Function GUCArrayAdd

src/backend/utils/misc/guc.c:11666–11738

* Add an entry to an option array. The array parameter may be NULL * to indicate the current table entry is NULL. */

 * to indicate the current table entry is NULL.
 */
ArrayType *
GUCArrayAdd(ArrayType *array, const char *name, const char *value)
{
	struct config_generic *record;
	Datum		datum;
	char	   *newval;
	ArrayType  *a;

	Assert(name);
	Assert(value);

	/* test if the option is valid and we're allowed to set it */
	(void) validate_option_array_item(name, value, false);

	/* normalize name (converts obsolete GUC names to modern spellings) */
	record = find_option(name, false, true, WARNING);
	if (record)
		name = record->name;

	/* build new item for array */
	newval = psprintf("%s=%s", name, value);
	datum = CStringGetTextDatum(newval);

	if (array)
	{
		int			index;
		bool		isnull;
		int			i;

		Assert(ARR_ELEMTYPE(array) == TEXTOID);
		Assert(ARR_NDIM(array) == 1);
		Assert(ARR_LBOUND(array)[0] == 1);

		index = ARR_DIMS(array)[0] + 1; /* add after end */

		for (i = 1; i <= ARR_DIMS(array)[0]; i++)
		{
			Datum		d;
			char	   *current;

			d = array_ref(array, 1, &i,
						  -1 /* varlenarray */ ,
						  -1 /* TEXT's typlen */ ,
						  false /* TEXT's typbyval */ ,
						  TYPALIGN_INT /* TEXT's typalign */ ,
						  &isnull);
			if (isnull)
				continue;
			current = TextDatumGetCString(d);

			/* check for match up through and including '=' */
			if (strncmp(current, newval, strlen(name) + 1) == 0)
			{
				index = i;
				break;
			}
		}