Autosave: Conditionally allow revisions to be saved

[jblz]

As is, when the DOING_AUTOSAVE constant is truthy, calling wp_save_post_revision immediately exits.

One of the first things that endpoints responsible for autosaves are doing is set this constant -- making it impossible to save a revision using the Revisions API during the same request context.

See:

• ​Gutenberg
• ​Jetpack

Endpoints (& other plugins) would benefit from a filter allowing revisions to be saved.

A particular use case is to occasionally save revisions for drafts during an autosave call (so there is less chance of irrecoverable data loss when the autosave is overwritten).

[jblz]

Replying to jblz:

...calling wp_save_post_revision immediately exits.

Should say ...immediately returns instead. (ref)

[adamsilverstein]

Hey @jblz - I think the filter is fine here. A unit test that validated the filter would be nice.

Note that the use case you describe "to occasionally save revisions for drafts during an autosave call" is similar to what we have discussed a little and started working on in https://core.trac.wordpress.org/ticket/43316?cversion=0&cnum_hist=65#comment:32 - it would be great to have something like this built into the core autosave endpoint.

[jblz]

Inverts the semantics of the filter (block vs. allow), pass $autosave as the default value, pass $post_id, include unit test

[jblz]

Thanks for taking a look, @adamsilverstein & for pointing me at #43316.

it would be great to have something like this built into the core autosave endpoint.

+1. It looks like WP_REST_Autosaves_Controller::create_item is in sync w/ Gutenberg -- I'll follow up w/ a PR there so we can see the usage in action a bit.

The latest patch introduces a new test to cover the filter.

---

@jorbin Thanks for ​the suggestions.

I inverted the filter, chose a different filter name that is more in line with the rest of the surrounding code, & included the $post_id in the filter application.

[jblz]

Gutenberg autosaves usage patch in progress here: ​https://github.com/WordPress/gutenberg/pull/9043

[jblz]

Change filter name -- "prevent" instead of "block" to reduce confusion

[azaozz]

@jblz as @adamsilverstein mentions above we've discussed this in core before and came up with a bit more "expanded" implementation, see #43760. It checks the changes/differences between the previously saved post data and the autosave, and creates a post revision. That check is of course filterable, and seems to do pretty much the same as the patch on this ticket.

Can you have a look at https://core.trac.wordpress.org/attachment/ticket/43760/43760.patch and see if it fits the needs for this ticket too? If yes, perhaps we can close this in favour of #43760.