Avoid trying to lock OLD/NEW in a rule with FOR UPDATE.

transformLockingClause neglected to exclude the pseudo-RTEs for
OLD/NEW when processing a rule's query.  This led to odd errors
or even crashes later on.  This bug is very ancient, but it's
not terribly surprising that nobody noticed, since the use-case
for SELECT FOR UPDATE in a non-view rule is somewhere between
thin and non-existent.  Still, crashing is not OK.

Per bug #17151 from Zhiyong Wu.  Thanks to Masahiko Sawada
for analysis of the problem.

Discussion: https://postgr.es/m/17151-c03a3e6e4ec9aadb@postgresql.org

src/backend/parser/analyze.c

@@ -2753,13 +2753,22 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 
 	if (lockedRels == NIL)
 	{
-		/* all regular tables used in query */
+		/*
+		 * Lock all regular tables used in query and its subqueries.  We
+		 * examine inFromCl to exclude auto-added RTEs, particularly NEW/OLD
+		 * in rules.  This is a bit of an abuse of a mostly-obsolete flag, but
+		 * it's convenient.  We can't rely on the namespace mechanism that has
+		 * largely replaced inFromCl, since for example we need to lock
+		 * base-relation RTEs even if they are masked by upper joins.
+		 */
 		i = 0;
 		foreach(rt, qry->rtable)
 		{
 			RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);
 
 			++i;
+			if (!rte->inFromCl)
+				continue;
 			switch (rte->rtekind)
 			{
 				case RTE_RELATION:
@@ -2789,7 +2798,11 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 	}
 	else
 	{
-		/* just the named tables */
+		/*
+		 * Lock just the named tables.  As above, we allow locking any base
+		 * relation regardless of alias-visibility rules, so we need to
+		 * examine inFromCl to exclude OLD/NEW.
+		 */
 		foreach(l, lockedRels)
 		{
 			RangeVar   *thisrel = (RangeVar *) lfirst(l);
@@ -2810,6 +2823,8 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 				RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);
 
 				++i;
+				if (!rte->inFromCl)
+					continue;
 				if (strcmp(rte->eref->aliasname, thisrel->relname) == 0)
 				{
 					switch (rte->rtekind)

src/include/nodes/parsenodes.h

@@ -915,10 +915,10 @@ typedef struct PartitionCmd
  *	  inFromCl marks those range variables that are listed in the FROM clause.
  *	  It's false for RTEs that are added to a query behind the scenes, such
  *	  as the NEW and OLD variables for a rule, or the subqueries of a UNION.
- *	  This flag is not used anymore during parsing, since the parser now uses
- *	  a separate "namespace" data structure to control visibility, but it is
- *	  needed by ruleutils.c to determine whether RTEs should be shown in
- *	  decompiled queries.
+ *	  This flag is not used during parsing (except in transformLockingClause,
+ *	  q.v.); the parser now uses a separate "namespace" data structure to
+ *	  control visibility.  But it is needed by ruleutils.c to determine
+ *	  whether RTEs should be shown in decompiled queries.
  *
  *	  requiredPerms and checkAsUser specify run-time access permissions
  *	  checks to be performed at query startup.  The user must have *all*

src/test/regress/expected/rules.out

@@ -2887,6 +2887,31 @@ select * from only t1_2;
 (10 rows)
 
 reset constraint_exclusion;
+-- test FOR UPDATE in rules
+create table rules_base(f1 int, f2 int);
+insert into rules_base values(1,2), (11,12);
+create rule r1 as on update to rules_base do instead
+  select * from rules_base where f1 = 1 for update;
+update rules_base set f2 = f2 + 1;
+ f1 | f2 
+----+----
+  1 |  2
+(1 row)
+
+create or replace rule r1 as on update to rules_base do instead
+  select * from rules_base where f1 = 11 for update of rules_base;
+update rules_base set f2 = f2 + 1;
+ f1 | f2 
+----+----
+ 11 | 12
+(1 row)
+
+create or replace rule r1 as on update to rules_base do instead
+  select * from rules_base where f1 = 11 for update of old; -- error
+ERROR:  relation "old" in FOR UPDATE clause not found in FROM clause
+LINE 2:   select * from rules_base where f1 = 11 for update of old;
+                                                               ^
+drop table rules_base;
 -- test various flavors of pg_get_viewdef()
 select pg_get_viewdef('shoe'::regclass) as unpretty;
                     unpretty                    

src/test/regress/sql/rules.sql

@@ -992,6 +992,20 @@ select * from only t1_2;
 
 reset constraint_exclusion;
 
+-- test FOR UPDATE in rules
+
+create table rules_base(f1 int, f2 int);
+insert into rules_base values(1,2), (11,12);
+create rule r1 as on update to rules_base do instead
+  select * from rules_base where f1 = 1 for update;
+update rules_base set f2 = f2 + 1;
+create or replace rule r1 as on update to rules_base do instead
+  select * from rules_base where f1 = 11 for update of rules_base;
+update rules_base set f2 = f2 + 1;
+create or replace rule r1 as on update to rules_base do instead
+  select * from rules_base where f1 = 11 for update of old; -- error
+drop table rules_base;
+
 -- test various flavors of pg_get_viewdef()
 
 select pg_get_viewdef('shoe'::regclass) as unpretty;