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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/tablecmds.c
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@ -2097,7 +2097,7 @@ ExecuteTruncateGuts(List *explicit_rels,
* Assemble an array of relids so we can write a single WAL record for the
* whole action.
*/
if (list_length(relids_logged) > 0)
if (relids_logged != NIL)
{
xl_heap_truncate xlrec;
int i = 0;
@ -16264,11 +16264,11 @@ ATPrepChangePersistence(Relation rel, bool toLogged)
}
/*
* Check that the table is not part any publication when changing to
* UNLOGGED as UNLOGGED tables can't be published.
* Check that the table is not part of any publication when changing to
* UNLOGGED, as UNLOGGED tables can't be published.
*/
if (!toLogged &&
list_length(GetRelationPublications(RelationGetRelid(rel))) > 0)
GetRelationPublications(RelationGetRelid(rel)) != NIL)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("cannot change table \"%s\" to unlogged because it is part of a publication",