From 5ca0fe5c8ad7987beee95669124c7e245f2816d8 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Tue, 12 Jul 2022 16:11:04 +0200
Subject: [PATCH] Add copy/equal support for XID lists

Commit f10a025cfe97 added support for List to store Xids, but didn't
handle the new type in all cases.  Add some obviously necessary pieces.
As far as I am aware, this is all dead code as far as core code is
concerned, but it seems unacceptable not to have it in case third-party
code wants to rely on this type of list.  (Some parts of the List API
remain unimplemented, but that can be fixed as and when needed -- see
lack of list_intersection_oid, list_deduplicate_int as precedents.)

Discussion: https://postgr.es/m/20220708164534.nbejhgt4ajz35p65@alvherre.pgsql
---
 src/backend/nodes/copyfuncs.c                    | 5 +++--
 src/backend/nodes/equalfuncs.c                   | 8 ++++++++
 src/test/modules/test_oat_hooks/test_oat_hooks.c | 3 +++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index b8e40a4195..e76fda8eba 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -187,11 +187,12 @@ copyObjectImpl(const void *from)
 			break;
 
 			/*
-			 * Lists of integers and OIDs don't need to be deep-copied, so we
-			 * perform a shallow copy via list_copy()
+			 * Lists of integers, OIDs and XIDs don't need to be deep-copied,
+			 * so we perform a shallow copy via list_copy()
 			 */
 		case T_IntList:
 		case T_OidList:
+		case T_XidList:
 			retval = list_copy(from);
 			break;
 
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 8d54e1a486..0373aa30fe 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -188,6 +188,13 @@ _equalList(const List *a, const List *b)
 					return false;
 			}
 			break;
+		case T_XidList:
+			forboth(item_a, a, item_b, b)
+			{
+				if (lfirst_xid(item_a) != lfirst_xid(item_b))
+					return false;
+			}
+			break;
 		default:
 			elog(ERROR, "unrecognized list node type: %d",
 				 (int) a->type);
@@ -238,6 +245,7 @@ equal(const void *a, const void *b)
 		case T_List:
 		case T_IntList:
 		case T_OidList:
+		case T_XidList:
 			retval = _equalList(a, b);
 			break;
 
diff --git a/src/test/modules/test_oat_hooks/test_oat_hooks.c b/src/test/modules/test_oat_hooks/test_oat_hooks.c
index 0ad77e743d..1f40d632e0 100644
--- a/src/test/modules/test_oat_hooks/test_oat_hooks.c
+++ b/src/test/modules/test_oat_hooks/test_oat_hooks.c
@@ -1122,6 +1122,9 @@ nodetag_to_string(NodeTag tag)
 		case T_OidList:
 			return "OidList";
 			break;
+		case T_XidList:
+			return "XidList";
+			break;
 		case T_ExtensibleNode:
 			return "ExtensibleNode";
 			break;