Function FinishSortSupportFunction

src/backend/utils/sort/sortsupport.c:94–125

* Look up and call sortsupport function to setup SortSupport comparator; * or if no such function exists or it declines to set up the appropriate * state, prepare a suitable shim. */

 * state, prepare a suitable shim.
 */
static void
FinishSortSupportFunction(Oid opfamily, Oid opcintype, SortSupport ssup)
{
	Oid			sortSupportFunction;

	/* Look for a sort support function */
	sortSupportFunction = get_opfamily_proc(opfamily, opcintype, opcintype,
											BTSORTSUPPORT_PROC);
	if (OidIsValid(sortSupportFunction))
	{
		/*
		 * The sort support function can provide a comparator, but it can also
		 * choose not to so (e.g. based on the selected collation).
		 */
		OidFunctionCall1(sortSupportFunction, PointerGetDatum(ssup));
	}

	if (ssup->comparator == NULL)
	{
		Oid			sortFunction;

		sortFunction = get_opfamily_proc(opfamily, opcintype, opcintype,
										 BTORDER_PROC);

		if (!OidIsValid(sortFunction))
			elog(ERROR, "missing support function %d(%u,%u) in opfamily %u",
				 BTORDER_PROC, opcintype, opcintype, opfamily);

		/* We'll use a shim to call the old-style btree comparator */
		PrepareSortSupportComparisonShim(sortFunction, ssup);
	}
}

/*
 * Fill in SortSupport given an ordering operator (btree "<" or ">" operator).