Sort the dependent objects before deletion in DROP OWNED BY.

This finishes a task we left undone in commit f1ad067fc, by extending
the delete-in-descending-OID-order rule to deletions triggered by
DROP OWNED BY.  We've coped with machine-dependent deletion orders
one time too many, and the new issues caused by Peter G's recent
nbtree hacking seem like the last straw.

Discussion: https://postgr.es/m/E1h6eep-0001Mw-Vd@gemulon.postgresql.org

src/backend/catalog/dependency.c

@@ -2610,6 +2610,23 @@ record_object_address_dependencies(const ObjectAddress *depender,
 							   behavior);
 }
 
+/*
+ * Sort the items in an ObjectAddresses array.
+ *
+ * The major sort key is OID-descending, so that newer objects will be listed
+ * first in most cases.  This is primarily useful for ensuring stable outputs
+ * from regression tests; it's not recommended if the order of the objects is
+ * determined by user input, such as the order of targets in a DROP command.
+ */
+void
+sort_object_addresses(ObjectAddresses *addrs)
+{
+	if (addrs->numrefs > 1)
+		qsort((void *) addrs->refs, addrs->numrefs,
+			  sizeof(ObjectAddress),
+			  object_address_comparator);
+}
+
 /*
  * Clean up when done with an ObjectAddresses array.
  */

src/backend/catalog/pg_shdepend.c

@@ -1266,6 +1266,14 @@ shdepDropOwned(List *roleids, DropBehavior behavior)
 		systable_endscan(scan);
 	}
 
+	/*
+	 * For stability of deletion-report ordering, sort the objects into
+	 * approximate reverse creation order before deletion.  (This might also
+	 * make the deletion go a bit faster, since there's less chance of having
+	 * to rearrange the objects due to dependencies.)
+	 */
+	sort_object_addresses(deleteobjs);
+
 	/* the dependency mechanism does the actual work */
 	performMultipleDeletions(deleteobjs, behavior, 0);
 

src/include/catalog/dependency.h

@@ -170,6 +170,8 @@ extern void record_object_address_dependencies(const ObjectAddress *depender,
 								   ObjectAddresses *referenced,
 								   DependencyType behavior);
 
+extern void sort_object_addresses(ObjectAddresses *addrs);
+
 extern void free_object_addresses(ObjectAddresses *addrs);
 
 /* in pg_depend.c */