Improve synchronization (don't lose tasks)

[ltguillaume]

Situation

1. Create a new tasks on my mobile phone, without syncing yet (e.g. there is no connection or the sync interval is long)
2. Get home and do some stuff in SP on your computer and sync
3. Open the mobile app and sync
4. Get a conflict dialog: you'll have to choose between losing the tasks from step 1 (Keep remote), or those from step 3 (Keep local).

Possible solution

Edit: For ready-made conflict-free sync implementations, see #4857.
Apart from the ideal situation of implementing a journaling approach, where every operation is recorded, allowing for granular syncing, implementing the following should be an improvement:

1. Check the remote's modified attribute against each local task's: newer remote tasks overwrite local; older remote tasks are synced to the remote; same timestamp is no action.
2. Start saving IDs of removed task with a modification attribute: if the modification attribute in the removed tasks list is newer, the task is also removed on the syncing device, otherwise the task is "restored".
3. Tasks only on remote or only on local are obviously synced

This would already be significantly more granular and would prevent a lot of cases where actual data loss or/by conflict dialogs would otherwise occur.

[johannesjo]

Thank you! I am all for improving this, once the dust with the current sync problems has been settled :)

[youssefadly237]

@johannesjo

thanks for this great app

I find this issue super annoying tbh, why 2 diffrent tasks cause a merge conflict

[blefuscu]

Link this to the relevant FR/issue about all this: #4857