Use hashed deviceName + system version as default user identifier on macOS about swiftclient

[winsmith]

I totally agree with your suggestion!

[Jeehut]

Alright, then expect a PR from me with my above outlined solution sometime soon.

[Jeehut]

@winsmith I just noticed this warning in my console for my macOS app:

[Telemetry] On this platform, Telemetry can't generate a unique user identifier. It is recommended you supply one yourself. More info: https://telemetrydeck.com/pages/signal-reference.html

From this code I derived that you're using identifierForVendor to retrieve a unique ID for the user on other platforms. From what I understand, this ID provided by Apple behaves very much like a self-generated UUID() on first app start that was persisted somewhere accessible by the app. The only 2 differences to a self-generated UUID are:

1. Apples UUID is the same for all apps of the same vendor on the same device.
2. The system takes care of persisting this UUID on behalf of the developer.

As such a thing is not available on macOS, I believe the closest thing to that would be a self-generated UUID based on nothing (no deviceName or system version needed). This UUID needs to be persisted and to not meddle with the developers data, I suggest using the UserDefaults with a custom suiteName such as TelemetryDeck for that. This way TelemetryDeck could take care of persisting the default identifier on behalf of the developer. Overriding it of course should still be possible and developer who followed the warning and have overridden it should not see any effect of this default ID change.

The last difference to identifierForVendor would then be that multiple apps of the same vendor on the same device would still have different unique identifiers. I suggest that this is covered by providing a hook the developer can opt-in to by passing the user defaults object of their app group if they really want this behavior. By default, this would be the only difference to identifierForVendor.

The solution you suggest in my opinion is not safe to be unique. Two users with the same system and build version, and with the same name (e.g. "Daniel") and device could easily end up having the same identifier which could lead to a lot of confusion when tracking funnels, for example. I think, a persisted UUID is a better default here.

As I need this right now, I would be up to implement it like outlined above if you agree with my suggestion.