Revisions needs to gracefully handle AJAX failures.

[markjaquith]

Currently we just leave the spinner going.

Simple error message.

Related, #24757. Me: "Perhaps if the request times out, errors out, or takes more than X seconds, we need to cut in half the number of revisions we just tried to request."

24758.2.diff​ implements Nacin's suggestion. on .fail(), it cuts the number in half. I tested this by setting the AJAX callback to fail if the number of requested comparisons was greater than 5. It cut down from 40 to 20, then 20 to 10, then 10 to 5, which worked, so it did the rest of them by 5. Nice.

24758.3.diff​ makes sane the promise attempt.

To test this, I simply produced a fatal error in wp_ajax_get_revision_diffs. On a post with 200 revisions the number goes down: 20, 10, 5, 3, 2, 1. Works so far. But I didn't get the error message and it still hammers the server with a request. Shouldn't we stop after X failed request?

Yeah, it should stop after 1.

Stops after 1

24758.5.diff​ stops after one, and properly displays the error message. Tested with a fatal error in wp_ajax_get_revision_diffs().

New error message.

The error message is not displayed on first load. But requests stop.

Replying to ocean90:

The error message is not displayed on first load. But requests stop.

the first diff is now preloaded in php so you will never see an error on first load. i set up a random error in wp_ajax_get_revision_diffs() and tested, with 24758.6.diff​ i do see the error message briefly, until the ajax re-fires and loads correctly. i also observed the number of diffs bundled per request reducing to 1 and then giving up on further requests.

looks good!

Smaller spinner. Tweaked error message.

Good to go here on .10.diff.

In 24732:

Revisions: Better error handling.

• Shows an error message if the current diff can't be loaded.
• For bulk pre-loading, catches errors, and cuts subsequent requests in half, until eventually giving up.
• Some CSS fixes related to this, and the loading spinner.
• wp.revisions.loadAll() now returns a promise representing whether or not all revisions could be loaded.

Fixes #24758.