rewriteManip.c

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/*-------------------------------------------------------------------------
 *
 * rewriteManip.c
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/rewrite/rewriteManip.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "catalog/pg_type.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/pathnodes.h"
#include "nodes/plannodes.h"
#include "parser/parse_coerce.h"
#include "parser/parse_relation.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"
#include "utils/lsyscache.h"
 
 
typedef struct
{
    int         sublevels_up;
} contain_aggs_of_level_context;
 
typedef struct
{
    int         agg_location;
    int         sublevels_up;
} locate_agg_of_level_context;
 
typedef struct
{
    int         win_location;
} locate_windowfunc_context;
 
typedef struct
{
    const Bitmapset *target_relids;
    const Bitmapset *added_relids;
    int         sublevels_up;
} add_nulling_relids_context;
 
typedef struct
{
    const Bitmapset *removable_relids;
    const Bitmapset *except_relids;
    int         sublevels_up;
} remove_nulling_relids_context;
 
static bool contain_aggs_of_level_walker(Node *node,
                                         contain_aggs_of_level_context *context);
static bool locate_agg_of_level_walker(Node *node,
                                       locate_agg_of_level_context *context);
static bool contain_windowfuncs_walker(Node *node, void *context);
static bool locate_windowfunc_walker(Node *node,
                                     locate_windowfunc_context *context);
static bool checkExprHasSubLink_walker(Node *node, void *context);
static Relids offset_relid_set(Relids relids, int offset);
static Node *add_nulling_relids_mutator(Node *node,
                                        add_nulling_relids_context *context);
static Node *remove_nulling_relids_mutator(Node *node,
                                           remove_nulling_relids_context *context);
 
 
/*
 * contain_aggs_of_level -
 *  Check if an expression contains an aggregate function call of a
 *  specified query level.
 *
 * The objective of this routine is to detect whether there are aggregates
 * belonging to the given query level.  Aggregates belonging to subqueries
 * or outer queries do NOT cause a true result.  We must recurse into
 * subqueries to detect outer-reference aggregates that logically belong to
 * the specified query level.
 */
bool
contain_aggs_of_level(Node *node, int levelsup)
{
    contain_aggs_of_level_context context;
 
    context.sublevels_up = levelsup;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    return query_or_expression_tree_walker(node,
                                           contain_aggs_of_level_walker,
                                           &context,
                                           0);
}
 
static bool
contain_aggs_of_level_walker(Node *node,
                             contain_aggs_of_level_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Aggref))
    {
        if (((Aggref *) node)->agglevelsup == context->sublevels_up)
            return true;        /* abort the tree traversal and return true */
        /* else fall through to examine argument */
    }
    if (IsA(node, GroupingFunc))
    {
        if (((GroupingFunc *) node)->agglevelsup == context->sublevels_up)
            return true;
        /* else fall through to examine argument */
    }
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node,
                                   contain_aggs_of_level_walker,
                                   context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, contain_aggs_of_level_walker,
                                  context);
}
 
/*
 * locate_agg_of_level -
 *    Find the parse location of any aggregate of the specified query level.
 *
 * Returns -1 if no such agg is in the querytree, or if they all have
 * unknown parse location.  (The former case is probably caller error,
 * but we don't bother to distinguish it from the latter case.)
 *
 * Note: it might seem appropriate to merge this functionality into
 * contain_aggs_of_level, but that would complicate that function's API.
 * Currently, the only uses of this function are for error reporting,
 * and so shaving cycles probably isn't very important.
 */
int
locate_agg_of_level(Node *node, int levelsup)
{
    locate_agg_of_level_context context;
 
    context.agg_location = -1;  /* in case we find nothing */
    context.sublevels_up = levelsup;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    (void) query_or_expression_tree_walker(node,
                                           locate_agg_of_level_walker,
                                           &context,
                                           0);
 
    return context.agg_location;
}
 
static bool
locate_agg_of_level_walker(Node *node,
                           locate_agg_of_level_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Aggref))
    {
        if (((Aggref *) node)->agglevelsup == context->sublevels_up &&
            ((Aggref *) node)->location >= 0)
        {
            context->agg_location = ((Aggref *) node)->location;
            return true;        /* abort the tree traversal and return true */
        }
        /* else fall through to examine argument */
    }
    if (IsA(node, GroupingFunc))
    {
        if (((GroupingFunc *) node)->agglevelsup == context->sublevels_up &&
            ((GroupingFunc *) node)->location >= 0)
        {
            context->agg_location = ((GroupingFunc *) node)->location;
            return true;        /* abort the tree traversal and return true */
        }
    }
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node,
                                   locate_agg_of_level_walker,
                                   context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, locate_agg_of_level_walker, context);
}
 
/*
 * contain_windowfuncs -
 *  Check if an expression contains a window function call of the
 *  current query level.
 */
bool
contain_windowfuncs(Node *node)
{
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    return query_or_expression_tree_walker(node,
                                           contain_windowfuncs_walker,
                                           NULL,
                                           0);
}
 
static bool
contain_windowfuncs_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, WindowFunc))
        return true;            /* abort the tree traversal and return true */
    /* Mustn't recurse into subselects */
    return expression_tree_walker(node, contain_windowfuncs_walker, context);
}
 
/*
 * locate_windowfunc -
 *    Find the parse location of any windowfunc of the current query level.
 *
 * Returns -1 if no such windowfunc is in the querytree, or if they all have
 * unknown parse location.  (The former case is probably caller error,
 * but we don't bother to distinguish it from the latter case.)
 *
 * Note: it might seem appropriate to merge this functionality into
 * contain_windowfuncs, but that would complicate that function's API.
 * Currently, the only uses of this function are for error reporting,
 * and so shaving cycles probably isn't very important.
 */
int
locate_windowfunc(Node *node)
{
    locate_windowfunc_context context;
 
    context.win_location = -1;  /* in case we find nothing */
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    (void) query_or_expression_tree_walker(node,
                                           locate_windowfunc_walker,
                                           &context,
                                           0);
 
    return context.win_location;
}
 
static bool
locate_windowfunc_walker(Node *node, locate_windowfunc_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, WindowFunc))
    {
        if (((WindowFunc *) node)->location >= 0)
        {
            context->win_location = ((WindowFunc *) node)->location;
            return true;        /* abort the tree traversal and return true */
        }
        /* else fall through to examine argument */
    }
    /* Mustn't recurse into subselects */
    return expression_tree_walker(node, locate_windowfunc_walker, context);
}
 
/*
 * checkExprHasSubLink -
 *  Check if an expression contains a SubLink.
 */
bool
checkExprHasSubLink(Node *node)
{
    /*
     * If a Query is passed, examine it --- but we should not recurse into
     * sub-Queries that are in its rangetable or CTE list.
     */
    return query_or_expression_tree_walker(node,
                                           checkExprHasSubLink_walker,
                                           NULL,
                                           QTW_IGNORE_RC_SUBQUERIES);
}
 
static bool
checkExprHasSubLink_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, SubLink))
        return true;            /* abort the tree traversal and return true */
    return expression_tree_walker(node, checkExprHasSubLink_walker, context);
}
 
/*
 * Check for MULTIEXPR Param within expression tree
 *
 * We intentionally don't descend into SubLinks: only Params at the current
 * query level are of interest.
 */
static bool
contains_multiexpr_param(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Param))
    {
        if (((Param *) node)->paramkind == PARAM_MULTIEXPR)
            return true;        /* abort the tree traversal and return true */
        return false;
    }
    return expression_tree_walker(node, contains_multiexpr_param, context);
}
 
/*
 * CombineRangeTables
 *      Adds the RTEs of 'src_rtable' into 'dst_rtable'
 *
 * This also adds the RTEPermissionInfos of 'src_perminfos' (belonging to the
 * RTEs in 'src_rtable') into *dst_perminfos and also updates perminfoindex of
 * the RTEs in 'src_rtable' to now point to the perminfos' indexes in
 * *dst_perminfos.
 *
 * Note that this changes both 'dst_rtable' and 'dst_perminfos' destructively,
 * so the caller should have better passed safe-to-modify copies.
 */
void
CombineRangeTables(List **dst_rtable, List **dst_perminfos,
                   List *src_rtable, List *src_perminfos)
{
    ListCell   *l;
    int         offset = list_length(*dst_perminfos);
 
    if (offset > 0)
    {
        foreach(l, src_rtable)
        {
            RangeTblEntry *rte = lfirst_node(RangeTblEntry, l);
 
            if (rte->perminfoindex > 0)
                rte->perminfoindex += offset;
        }
    }
 
    *dst_perminfos = list_concat(*dst_perminfos, src_perminfos);
    *dst_rtable = list_concat(*dst_rtable, src_rtable);
}
 
/*
 * OffsetVarNodes - adjust Vars when appending one query's RT to another
 *
 * Find all Var nodes in the given tree with varlevelsup == sublevels_up,
 * and increment their varno fields (rangetable indexes) by 'offset'.
 * The varnosyn fields are adjusted similarly.  Also, adjust other nodes
 * that contain rangetable indexes, such as RangeTblRef and JoinExpr.
 *
 * NOTE: although this has the form of a walker, we cheat and modify the
 * nodes in-place.  The given expression tree should have been copied
 * earlier to ensure that no unwanted side-effects occur!
 */
 
typedef struct
{
    int         offset;
    int         sublevels_up;
} OffsetVarNodes_context;
 
static bool
OffsetVarNodes_walker(Node *node, OffsetVarNodes_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup == context->sublevels_up)
        {
            var->varno += context->offset;
            var->varnullingrels = offset_relid_set(var->varnullingrels,
                                                   context->offset);
            if (var->varnosyn > 0)
                var->varnosyn += context->offset;
        }
        return false;
    }
    if (IsA(node, CurrentOfExpr))
    {
        CurrentOfExpr *cexpr = (CurrentOfExpr *) node;
 
        if (context->sublevels_up == 0)
            cexpr->cvarno += context->offset;
        return false;
    }
    if (IsA(node, RangeTblRef))
    {
        RangeTblRef *rtr = (RangeTblRef *) node;
 
        if (context->sublevels_up == 0)
            rtr->rtindex += context->offset;
        /* the subquery itself is visited separately */
        return false;
    }
    if (IsA(node, JoinExpr))
    {
        JoinExpr   *j = (JoinExpr *) node;
 
        if (j->rtindex && context->sublevels_up == 0)
            j->rtindex += context->offset;
        /* fall through to examine children */
    }
    if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;
 
        if (phv->phlevelsup == context->sublevels_up)
        {
            phv->phrels = offset_relid_set(phv->phrels,
                                           context->offset);
            phv->phnullingrels = offset_relid_set(phv->phnullingrels,
                                                  context->offset);
        }
        /* fall through to examine children */
    }
    if (IsA(node, AppendRelInfo))
    {
        AppendRelInfo *appinfo = (AppendRelInfo *) node;
 
        if (context->sublevels_up == 0)
        {
            appinfo->parent_relid += context->offset;
            appinfo->child_relid += context->offset;
        }
        /* fall through to examine children */
    }
    /* Shouldn't need to handle other planner auxiliary nodes here */
    Assert(!IsA(node, PlanRowMark));
    Assert(!IsA(node, SpecialJoinInfo));
    Assert(!IsA(node, PlaceHolderInfo));
    Assert(!IsA(node, MinMaxAggInfo));
 
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node, OffsetVarNodes_walker,
                                   context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, OffsetVarNodes_walker, context);
}
 
void
OffsetVarNodes(Node *node, int offset, int sublevels_up)
{
    OffsetVarNodes_context context;
 
    context.offset = offset;
    context.sublevels_up = sublevels_up;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, go straight to query_tree_walker to make sure that
     * sublevels_up doesn't get incremented prematurely.
     */
    if (node && IsA(node, Query))
    {
        Query      *qry = (Query *) node;
 
        /*
         * If we are starting at a Query, and sublevels_up is zero, then we
         * must also fix rangetable indexes in the Query itself --- namely
         * resultRelation, mergeTargetRelation, exclRelIndex and rowMarks
         * entries.  sublevels_up cannot be zero when recursing into a
         * subquery, so there's no need to have the same logic inside
         * OffsetVarNodes_walker.
         */
        if (sublevels_up == 0)
        {
            ListCell   *l;
 
            if (qry->resultRelation)
                qry->resultRelation += offset;
 
            if (qry->mergeTargetRelation)
                qry->mergeTargetRelation += offset;
 
            if (qry->onConflict && qry->onConflict->exclRelIndex)
                qry->onConflict->exclRelIndex += offset;
 
            foreach(l, qry->rowMarks)
            {
                RowMarkClause *rc = (RowMarkClause *) lfirst(l);
 
                rc->rti += offset;
            }
        }
        query_tree_walker(qry, OffsetVarNodes_walker, &context, 0);
    }
    else
        OffsetVarNodes_walker(node, &context);
}
 
static Relids
offset_relid_set(Relids relids, int offset)
{
    Relids      result = NULL;
    int         rtindex;
 
    rtindex = -1;
    while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
        result = bms_add_member(result, rtindex + offset);
    return result;
}
 
/*
 * ChangeVarNodes - adjust Var nodes for a specific change of RT index
 *
 * Find all Var nodes in the given tree belonging to a specific relation
 * (identified by sublevels_up and rt_index), and change their varno fields
 * to 'new_index'.  The varnosyn fields are changed too.  Also, adjust other
 * nodes that contain rangetable indexes, such as RangeTblRef and JoinExpr.
 * Specifying 'change_RangeTblRef' to false allows skipping RangeTblRef.
 * See ChangeVarNodesExtended for details.
 *
 * NOTE: although this has the form of a walker, we cheat and modify the
 * nodes in-place.  The given expression tree should have been copied
 * earlier to ensure that no unwanted side-effects occur!
 */
 
static bool
ChangeVarNodes_walker(Node *node, ChangeVarNodes_context *context)
{
    if (node == NULL)
        return false;
 
    if (context->callback && context->callback(node, context))
        return false;
 
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup == context->sublevels_up)
        {
            if (var->varno == context->rt_index)
                var->varno = context->new_index;
            var->varnullingrels = adjust_relid_set(var->varnullingrels,
                                                   context->rt_index,
                                                   context->new_index);
            if (var->varnosyn == context->rt_index)
                var->varnosyn = context->new_index;
        }
        return false;
    }
    if (IsA(node, CurrentOfExpr))
    {
        CurrentOfExpr *cexpr = (CurrentOfExpr *) node;
 
        if (context->sublevels_up == 0 &&
            cexpr->cvarno == context->rt_index)
            cexpr->cvarno = context->new_index;
        return false;
    }
    if (IsA(node, RangeTblRef))
    {
        RangeTblRef *rtr = (RangeTblRef *) node;
 
        if (context->sublevels_up == 0 &&
            rtr->rtindex == context->rt_index)
            rtr->rtindex = context->new_index;
        /* the subquery itself is visited separately */
        return false;
    }
    if (IsA(node, JoinExpr))
    {
        JoinExpr   *j = (JoinExpr *) node;
 
        if (context->sublevels_up == 0 &&
            j->rtindex == context->rt_index)
            j->rtindex = context->new_index;
        /* fall through to examine children */
    }
    if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;
 
        if (phv->phlevelsup == context->sublevels_up)
        {
            phv->phrels = adjust_relid_set(phv->phrels,
                                           context->rt_index,
                                           context->new_index);
            phv->phnullingrels = adjust_relid_set(phv->phnullingrels,
                                                  context->rt_index,
                                                  context->new_index);
        }
        /* fall through to examine children */
    }
    if (IsA(node, PlanRowMark))
    {
        PlanRowMark *rowmark = (PlanRowMark *) node;
 
        if (context->sublevels_up == 0)
        {
            if (rowmark->rti == context->rt_index)
                rowmark->rti = context->new_index;
            if (rowmark->prti == context->rt_index)
                rowmark->prti = context->new_index;
        }
        return false;
    }
    if (IsA(node, AppendRelInfo))
    {
        AppendRelInfo *appinfo = (AppendRelInfo *) node;
 
        if (context->sublevels_up == 0)
        {
            if (appinfo->parent_relid == context->rt_index)
                appinfo->parent_relid = context->new_index;
            if (appinfo->child_relid == context->rt_index)
                appinfo->child_relid = context->new_index;
        }
        /* fall through to examine children */
    }
    /* Shouldn't need to handle other planner auxiliary nodes here */
    Assert(!IsA(node, SpecialJoinInfo));
    Assert(!IsA(node, PlaceHolderInfo));
    Assert(!IsA(node, MinMaxAggInfo));
 
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node, ChangeVarNodes_walker,
                                   context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, ChangeVarNodes_walker, context);
}
 
/*
 * ChangeVarNodesExtended - similar to ChangeVarNodes, but with an  additional
 *                          'callback' param
 *
 * ChangeVarNodes changes a given node and all of its underlying nodes.
 * This version of function additionally takes a callback, which has a
 * chance to process a node before ChangeVarNodes_walker.  A callback
 * returns a boolean value indicating if given node should be skipped from
 * further processing by ChangeVarNodes_walker.  The callback is called
 * only for expressions and other children nodes of a Query processed by
 * a walker.  Initial processing of the root Query doesn't involve the
 * callback.
 */
void
ChangeVarNodesExtended(Node *node, int rt_index, int new_index,
                       int sublevels_up, ChangeVarNodes_callback callback)
{
    ChangeVarNodes_context context;
 
    context.rt_index = rt_index;
    context.new_index = new_index;
    context.sublevels_up = sublevels_up;
    context.callback = callback;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, go straight to query_tree_walker to make sure that
     * sublevels_up doesn't get incremented prematurely.
     */
    if (node && IsA(node, Query))
    {
        Query      *qry = (Query *) node;
 
        /*
         * If we are starting at a Query, and sublevels_up is zero, then we
         * must also fix rangetable indexes in the Query itself --- namely
         * resultRelation, mergeTargetRelation, exclRelIndex  and rowMarks
         * entries.  sublevels_up cannot be zero when recursing into a
         * subquery, so there's no need to have the same logic inside
         * ChangeVarNodes_walker.
         */
        if (sublevels_up == 0)
        {
            ListCell   *l;
 
            if (qry->resultRelation == rt_index)
                qry->resultRelation = new_index;
 
            if (qry->mergeTargetRelation == rt_index)
                qry->mergeTargetRelation = new_index;
 
            /* this is unlikely to ever be used, but ... */
            if (qry->onConflict && qry->onConflict->exclRelIndex == rt_index)
                qry->onConflict->exclRelIndex = new_index;
 
            foreach(l, qry->rowMarks)
            {
                RowMarkClause *rc = (RowMarkClause *) lfirst(l);
 
                if (rc->rti == rt_index)
                    rc->rti = new_index;
            }
        }
        query_tree_walker(qry, ChangeVarNodes_walker, &context, 0);
    }
    else
        ChangeVarNodes_walker(node, &context);
}
 
void
ChangeVarNodes(Node *node, int rt_index, int new_index, int sublevels_up)
{
    ChangeVarNodesExtended(node, rt_index, new_index, sublevels_up, NULL);
}
 
/*
 * ChangeVarNodesWalkExpression - process expression within the custom
 *                                callback provided to the
 *                                ChangeVarNodesExtended.
 */
bool
ChangeVarNodesWalkExpression(Node *node, ChangeVarNodes_context *context)
{
    return expression_tree_walker(node,
                                  ChangeVarNodes_walker,
                                  (void *) context);
}
 
/*
 * adjust_relid_set - substitute newrelid for oldrelid in a Relid set
 *
 * Attempt to remove oldrelid from a Relid set (as long as it's not a special
 * varno).  If oldrelid was found and removed, insert newrelid into a Relid
 * set (as long as it's not a special varno).  Therefore, when oldrelid is
 * a special varno, this function does nothing.  When newrelid is a special
 * varno, this function behaves as delete.
 */
Relids
adjust_relid_set(Relids relids, int oldrelid, int newrelid)
{
    if (!IS_SPECIAL_VARNO(oldrelid) && bms_is_member(oldrelid, relids))
    {
        /* Ensure we have a modifiable copy */
        relids = bms_copy(relids);
        /* Remove old, add new */
        relids = bms_del_member(relids, oldrelid);
        if (!IS_SPECIAL_VARNO(newrelid))
            relids = bms_add_member(relids, newrelid);
    }
    return relids;
}
 
/*
 * IncrementVarSublevelsUp - adjust Var nodes when pushing them down in tree
 *
 * Find all Var nodes in the given tree having varlevelsup >= min_sublevels_up,
 * and add delta_sublevels_up to their varlevelsup value.  This is needed when
 * an expression that's correct for some nesting level is inserted into a
 * subquery.  Ordinarily the initial call has min_sublevels_up == 0 so that
 * all Vars are affected.  The point of min_sublevels_up is that we can
 * increment it when we recurse into a sublink, so that local variables in
 * that sublink are not affected, only outer references to vars that belong
 * to the expression's original query level or parents thereof.
 *
 * Likewise for other nodes containing levelsup fields, such as Aggref.
 *
 * NOTE: although this has the form of a walker, we cheat and modify the
 * Var nodes in-place.  The given expression tree should have been copied
 * earlier to ensure that no unwanted side-effects occur!
 */
 
typedef struct
{
    int         delta_sublevels_up;
    int         min_sublevels_up;
} IncrementVarSublevelsUp_context;
 
static bool
IncrementVarSublevelsUp_walker(Node *node,
                               IncrementVarSublevelsUp_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup >= context->min_sublevels_up)
            var->varlevelsup += context->delta_sublevels_up;
        return false;           /* done here */
    }
    if (IsA(node, CurrentOfExpr))
    {
        /* this should not happen */
        if (context->min_sublevels_up == 0)
            elog(ERROR, "cannot push down CurrentOfExpr");
        return false;
    }
    if (IsA(node, Aggref))
    {
        Aggref     *agg = (Aggref *) node;
 
        if (agg->agglevelsup >= context->min_sublevels_up)
            agg->agglevelsup += context->delta_sublevels_up;
        /* fall through to recurse into argument */
    }
    if (IsA(node, GroupingFunc))
    {
        GroupingFunc *grp = (GroupingFunc *) node;
 
        if (grp->agglevelsup >= context->min_sublevels_up)
            grp->agglevelsup += context->delta_sublevels_up;
        /* fall through to recurse into argument */
    }
    if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;
 
        if (phv->phlevelsup >= context->min_sublevels_up)
            phv->phlevelsup += context->delta_sublevels_up;
        /* fall through to recurse into argument */
    }
    if (IsA(node, ReturningExpr))
    {
        ReturningExpr *rexpr = (ReturningExpr *) node;
 
        if (rexpr->retlevelsup >= context->min_sublevels_up)
            rexpr->retlevelsup += context->delta_sublevels_up;
        /* fall through to recurse into argument */
    }
    if (IsA(node, RangeTblEntry))
    {
        RangeTblEntry *rte = (RangeTblEntry *) node;
 
        if (rte->rtekind == RTE_CTE)
        {
            if (rte->ctelevelsup >= context->min_sublevels_up)
                rte->ctelevelsup += context->delta_sublevels_up;
        }
        return false;           /* allow range_table_walker to continue */
    }
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        context->min_sublevels_up++;
        result = query_tree_walker((Query *) node,
                                   IncrementVarSublevelsUp_walker,
                                   context,
                                   QTW_EXAMINE_RTES_BEFORE);
        context->min_sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, IncrementVarSublevelsUp_walker, context);
}
 
void
IncrementVarSublevelsUp(Node *node, int delta_sublevels_up,
                        int min_sublevels_up)
{
    IncrementVarSublevelsUp_context context;
 
    context.delta_sublevels_up = delta_sublevels_up;
    context.min_sublevels_up = min_sublevels_up;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    query_or_expression_tree_walker(node,
                                    IncrementVarSublevelsUp_walker,
                                    &context,
                                    QTW_EXAMINE_RTES_BEFORE);
}
 
/*
 * IncrementVarSublevelsUp_rtable -
 *  Same as IncrementVarSublevelsUp, but to be invoked on a range table.
 */
void
IncrementVarSublevelsUp_rtable(List *rtable, int delta_sublevels_up,
                               int min_sublevels_up)
{
    IncrementVarSublevelsUp_context context;
 
    context.delta_sublevels_up = delta_sublevels_up;
    context.min_sublevels_up = min_sublevels_up;
 
    range_table_walker(rtable,
                       IncrementVarSublevelsUp_walker,
                       &context,
                       QTW_EXAMINE_RTES_BEFORE);
}
 
/*
 * SetVarReturningType - adjust Var nodes for a specified varreturningtype.
 *
 * Find all Var nodes referring to the specified result relation in the given
 * expression and set their varreturningtype to the specified value.
 *
 * NOTE: although this has the form of a walker, we cheat and modify the
 * Var nodes in-place.  The given expression tree should have been copied
 * earlier to ensure that no unwanted side-effects occur!
 */
 
typedef struct
{
    int         result_relation;
    int         sublevels_up;
    VarReturningType returning_type;
} SetVarReturningType_context;
 
static bool
SetVarReturningType_walker(Node *node, SetVarReturningType_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varno == context->result_relation &&
            var->varlevelsup == context->sublevels_up)
            var->varreturningtype = context->returning_type;
 
        return false;
    }
 
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node, SetVarReturningType_walker,
                                   context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, SetVarReturningType_walker, context);
}
 
static void
SetVarReturningType(Node *node, int result_relation, int sublevels_up,
                    VarReturningType returning_type)
{
    SetVarReturningType_context context;
 
    context.result_relation = result_relation;
    context.sublevels_up = sublevels_up;
    context.returning_type = returning_type;
 
    /* Expect to start with an expression */
    SetVarReturningType_walker(node, &context);
}
 
/*
 * rangeTableEntry_used - detect whether an RTE is referenced somewhere
 *  in var nodes or join or setOp trees of a query or expression.
 */
 
typedef struct
{
    int         rt_index;
    int         sublevels_up;
} rangeTableEntry_used_context;
 
static bool
rangeTableEntry_used_walker(Node *node,
                            rangeTableEntry_used_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup == context->sublevels_up &&
            (var->varno == context->rt_index ||
             bms_is_member(context->rt_index, var->varnullingrels)))
            return true;
        return false;
    }
    if (IsA(node, CurrentOfExpr))
    {
        CurrentOfExpr *cexpr = (CurrentOfExpr *) node;
 
        if (context->sublevels_up == 0 &&
            cexpr->cvarno == context->rt_index)
            return true;
        return false;
    }
    if (IsA(node, RangeTblRef))
    {
        RangeTblRef *rtr = (RangeTblRef *) node;
 
        if (rtr->rtindex == context->rt_index &&
            context->sublevels_up == 0)
            return true;
        /* the subquery itself is visited separately */
        return false;
    }
    if (IsA(node, JoinExpr))
    {
        JoinExpr   *j = (JoinExpr *) node;
 
        if (j->rtindex == context->rt_index &&
            context->sublevels_up == 0)
            return true;
        /* fall through to examine children */
    }
    /* Shouldn't need to handle planner auxiliary nodes here */
    Assert(!IsA(node, PlaceHolderVar));
    Assert(!IsA(node, PlanRowMark));
    Assert(!IsA(node, SpecialJoinInfo));
    Assert(!IsA(node, AppendRelInfo));
    Assert(!IsA(node, PlaceHolderInfo));
    Assert(!IsA(node, MinMaxAggInfo));
 
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node, rangeTableEntry_used_walker,
                                   context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, rangeTableEntry_used_walker, context);
}
 
bool
rangeTableEntry_used(Node *node, int rt_index, int sublevels_up)
{
    rangeTableEntry_used_context context;
 
    context.rt_index = rt_index;
    context.sublevels_up = sublevels_up;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    return query_or_expression_tree_walker(node,
                                           rangeTableEntry_used_walker,
                                           &context,
                                           0);
}
 
 
/*
 * If the given Query is an INSERT ... SELECT construct, extract and
 * return the sub-Query node that represents the SELECT part.  Otherwise
 * return the given Query.
 *
 * If subquery_ptr is not NULL, then *subquery_ptr is set to the location
 * of the link to the SELECT subquery inside parsetree, or NULL if not an
 * INSERT ... SELECT.
 *
 * This is a hack needed because transformations on INSERT ... SELECTs that
 * appear in rule actions should be applied to the source SELECT, not to the
 * INSERT part.  Perhaps this can be cleaned up with redesigned querytrees.
 */
Query *
getInsertSelectQuery(Query *parsetree, Query ***subquery_ptr)
{
    Query      *selectquery;
    RangeTblEntry *selectrte;
    RangeTblRef *rtr;
 
    if (subquery_ptr)
        *subquery_ptr = NULL;
 
    if (parsetree == NULL)
        return parsetree;
    if (parsetree->commandType != CMD_INSERT)
        return parsetree;
 
    /*
     * Currently, this is ONLY applied to rule-action queries, and so we
     * expect to find the OLD and NEW placeholder entries in the given query.
     * If they're not there, it must be an INSERT/SELECT in which they've been
     * pushed down to the SELECT.
     */
    if (list_length(parsetree->rtable) >= 2 &&
        strcmp(rt_fetch(PRS2_OLD_VARNO, parsetree->rtable)->eref->aliasname,
               "old") == 0 &&
        strcmp(rt_fetch(PRS2_NEW_VARNO, parsetree->rtable)->eref->aliasname,
               "new") == 0)
        return parsetree;
    Assert(parsetree->jointree && IsA(parsetree->jointree, FromExpr));
    if (list_length(parsetree->jointree->fromlist) != 1)
        elog(ERROR, "expected to find SELECT subquery");
    rtr = (RangeTblRef *) linitial(parsetree->jointree->fromlist);
    if (!IsA(rtr, RangeTblRef))
        elog(ERROR, "expected to find SELECT subquery");
    selectrte = rt_fetch(rtr->rtindex, parsetree->rtable);
    if (!(selectrte->rtekind == RTE_SUBQUERY &&
          selectrte->subquery &&
          IsA(selectrte->subquery, Query) &&
          selectrte->subquery->commandType == CMD_SELECT))
        elog(ERROR, "expected to find SELECT subquery");
    selectquery = selectrte->subquery;
    if (list_length(selectquery->rtable) >= 2 &&
        strcmp(rt_fetch(PRS2_OLD_VARNO, selectquery->rtable)->eref->aliasname,
               "old") == 0 &&
        strcmp(rt_fetch(PRS2_NEW_VARNO, selectquery->rtable)->eref->aliasname,
               "new") == 0)
    {
        if (subquery_ptr)
            *subquery_ptr = &(selectrte->subquery);
        return selectquery;
    }
    elog(ERROR, "could not find rule placeholders");
    return NULL;                /* not reached */
}
 
 
/*
 * Add the given qualifier condition to the query's WHERE clause
 */
void
AddQual(Query *parsetree, Node *qual)
{
    Node       *copy;
 
    if (qual == NULL)
        return;
 
    if (parsetree->commandType == CMD_UTILITY)
    {
        /*
         * There's noplace to put the qual on a utility statement.
         *
         * If it's a NOTIFY, silently ignore the qual; this means that the
         * NOTIFY will execute, whether or not there are any qualifying rows.
         * While clearly wrong, this is much more useful than refusing to
         * execute the rule at all, and extra NOTIFY events are harmless for
         * typical uses of NOTIFY.
         *
         * If it isn't a NOTIFY, error out, since unconditional execution of
         * other utility stmts is unlikely to be wanted.  (This case is not
         * currently allowed anyway, but keep the test for safety.)
         */
        if (parsetree->utilityStmt && IsA(parsetree->utilityStmt, NotifyStmt))
            return;
        else
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("conditional utility statements are not implemented")));
    }
 
    if (parsetree->setOperations != NULL)
    {
        /*
         * There's noplace to put the qual on a setop statement, either. (This
         * could be fixed, but right now the planner simply ignores any qual
         * condition on a setop query.)
         */
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("conditional UNION/INTERSECT/EXCEPT statements are not implemented")));
    }
 
    /* INTERSECT wants the original, but we need to copy - Jan */
    copy = copyObject(qual);
 
    parsetree->jointree->quals = make_and_qual(parsetree->jointree->quals,
                                               copy);
 
    /*
     * We had better not have stuck an aggregate into the WHERE clause.
     */
    Assert(!contain_aggs_of_level(copy, 0));
 
    /*
     * Make sure query is marked correctly if added qual has sublinks. Need
     * not search qual when query is already marked.
     */
    if (!parsetree->hasSubLinks)
        parsetree->hasSubLinks = checkExprHasSubLink(copy);
}
 
 
/*
 * Invert the given clause and add it to the WHERE qualifications of the
 * given querytree.  Inversion means "x IS NOT TRUE", not just "NOT x",
 * else we will do the wrong thing when x evaluates to NULL.
 */
void
AddInvertedQual(Query *parsetree, Node *qual)
{
    BooleanTest *invqual;
 
    if (qual == NULL)
        return;
 
    /* Need not copy input qual, because AddQual will... */
    invqual = makeNode(BooleanTest);
    invqual->arg = (Expr *) qual;
    invqual->booltesttype = IS_NOT_TRUE;
    invqual->location = -1;
 
    AddQual(parsetree, (Node *) invqual);
}
 
 
/*
 * add_nulling_relids() finds Vars and PlaceHolderVars that belong to any
 * of the target_relids, and adds added_relids to their varnullingrels
 * and phnullingrels fields.  If target_relids is NULL, all level-zero
 * Vars and PHVs are modified.
 */
Node *
add_nulling_relids(Node *node,
                   const Bitmapset *target_relids,
                   const Bitmapset *added_relids)
{
    add_nulling_relids_context context;
 
    context.target_relids = target_relids;
    context.added_relids = added_relids;
    context.sublevels_up = 0;
    return query_or_expression_tree_mutator(node,
                                            add_nulling_relids_mutator,
                                            &context,
                                            0);
}
 
static Node *
add_nulling_relids_mutator(Node *node,
                           add_nulling_relids_context *context)
{
    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup == context->sublevels_up &&
            (context->target_relids == NULL ||
             bms_is_member(var->varno, context->target_relids)))
        {
            Relids      newnullingrels = bms_union(var->varnullingrels,
                                                   context->added_relids);
 
            /* Copy the Var ... */
            var = copyObject(var);
            /* ... and replace the copy's varnullingrels field */
            var->varnullingrels = newnullingrels;
            return (Node *) var;
        }
        /* Otherwise fall through to copy the Var normally */
    }
    else if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;
 
        if (phv->phlevelsup == context->sublevels_up &&
            (context->target_relids == NULL ||
             bms_overlap(phv->phrels, context->target_relids)))
        {
            Relids      newnullingrels = bms_union(phv->phnullingrels,
                                                   context->added_relids);
 
            /*
             * We don't modify the contents of the PHV's expression, only add
             * to phnullingrels.  This corresponds to assuming that the PHV
             * will be evaluated at the same level as before, then perhaps be
             * nulled as it bubbles up.  Hence, just flat-copy the node ...
             */
            phv = makeNode(PlaceHolderVar);
            memcpy(phv, node, sizeof(PlaceHolderVar));
            /* ... and replace the copy's phnullingrels field */
            phv->phnullingrels = newnullingrels;
            return (Node *) phv;
        }
        /* Otherwise fall through to copy the PlaceHolderVar normally */
    }
    else if (IsA(node, Query))
    {
        /* Recurse into RTE or sublink subquery */
        Query      *newnode;
 
        context->sublevels_up++;
        newnode = query_tree_mutator((Query *) node,
                                     add_nulling_relids_mutator,
                                     context,
                                     0);
        context->sublevels_up--;
        return (Node *) newnode;
    }
    return expression_tree_mutator(node, add_nulling_relids_mutator, context);
}
 
/*
 * remove_nulling_relids() removes mentions of the specified RT index(es)
 * in Var.varnullingrels and PlaceHolderVar.phnullingrels fields within
 * the given expression, except in nodes belonging to rels listed in
 * except_relids.
 */
Node *
remove_nulling_relids(Node *node,
                      const Bitmapset *removable_relids,
                      const Bitmapset *except_relids)
{
    remove_nulling_relids_context context;
 
    context.removable_relids = removable_relids;
    context.except_relids = except_relids;
    context.sublevels_up = 0;
    return query_or_expression_tree_mutator(node,
                                            remove_nulling_relids_mutator,
                                            &context,
                                            0);
}
 
static Node *
remove_nulling_relids_mutator(Node *node,
                              remove_nulling_relids_context *context)
{
    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup == context->sublevels_up &&
            !bms_is_member(var->varno, context->except_relids) &&
            bms_overlap(var->varnullingrels, context->removable_relids))
        {
            /* Copy the Var ... */
            var = copyObject(var);
            /* ... and replace the copy's varnullingrels field */
            var->varnullingrels = bms_difference(var->varnullingrels,
                                                 context->removable_relids);
            return (Node *) var;
        }
        /* Otherwise fall through to copy the Var normally */
    }
    else if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;
 
        if (phv->phlevelsup == context->sublevels_up &&
            !bms_overlap(phv->phrels, context->except_relids))
        {
            /*
             * Note: it might seem desirable to remove the PHV altogether if
             * phnullingrels goes to empty.  Currently we dare not do that
             * because we use PHVs in some cases to enforce separate identity
             * of subexpressions; see wrap_option usages in prepjointree.c.
             */
            /* Copy the PlaceHolderVar and mutate what's below ... */
            phv = (PlaceHolderVar *)
                expression_tree_mutator(node,
                                        remove_nulling_relids_mutator,
                                        context);
            /* ... and replace the copy's phnullingrels field */
            phv->phnullingrels = bms_difference(phv->phnullingrels,
                                                context->removable_relids);
            /* We must also update phrels, if it contains a removable RTI */
            phv->phrels = bms_difference(phv->phrels,
                                         context->removable_relids);
            Assert(!bms_is_empty(phv->phrels));
            return (Node *) phv;
        }
        /* Otherwise fall through to copy the PlaceHolderVar normally */
    }
    else if (IsA(node, Query))
    {
        /* Recurse into RTE or sublink subquery */
        Query      *newnode;
 
        context->sublevels_up++;
        newnode = query_tree_mutator((Query *) node,
                                     remove_nulling_relids_mutator,
                                     context,
                                     0);
        context->sublevels_up--;
        return (Node *) newnode;
    }
    return expression_tree_mutator(node, remove_nulling_relids_mutator, context);
}
 
 
/*
 * replace_rte_variables() finds all Vars in an expression tree
 * that reference a particular RTE, and replaces them with substitute
 * expressions obtained from a caller-supplied callback function.
 *
 * When invoking replace_rte_variables on a portion of a Query, pass the
 * address of the containing Query's hasSubLinks field as outer_hasSubLinks.
 * Otherwise, pass NULL, but inserting a SubLink into a non-Query expression
 * will then cause an error.
 *
 * Note: the business with inserted_sublink is needed to update hasSubLinks
 * in subqueries when the replacement adds a subquery inside a subquery.
 * Messy, isn't it?  We do not need to do similar pushups for hasAggs,
 * because it isn't possible for this transformation to insert a level-zero
 * aggregate reference into a subquery --- it could only insert outer aggs.
 * Likewise for hasWindowFuncs.
 *
 * Note: usually, we'd not expose the mutator function or context struct
 * for a function like this.  We do so because callbacks often find it
 * convenient to recurse directly to the mutator on sub-expressions of
 * what they will return.
 */
Node *
replace_rte_variables(Node *node, int target_varno, int sublevels_up,
                      replace_rte_variables_callback callback,
                      void *callback_arg,
                      bool *outer_hasSubLinks)
{
    Node       *result;
    replace_rte_variables_context context;
 
    context.callback = callback;
    context.callback_arg = callback_arg;
    context.target_varno = target_varno;
    context.sublevels_up = sublevels_up;
 
    /*
     * We try to initialize inserted_sublink to true if there is no need to
     * detect new sublinks because the query already has some.
     */
    if (node && IsA(node, Query))
        context.inserted_sublink = ((Query *) node)->hasSubLinks;
    else if (outer_hasSubLinks)
        context.inserted_sublink = *outer_hasSubLinks;
    else
        context.inserted_sublink = false;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    result = query_or_expression_tree_mutator(node,
                                              replace_rte_variables_mutator,
                                              &context,
                                              0);
 
    if (context.inserted_sublink)
    {
        if (result && IsA(result, Query))
            ((Query *) result)->hasSubLinks = true;
        else if (outer_hasSubLinks)
            *outer_hasSubLinks = true;
        else
            elog(ERROR, "replace_rte_variables inserted a SubLink, but has noplace to record it");
    }
 
    return result;
}
 
Node *
replace_rte_variables_mutator(Node *node,
                              replace_rte_variables_context *context)
{
    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varno == context->target_varno &&
            var->varlevelsup == context->sublevels_up)
        {
            /* Found a matching variable, make the substitution */
            Node       *newnode;
 
            newnode = context->callback(var, context);
            /* Detect if we are adding a sublink to query */
            if (!context->inserted_sublink)
                context->inserted_sublink = checkExprHasSubLink(newnode);
            return newnode;
        }
        /* otherwise fall through to copy the var normally */
    }
    else if (IsA(node, CurrentOfExpr))
    {
        CurrentOfExpr *cexpr = (CurrentOfExpr *) node;
 
        if (cexpr->cvarno == context->target_varno &&
            context->sublevels_up == 0)
        {
            /*
             * We get here if a WHERE CURRENT OF expression turns out to apply
             * to a view.  Someday we might be able to translate the
             * expression to apply to an underlying table of the view, but
             * right now it's not implemented.
             */
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("WHERE CURRENT OF on a view is not implemented")));
        }
        /* otherwise fall through to copy the expr normally */
    }
    else if (IsA(node, Query))
    {
        /* Recurse into RTE subquery or not-yet-planned sublink subquery */
        Query      *newnode;
        bool        save_inserted_sublink;
 
        context->sublevels_up++;
        save_inserted_sublink = context->inserted_sublink;
        context->inserted_sublink = ((Query *) node)->hasSubLinks;
        newnode = query_tree_mutator((Query *) node,
                                     replace_rte_variables_mutator,
                                     context,
                                     0);
        newnode->hasSubLinks |= context->inserted_sublink;
        context->inserted_sublink = save_inserted_sublink;
        context->sublevels_up--;
        return (Node *) newnode;
    }
    return expression_tree_mutator(node, replace_rte_variables_mutator, context);
}
 
 
/*
 * map_variable_attnos() finds all user-column Vars in an expression tree
 * that reference a particular RTE, and adjusts their varattnos according
 * to the given mapping array (varattno n is replaced by attno_map[n-1]).
 * Vars for system columns are not modified.
 *
 * A zero in the mapping array represents a dropped column, which should not
 * appear in the expression.
 *
 * If the expression tree contains a whole-row Var for the target RTE,
 * *found_whole_row is set to true.  In addition, if to_rowtype is
 * not InvalidOid, we replace the Var with a Var of that vartype, inserting
 * a ConvertRowtypeExpr to map back to the rowtype expected by the expression.
 * (Therefore, to_rowtype had better be a child rowtype of the rowtype of the
 * RTE we're changing references to.)  Callers that don't provide to_rowtype
 * should report an error if *found_whole_row is true; we don't do that here
 * because we don't know exactly what wording for the error message would
 * be most appropriate.  The caller will be aware of the context.
 *
 * This could be built using replace_rte_variables and a callback function,
 * but since we don't ever need to insert sublinks, replace_rte_variables is
 * overly complicated.
 */
 
typedef struct
{
    int         target_varno;   /* RTE index to search for */
    int         sublevels_up;   /* (current) nesting depth */
    const AttrMap *attno_map;   /* map array for user attnos */
    Oid         to_rowtype;     /* change whole-row Vars to this type */
    bool       *found_whole_row;    /* output flag */
} map_variable_attnos_context;
 
static Node *
map_variable_attnos_mutator(Node *node,
                            map_variable_attnos_context *context)
{
    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varno == context->target_varno &&
            var->varlevelsup == context->sublevels_up)
        {
            /* Found a matching variable, make the substitution */
            Var        *newvar = (Var *) palloc(sizeof(Var));
            int         attno = var->varattno;
 
            *newvar = *var;     /* initially copy all fields of the Var */
 
            if (attno > 0)
            {
                /* user-defined column, replace attno */
                if (attno > context->attno_map->maplen ||
                    context->attno_map->attnums[attno - 1] == 0)
                    elog(ERROR, "unexpected varattno %d in expression to be mapped",
                         attno);
                newvar->varattno = context->attno_map->attnums[attno - 1];
                /* If the syntactic referent is same RTE, fix it too */
                if (newvar->varnosyn == context->target_varno)
                    newvar->varattnosyn = newvar->varattno;
            }
            else if (attno == 0)
            {
                /* whole-row variable, warn caller */
                *(context->found_whole_row) = true;
 
                /* If the caller expects us to convert the Var, do so. */
                if (OidIsValid(context->to_rowtype) &&
                    context->to_rowtype != var->vartype)
                {
                    ConvertRowtypeExpr *r;
 
                    /* This certainly won't work for a RECORD variable. */
                    Assert(var->vartype != RECORDOID);
 
                    /* Var itself is changed to the requested type. */
                    newvar->vartype = context->to_rowtype;
 
                    /*
                     * Add a conversion node on top to convert back to the
                     * original type expected by the expression.
                     */
                    r = makeNode(ConvertRowtypeExpr);
                    r->arg = (Expr *) newvar;
                    r->resulttype = var->vartype;
                    r->convertformat = COERCE_IMPLICIT_CAST;
                    r->location = -1;
 
                    return (Node *) r;
                }
            }
            return (Node *) newvar;
        }
        /* otherwise fall through to copy the var normally */
    }
    else if (IsA(node, ConvertRowtypeExpr))
    {
        ConvertRowtypeExpr *r = (ConvertRowtypeExpr *) node;
        Var        *var = (Var *) r->arg;
 
        /*
         * If this is coercing a whole-row Var that we need to convert, then
         * just convert the Var without adding an extra ConvertRowtypeExpr.
         * Effectively we're simplifying var::parenttype::grandparenttype into
         * just var::grandparenttype.  This avoids building stacks of CREs if
         * this function is applied repeatedly.
         */
        if (IsA(var, Var) &&
            var->varno == context->target_varno &&
            var->varlevelsup == context->sublevels_up &&
            var->varattno == 0 &&
            OidIsValid(context->to_rowtype) &&
            context->to_rowtype != var->vartype)
        {
            ConvertRowtypeExpr *newnode;
            Var        *newvar = (Var *) palloc(sizeof(Var));
 
            /* whole-row variable, warn caller */
            *(context->found_whole_row) = true;
 
            *newvar = *var;     /* initially copy all fields of the Var */
 
            /* This certainly won't work for a RECORD variable. */
            Assert(var->vartype != RECORDOID);
 
            /* Var itself is changed to the requested type. */
            newvar->vartype = context->to_rowtype;
 
            newnode = (ConvertRowtypeExpr *) palloc(sizeof(ConvertRowtypeExpr));
            *newnode = *r;      /* initially copy all fields of the CRE */
            newnode->arg = (Expr *) newvar;
 
            return (Node *) newnode;
        }
        /* otherwise fall through to process the expression normally */
    }
    else if (IsA(node, Query))
    {
        /* Recurse into RTE subquery or not-yet-planned sublink subquery */
        Query      *newnode;
 
        context->sublevels_up++;
        newnode = query_tree_mutator((Query *) node,
                                     map_variable_attnos_mutator,
                                     context,
                                     0);
        context->sublevels_up--;
        return (Node *) newnode;
    }
    return expression_tree_mutator(node, map_variable_attnos_mutator, context);
}
 
Node *
map_variable_attnos(Node *node,
                    int target_varno, int sublevels_up,
                    const AttrMap *attno_map,
                    Oid to_rowtype, bool *found_whole_row)
{
    map_variable_attnos_context context;
 
    context.target_varno = target_varno;
    context.sublevels_up = sublevels_up;
    context.attno_map = attno_map;
    context.to_rowtype = to_rowtype;
    context.found_whole_row = found_whole_row;
 
    *found_whole_row = false;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    return query_or_expression_tree_mutator(node,
                                            map_variable_attnos_mutator,
                                            &context,
                                            0);
}
 
 
/*
 * ReplaceVarsFromTargetList - replace Vars with items from a targetlist
 *
 * Vars matching target_varno and sublevels_up are replaced by the
 * entry with matching resno from targetlist, if there is one.
 *
 * If there is no matching resno for such a Var, the action depends on the
 * nomatch_option:
 *  REPLACEVARS_REPORT_ERROR: throw an error
 *  REPLACEVARS_CHANGE_VARNO: change Var's varno to nomatch_varno
 *  REPLACEVARS_SUBSTITUTE_NULL: replace Var with a NULL Const of same type
 *
 * The caller must also provide target_rte, the RTE describing the target
 * relation.  This is needed to handle whole-row Vars referencing the target.
 * We expand such Vars into RowExpr constructs.
 *
 * In addition, for INSERT/UPDATE/DELETE/MERGE queries, the caller must
 * provide result_relation, the index of the result relation in the rewritten
 * query.  This is needed to handle OLD/NEW RETURNING list Vars referencing
 * target_varno.  When such Vars are expanded, their varreturningtype is
 * copied onto any replacement Vars referencing result_relation.  In addition,
 * if the replacement expression from the targetlist is not simply a Var
 * referencing result_relation, it is wrapped in a ReturningExpr node (causing
 * the executor to return NULL if the OLD/NEW row doesn't exist).
 *
 * Note that ReplaceVarFromTargetList always generates the replacement
 * expression with varlevelsup = 0.  The caller is responsible for adjusting
 * the varlevelsup if needed.  This simplifies the caller's life if it wants to
 * cache the replacement expressions.
 *
 * outer_hasSubLinks works the same as for replace_rte_variables().
 */
 
typedef struct
{
    RangeTblEntry *target_rte;
    List       *targetlist;
    int         result_relation;
    ReplaceVarsNoMatchOption nomatch_option;
    int         nomatch_varno;
} ReplaceVarsFromTargetList_context;
 
static Node *
ReplaceVarsFromTargetList_callback(Var *var,
                                   replace_rte_variables_context *context)
{
    ReplaceVarsFromTargetList_context *rcon = (ReplaceVarsFromTargetList_context *) context->callback_arg;
    Node       *newnode;
 
    newnode = ReplaceVarFromTargetList(var,
                                       rcon->target_rte,
                                       rcon->targetlist,
                                       rcon->result_relation,
                                       rcon->nomatch_option,
                                       rcon->nomatch_varno);
 
    /* Must adjust varlevelsup if replaced Var is within a subquery */
    if (var->varlevelsup > 0)
        IncrementVarSublevelsUp(newnode, var->varlevelsup, 0);
 
    return newnode;
}
 
Node *
ReplaceVarFromTargetList(Var *var,
                         RangeTblEntry *target_rte,
                         List *targetlist,
                         int result_relation,
                         ReplaceVarsNoMatchOption nomatch_option,
                         int nomatch_varno)
{
    TargetEntry *tle;
 
    if (var->varattno == InvalidAttrNumber)
    {
        /* Must expand whole-tuple reference into RowExpr */
        RowExpr    *rowexpr;
        List       *colnames;
        List       *fields;
        ListCell   *lc;
 
        /*
         * If generating an expansion for a var of a named rowtype (ie, this
         * is a plain relation RTE), then we must include dummy items for
         * dropped columns.  If the var is RECORD (ie, this is a JOIN), then
         * omit dropped columns.  In the latter case, attach column names to
         * the RowExpr for use of the executor and ruleutils.c.
         *
         * In order to be able to cache the results, we always generate the
         * expansion with varlevelsup = 0.  The caller is responsible for
         * adjusting it if needed.
         *
         * The varreturningtype is copied onto each individual field Var, so
         * that it is handled correctly when we recurse.
         */
        expandRTE(target_rte,
                  var->varno, 0 /* not varlevelsup */ ,
                  var->varreturningtype, var->location,
                  (var->vartype != RECORDOID),
                  &colnames, &fields);
        rowexpr = makeNode(RowExpr);
        /* the fields will be set below */
        rowexpr->args = NIL;
        rowexpr->row_typeid = var->vartype;
        rowexpr->row_format = COERCE_IMPLICIT_CAST;
        rowexpr->colnames = (var->vartype == RECORDOID) ? colnames : NIL;
        rowexpr->location = var->location;
        /* Adjust the generated per-field Vars... */
        foreach(lc, fields)
        {
            Node       *field = lfirst(lc);
 
            if (field && IsA(field, Var))
                field = ReplaceVarFromTargetList((Var *) field,
                                                 target_rte,
                                                 targetlist,
                                                 result_relation,
                                                 nomatch_option,
                                                 nomatch_varno);
            rowexpr->args = lappend(rowexpr->args, field);
        }
 
        /* Wrap it in a ReturningExpr, if needed, per comments above */
        if (var->varreturningtype != VAR_RETURNING_DEFAULT)
        {
            ReturningExpr *rexpr = makeNode(ReturningExpr);
 
            rexpr->retlevelsup = 0;
            rexpr->retold = (var->varreturningtype == VAR_RETURNING_OLD);
            rexpr->retexpr = (Expr *) rowexpr;
 
            return (Node *) rexpr;
        }
 
        return (Node *) rowexpr;
    }
 
    /* Normal case referencing one targetlist element */
    tle = get_tle_by_resno(targetlist, var->varattno);
 
    if (tle == NULL || tle->resjunk)
    {
        /* Failed to find column in targetlist */
        switch (nomatch_option)
        {
            case REPLACEVARS_REPORT_ERROR:
                /* fall through, throw error below */
                break;
 
            case REPLACEVARS_CHANGE_VARNO:
                var = copyObject(var);
                var->varno = nomatch_varno;
                var->varlevelsup = 0;
                /* we leave the syntactic referent alone */
                return (Node *) var;
 
            case REPLACEVARS_SUBSTITUTE_NULL:
                {
                    /*
                     * If Var is of domain type, we must add a CoerceToDomain
                     * node, in case there is a NOT NULL domain constraint.
                     */
                    int16       vartyplen;
                    bool        vartypbyval;
 
                    get_typlenbyval(var->vartype, &vartyplen, &vartypbyval);
                    return coerce_null_to_domain(var->vartype,
                                                 var->vartypmod,
                                                 var->varcollid,
                                                 vartyplen,
                                                 vartypbyval);
                }
        }
        elog(ERROR, "could not find replacement targetlist entry for attno %d",
             var->varattno);
        return NULL;            /* keep compiler quiet */
    }
    else
    {
        /* Make a copy of the tlist item to return */
        Expr       *newnode = copyObject(tle->expr);
 
        /*
         * Check to see if the tlist item contains a PARAM_MULTIEXPR Param,
         * and throw error if so.  This case could only happen when expanding
         * an ON UPDATE rule's NEW variable and the referenced tlist item in
         * the original UPDATE command is part of a multiple assignment. There
         * seems no practical way to handle such cases without multiple
         * evaluation of the multiple assignment's sub-select, which would
         * create semantic oddities that users of rules would probably prefer
         * not to cope with.  So treat it as an unimplemented feature.
         */
        if (contains_multiexpr_param((Node *) newnode, NULL))
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("NEW variables in ON UPDATE rules cannot reference columns that are part of a multiple assignment in the subject UPDATE command")));
 
        /* Handle any OLD/NEW RETURNING list Vars */
        if (var->varreturningtype != VAR_RETURNING_DEFAULT)
        {
            /*
             * Copy varreturningtype onto any Vars in the tlist item that
             * refer to result_relation (which had better be non-zero).
             */
            if (result_relation == 0)
                elog(ERROR, "variable returning old/new found outside RETURNING list");
 
            SetVarReturningType((Node *) newnode, result_relation,
                                0, var->varreturningtype);
 
            /* Wrap it in a ReturningExpr, if needed, per comments above */
            if (!IsA(newnode, Var) ||
                ((Var *) newnode)->varno != result_relation ||
                ((Var *) newnode)->varlevelsup != 0)
            {
                ReturningExpr *rexpr = makeNode(ReturningExpr);
 
                rexpr->retlevelsup = 0;
                rexpr->retold = (var->varreturningtype == VAR_RETURNING_OLD);
                rexpr->retexpr = newnode;
 
                newnode = (Expr *) rexpr;
            }
        }
 
        return (Node *) newnode;
    }
}
 
Node *
ReplaceVarsFromTargetList(Node *node,
                          int target_varno, int sublevels_up,
                          RangeTblEntry *target_rte,
                          List *targetlist,
                          int result_relation,
                          ReplaceVarsNoMatchOption nomatch_option,
                          int nomatch_varno,
                          bool *outer_hasSubLinks)
{
    ReplaceVarsFromTargetList_context context;
 
    context.target_rte = target_rte;
    context.targetlist = targetlist;
    context.result_relation = result_relation;
    context.nomatch_option = nomatch_option;
    context.nomatch_varno = nomatch_varno;
 
    return replace_rte_variables(node, target_varno, sublevels_up,
                                 ReplaceVarsFromTargetList_callback,
                                 &context,
                                 outer_hasSubLinks);
}