Fix StatisticsObjIsVisibleExt() for pg_temp.

Neighbor get_statistics_object_oid() ignores objects in pg_temp, as has
been the standard for non-relation, non-type namespace searches since
CVE-2007-2138.  Hence, most operations that name a statistics object
correctly decline to map an unqualified name to a statistics object in
pg_temp.  StatisticsObjIsVisibleExt() did not.  Consequently,
pg_statistics_obj_is_visible() wrongly returned true for such objects,
psql \dX wrongly listed them, and getObjectDescription()-based ereport()
and pg_describe_object() wrongly omitted namespace qualification.  Any
malfunction beyond that would depend on how a human or application acts
on those wrong indications.  Commit
d99d58cdc8 introduced this.  Back-patch to
v13 (all supported versions).

Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://postgr.es/m/20250920162116.2e.nmisch@google.com
Backpatch-through: 13

src/backend/catalog/namespace.c

@@ -2316,6 +2316,9 @@ StatisticsObjIsVisible(Oid relid)
 		{
 			Oid			namespaceId = lfirst_oid(l);
 
+			if (namespaceId == myTempNamespace)
+				continue;		/* do not look in temp namespace */
+
 			if (namespaceId == stxnamespace)
 			{
 				/* Found it first in path */

src/test/regress/expected/stats_ext.out

@@ -97,6 +97,20 @@ ALTER STATISTICS ab1_a_b_stats RENAME TO ab1_a_b_stats_new;
 ERROR:  must be owner of statistics object ab1_a_b_stats
 RESET SESSION AUTHORIZATION;
 DROP ROLE regress_stats_ext;
+CREATE STATISTICS pg_temp.stats_ext_temp ON a, b FROM ab1;
+SELECT regexp_replace(pg_describe_object(tableoid, oid, 0),
+                      'pg_temp_[0-9]*', 'pg_temp_REDACTED') AS descr,
+       pg_statistics_obj_is_visible(oid) AS visible
+  FROM pg_statistic_ext
+ WHERE stxname = 'stats_ext_temp';
+                       descr                       | visible 
+---------------------------------------------------+---------
+ statistics object pg_temp_REDACTED.stats_ext_temp | f
+(1 row)
+
+DROP STATISTICS stats_ext_temp;  -- shall fail
+ERROR:  statistics object "stats_ext_temp" does not exist
+DROP STATISTICS pg_temp.stats_ext_temp;
 CREATE STATISTICS IF NOT EXISTS ab1_a_b_stats ON a, b FROM ab1;
 NOTICE:  statistics object "ab1_a_b_stats" already exists, skipping
 DROP STATISTICS ab1_a_b_stats;

src/test/regress/sql/stats_ext.sql

@@ -68,6 +68,14 @@ DROP STATISTICS ab1_a_b_stats;
 ALTER STATISTICS ab1_a_b_stats RENAME TO ab1_a_b_stats_new;
 RESET SESSION AUTHORIZATION;
 DROP ROLE regress_stats_ext;
+CREATE STATISTICS pg_temp.stats_ext_temp ON a, b FROM ab1;
+SELECT regexp_replace(pg_describe_object(tableoid, oid, 0),
+                      'pg_temp_[0-9]*', 'pg_temp_REDACTED') AS descr,
+       pg_statistics_obj_is_visible(oid) AS visible
+  FROM pg_statistic_ext
+ WHERE stxname = 'stats_ext_temp';
+DROP STATISTICS stats_ext_temp;  -- shall fail
+DROP STATISTICS pg_temp.stats_ext_temp;
 
 CREATE STATISTICS IF NOT EXISTS ab1_a_b_stats ON a, b FROM ab1;
 DROP STATISTICS ab1_a_b_stats;