/*-------------------------------------------------------------------------

 *

 * rewriteDefine.c

 *    routines for defining a rewrite rule

 *

 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group

 * Portions Copyright (c) 1994, Regents of the University of California

 *

 *

 * IDENTIFICATION

 *    src/backend/rewrite/rewriteDefine.c

 *

 *-------------------------------------------------------------------------

 */

#include "postgres.h"

#include "access/htup_details.h"

#include "access/relation.h"

#include "access/table.h"

#include "catalog/catalog.h"

#include "catalog/dependency.h"

#include "catalog/indexing.h"

#include "catalog/namespace.h"

#include "catalog/objectaccess.h"

#include "catalog/pg_rewrite.h"

#include "miscadmin.h"

#include "nodes/nodeFuncs.h"

#include "parser/parse_utilcmd.h"

#include "rewrite/rewriteDefine.h"

#include "rewrite/rewriteManip.h"

#include "rewrite/rewriteSupport.h"

#include "utils/acl.h"

#include "utils/builtins.h"

#include "utils/inval.h"

#include "utils/lsyscache.h"

#include "utils/rel.h"

#include "utils/syscache.h"

static void checkRuleResultList(List *targetList, TupleDesc resultDesc,

                bool isSelect, bool requireColumnNameMatch);

static bool setRuleCheckAsUser_walker(Node *node, Oid *context);

static void setRuleCheckAsUser_Query(Query *qry, Oid userid);

/*

 * InsertRule -

 *    takes the arguments and inserts them as a row into the system

 *    relation "pg_rewrite"

 */

static Oid

InsertRule(const char *rulname,

       int evtype,

       Oid eventrel_oid,

       bool evinstead,

       Node *event_qual,

       List *action,

       bool replace)

{

  char     *evqual = nodeToString(event_qual);

  char     *actiontree = nodeToString((Node *) action);

  Datum   values[Natts_pg_rewrite];

  bool    nulls[Natts_pg_rewrite] = {0};

  NameData  rname;

  Relation  pg_rewrite_desc;

  HeapTuple tup,

        oldtup;

  Oid     rewriteObjectId;

  ObjectAddress myself,

        referenced;

  bool    is_update = false;

  /*

   * Set up *nulls and *values arrays

   */

  namestrcpy(&rname, rulname);

  values[Anum_pg_rewrite_rulename - 1] = NameGetDatum(&rname);

  values[Anum_pg_rewrite_ev_class - 1] = ObjectIdGetDatum(eventrel_oid);

  values[Anum_pg_rewrite_ev_type - 1] = CharGetDatum(evtype + '0');

  values[Anum_pg_rewrite_ev_enabled - 1] = CharGetDatum(RULE_FIRES_ON_ORIGIN);

  values[Anum_pg_rewrite_is_instead - 1] = BoolGetDatum(evinstead);

  values[Anum_pg_rewrite_ev_qual - 1] = CStringGetTextDatum(evqual);

  values[Anum_pg_rewrite_ev_action - 1] = CStringGetTextDatum(actiontree);

  /*

   * Ready to store new pg_rewrite tuple

   */

  pg_rewrite_desc = table_open(RewriteRelationId, RowExclusiveLock);

  /*

   * Check to see if we are replacing an existing tuple

   */

  oldtup = SearchSysCache2(RULERELNAME,

               ObjectIdGetDatum(eventrel_oid),

               PointerGetDatum(rulname));

  if (HeapTupleIsValid(oldtup))

  {

    bool    replaces[Natts_pg_rewrite] = {0};

    if (!replace)

      ereport(ERROR,

          (errcode(ERRCODE_DUPLICATE_OBJECT),

           errmsg("rule \"%s\" for relation \"%s\" already exists",

              rulname, get_rel_name(eventrel_oid))));

    /*

     * When replacing, we don't need to replace every attribute

     */

    replaces[Anum_pg_rewrite_ev_type - 1] = true;

    replaces[Anum_pg_rewrite_is_instead - 1] = true;

    replaces[Anum_pg_rewrite_ev_qual - 1] = true;

    replaces[Anum_pg_rewrite_ev_action - 1] = true;

    tup = heap_modify_tuple(oldtup, RelationGetDescr(pg_rewrite_desc),

                values, nulls, replaces);

    CatalogTupleUpdate(pg_rewrite_desc, &tup->t_self, tup);

    ReleaseSysCache(oldtup);

    rewriteObjectId = ((Form_pg_rewrite) GETSTRUCT(tup))->oid;

    is_update = true;

  }

  else

  {

    rewriteObjectId = GetNewOidWithIndex(pg_rewrite_desc,

                       RewriteOidIndexId,

                       Anum_pg_rewrite_oid);

    values[Anum_pg_rewrite_oid - 1] = ObjectIdGetDatum(rewriteObjectId);

    tup = heap_form_tuple(pg_rewrite_desc->rd_att, values, nulls);

    CatalogTupleInsert(pg_rewrite_desc, tup);

  }

  heap_freetuple(tup);

  /* If replacing, get rid of old dependencies and make new ones */

  if (is_update)

    deleteDependencyRecordsFor(RewriteRelationId, rewriteObjectId, false);

  /*

   * Install dependency on rule's relation to ensure it will go away on

   * relation deletion.  If the rule is ON SELECT, make the dependency

   * implicit --- this prevents deleting a view's SELECT rule.  Other kinds

   * of rules can be AUTO.

   */

  myself.classId = RewriteRelationId;

  myself.objectId = rewriteObjectId;

  myself.objectSubId = 0;

  referenced.classId = RelationRelationId;

  referenced.objectId = eventrel_oid;

  referenced.objectSubId = 0;

  recordDependencyOn(&myself, &referenced,

             (evtype == CMD_SELECT) ? DEPENDENCY_INTERNAL : DEPENDENCY_AUTO);

  /*

   * Also install dependencies on objects referenced in action and qual.

   */

  recordDependencyOnExpr(&myself, (Node *) action, NIL,

               DEPENDENCY_NORMAL);

  if (event_qual != NULL)

  {

    /* Find query containing OLD/NEW rtable entries */

    Query    *qry = linitial_node(Query, action);

    qry = getInsertSelectQuery(qry, NULL);

    recordDependencyOnExpr(&myself, event_qual, qry->rtable,

                 DEPENDENCY_NORMAL);

  }

  /* Post creation hook for new rule */

  InvokeObjectPostCreateHook(RewriteRelationId, rewriteObjectId, 0);

  table_close(pg_rewrite_desc, RowExclusiveLock);

  return rewriteObjectId;

}

/*

 * DefineRule

 *    Execute a CREATE RULE command.

 */

ObjectAddress

DefineRule(RuleStmt *stmt, const char *queryString)

{

  List     *actions;

  Node     *whereClause;

  Oid     relId;

  /* Parse analysis. */

  transformRuleStmt(stmt, queryString, &actions, &whereClause);

  /*

   * Find and lock the relation.  Lock level should match

   * DefineQueryRewrite.

   */

  relId = RangeVarGetRelid(stmt->relation, AccessExclusiveLock, false);

  /* ... and execute */

  return DefineQueryRewrite(stmt->rulename,

                relId,

                whereClause,

                stmt->event,

                stmt->instead,

                stmt->replace,

                actions);

}

/*

 * DefineQueryRewrite

 *    Create a rule

 *

 * This is essentially the same as DefineRule() except that the rule's

 * action and qual have already been passed through parse analysis.

 */

ObjectAddress

DefineQueryRewrite(const char *rulename,

           Oid event_relid,

           Node *event_qual,

           CmdType event_type,

           bool is_instead,

           bool replace,

           List *action)

{

  Relation  event_relation;

  ListCell   *l;

  Query    *query;

  Oid     ruleId = InvalidOid;

  ObjectAddress address;

  /*

   * If we are installing an ON SELECT rule, we had better grab

   * AccessExclusiveLock to ensure no SELECTs are currently running on the

   * event relation. For other types of rules, it would be sufficient to

   * grab ShareRowExclusiveLock to lock out insert/update/delete actions and

   * to ensure that we lock out current CREATE RULE statements; but because

   * of race conditions in access to catalog entries, we can't do that yet.

   *

   * Note that this lock level should match the one used in DefineRule.

   */

  event_relation = table_open(event_relid, AccessExclusiveLock);

  /*

   * Verify relation is of a type that rules can sensibly be applied to.

   * Internal callers can target materialized views, but transformRuleStmt()

   * blocks them for users.  Don't mention them in the error message.

   */

  if (event_relation->rd_rel->relkind != RELKIND_RELATION &&

    event_relation->rd_rel->relkind != RELKIND_MATVIEW &&

    event_relation->rd_rel->relkind != RELKIND_VIEW &&

    event_relation->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)

    ereport(ERROR,

        (errcode(ERRCODE_WRONG_OBJECT_TYPE),

         errmsg("relation \"%s\" cannot have rules",

            RelationGetRelationName(event_relation)),

         errdetail_relkind_not_supported(event_relation->rd_rel->relkind)));

  if (!allowSystemTableMods && IsSystemRelation(event_relation))

    ereport(ERROR,

        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),

         errmsg("permission denied: \"%s\" is a system catalog",

            RelationGetRelationName(event_relation))));

  /*

   * Check user has permission to apply rules to this relation.

   */

  if (!object_ownercheck(RelationRelationId, event_relid, GetUserId()))

    aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(event_relation->rd_rel->relkind),

             RelationGetRelationName(event_relation));

  /*

   * No rule actions that modify OLD or NEW

   */

  foreach(l, action)

  {

    query = lfirst_node(Query, l);

    if (query->resultRelation == 0)

      continue;

    /* Don't be fooled by INSERT/SELECT */

    if (query != getInsertSelectQuery(query, NULL))

      continue;

    if (query->resultRelation == PRS2_OLD_VARNO)

      ereport(ERROR,

          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

           errmsg("rule actions on OLD are not implemented"),

           errhint("Use views or triggers instead.")));

    if (query->resultRelation == PRS2_NEW_VARNO)

      ereport(ERROR,

          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

           errmsg("rule actions on NEW are not implemented"),

           errhint("Use triggers instead.")));

  }

  if (event_type == CMD_SELECT)

  {

    /*

     * Rules ON SELECT are restricted to view definitions

     *

     * So this had better be a view, ...

     */

    if (event_relation->rd_rel->relkind != RELKIND_VIEW &&

      event_relation->rd_rel->relkind != RELKIND_MATVIEW)

      ereport(ERROR,

          (errcode(ERRCODE_WRONG_OBJECT_TYPE),

           errmsg("relation \"%s\" cannot have ON SELECT rules",

              RelationGetRelationName(event_relation)),

           errdetail_relkind_not_supported(event_relation->rd_rel->relkind)));

    /*

     * ... there cannot be INSTEAD NOTHING, ...

     */

    if (action == NIL)

      ereport(ERROR,

          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

           errmsg("INSTEAD NOTHING rules on SELECT are not implemented"),

           errhint("Use views instead.")));

    /*

     * ... there cannot be multiple actions, ...

     */

    if (list_length(action) > 1)

      ereport(ERROR,

          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

           errmsg("multiple actions for rules on SELECT are not implemented")));

    /*

     * ... the one action must be a SELECT, ...

     */

    query = linitial_node(Query, action);

    if (!is_instead ||

      query->commandType != CMD_SELECT)

      ereport(ERROR,

          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

           errmsg("rules on SELECT must have action INSTEAD SELECT")));

    /*

     * ... it cannot contain data-modifying WITH ...

     */

    if (query->hasModifyingCTE)

      ereport(ERROR,

          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

           errmsg("rules on SELECT must not contain data-modifying statements in WITH")));

    /*

     * ... there can be no rule qual, ...

     */

    if (event_qual != NULL)

      ereport(ERROR,

          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

           errmsg("event qualifications are not implemented for rules on SELECT")));

    /*

     * ... the targetlist of the SELECT action must exactly match the

     * event relation, ...

     */

    checkRuleResultList(query->targetList,

              RelationGetDescr(event_relation),

              true,

              event_relation->rd_rel->relkind !=

              RELKIND_MATVIEW);

    /*

     * ... there must not be another ON SELECT rule already ...

     */

    if (!replace && event_relation->rd_rules != NULL)

    {

      int     i;

      for (i = 0; i < event_relation->rd_rules->numLocks; i++)

      {

        RewriteRule *rule;

        rule = event_relation->rd_rules->rules[i];

        if (rule->event == CMD_SELECT)

          ereport(ERROR,

              (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),

               errmsg("\"%s\" is already a view",

                  RelationGetRelationName(event_relation))));

      }

    }

    /*

     * ... and finally the rule must be named _RETURN.

     */

    if (strcmp(rulename, ViewSelectRuleName) != 0)

    {

      /*

       * In versions before 7.3, the expected name was _RETviewname. For

       * backwards compatibility with old pg_dump output, accept that

       * and silently change it to _RETURN.  Since this is just a quick

       * backwards-compatibility hack, limit the number of characters

       * checked to a few less than NAMEDATALEN; this saves having to

       * worry about where a multibyte character might have gotten

       * truncated.

       */

      if (strncmp(rulename, "_RET", 4) != 0 ||

        strncmp(rulename + 4, RelationGetRelationName(event_relation),

            NAMEDATALEN - 4 - 4) != 0)

        ereport(ERROR,

            (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

             errmsg("view rule for \"%s\" must be named \"%s\"",

                RelationGetRelationName(event_relation),

                ViewSelectRuleName)));

      rulename = pstrdup(ViewSelectRuleName);

    }

  }

  else

  {

    /*

     * For non-SELECT rules, a RETURNING list can appear in at most one of

     * the actions ... and there can't be any RETURNING list at all in a

     * conditional or non-INSTEAD rule.  (Actually, there can be at most

     * one RETURNING list across all rules on the same event, but it seems

     * best to enforce that at rule expansion time.)  If there is a

     * RETURNING list, it must match the event relation.

     */

    bool    haveReturning = false;

    foreach(l, action)

    {

      query = lfirst_node(Query, l);

      if (!query->returningList)

        continue;

      if (haveReturning)

        ereport(ERROR,

            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

             errmsg("cannot have multiple RETURNING lists in a rule")));

      haveReturning = true;

      if (event_qual != NULL)

        ereport(ERROR,

            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

             errmsg("RETURNING lists are not supported in conditional rules")));

      if (!is_instead)

        ereport(ERROR,

            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

             errmsg("RETURNING lists are not supported in non-INSTEAD rules")));

      checkRuleResultList(query->returningList,

                RelationGetDescr(event_relation),

                false, false);

    }

    /*

     * And finally, if it's not an ON SELECT rule then it must *not* be

     * named _RETURN.  This prevents accidentally or maliciously replacing

     * a view's ON SELECT rule with some other kind of rule.

     */

    if (strcmp(rulename, ViewSelectRuleName) == 0)

      ereport(ERROR,

          (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

           errmsg("non-view rule for \"%s\" must not be named \"%s\"",

              RelationGetRelationName(event_relation),

              ViewSelectRuleName)));

  }

  /*

   * This rule is allowed - prepare to install it.

   */

  /* discard rule if it's null action and not INSTEAD; it's a no-op */

  if (action != NIL || is_instead)

  {

    ruleId = InsertRule(rulename,

              event_type,

              event_relid,

              is_instead,

              event_qual,

              action,

              replace);

    /*

     * Set pg_class 'relhasrules' field true for event relation.

     *

     * Important side effect: an SI notice is broadcast to force all

     * backends (including me!) to update relcache entries with the new

     * rule.

     */

    SetRelationRuleStatus(event_relid, true);

  }

  ObjectAddressSet(address, RewriteRelationId, ruleId);

  /* Close rel, but keep lock till commit... */

  table_close(event_relation, NoLock);

  return address;

}

/*

 * checkRuleResultList

 *    Verify that targetList produces output compatible with a tupledesc

 *

 * The targetList might be either a SELECT targetlist, or a RETURNING list;

 * isSelect tells which.  This is used for choosing error messages.

 *

 * A SELECT targetlist may optionally require that column names match.

 */

static void

checkRuleResultList(List *targetList, TupleDesc resultDesc, bool isSelect,

          bool requireColumnNameMatch)

{

  ListCell   *tllist;

  int     i;

  /* Only a SELECT may require a column name match. */

  Assert(isSelect || !requireColumnNameMatch);

  i = 0;

  foreach(tllist, targetList)

  {

    TargetEntry *tle = (TargetEntry *) lfirst(tllist);

    Oid     tletypid;

    int32   tletypmod;

    Form_pg_attribute attr;

    char     *attname;

    /* resjunk entries may be ignored */

    if (tle->resjunk)

      continue;

    i++;

    if (i > resultDesc->natts)

      ereport(ERROR,

          (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

           isSelect ?

           errmsg("SELECT rule's target list has too many entries") :

           errmsg("RETURNING list has too many entries")));

    attr = TupleDescAttr(resultDesc, i - 1);

    attname = NameStr(attr->attname);

    /*

     * Disallow dropped columns in the relation.  This is not really

     * expected to happen when creating an ON SELECT rule.  It'd be

     * possible if someone tried to convert a relation with dropped

     * columns to a view, but the only case we care about supporting

     * table-to-view conversion for is pg_dump, and pg_dump won't do that.

     *

     * Unfortunately, the situation is also possible when adding a rule

     * with RETURNING to a regular table, and rejecting that case is

     * altogether more annoying.  In principle we could support it by

     * modifying the targetlist to include dummy NULL columns

     * corresponding to the dropped columns in the tupdesc.  However,

     * places like ruleutils.c would have to be fixed to not process such

     * entries, and that would take an uncertain and possibly rather large

     * amount of work.  (Note we could not dodge that by marking the dummy

     * columns resjunk, since it's precisely the non-resjunk tlist columns

     * that are expected to correspond to table columns.)

     */

    if (attr->attisdropped)

      ereport(ERROR,

          (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

           isSelect ?

           errmsg("cannot convert relation containing dropped columns to view") :

           errmsg("cannot create a RETURNING list for a relation containing dropped columns")));

    /* Check name match if required; no need for two error texts here */

    if (requireColumnNameMatch && strcmp(tle->resname, attname) != 0)

      ereport(ERROR,

          (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

           errmsg("SELECT rule's target entry %d has different column name from column \"%s\"",

              i, attname),

           errdetail("SELECT target entry is named \"%s\".",

                 tle->resname)));

    /* Check type match. */

    tletypid = exprType((Node *) tle->expr);

    if (attr->atttypid != tletypid)

      ereport(ERROR,

          (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

           isSelect ?

           errmsg("SELECT rule's target entry %d has different type from column \"%s\"",

              i, attname) :

           errmsg("RETURNING list's entry %d has different type from column \"%s\"",

              i, attname),

           isSelect ?

           errdetail("SELECT target entry has type %s, but column has type %s.",

                 format_type_be(tletypid),

                 format_type_be(attr->atttypid)) :

           errdetail("RETURNING list entry has type %s, but column has type %s.",

                 format_type_be(tletypid),

                 format_type_be(attr->atttypid))));

    /*

     * Allow typmods to be different only if one of them is -1, ie,

     * "unspecified".  This is necessary for cases like "numeric", where

     * the table will have a filled-in default length but the select

     * rule's expression will probably have typmod = -1.

     */

    tletypmod = exprTypmod((Node *) tle->expr);

    if (attr->atttypmod != tletypmod &&

      attr->atttypmod != -1 && tletypmod != -1)

      ereport(ERROR,

          (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

           isSelect ?

           errmsg("SELECT rule's target entry %d has different size from column \"%s\"",

              i, attname) :

           errmsg("RETURNING list's entry %d has different size from column \"%s\"",

              i, attname),

           isSelect ?

           errdetail("SELECT target entry has type %s, but column has type %s.",

                 format_type_with_typemod(tletypid, tletypmod),

                 format_type_with_typemod(attr->atttypid,

                            attr->atttypmod)) :

           errdetail("RETURNING list entry has type %s, but column has type %s.",

                 format_type_with_typemod(tletypid, tletypmod),

                 format_type_with_typemod(attr->atttypid,

                            attr->atttypmod))));

  }

  if (i != resultDesc->natts)

    ereport(ERROR,

        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

         isSelect ?

         errmsg("SELECT rule's target list has too few entries") :

         errmsg("RETURNING list has too few entries")));

}

/*

 * setRuleCheckAsUser

 *    Recursively scan a query or expression tree and set the checkAsUser

 *    field to the given userid in all RTEPermissionInfos of the query.

 */

void

setRuleCheckAsUser(Node *node, Oid userid)

{

  (void) setRuleCheckAsUser_walker(node, &userid);

}

static bool

setRuleCheckAsUser_walker(Node *node, Oid *context)

{

  if (node == NULL)

    return false;

  if (IsA(node, Query))

  {

    setRuleCheckAsUser_Query((Query *) node, *context);

    return false;

  }

  return expression_tree_walker(node, setRuleCheckAsUser_walker,

                  context);

}

static void

setRuleCheckAsUser_Query(Query *qry, Oid userid)

{

  ListCell   *l;

  /* Set in all RTEPermissionInfos for this query. */

  foreach(l, qry->rteperminfos)

  {

    RTEPermissionInfo *perminfo = lfirst_node(RTEPermissionInfo, l);

    perminfo->checkAsUser = userid;

  }

  /* Now recurse to any subquery RTEs */

  foreach(l, qry->rtable)

  {

    RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

    if (rte->rtekind == RTE_SUBQUERY)

      setRuleCheckAsUser_Query(rte->subquery, userid);

  }

  /* Recurse into subquery-in-WITH */

  foreach(l, qry->cteList)

  {

    CommonTableExpr *cte = (CommonTableExpr *) lfirst(l);

    setRuleCheckAsUser_Query(castNode(Query, cte->ctequery), userid);

  }

  /* If there are sublinks, search for them and process their RTEs */

  if (qry->hasSubLinks)

    query_tree_walker(qry, setRuleCheckAsUser_walker, &userid,

              QTW_IGNORE_RC_SUBQUERIES);

}

/*

 * Change the firing semantics of an existing rule.

 */

void

EnableDisableRule(Relation rel, const char *rulename,

          char fires_when)

{

  Relation  pg_rewrite_desc;

  Oid     owningRel = RelationGetRelid(rel);

  Oid     eventRelationOid;

  HeapTuple ruletup;

  Form_pg_rewrite ruleform;

  bool    changed = false;

  /*

   * Find the rule tuple to change.

   */

  pg_rewrite_desc = table_open(RewriteRelationId, RowExclusiveLock);

  ruletup = SearchSysCacheCopy2(RULERELNAME,

                  ObjectIdGetDatum(owningRel),

                  PointerGetDatum(rulename));

  if (!HeapTupleIsValid(ruletup))

    ereport(ERROR,

        (errcode(ERRCODE_UNDEFINED_OBJECT),

         errmsg("rule \"%s\" for relation \"%s\" does not exist",

            rulename, get_rel_name(owningRel))));

  ruleform = (Form_pg_rewrite) GETSTRUCT(ruletup);

  /*

   * Verify that the user has appropriate permissions.

   */

  eventRelationOid = ruleform->ev_class;

  Assert(eventRelationOid == owningRel);

  if (!object_ownercheck(RelationRelationId, eventRelationOid, GetUserId()))

    aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(get_rel_relkind(eventRelationOid)),

             get_rel_name(eventRelationOid));

  /*

   * Change ev_enabled if it is different from the desired new state.

   */

  if (DatumGetChar(ruleform->ev_enabled) !=

    fires_when)

  {

    ruleform->ev_enabled = CharGetDatum(fires_when);

    CatalogTupleUpdate(pg_rewrite_desc, &ruletup->t_self, ruletup);

    changed = true;

  }

  InvokeObjectPostAlterHook(RewriteRelationId, ruleform->oid, 0);

  heap_freetuple(ruletup);

  table_close(pg_rewrite_desc, RowExclusiveLock);

  /*

   * If we changed anything, broadcast a SI inval message to force each

   * backend (including our own!) to rebuild relation's relcache entry.

   * Otherwise they will fail to apply the change promptly.

   */

  if (changed)

    CacheInvalidateRelcache(rel);

}

/*

 * Perform permissions and integrity checks before acquiring a relation lock.

 */

static void

RangeVarCallbackForRenameRule(const RangeVar *rv, Oid relid, Oid oldrelid,

                void *arg)

{

  HeapTuple tuple;

  Form_pg_class form;

  tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));

  if (!HeapTupleIsValid(tuple))

    return;         /* concurrently dropped */

  form = (Form_pg_class) GETSTRUCT(tuple);

  /* only tables and views can have rules */

  if (form->relkind != RELKIND_RELATION &&

    form->relkind != RELKIND_VIEW &&

    form->relkind != RELKIND_PARTITIONED_TABLE)

    ereport(ERROR,

        (errcode(ERRCODE_WRONG_OBJECT_TYPE),

         errmsg("relation \"%s\" cannot have rules", rv->relname),

         errdetail_relkind_not_supported(form->relkind)));

  if (!allowSystemTableMods && IsSystemClass(relid, form))

    ereport(ERROR,

        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),

         errmsg("permission denied: \"%s\" is a system catalog",

            rv->relname)));

  /* you must own the table to rename one of its rules */

  if (!object_ownercheck(RelationRelationId, relid, GetUserId()))

    aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(get_rel_relkind(relid)), rv->relname);

  ReleaseSysCache(tuple);

}

/*

 * Rename an existing rewrite rule.

 */

ObjectAddress

RenameRewriteRule(RangeVar *relation, const char *oldName,

          const char *newName)

{

  Oid     relid;

  Relation  targetrel;

  Relation  pg_rewrite_desc;

  HeapTuple ruletup;

  Form_pg_rewrite ruleform;

  Oid     ruleOid;

  ObjectAddress address;

  /*

   * Look up name, check permissions, and acquire lock (which we will NOT

   * release until end of transaction).

   */

  relid = RangeVarGetRelidExtended(relation, AccessExclusiveLock,

                   0,

                   RangeVarCallbackForRenameRule,

                   NULL);

  /* Have lock already, so just need to build relcache entry. */

  targetrel = relation_open(relid, NoLock);

  /* Prepare to modify pg_rewrite */

  pg_rewrite_desc = table_open(RewriteRelationId, RowExclusiveLock);

  /* Fetch the rule's entry (it had better exist) */

  ruletup = SearchSysCacheCopy2(RULERELNAME,

                  ObjectIdGetDatum(relid),

                  PointerGetDatum(oldName));

  if (!HeapTupleIsValid(ruletup))

    ereport(ERROR,

        (errcode(ERRCODE_UNDEFINED_OBJECT),

         errmsg("rule \"%s\" for relation \"%s\" does not exist",

            oldName, RelationGetRelationName(targetrel))));

  ruleform = (Form_pg_rewrite) GETSTRUCT(ruletup);

  ruleOid = ruleform->oid;

  /* rule with the new name should not already exist */

  if (IsDefinedRewriteRule(relid, newName))

    ereport(ERROR,

        (errcode(ERRCODE_DUPLICATE_OBJECT),

         errmsg("rule \"%s\" for relation \"%s\" already exists",

            newName, RelationGetRelationName(targetrel))));

  /*

   * We disallow renaming ON SELECT rules, because they should always be

   * named "_RETURN".

   */

  if (ruleform->ev_type == CMD_SELECT + '0')

    ereport(ERROR,

        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),

         errmsg("renaming an ON SELECT rule is not allowed")));

  /* OK, do the update */

  namestrcpy(&(ruleform->rulename), newName);

  CatalogTupleUpdate(pg_rewrite_desc, &ruletup->t_self, ruletup);

  InvokeObjectPostAlterHook(RewriteRelationId, ruleOid, 0);

  heap_freetuple(ruletup);

  table_close(pg_rewrite_desc, RowExclusiveLock);

  /*

   * Invalidate relation's relcache entry so that other backends (and this

   * one too!) are sent SI message to make them rebuild relcache entries.

   * (Ideally this should happen automatically...)

   */

  CacheInvalidateRelcache(targetrel);

  ObjectAddressSet(address, RewriteRelationId, ruleOid);

  /*

   * Close rel, but keep exclusive lock!

   */

  relation_close(targetrel, NoLock);

  return address;

}