Fix lost persistence setting during REINDEX INDEX

ReindexIndex() trusts a parser-built RangeVar with the persistence to
use for the new copy of the index; but the parser naturally does not
know what's the persistence of the original index.  To find out the
correct persistence, grab it from relcache.

This bug was introduced by commit 85b506bb, and therefore no
backpatch is necessary.

Bug reported by Thom Brown, analysis and patch by Michael Paquier; test
case provided by Fabrízio de Royes Mello.

src/backend/commands/indexcmds.c

@@ -1685,14 +1685,28 @@ ReindexIndex(RangeVar *indexRelation)
 {
 	Oid			indOid;
 	Oid			heapOid = InvalidOid;
+	Relation	irel;
+	char		persistence;
 
-	/* lock level used here should match index lock reindex_index() */
+	/*
+	 * Find and lock index, and check permissions on table; use callback to
+	 * obtain lock on table first, to avoid deadlock hazard.  The lock level
+	 * used here must match the index lock obtained in reindex_index().
+	 */
 	indOid = RangeVarGetRelidExtended(indexRelation, AccessExclusiveLock,
 									  false, false,
 									  RangeVarCallbackForReindexIndex,
 									  (void *) &heapOid);
 
-	reindex_index(indOid, false, indexRelation->relpersistence);
+	/*
+	 * Obtain the current persistence of the existing index.  We already hold
+	 * lock on the index.
+	 */
+	irel = index_open(indOid, NoLock);
+	persistence = irel->rd_rel->relpersistence;
+	index_close(irel, NoLock);
+
+	reindex_index(indOid, false, persistence);
 
 	return indOid;
 }

src/test/regress/expected/create_table.out

@@ -208,6 +208,28 @@ CREATE TABLE IF NOT EXISTS test_tsvector(
 );
 NOTICE:  relation "test_tsvector" already exists, skipping
 CREATE UNLOGGED TABLE unlogged1 (a int primary key);			-- OK
+CREATE TEMPORARY TABLE unlogged2 (a int primary key);			-- OK
+SELECT relname, relkind, relpersistence FROM pg_class WHERE relname ~ '^unlogged\d' ORDER BY relname;
+    relname     | relkind | relpersistence 
+----------------+---------+----------------
+ unlogged1      | r       | u
+ unlogged1_pkey | i       | u
+ unlogged2      | r       | t
+ unlogged2_pkey | i       | t
+(4 rows)
+
+REINDEX INDEX unlogged1_pkey;
+REINDEX INDEX unlogged2_pkey;
+SELECT relname, relkind, relpersistence FROM pg_class WHERE relname ~ '^unlogged\d' ORDER BY relname;
+    relname     | relkind | relpersistence 
+----------------+---------+----------------
+ unlogged1      | r       | u
+ unlogged1_pkey | i       | u
+ unlogged2      | r       | t
+ unlogged2_pkey | i       | t
+(4 rows)
+
+DROP TABLE unlogged2;
 INSERT INTO unlogged1 VALUES (42);
 CREATE UNLOGGED TABLE public.unlogged2 (a int primary key);		-- also OK
 CREATE UNLOGGED TABLE pg_temp.unlogged3 (a int primary key);	-- not OK

src/test/regress/sql/create_table.sql

@@ -246,6 +246,12 @@ CREATE TABLE IF NOT EXISTS test_tsvector(
 );
 
 CREATE UNLOGGED TABLE unlogged1 (a int primary key);			-- OK
+CREATE TEMPORARY TABLE unlogged2 (a int primary key);			-- OK
+SELECT relname, relkind, relpersistence FROM pg_class WHERE relname ~ '^unlogged\d' ORDER BY relname;
+REINDEX INDEX unlogged1_pkey;
+REINDEX INDEX unlogged2_pkey;
+SELECT relname, relkind, relpersistence FROM pg_class WHERE relname ~ '^unlogged\d' ORDER BY relname;
+DROP TABLE unlogged2;
 INSERT INTO unlogged1 VALUES (42);
 CREATE UNLOGGED TABLE public.unlogged2 (a int primary key);		-- also OK
 CREATE UNLOGGED TABLE pg_temp.unlogged3 (a int primary key);	-- not OK