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Avoid using list_length() to test for empty list.

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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
This commit is contained in:
Tom Lane
2022-08-17 11:12:35 -04:00
parent 4a319fce76
commit efd0c16bec
28 changed files with 47 additions and 48 deletions
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8
src/backend/commands/event_trigger.c
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@ -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;