History diff does not show retagging

[cellio]

https://meta.codidact.com/questions/279624

In the revision history, the diff for a revision that changed tags shows the resulting tags on both sides of the diff, instead of the difference. I haven't yet seen a proposed edit with these conditions, so don't know if it occurs there too. I'm pretty sure we had before-and-after tags properly showing before the latest updates, so this is probably a regression.

Example post where this happens: https://meta.codidact.com/questions/279268

Priority medium if it only affects histories, but high if it affects suggested edits too. Setting to high initially for visibility.

[cellio]

Another case: I approved one edit (which came through as two?) here, to add the status tag: https://meta.codidact.com/posts/279669/history. When reviewing the edit I saw the tag diff. The history does not show it.

[cellio]

And I saw the tag in the edit review, so lowering the priority as previously stated.

[cellio]

More cases: https://judaism.codidact.com/posts/280935/history https://judaism.codidact.com/posts/280934/history

This bug is making it difficult for communities to audit edits. The inability to see tag edits has already caused friction on another community. How hard is this to fix?

[cellio]

I'm not seeing any diff at all now for the questions I linked, for example:

That was almost certainly a tag-only edit.

[ArtOfCode-]

As with a lot of things, this isn't retroactive - we don't have the data for what those edits were, the database thinks the before and after tags are the same, so it doesn't show the unchanged state.

[cellio]

Oh, gotcha -- so shouldn't happen again, but history is what it is. Thanks.

[cellio]

New case (edit 2021-06-01): https://meta.codidact.com/posts/280367/history

Reported in a comment here: https://meta.codidact.com/posts/281137#answer-281137

[trichoplax]

Does the latest edit on this post suggest that this bug is fixed, or is it suspected to be occasional?

[cellio]

Looks like's showing the correct history now, so I'll close. If we see a new case we can look at it then.

[MoshiKoi]

Apparently this has happened again

https://meta.codidact.com/posts/288657

[Taeir]

Looks like a classic case of Object Oriented issues with multiple things pointing to the same array when they should have been pointing to different but initially equal arrays.