[cloud_firestore] CACHE_SIZE_UNLIMITED support on iOS

[healy-devs]

Hi FlutterFire team,

I have a question to the current implementation of Cloud Firestore latest version.
Could you please confirm if CACHE_SIZE_UNLIMITED is still supported for iOS when persistenceEnabled is true?

I noticed that there was a crash fix and a change to CACHE_SIZE_UNLIMITED from v4.8.2.

As far as I understand based on the current implementation of iOS code on the master branch, if cacheSizeBytes is set to CACHE_SIZE_UNLIMITED (= -1), cache setting is set to the max. cache size because it seems there was an issue with kFIRFirestoreCacheSizeUnlimited.

The Firestore doc and the explanation from Firebase iOS SDK team say that the cache size should be set to CACHE_SIZE_UNLIMITED (= -1) in order to disable clean-up. However, as it is set to max. cache size in cloud_firestore, I assume that this clean-up will happen when the cache size reaches to the max. size.

Furthermore, the Android implementation still sets the cache size to CACHE_SIZE_UNLIMITED if the cache size is -1, which is different to the iOS implementation. Because of this, clean-up on Android would not take place.

The reason why I am asking for this confirmation is that because many my iOS app users are reporting data loss after I upgraded cloud_firestore package from v4.1.0 to v4.9.3. I assume that it is because of the cache clean-up and being in offline mode.

I look forward to your feedback.

Thank you and best regards,