FCM token constantly changes if retrieved before APNS token set

[kodebach]

I'm not sure, where this fits best, not really a bug report, but also not a feature request, so I'm just gonna post it here ...

When you access the FCM token before the SDK got the APNS device token (manually or via swizzling) you currently get this warning:

firebase-ios-sdk/FirebaseMessaging/Sources/FIRMessaging.m

Lines 529 to 534 in 5288794

	FIRMessagingLoggerWarn(kFIRMessagingMessageCodeAPNSTokenNotAvailableDuringTokenFetch,
	@"APNS device token not set before retrieving FCM Token for Sender ID "
	@"'%@'."
	@"Be sure to re-retrieve the FCM token once the APNS device token is "
	@"set.",
	senderID);

That seems rather benign. As long as you re-retrieve the token things should be fine. However, it doesn't say that actually you will get a different token every time. This caused a lot of churn in our backend. Every time somebody opened the app on iOS we accidentally loaded the FCM token before the APNS token was set, and then again afterwards. Both times created two completely unique FCM tokens, causing an update in the backend.

It might be best to add to the warning that the check for an unchanged APNS token on the FCM side will not work.