Replace deprecated who argument from user query

[grappler]

What problem does this address?

In WordPress 5.9 the who argument has been deprecated. Trac Ticket

Gutenberg is still using the who argument and recommending it to be used.

gutenberg/packages/editor/src/components/post-author/constants.js

Line 2 in 08cf4a9

who: 'authors',

gutenberg/packages/block-library/src/avatar/user-control.js

Line 11 in 23f11a1

who: 'authors',

gutenberg/packages/block-library/src/query/edit/inspector-controls/author-control.js

Line 15 in 08cf4a9

who: 'authors',

gutenberg/packages/block-library/src/post-author/edit.js

Line 43 in 760815a

authors: getUsers( { who: 'authors' } ),

gutenberg/packages/core-data/README.md

Line 26 in 711ea0e

return select( 'core' ).getUsers( { who: 'authors' } );

What is your proposed solution?

My suggestion would be to use the capability argument. The following code snippet fetches the edit_post capability for the current post type. This code is only compatible with WordPress 5.9. Either Gutenberg will need to increase the minimum supported version or include a check and a fallback with who: 'authors'.

const AUTHORS_QUERY = {
	per_page: 50,
	_fields: 'id,name',
	context: 'edit', // Allows non-admins to perform requests.
};
const currentPostType = wp.data.select('core/editor').getCurrentPostType();
const editPostCap = wp.data.select('core').getPostType( currentPostType ).capabilities.edit_post;
wp.data.select('core').getUsers( { ...AUTHORS_QUERY, capability: [ editPostCap ] } );

So that everyone does not have to figure out the edit_post capability, it might be best to create a helper function. Though in WordPress 5.9 the getAuthors function was deprecated #33725

Related Issues: #39035 & #17364

[ocean90]

Noting that the current request already generates a X-WP-DeprecatedParam header for this:

X-WP-DeprecatedParam: WP_User_Query (since 5.9.0; <code>who</code> is deprecated. Use <code>capability</code> instead.)

@TimothyBJacobs @spacedmonkey @youknowriad Do you have some ideas how we can detect whether who or capability should be used?

[TimothyBJacobs]

I'm not sure what the progress is on the client having knowledge of the REST API schemas, cc @youknowriad. But the best way would be to look at the schema for the endpoint and check for the presence of the capability property in the GET args.

[grappler]

The only reason that I can see why we would need to check for the support is to be able to run the Gutenberg plugin on WordPress 5.8. Depending on the time it takes for a patch, WordPress 6.0 will have been released.

It might make more sense to increase the minimum required WP version.

gutenberg/gutenberg.php

Line 6 in 956a836

* Requires at least: 5.8

[ocean90]

As of #41306 the plugin now requires 5.9 so I guess we can switch the query to use capability now.