CollectionChangeSet.collection_was_cleared incorrect for dictionaries

[nirinchev]

In the .NET SDK we have a test calling Dictionary::remove_all and then verifying that the resulting notification has marked the collection as cleared (CollectionChangeSet.collection_was_cleared should be true). This works for lists and sets but not dictionaries.

[sync-by-unito]

➤ ironage commented:

[~[email protected]] is this blocking you?

We emulate dictionary clear by removing all elements one by one because we didn't add an explicit clear instruction for notifications https://github.com/realm/realm-core/blob/master/src/realm/dictionary.cpp#L721

[nirinchev]

Not blocking per se (we can always disable that assertion from the tests), just found it inconsistent and figured I'll file a ticket.

[ironage]

Fixing this inconsistency involves actually emitting the correct clear instruction to the replication system for both notifications and sync. This implies a change in behaviour for niche sync cases when resolving conflicting clear/add (instead of remove/add) but this could be considered a "fix" instead of a breaking change because that is the expected collection behaviour. However, because both the client and the server's OT semantics for clearing a dictionary are already in place, we should be able to just add this without bumping the sync protocol version.

[nicola-cab]

When the next-major branch is merged, this issue will go away.