Inconsistency in absolute position index across clients after an undo operation about yjs HOT 1 CLOSED

Yes, this is the expected behavior. I'll try to explain what is happening internally so you can understand it better. Below is a fix to get consistent behavior.

In Yjs we can't undo deletions (as in undeleting the internal item representation). Instead, we re-insert content. The advantage is that we can perform very aggressive garbage-collection. This means that after performing undo/redo, relative positions are not always placed at the position where they intuitively should be. This is a tradeoff - but I think it's worth it.

Intuitively, the relative position should be at index 2 after performing undo. We can't ensure that.

When you insert ab|cde, and point the relative position to the character c, the relative position will still point to the deleted character c, even though it is not visible anymore. After undoing the deletion, a new character c will be inserted: abc|cde (note that the second character c is basically invisible now).

The correct relative position in your scenario (at least technically) is position 3.

Now, to the weird part. We can restore the intuitively correct position if we have access to the UndoManager that performed the undo operation. The client that performed undo knows more about the document state. It knows that the second c character is "redone" by the first c insertion. So it "follows" the "redo-path" and figures out that position 2 is more accurate. However, the "redo-path" is not persisted in the Yjs document and will eventually be lost.

Since relative positions are mainly used to restore the cursor state after a client performs an undo, this is the default behavior. In your case, I recommend not following the redo path to achieve consistent behavior.

TLDR:
Add false to createAbsolutePositionFromRelativePosition(rpos, doc, false) to get consistent behavior across all clients. This disables "following the redo-path". This feature is available in the latest Yjs release.

Feel free to ping me to chat more about a commenting solution based on relative positions.

from yjs.