Avoid using list_length() to test for empty list.

The standard way to check for list emptiness is to compare the
List pointer to NIL; our list code goes out of its way to ensure
that that is the only representation of an empty list.  (An
acceptable alternative is a plain boolean test for non-null
pointer, but explicit mention of NIL is usually preferable.)

Various places didn't get that memo and expressed the condition
with list_length(), which might not be so bad except that there
were such a variety of ways to check it exactly: equal to zero,
less than or equal to zero, less than one, yadda yadda.  In the
name of code readability, let's standardize all those spellings
as "list == NIL" or "list != NIL".  (There's probably some
microscopic efficiency gain too, though few of these look to be
at all performance-critical.)

A very small number of cases were left as-is because they seemed
more consistent with other adjacent list_length tests that way.

Peter Smith, with bikeshedding from a number of us

Discussion: https://postgr.es/m/CAHut+PtQYe+ENX5KrONMfugf0q6NHg4hR5dAhqEXEc2eefFeig@mail.gmail.com

1 files changed, 4 insertions, 4 deletions

diff --git a/src/backend/commands/event_trigger.c b/src/backend/commands/event_trigger.c
index eef3e5d56e5..9f8fee7c168 100644
--- a/src/backend/commands/event_trigger.c
+++ b/src/backend/commands/event_trigger.c
@@ -1143,9 +1143,9 @@ trackDroppedObjectsNeeded(void)
 	 * true if any sql_drop, table_rewrite, ddl_command_end event trigger
 	 * exists
 	 */
-	return list_length(EventCacheLookup(EVT_SQLDrop)) > 0 ||
-		list_length(EventCacheLookup(EVT_TableRewrite)) > 0 ||
-		list_length(EventCacheLookup(EVT_DDLCommandEnd)) > 0;
+	return (EventCacheLookup(EVT_SQLDrop) != NIL) ||
+		(EventCacheLookup(EVT_TableRewrite) != NIL) ||
+		(EventCacheLookup(EVT_DDLCommandEnd) != NIL);
 }
 
 /*
@@ -1616,7 +1616,7 @@ EventTriggerAlterTableEnd(void)
 	parent = currentEventTriggerState->currentCommand->parent;
 
 	/* If no subcommands, don't collect */
-	if (list_length(currentEventTriggerState->currentCommand->d.alterTable.subcmds) != 0)
+	if (currentEventTriggerState->currentCommand->d.alterTable.subcmds != NIL)
 	{
 		MemoryContext oldcxt;