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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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4
src/backend/commands/functioncmds.c
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@ -419,7 +419,7 @@ interpret_function_parameter_list(ParseState *pstate,
* Make sure no variables are referred to (this is probably dead
* code now that add_missing_from is history).
*/
if (list_length(pstate->p_rtable) != 0 ||
if (pstate->p_rtable != NIL ||
contain_var_clause(def))
ereport(ERROR,
(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
@ -1209,7 +1209,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
returnsSet = false;
}
if (list_length(trftypes_list) > 0)
if (trftypes_list != NIL)
{
ListCell *lc;
Datum *arr;