…heet history

Some spreadsheet can end up in a corrupted history state

Original Data ⮕ no revision (XX) ⮕ Snapshot ⮕ Active Revisions and where the original data differ from the snapshot.

XX: can occur after the script added https://github.com/odoo/upgrade/issues/6340. The migration script is supposed to rewrite the history of the spreadsheet when there are holes in the archived revisions continuity (eg. the history was original Data ⮕ rev **A** ⮕ rev **B** ⮕ rev **C** ⮕ snapshot ⮕ rev **D** and user deleted rev **B** for instance, the script deletes **A** and **C** and marks **D** as the very first revision).

Version history was designed with the idea to replay every single revision that existed since the creation of the spreadsheet and apply it to the original data, and in case of missing revisions, in our example, B is missing, we detect the lack of continuity, we start from the snapshot, and replay every single revision since that snapshot.

When the migration fixes the continuity, by deleting all the old revisions, and changing their order, we can no longer detect the lack of continuity and end up replay every available revision to the original data ,even though they are based on the snapshot.

In that scenario, since the revisions will be applied on the original data but since they are based on the state of the snapshot only, the final state of the spreadsheet will be corrupted since a part of the . If a user then decides to restore the spreadsheet to the version they see in the version history (which is corrupted as mentioned) and the last snapshot is overwritten with the corrupted state, effectively breaking the spreadsheet.

With this revision, we add a detection of this corrupted history state, in which case we enforce the history to be replayed from the snapshot and not the original data.

Task-6533708