rewriteManip.c

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/*-------------------------------------------------------------------------
 *
 * rewriteManip.c
 *
 * Portions Copyright (c) 1996-2013, 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/plannodes.h"
#include "optimizer/clauses.h"
#include "parser/parse_coerce.h"
#include "parser/parse_relation.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.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;

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 Relids adjust_relid_set(Relids relids, int oldrelid, int newrelid);


/*
 * 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,
                                           (void *) &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, Query))
    {
        /* Recurse into subselects */
        bool        result;

        context->sublevels_up++;
        result = query_tree_walker((Query *) node,
                                   contain_aggs_of_level_walker,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, contain_aggs_of_level_walker,
                                  (void *) 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,
                                           (void *) &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, Query))
    {
        /* Recurse into subselects */
        bool        result;

        context->sublevels_up++;
        result = query_tree_walker((Query *) node,
                                   locate_agg_of_level_walker,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, locate_agg_of_level_walker,
                                  (void *) 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,
                                  (void *) 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,
                                           (void *) &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,
                                  (void *) 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);
}


/*
 * 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 varnoold 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->varnoold += 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);
        }
        /* 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, LateralJoinInfo));
    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,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, OffsetVarNodes_walker,
                                  (void *) 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 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;
            foreach(l, qry->rowMarks)
            {
                RowMarkClause *rc = (RowMarkClause *) lfirst(l);

                rc->rti += offset;
            }
        }
        query_tree_walker(qry, OffsetVarNodes_walker,
                          (void *) &context, 0);
    }
    else
        OffsetVarNodes_walker(node, &context);
}

static Relids
offset_relid_set(Relids relids, int offset)
{
    Relids      result = NULL;
    Relids      tmprelids;
    int         rtindex;

    tmprelids = bms_copy(relids);
    while ((rtindex = bms_first_member(tmprelids)) >= 0)
        result = bms_add_member(result, rtindex + offset);
    bms_free(tmprelids);
    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 varnoold fields are changed too.  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         rt_index;
    int         new_index;
    int         sublevels_up;
} ChangeVarNodes_context;

static bool
ChangeVarNodes_walker(Node *node, ChangeVarNodes_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)
        {
            var->varno = context->new_index;
            var->varnoold = 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);
        }
        /* 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, LateralJoinInfo));
    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,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, ChangeVarNodes_walker,
                                  (void *) context);
}

void
ChangeVarNodes(Node *node, int rt_index, int new_index, int sublevels_up)
{
    ChangeVarNodes_context context;

    context.rt_index = rt_index;
    context.new_index = new_index;
    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 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;
            foreach(l, qry->rowMarks)
            {
                RowMarkClause *rc = (RowMarkClause *) lfirst(l);

                if (rc->rti == rt_index)
                    rc->rti = new_index;
            }
        }
        query_tree_walker(qry, ChangeVarNodes_walker,
                          (void *) &context, 0);
    }
    else
        ChangeVarNodes_walker(node, &context);
}

/*
 * Substitute newrelid for oldrelid in a Relid set
 */
static Relids
adjust_relid_set(Relids relids, int oldrelid, int newrelid)
{
    if (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);
        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, 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, 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,
                                   (void *) context,
                                   QTW_EXAMINE_RTES);
        context->min_sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, IncrementVarSublevelsUp_walker,
                                  (void *) 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,
                                    (void *) &context,
                                    QTW_EXAMINE_RTES);
}

/*
 * 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,
                       (void *) &context,
                       QTW_EXAMINE_RTES);
}


/*
 * 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)
            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, LateralJoinInfo));
    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,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, rangeTableEntry_used_walker,
                                  (void *) 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,
                                           (void *) &context,
                                           0);
}


/*
 * attribute_used -
 *  Check if a specific attribute number of a RTE is used
 *  somewhere in the query or expression.
 */

typedef struct
{
    int         rt_index;
    int         attno;
    int         sublevels_up;
} attribute_used_context;

static bool
attribute_used_walker(Node *node,
                      attribute_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 &&
            var->varattno == context->attno)
            return true;
        return false;
    }
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;

        context->sublevels_up++;
        result = query_tree_walker((Query *) node, attribute_used_walker,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, attribute_used_walker,
                                  (void *) context);
}

bool
attribute_used(Node *node, int rt_index, int attno, int sublevels_up)
{
    attribute_used_context context;

    context.rt_index = rt_index;
    context.attno = attno;
    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,
                                           attribute_used_walker,
                                           (void *) &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);
    Assert(IsA(rtr, RangeTblRef));
    selectrte = rt_fetch(rtr->rtindex, parsetree->rtable);
    selectquery = selectrte->subquery;
    if (!(selectquery && IsA(selectquery, Query) &&
          selectquery->commandType == CMD_SELECT))
        elog(ERROR, "expected to find SELECT 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 want's 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;

    AddQual(parsetree, (Node *) invqual);
}


/*
 * 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,
                                              (void *) &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,
                                     (void *) 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,
                                   (void *) 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,
 * the Var is not changed but *found_whole_row is returned as TRUE.
 * For most callers this is an error condition, but we leave it to the caller
 * to report the error so that useful context can be provided.  (In some
 * usages it would be appropriate to modify the Var's vartype and insert a
 * ConvertRowtypeExpr node to map back to the original vartype.  We might
 * someday extend this function's API to support that.  For now, the only
 * concession to that future need is that this function is a tree mutator
 * not just a walker.)
 *
 * 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 AttrNumber *attno_map;    /* map array for user attnos */
    int         map_length;         /* number of entries in attno_map[] */
    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;
            if (attno > 0)
            {
                /* user-defined column, replace attno */
                if (attno > context->map_length ||
                    context->attno_map[attno - 1] == 0)
                    elog(ERROR, "unexpected varattno %d in expression to be mapped",
                         attno);
                newvar->varattno = newvar->varoattno = context->attno_map[attno - 1];
            }
            else if (attno == 0)
            {
                /* whole-row variable, warn caller */
                *(context->found_whole_row) = true;
            }
            return (Node *) newvar;
        }
        /* otherwise fall through to copy the var 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,
                                     (void *) context,
                                     0);
        context->sublevels_up--;
        return (Node *) newnode;
    }
    return expression_tree_mutator(node, map_variable_attnos_mutator,
                                   (void *) context);
}

Node *
map_variable_attnos(Node *node,
                    int target_varno, int sublevels_up,
                    const AttrNumber *attno_map, int map_length,
                    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.map_length = map_length;
    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,
                                            (void *) &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.
 *
 * outer_hasSubLinks works the same as for replace_rte_variables().
 */

typedef struct
{
    RangeTblEntry *target_rte;
    List       *targetlist;
    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;
    TargetEntry *tle;

    if (var->varattno == InvalidAttrNumber)
    {
        /* Must expand whole-tuple reference into RowExpr */
        RowExpr    *rowexpr;
        List       *colnames;
        List       *fields;

        /*
         * 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.  Either way, attach column names to the
         * RowExpr for use of ruleutils.c.
         */
        expandRTE(rcon->target_rte,
                  var->varno, var->varlevelsup, var->location,
                  (var->vartype != RECORDOID),
                  &colnames, &fields);
        /* Adjust the generated per-field Vars... */
        fields = (List *) replace_rte_variables_mutator((Node *) fields,
                                                        context);
        rowexpr = makeNode(RowExpr);
        rowexpr->args = fields;
        rowexpr->row_typeid = var->vartype;
        rowexpr->row_format = COERCE_IMPLICIT_CAST;
        rowexpr->colnames = colnames;
        rowexpr->location = var->location;

        return (Node *) rowexpr;
    }

    /* Normal case referencing one targetlist element */
    tle = get_tle_by_resno(rcon->targetlist, var->varattno);

    if (tle == NULL || tle->resjunk)
    {
        /* Failed to find column in targetlist */
        switch (rcon->nomatch_option)
        {
            case REPLACEVARS_REPORT_ERROR:
                /* fall through, throw error below */
                break;

            case REPLACEVARS_CHANGE_VARNO:
                var = (Var *) copyObject(var);
                var->varno = rcon->nomatch_varno;
                var->varnoold = rcon->nomatch_varno;
                return (Node *) var;

            case REPLACEVARS_SUBSTITUTE_NULL:
                /*
                 * If Var is of domain type, we should add a CoerceToDomain
                 * node, in case there is a NOT NULL domain constraint.
                 */
                return coerce_to_domain((Node *) makeNullConst(var->vartype,
                                                               var->vartypmod,
                                                               var->varcollid),
                                        InvalidOid, -1,
                                        var->vartype,
                                        COERCE_IMPLICIT_CAST,
                                        -1,
                                        false,
                                        false);
        }
        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 */
        Node       *newnode = copyObject(tle->expr);

        /* Must adjust varlevelsup if tlist item is from higher query */
        if (var->varlevelsup > 0)
            IncrementVarSublevelsUp(newnode, var->varlevelsup, 0);

        return newnode;
    }
}

Node *
ReplaceVarsFromTargetList(Node *node,
                          int target_varno, int sublevels_up,
                          RangeTblEntry *target_rte,
                          List *targetlist,
                          ReplaceVarsNoMatchOption nomatch_option,
                          int nomatch_varno,
                          bool *outer_hasSubLinks)
{
    ReplaceVarsFromTargetList_context context;

    context.target_rte = target_rte;
    context.targetlist = targetlist;
    context.nomatch_option = nomatch_option;
    context.nomatch_varno = nomatch_varno;

    return replace_rte_variables(node, target_varno, sublevels_up,
                                 ReplaceVarsFromTargetList_callback,
                                 (void *) &context,
                                 outer_hasSubLinks);
}