Avoid using DefElemAction in AlterPublicationStmt

Create a new enum type for it.  This allows to add new values for future
functionality without disrupting unrelated uses of DefElem.

Discussion: https://postgr.es/m/202112302021.ca7ihogysgh3@alvherre.pgsql

src/backend/commands/publicationcmds.c

@@ -503,12 +503,12 @@ AlterPublicationTables(AlterPublicationStmt *stmt, HeapTuple tup,
 	 * possible that user has not specified any tables in which case we need
 	 * to remove all the existing tables.
 	 */
-	if (!tables && stmt->action != DEFELEM_SET)
+	if (!tables && stmt->action != AP_SetObjects)
 		return;
 
 	rels = OpenTableList(tables);
 
-	if (stmt->action == DEFELEM_ADD)
+	if (stmt->action == AP_AddObjects)
 	{
 		List	   *schemas = NIL;
 
@@ -521,9 +521,9 @@ AlterPublicationTables(AlterPublicationStmt *stmt, HeapTuple tup,
 											  PUBLICATIONOBJ_TABLE);
 		PublicationAddTables(pubid, rels, false, stmt);
 	}
-	else if (stmt->action == DEFELEM_DROP)
+	else if (stmt->action == AP_DropObjects)
 		PublicationDropTables(pubid, rels, false);
-	else						/* DEFELEM_SET */
+	else						/* AP_SetObjects */
 	{
 		List	   *oldrelids = GetPublicationRelations(pubid,
 														PUBLICATION_PART_ROOT);
@@ -598,7 +598,7 @@ AlterPublicationSchemas(AlterPublicationStmt *stmt,
 	 * possible that user has not specified any schemas in which case we need
 	 * to remove all the existing schemas.
 	 */
-	if (!schemaidlist && stmt->action != DEFELEM_SET)
+	if (!schemaidlist && stmt->action != AP_SetObjects)
 		return;
 
 	/*
@@ -606,7 +606,7 @@ AlterPublicationSchemas(AlterPublicationStmt *stmt,
 	 * concurrent schema deletion.
 	 */
 	LockSchemaList(schemaidlist);
-	if (stmt->action == DEFELEM_ADD)
+	if (stmt->action == AP_AddObjects)
 	{
 		List	   *rels;
 		List	   *reloids;
@@ -620,9 +620,9 @@ AlterPublicationSchemas(AlterPublicationStmt *stmt,
 		CloseTableList(rels);
 		PublicationAddSchemas(pubform->oid, schemaidlist, false, stmt);
 	}
-	else if (stmt->action == DEFELEM_DROP)
+	else if (stmt->action == AP_DropObjects)
 		PublicationDropSchemas(pubform->oid, schemaidlist, false);
-	else						/* DEFELEM_SET */
+	else						/* AP_SetObjects */
 	{
 		List	   *oldschemaids = GetPublicationSchemas(pubform->oid);
 		List	   *delschemas = NIL;
@@ -657,7 +657,7 @@ CheckAlterPublication(AlterPublicationStmt *stmt, HeapTuple tup,
 {
 	Form_pg_publication pubform = (Form_pg_publication) GETSTRUCT(tup);
 
-	if ((stmt->action == DEFELEM_ADD || stmt->action == DEFELEM_SET) &&
+	if ((stmt->action == AP_AddObjects || stmt->action == AP_SetObjects) &&
 		schemaidlist && !superuser())
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),

src/backend/parser/gram.y

@@ -9828,7 +9828,7 @@ AlterPublicationStmt:
 					n->pubname = $3;
 					n->pubobjects = $5;
 					preprocess_pubobj_list(n->pubobjects, yyscanner);
-					n->action = DEFELEM_ADD;
+					n->action = AP_AddObjects;
 					$$ = (Node *)n;
 				}
 			| ALTER PUBLICATION name SET pub_obj_list
@@ -9837,7 +9837,7 @@ AlterPublicationStmt:
 					n->pubname = $3;
 					n->pubobjects = $5;
 					preprocess_pubobj_list(n->pubobjects, yyscanner);
-					n->action = DEFELEM_SET;
+					n->action = AP_SetObjects;
 					$$ = (Node *)n;
 				}
 			| ALTER PUBLICATION name DROP pub_obj_list
@@ -9846,7 +9846,7 @@ AlterPublicationStmt:
 					n->pubname = $3;
 					n->pubobjects = $5;
 					preprocess_pubobj_list(n->pubobjects, yyscanner);
-					n->action = DEFELEM_DROP;
+					n->action = AP_DropObjects;
 					$$ = (Node *)n;
 				}
 		;

src/include/nodes/parsenodes.h

@@ -3674,6 +3674,13 @@ typedef struct CreatePublicationStmt
 	bool		for_all_tables; /* Special publication for all tables in db */
 } CreatePublicationStmt;
 
+typedef enum AlterPublicationAction
+{
+	AP_AddObjects,				/* add objects to publication */
+	AP_DropObjects,				/* remove objects from publication */
+	AP_SetObjects				/* set list of objects */
+} AlterPublicationAction;
+
 typedef struct AlterPublicationStmt
 {
 	NodeTag		type;
@@ -3688,8 +3695,8 @@ typedef struct AlterPublicationStmt
 	 */
 	List	   *pubobjects;		/* Optional list of publication objects */
 	bool		for_all_tables; /* Special publication for all tables in db */
-	DefElemAction action;		/* What action to perform with the
-								 * tables/schemas */
+	AlterPublicationAction action;	/* What action to perform with the given
+									 * objects */
 } AlterPublicationStmt;
 
 typedef struct CreateSubscriptionStmt