Links are not recursive across data bundles

[sosnik]

Version: 0.5.32

Issue description:

moment-timezone doesn't seem to recursively resolve links that point to other links outside of the bundle.

To illustrate, this is with vanilla moment.tz:

// US/Central is a link to America/Chicago
> moment.tz.zone('US/Central')
{
  name: 'US/Central',
  abbrs: [...],
  offsets: [...],
  untils: [...],
  population: ...
}
> moment().tz('US/Central').format('hh:mm Z z')
'03:05 -06:00 CST'
// Add a 'link to a link' within the current dataset
> moment.tz.link('US/Central|CT')
undefined
> moment.tz.zone('CT')
{
  name: 'CT',
  ...
}
> moment().tz('CT').format('hh:mm Z z')
'03:29 -06:00 CST'
// as expected

If, instead of using moment.tz.link() to create the link in the current dataset, I load a similar link (US/Pacific/PT) as part of a larger dataset using moment.tz.load(), the PT link will no longer resolve.

Below is an extract of my packed data that I am loading:

packedBundle = {
	version: '2020-abbr',
	zones: [...],
	links: [
		'US/Central|CT',
		'US/Pacific|PT',
		'Asia/Kabul|AFT'
		...
	]
}

Now it gets interesting:

> moment.tz.load(packedBundle)
undefined
// Asia/Kabul is a canonical location within the tz database (and moment's default dataset). Linking across bundles works here as expected.
> moment.tz.zone('AFT')
{
  name: 'AFT',
  abbrs: [ '+04', '+0430' ],
  untils: [ -788932800000, Infinity ],
  offsets: [ -240, -270 ],
  population: 4600000
}
// CT was linked using moment.tz.link() previously, so it works here:
> moment.tz.zone('CT')
{
  name: 'CT',
  abbrs: [...  ],
  untils: [...  ],
  offsets: [...  ],
  population: 9200000
}
// PT was linked to US/Pacific in the newly-loaded bundle as per the extract above. US/Pacific is a link to America/Los_Angeles within the tz database and the default dataset.
> moment.tz.zone('PT')
null
// Interestingly enough, US/Pacific no longer returns a zone object:
> moment.tz.zone('US/Pacific')
null

As you can see, links are not resolved recursively across datasets, Moreover, defining a link in a loaded dataset breaks link resolution in the original.

Initial Investigation

At first I thought that defining links in a new data bundle overrides all links from the vanilla data bundle. This is not the case:

> moment.tz.zone('America/Argentina/Catamarca')
{
  name: 'America/Argentina/Catamarca',
  ...
}
> moment.tz.zone('America/Catamarca')
{
  name: 'America/Catamarca',
}
// America/Catamarka links to America/Argentina/Catamarca within the vanilla dataset, as I didn't link to America/Catamarca within the dataset I was loading manually, the link still works

[gilmoreorless]

My guess is that this has the same root cause as https://github.com/moment/moment-timezone/issues/301#issuecomment-466765295

[sosnik]

Seems possible. In my particular usecase, I could work around this issue by:

1. Splitting out zones[] and links[] from the bundle and feeding them to moment with .add() and link() separately;
2. Overwriting the default data bundle (but reconciliation after updates will be annoying, not to mention portability);
3. Mapping links to destinations on my end before passing the "proper" input to moment for parsing.

Having said that, here's hoping for an official fix at the library level.

[sosnik]

Update: I attempted to load my set of links with the m.tz.link() method instead of the load() method. Link resolution is still broken:

> const moment = require('moment-timezone')
> const packedBundle = require('./tz.abbr.packed.json')
> moment.tz.add(packedBundle.zones) // adding just the zones
> moment.tz.zone('Atlantic Standard Time')
// This returns a zone object
> moment.tz.link(packedBundle.links)
> moment.tz.zone('CT')
// Returns null
> moment.tz.zone('US/Central')
// also returns null. Link resolution is indeed broken.

I am not (yet) sure why creating links in bulk causes an issue while doing it "manually" doesn't, but I am beginning to suspect that @gilmoreorless is right and this is similar to his issue.

[sosnik]

Iterating over links[] and adding them one at a time with m.tz.link() instead of chucking the whole array at it produces the same result: link resolution is still broken.

This leads me to question, at what point are things falling apart? Adding a single link (as seen in my original issue) does work.

[ichernev]

Close in favor of https://github.com/moment/moment-timezone/issues/301