Periodically delete amp_validation_error terms which no longer appear on the site

[westonruter]

We need to add a cronjob to delete amp_validation_error terms that have zero URLs associated with them.

See #1413

[westonruter]

This is obsolete as of #1429 since there is now a Clear Empty ability.

[westonruter]

Actually, this isn't really obsolete. For trashed posts, they can be deleted with a button or they will be removed after a month via WP Cron. Something similar should be done for amp_validation_error taxonomy terms.

There is still a code comment that references this:

amp-wp/includes/validation/class-amp-validation-error-taxonomy.php

Line 1580 in 2984fc9

* list table. A cron job could periodically delete terms that have no counts.

[swissspidy]

Makes sense to implement 👍 It's annoying to manually clear empty results every so often.

[amedina]

Can this be achieved at the time the counter reaches 0? I mean, at the very moment when the 0 value is computed, the orphan error is removed.

[westonruter]

That's possible but I think we'd lose out on something important: keeping track of validation errors that contain attributes with variable attributes. For example, if there is a script that contains a random string, this will generate a different validation error every time the page is checked and as soon as it is re-checked then the previous errors would have 0 found URLs. Being able to see a list of many such validation errors is important for debugging as it indicates the need for an amp_validation_error to normalize the variable bits.