Eliminate duplicate code in table.c.

Additionally improve the error message similar to how it was done in
2ed532ee8c.

Author: Junwang Zhao, Aleksander Alekseev
Reviewed-by: Amit Kapila, Alvaro Herrera, Kyotaro Horiguchi
Discussion: https://postgr.es/m/CAEG8a3KbVtBm_BYf5tGsKHvmMieQVsq_jBPOg75VViQB7ACL8Q%40mail.gmail.com

src/backend/access/table/table.c

@@ -25,6 +25,7 @@
 #include "access/table.h"
 #include "storage/lmgr.h"
 
+static inline void validate_relation_kind(Relation r);
 
 /* ----------------
  *		table_open - open a table relation by relation OID
@@ -42,17 +43,7 @@ table_open(Oid relationId, LOCKMODE lockmode)
 
 	r = relation_open(relationId, lockmode);
 
-	if (r->rd_rel->relkind == RELKIND_INDEX ||
-		r->rd_rel->relkind == RELKIND_PARTITIONED_INDEX)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is an index",
-						RelationGetRelationName(r))));
-	else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is a composite type",
-						RelationGetRelationName(r))));
+	validate_relation_kind(r);
 
 	return r;
 }
@@ -76,17 +67,7 @@ try_table_open(Oid relationId, LOCKMODE lockmode)
 	if (!r)
 		return NULL;
 
-	if (r->rd_rel->relkind == RELKIND_INDEX ||
-		r->rd_rel->relkind == RELKIND_PARTITIONED_INDEX)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is an index",
-						RelationGetRelationName(r))));
-	else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is a composite type",
-						RelationGetRelationName(r))));
+	validate_relation_kind(r);
 
 	return r;
 }
@@ -105,17 +86,7 @@ table_openrv(const RangeVar *relation, LOCKMODE lockmode)
 
 	r = relation_openrv(relation, lockmode);
 
-	if (r->rd_rel->relkind == RELKIND_INDEX ||
-		r->rd_rel->relkind == RELKIND_PARTITIONED_INDEX)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is an index",
-						RelationGetRelationName(r))));
-	else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is a composite type",
-						RelationGetRelationName(r))));
+	validate_relation_kind(r);
 
 	return r;
 }
@@ -137,19 +108,7 @@ table_openrv_extended(const RangeVar *relation, LOCKMODE lockmode,
 	r = relation_openrv_extended(relation, lockmode, missing_ok);
 
 	if (r)
-	{
-		if (r->rd_rel->relkind == RELKIND_INDEX ||
-			r->rd_rel->relkind == RELKIND_PARTITIONED_INDEX)
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("\"%s\" is an index",
-							RelationGetRelationName(r))));
-		else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("\"%s\" is a composite type",
-							RelationGetRelationName(r))));
-	}
+		validate_relation_kind(r);
 
 	return r;
 }
@@ -168,3 +127,22 @@ table_close(Relation relation, LOCKMODE lockmode)
 {
 	relation_close(relation, lockmode);
 }
+
+/* ----------------
+ *		validate_relation_kind - check the relation's kind
+ *
+ *		Make sure relkind is not index or composite type
+ * ----------------
+ */
+static inline void
+validate_relation_kind(Relation r)
+{
+	if (r->rd_rel->relkind == RELKIND_INDEX ||
+		r->rd_rel->relkind == RELKIND_PARTITIONED_INDEX ||
+		r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("cannot open relation \"%s\"",
+						RelationGetRelationName(r)),
+				 errdetail_relkind_not_supported(r->rd_rel->relkind)));
+}

src/test/regress/expected/tid.out

@@ -61,7 +61,8 @@ DROP SEQUENCE tid_seq;
 -- Index, fails with incorrect relation type
 CREATE INDEX tid_ind ON tid_tab(a);
 SELECT currtid2('tid_ind'::text, '(0,1)'::tid); -- fails
-ERROR:  "tid_ind" is an index
+ERROR:  cannot open relation "tid_ind"
+DETAIL:  This operation is not supported for indexes.
 DROP INDEX tid_ind;
 -- Partitioned table, no storage
 CREATE TABLE tid_part (a int) PARTITION BY RANGE (a);