Sync empty taxonomies to distributed posts.

[peterwilsoncc]

Description of the Change

This modifies prepare_taxonomy_terms() to include both populated and unpopulated taxonomies when distributing sites.

This allows for the situation in which an original post is updated to remove all terms within a shared taxonomy.

To account for empty arrays being stripped from $_POST data (I've not been able to determine where this happens), update notifications are now sent as JSON encoded data to the remote sites REST API. This may be a backward compatibility issue for sites using hooks and getting POSTed data rather than using the $request object.

Taxonomy updates are limited to those shown in the REST API.

Closes #625

How to test the Change

1. Check out the develop branch.
2. Create a post and assign it two or more tags.
3. Distribute the post
4. Observe distributed version of post has two tags
5. Delete one tag on original post, update it.
6. Observe distributed version of post has one tag.
7. Delete all tags on original post, update it.
8. Observe distributed version of post has one tag (error).
9. Check out this branch and repeat
10. After deleting tags on the original post, the distributed version should have no tags.

Notes

1. E2E tests are failing for trunk due to a bug in @wordpress/env -- it was fixed five days ago but is still to be released WordPress/gutenberg@3983fee
2. I've had to change some of the tests to work around an issue in wp_mocks. I've created an issue and linked to that within the comments.

Changelog Entry

Fixed - Distribute empty taxonomies to external sites.

Credits

Props @peterwilsoncc, @manolobevia, @jeffpaul, @cadic

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[peterwilsoncc]

The tests here are failing because the following returns null rather than an empty array. I've tried figuring out why but need some help from someone else.

\WP_Mock::userFunction(
	'\Distributor\Utils\prepare_taxonomy_terms', [
		'return' => [],
	]
);

I did a var_dump on the following line within test_send_notifications_remote_post_exists()

/vagrant/content/plugins/distributor/tests/php/SubscriptionsTest.php:514:NULL

[cadic]

The code looks good.

BTW, I was not able to replicate the original issue (at develop branch: after second-the-last tag was deleted in the original post, the distributed post has no tags as well on the step 8).

[peterwilsoncc]

@cadic Do you recall if you were testing on an internal (multisite) connection or an external connection?

[cadic]

@peterwilsoncc oh, thanks for clarifying that, it does reproduce with the external connection.

[peterwilsoncc]

Thanks Max, sorry I missed that step in the reproduction notes.