Preserve opclass parameters across REINDEX CONCURRENTLY

The opclass parameter Datums from the old index are fetched in the same
way as for predicates and expressions, by grabbing them directly from
the system catalogs.  They are then copied into the new IndexInfo that
will be used for the creation of the new copy.

This caused the new index to be rebuilt with default parameters rather
than the ones pre-defined by a user.  The only way to get back a new
index with correct opclass parameters would be to recreate a new index
from scratch.

The issue has been introduced by 911e7020.

Author: Michael Paquier
Reviewed-by: Zhihong Yu
Discussion: https://postgr.es/m/YX0CG/QpLXcPr8HJ@paquier.xyz
Backpatch-through: 13

src/backend/catalog/index.c

@@ -73,6 +73,7 @@
 #include "storage/procarray.h"
 #include "storage/smgr.h"
 #include "utils/builtins.h"
+#include "utils/datum.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
 #include "utils/inval.h"
@@ -1365,6 +1366,15 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId,
 		newInfo->ii_IndexAttrNumbers[i] = oldInfo->ii_IndexAttrNumbers[i];
 	}
 
+	/* Extract opclass parameters for each attribute, if any */
+	if (oldInfo->ii_OpclassOptions != NULL)
+	{
+		newInfo->ii_OpclassOptions = palloc0(sizeof(Datum) *
+											 newInfo->ii_NumIndexAttrs);
+		for (int i = 0; i < newInfo->ii_NumIndexAttrs; i++)
+			newInfo->ii_OpclassOptions[i] = get_attoptions(oldIndexId, i + 1);
+	}
+
 	/*
 	 * Now create the new index.
 	 *

src/test/regress/expected/create_index.out

@@ -2176,6 +2176,25 @@ SELECT indexrelid::regclass, indisreplident FROM pg_index
 (1 row)
 
 DROP TABLE concur_replident;
+-- Check that opclass parameters are preserved
+CREATE TABLE concur_appclass_tab(i tsvector, j tsvector, k tsvector);
+CREATE INDEX concur_appclass_ind on concur_appclass_tab
+  USING gist (i tsvector_ops (siglen='1000'), j tsvector_ops (siglen='500'));
+CREATE INDEX concur_appclass_ind_2 on concur_appclass_tab
+  USING gist (k tsvector_ops (siglen='300'), j tsvector_ops);
+REINDEX TABLE CONCURRENTLY concur_appclass_tab;
+\d concur_appclass_tab
+         Table "public.concur_appclass_tab"
+ Column |   Type   | Collation | Nullable | Default 
+--------+----------+-----------+----------+---------
+ i      | tsvector |           |          | 
+ j      | tsvector |           |          | 
+ k      | tsvector |           |          | 
+Indexes:
+    "concur_appclass_ind" gist (i tsvector_ops (siglen='1000'), j tsvector_ops (siglen='500'))
+    "concur_appclass_ind_2" gist (k tsvector_ops (siglen='300'), j)
+
+DROP TABLE concur_appclass_tab;
 -- Partitions
 -- Create some partitioned tables
 CREATE TABLE concur_reindex_part (c1 int, c2 int) PARTITION BY RANGE (c1);

src/test/regress/sql/create_index.sql

@@ -888,6 +888,15 @@ REINDEX TABLE CONCURRENTLY concur_replident;
 SELECT indexrelid::regclass, indisreplident FROM pg_index
   WHERE indrelid = 'concur_replident'::regclass;
 DROP TABLE concur_replident;
+-- Check that opclass parameters are preserved
+CREATE TABLE concur_appclass_tab(i tsvector, j tsvector, k tsvector);
+CREATE INDEX concur_appclass_ind on concur_appclass_tab
+  USING gist (i tsvector_ops (siglen='1000'), j tsvector_ops (siglen='500'));
+CREATE INDEX concur_appclass_ind_2 on concur_appclass_tab
+  USING gist (k tsvector_ops (siglen='300'), j tsvector_ops);
+REINDEX TABLE CONCURRENTLY concur_appclass_tab;
+\d concur_appclass_tab
+DROP TABLE concur_appclass_tab;
 
 -- Partitions
 -- Create some partitioned tables