Polyfill: `ParseISODateTime(isoString, { zoneRequired: true })` doesn't actually require a zone. Expected?

[justingrant]

While investigating TS errors in temporal-polyfill, I noticed that proposal-temporal polyfill's implementation of ParseISODateTime adds a zoneRequired option. (It's not in the spec, this is just in the polyfill.) What is this option used for?

I'm asking because strings that have no time zone nor offset will still return a successful match from that function, albeit with the timezone and offset fields undefined. Is this expected? If yes, then what's the purpose of that option?

Repro:

zoneRequiredRegex = new RegExp('^((?:[+\\u2212-]\\d{6}|\\d{4}))(?:-((?:0[1-9]|1[0-2]))-((?:0[1-9]|[12]\\d|3[01]))|((?:0[1-9]|1[0-2]))((?:0[1-9]|[12]\\d|3[01])))(?:(?:T|\\s+)(\\d{2})(?::(\\d{2})(?::(\\d{2})(?:[.,](\\d{1,9}))?)?|(\\d{2})(?:(\\d{2})(?:[.,](\\d{1,9}))?)?)?)?(?:([zZ])|(?:([+\\u2212-])([01][0-9]|2[0-3])(?::?([0-5][0-9])(?::?([0-5][0-9])(?:[.,](\\d{1,9}))?)?)?)?)(?:\\[((?:(?:\\.[-A-Za-z_]|\\.\\.[-A-Za-z._]{1,12}|\\.[-A-Za-z_][-A-Za-z._]{0,12}|[A-Za-z_][-A-Za-z._]{0,13})(?:\\/(?:\\.[-A-Za-z_]|\\.\\.[-A-Za-z._]{1,12}|\\.[-A-Za-z_][-A-Za-z._]{0,12}|[A-Za-z_][-A-Za-z._]{0,13}))*|Etc\\/GMT[-+]\\d{1,2}|(?:[+\\u2212-][0-2][0-9](?::?[0-5][0-9](?::?[0-5][0-9](?:[.,]\\d{1,9})?)?)?)))\\])?(?:\\[u-ca=((?:[A-Za-z0-9]{3,8}(?:-[A-Za-z0-9]{3,8})*))\\])?$', 'i');
zoneRequiredRegex.test('2021-08-19T17:30');
// => true

[ptomato]

I think this is a bug. My guess is that zonesplit in lib/regex.mjs ought not to match an empty string, but it does.

[justingrant]

Turns out that only one caller of ParseISODateTime(isoString, { zoneRequired: true }) actually depends on zoneRequired working properly. All others seem to assume it won't work and check the returned components in order to know which errors to show. Furthermore, this option isn't in the spec. Therefore, I think the best solution is to remove this option completely and to do some refactoring of a few parsing methods to more closely align with the spec. PR coming.