                MUTATE(newnode->quals, join->quals, Node *);
                /* We do not mutate alias or using by default */
                return (Node *) newnode;
            }
            break;
        case T_SetOperationStmt:
            {
                SetOperationStmt *setop = (SetOperationStmt *) node;
                SetOperationStmt *newnode;

                FLATCOPY(newnode, setop, SetOperationStmt);
                MUTATE(newnode->larg, setop->larg, Node *);
                MUTATE(newnode->rarg, setop->rarg, Node *);
                /* We do not mutate groupClauses by default */
                return (Node *) newnode;
            }
            break;
        case T_PlaceHolderVar:
            {
                PlaceHolderVar *phv = (PlaceHolderVar *) node;
                PlaceHolderVar *newnode;

                FLATCOPY(newnode, phv, PlaceHolderVar);
                MUTATE(newnode->phexpr, phv->phexpr, Expr *);
                /* Assume we need not copy the relids bitmapset */
                return (Node *) newnode;
            }
            break;
        case T_AppendRelInfo:
            {
                AppendRelInfo *appinfo = (AppendRelInfo *) node;
                AppendRelInfo *newnode;

                FLATCOPY(newnode, appinfo, AppendRelInfo);
                MUTATE(newnode->translated_vars, appinfo->translated_vars, List *);
                return (Node *) newnode;
            }
            break;
        case T_PlaceHolderInfo:
            {
                PlaceHolderInfo *phinfo = (PlaceHolderInfo *) node;
                PlaceHolderInfo *newnode;

                FLATCOPY(newnode, phinfo, PlaceHolderInfo);
                MUTATE(newnode->ph_var, phinfo->ph_var, PlaceHolderVar *);
                /* Assume we need not copy the relids bitmapsets */
                return (Node *) newnode;
            }
            break;
        default:
            elog(ERROR, "unrecognized node type: %d",
                 (int) nodeTag(node));
            break;
    }
    /* can't get here, but keep compiler happy */
    return NULL;
}


/*
 * query_tree_mutator --- initiate modification of a Query's expressions
 *
 * This routine exists just to reduce the number of places that need to know
 * where all the expression subtrees of a Query are.  Note it can be used
 * for starting a walk at top level of a Query regardless of whether the
 * mutator intends to descend into subqueries.  It is also useful for
 * descending into subqueries within a mutator.
 *
 * Some callers want to suppress mutating of certain items in the Query,
 * typically because they need to process them specially, or don't actually
 * want to recurse into subqueries.  This is supported by the flags argument,
 * which is the bitwise OR of flag values to suppress mutating of
 * indicated items.  (More flag bits may be added as needed.)
 *
 * Normally the Query node itself is copied, but some callers want it to be
 * modified in-place; they must pass QTW_DONT_COPY_QUERY in flags.  All
 * modified substructure is safely copied in any case.
 */
Query *
query_tree_mutator(Query *query,
                   Node *(*mutator) (),
                   void *context,
                   int flags)
{
    Assert(query != NULL && IsA(query, Query));

    if (!(flags & QTW_DONT_COPY_QUERY))
    {
        Query      *newquery;

        FLATCOPY(newquery, query, Query);
        query = newquery;
    }

    MUTATE(query->targetList, query->targetList, List *);
    MUTATE(query->returningList, query->returningList, List *);
    MUTATE(query->jointree, query->jointree, FromExpr *);
    MUTATE(query->setOperations, query->setOperations, Node *);
    MUTATE(query->havingQual, query->havingQual, Node *);
    MUTATE(query->limitOffset, query->limitOffset, Node *);
    MUTATE(query->limitCount, query->limitCount, Node *);
    if (!(flags & QTW_IGNORE_CTE_SUBQUERIES))
        MUTATE(query->cteList, query->cteList, List *);
    else    /* else copy CTE list as-is */
        query->cteList = copyObject(query->cteList);
    query->rtable = range_table_mutator(query->rtable,
                                        mutator, context, flags);
    return query;
}

/*
 * range_table_mutator is just the part of query_tree_mutator that processes
 * a query's rangetable.  This is split out since it can be useful on
 * its own.
 */
List *
range_table_mutator(List *rtable,
                    Node *(*mutator) (),
                    void *context,
                    int flags)
{
    List       *newrt = NIL;
    ListCell   *rt;

    foreach(rt, rtable)
    {
        RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);
        RangeTblEntry *newrte;

        FLATCOPY(newrte, rte, RangeTblEntry);
        switch (rte->rtekind)
        {
            case RTE_RELATION:
            case RTE_CTE:
                /* we don't bother to copy eref, aliases, etc; OK? */
                break;
            case RTE_SUBQUERY:
                if (!(flags & QTW_IGNORE_RT_SUBQUERIES))
                {
                    CHECKFLATCOPY(newrte->subquery, rte->subquery, Query);
                    MUTATE(newrte->subquery, newrte->subquery, Query *);
                }
                else
                {
                    /* else, copy RT subqueries as-is */
                    newrte->subquery = copyObject(rte->subquery);
                }
                break;
            case RTE_JOIN:
                if (!(flags & QTW_IGNORE_JOINALIASES))
                    MUTATE(newrte->joinaliasvars, rte->joinaliasvars, List *);
                else
                {
                    /* else, copy join aliases as-is */
                    newrte->joinaliasvars = copyObject(rte->joinaliasvars);
                }
                break;
            case RTE_FUNCTION:
                MUTATE(newrte->funcexpr, rte->funcexpr, Node *);
                break;
            case RTE_VALUES:
                MUTATE(newrte->values_lists, rte->values_lists, List *);
                break;
        }
        newrt = lappend(newrt, newrte);
    }
    return newrt;
}

/*
 * query_or_expression_tree_walker --- hybrid form
 *
 * This routine will invoke query_tree_walker if called on a Query node,
 * else will invoke the walker directly.  This is a useful way of starting
 * the recursion when the walker's normal change of state is not appropriate
 * for the outermost Query node.
 */
bool
query_or_expression_tree_walker(Node *node,
                                bool (*walker) (),
                                void *context,
                                int flags)
{
    if (node && IsA(node, Query))
        return query_tree_walker((Query *) node,
                                 walker,
                                 context,
                                 flags);
    else
        return walker(node, context);
}

/*
 * query_or_expression_tree_mutator --- hybrid form
 *
 * This routine will invoke query_tree_mutator if called on a Query node,
 * else will invoke the mutator directly.  This is a useful way of starting
 * the recursion when the mutator's normal change of state is not appropriate
 * for the outermost Query node.
 */
Node *
query_or_expression_tree_mutator(Node *node,
                                 Node *(*mutator) (),
                                 void *context,
                                 int flags)
{
    if (node && IsA(node, Query))
        return (Node *) query_tree_mutator((Query *) node,
                                           mutator,
                                           context,
                                           flags);
    else
        return mutator(node, context);
}


/*
 * raw_expression_tree_walker --- walk raw parse trees
 *
 * This has exactly the same API as expression_tree_walker, but instead of
 * walking post-analysis parse trees, it knows how to walk the node types
 * found in raw grammar output.  (There is not currently any need for a
 * combined walker, so we keep them separate in the name of efficiency.)
 * Unlike expression_tree_walker, there is no special rule about query
 * boundaries: we descend to everything that's possibly interesting.
 *
 * Currently, the node type coverage extends to SelectStmt and everything
 * that could appear under it, but not other statement types.
 */
bool
raw_expression_tree_walker(Node *node,
                           bool (*walker) (),
                           void *context)
{
    ListCell   *temp;

    /*
     * The walker has already visited the current node, and so we need only
     * recurse into any sub-nodes it has.
     */
    if (node == NULL)
        return false;

    /* Guard against stack overflow due to overly complex expressions */
    check_stack_depth();

    switch (nodeTag(node))
    {
        case T_SetToDefault:
        case T_CurrentOfExpr:
        case T_Integer:
        case T_Float:
        case T_String:
        case T_BitString:
        case T_Null:
        case T_ParamRef:
        case T_A_Const:
        case T_A_Star:
            /* primitive node types with no subnodes */
            break;
        case T_Alias:
            /* we assume the colnames list isn't interesting */
            break;
        case T_RangeVar:
            return walker(((RangeVar *) node)->alias, context);
        case T_SubLink:
            {
                SubLink    *sublink = (SubLink *) node;

                if (walker(sublink->testexpr, context))
                    return true;
                /* we assume the operName is not interesting */
                if (walker(sublink->subselect, context))
                    return true;
            }
            break;
        case T_CaseExpr:
            {
                CaseExpr   *caseexpr = (CaseExpr *) node;

                if (walker(caseexpr->arg, context))
                    return true;
                /* we assume walker doesn't care about CaseWhens, either */
                foreach(temp, caseexpr->args)
                {
                    CaseWhen   *when = (CaseWhen *) lfirst(temp);

                    Assert(IsA(when, CaseWhen));
                    if (walker(when->expr, context))
                        return true;
                    if (walker(when->result, context))
                        return true;
                }
                if (walker(caseexpr->defresult, context))
                    return true;
            }
            break;
        case T_RowExpr:
            /* Assume colnames isn't interesting */
            return walker(((RowExpr *) node)->args, context);
        case T_CoalesceExpr:
            return walker(((CoalesceExpr *) node)->args, context);
        case T_MinMaxExpr:
            return walker(((MinMaxExpr *) node)->args, context);
        case T_XmlExpr:
            {
                XmlExpr    *xexpr = (XmlExpr *) node;

                if (walker(xexpr->named_args, context))
                    return true;
                /* we assume walker doesn't care about arg_names */
                if (walker(xexpr->args, context))
                    return true;
            }
            break;
        case T_NullTest:
            return walker(((NullTest *) node)->arg, context);
        case T_BooleanTest:
            return walker(((BooleanTest *) node)->arg, context);
        case T_JoinExpr:
            {
                JoinExpr   *join = (JoinExpr *) node;

                if (walker(join->larg, context))
                    return true;
                if (walker(join->rarg, context))
                    return true;
                if (walker(join->quals, context))
                    return true;
                if (walker(join->alias, context))
                    return true;
                /* using list is deemed uninteresting */
            }
            break;
        case T_IntoClause:
            {
                IntoClause *into = (IntoClause *) node;

                if (walker(into->rel, context))
                    return true;
                /* colNames, options are deemed uninteresting */
                /* viewQuery should be null in raw parsetree, but check it */
                if (walker(into->viewQuery, context))
                    return true;
            }
            break;
        case T_List:
            foreach(temp, (List *) node)
            {
                if (walker((Node *) lfirst(temp), context))
                    return true;
            }
            break;
        case T_InsertStmt:
            {
                InsertStmt *stmt = (InsertStmt *) node;

                if (walker(stmt->relation, context))
                    return true;
                if (walker(stmt->cols, context))
                    return true;
                if (walker(stmt->selectStmt, context))
                    return true;
                if (walker(stmt->returningList, context))
                    return true;
                if (walker(stmt->withClause, context))
                    return true;
            }
            break;
        case T_DeleteStmt:
            {
                DeleteStmt *stmt = (DeleteStmt *) node;

                if (walker(stmt->relation, context))
                    return true;
                if (walker(stmt->usingClause, context))
                    return true;
                if (walker(stmt->whereClause, context))
                    return true;
                if (walker(stmt->returningList, context))
                    return true;
                if (walker(stmt->withClause, context))
                    return true;
            }
            break;
        case T_UpdateStmt:
            {
                UpdateStmt *stmt = (UpdateStmt *) node;

                if (walker(stmt->relation, context))
                    return true;
                if (walker(stmt->targetList, context))
                    return true;
                if (walker(stmt->whereClause, context))
                    return true;
                if (walker(stmt->fromClause, context))
                    return true;
                if (walker(stmt->returningList, context))
                    return true;
                if (walker(stmt->withClause, context))
                    return true;
            }
            break;
        case T_SelectStmt:
            {
                SelectStmt *stmt = (SelectStmt *) node;

                if (walker(stmt->distinctClause, context))
                    return true;
                if (walker(stmt->intoClause, context))
                    return true;
                if (walker(stmt->targetList, context))
                    return true;
                if (walker(stmt->fromClause, context))
                    return true;
                if (walker(stmt->whereClause, context))
                    return true;
                if (walker(stmt->groupClause, context))
                    return true;
                if (walker(stmt->havingClause, context))
                    return true;
                if (walker(stmt->windowClause, context))
                    return true;
                if (walker(stmt->valuesLists, context))
                    return true;
                if (walker(stmt->sortClause, context))
                    return true;
                if (walker(stmt->limitOffset, context))
                    return true;
                if (walker(stmt->limitCount, context))
                    return true;
                if (walker(stmt->lockingClause, context))
                    return true;
                if (walker(stmt->withClause, context))
                    return true;
                if (walker(stmt->larg, context))
                    return true;
                if (walker(stmt->rarg, context))
                    return true;
            }
            break;
        case T_A_Expr:
            {
                A_Expr     *expr = (A_Expr *) node;

                if (walker(expr->lexpr, context))
                    return true;
                if (walker(expr->rexpr, context))
                    return true;
                /* operator name is deemed uninteresting */
            }
            break;
        case T_ColumnRef:
            /* we assume the fields contain nothing interesting */
            break;
        case T_FuncCall:
            {
                FuncCall   *fcall = (FuncCall *) node;

                if (walker(fcall->args, context))
                    return true;
                if (walker(fcall->agg_order, context))
                    return true;
                if (walker(fcall->over, context))
                    return true;
                /* function name is deemed uninteresting */
            }
            break;
        case T_NamedArgExpr:
            return walker(((NamedArgExpr *) node)->arg, context);
        case T_A_Indices:
            {
                A_Indices  *indices = (A_Indices *) node;

                if (walker(indices->lidx, context))
                    return true;
                if (walker(indices->uidx, context))
                    return true;
            }
            break;
        case T_A_Indirection:
            {
                A_Indirection *indir = (A_Indirection *) node;

                if (walker(indir->arg, context))
                    return true;
                if (walker(indir->indirection, context))
                    return true;
            }
            break;
        case T_A_ArrayExpr:
            return walker(((A_ArrayExpr *) node)->elements, context);
        case T_ResTarget:
            {
                ResTarget  *rt = (ResTarget *) node;

                if (walker(rt->indirection, context))
                    return true;
                if (walker(rt->val, context))
                    return true;
            }
            break;
        case T_TypeCast:
            {
                TypeCast   *tc = (TypeCast *) node;

                if (walker(tc->arg, context))
                    return true;
                if (walker(tc->typeName, context))
                    return true;
            }
            break;
        case T_CollateClause:
            return walker(((CollateClause *) node)->arg, context);
        case T_SortBy:
            return walker(((SortBy *) node)->node, context);
        case T_WindowDef:
            {
                WindowDef  *wd = (WindowDef *) node;

                if (walker(wd->partitionClause, context))
                    return true;
                if (walker(wd->orderClause, context))
                    return true;
                if (walker(wd->startOffset, context))
                    return true;
                if (walker(wd->endOffset, context))
                    return true;
            }
            break;
        case T_RangeSubselect:
            {
                RangeSubselect *rs = (RangeSubselect *) node;

                if (walker(rs->subquery, context))
                    return true;
                if (walker(rs->alias, context))
                    return true;
            }
            break;
        case T_RangeFunction:
            {
                RangeFunction *rf = (RangeFunction *) node;

                if (walker(rf->funccallnode, context))
                    return true;
                if (walker(rf->alias, context))
                    return true;
            }
            break;
        case T_TypeName:
            {
                TypeName   *tn = (TypeName *) node;

                if (walker(tn->typmods, context))
                    return true;
                if (walker(tn->arrayBounds, context))
                    return true;
                /* type name itself is deemed uninteresting */
            }
            break;
        case T_ColumnDef:
            {
                ColumnDef  *coldef = (ColumnDef *) node;

                if (walker(coldef->typeName, context))
                    return true;
                if (walker(coldef->raw_default, context))
                    return true;
                if (walker(coldef->collClause, context))
                    return true;
                /* for now, constraints are ignored */
            }
            break;
        case T_LockingClause:
            return walker(((LockingClause *) node)->lockedRels, context);
        case T_XmlSerialize:
            {
                XmlSerialize *xs = (XmlSerialize *) node;

                if (walker(xs->expr, context))
                    return true;
                if (walker(xs->typeName, context))
                    return true;
            }
            break;
        case T_WithClause:
            return walker(((WithClause *) node)->ctes, context);
        case T_CommonTableExpr:
            return walker(((CommonTableExpr *) node)->ctequery, context);
        default:
            elog(ERROR, "unrecognized node type: %d",
                 (int) nodeTag(node));
            break;
    }
    return false;
}