src/vs/base/common/glob.ts/hasSiblingFn
export function hasSiblingFn(siblingsFn?: () => string[]) {
	if (!siblingsFn) {
		return undefined;
	}

	let siblings: Record<string, true>;
	return (name: string) => {
		if (!siblings) {
			const list = siblingsFn();
			siblings = list ? listToMap(list) : {};
		}
		return !!siblings[name];
	};
}