Return original autosave after saving with unchanged data

[adamsilverstein]

This is a follow up to https://core.trac.wordpress.org/ticket/49532. In https://core.trac.wordpress.org/changeset/55154 the autosave endpoint was adjusted so that if the autosave was a duplicate (no data had changed) an error was returned. This fixed an issue where the autosave would be deleted and recreated each time the (unchanged) data was saved.

Unfortunately, this caused at least two regressions as noted in https://core.trac.wordpress.org/ticket/49532#comment:33 and ​https://github.com/WordPress/gutenberg/issues/51088.

After reviewing this more carefully, a better approach would be to return the original autosave instead of an error - that way, endpoint consumers will get the data back in the shape the expect and the autosave will work as expected.

Patch incoming

Trac ticket: https://core.trac.wordpress.org/ticket/58739

[Mamaduka]

Thank you, Adam!

I re-tested the patch, and it works as expected.

There's no longer a 400 error when previewing an already published post, and thumbnail changes are reflected in the previews.

[adamsilverstein]

In 56163:

Revisions: return existing autosave after saving with unchanged data.

Correctly return the existing autosave when an unchanged autosave is saved, instead of returning an error.

Fix regressions after r55154 where an error and not the original autosave was returned when saving with unchanged data (for example, clicking the preview button repeatedly). Returning the autosave (ID) is the expected behavior for the endpoint.

Follow up to [55154]

Props Mamaduka, jeroenrotty, mrfoxtalbot.
Fixes #58739.

[spacedmonkey]

@adamsilverstein This is a change in behaviour for the REST API. As this is a change, it needs to be either called out in the field guide or have a dev note.

[adamsilverstein]

Thinking more appropriate for field guide since it is a relatively small change/note and more than likely fixes a bug for developers rather than needing them to make some change in their code. Before 6.2 the endpoint always returned an autosave and this restores that behavior, so probably what developers already expect from the endpoint.