Limit users query in search_authors

[leogermani]

When we call search_authors, CAP is also taking the opportunity to update the user terms.

In order to do that, it queries for all users in the database:

https://github.com/Automattic/Co-Authors-Plus/blob/e727fe75d432dda5e4ffea6799df85ff21a00531/co-authors-plus.php#L1296

When a site has too many users, this can be a problem, especially because this can be called with an empty search and would try to load all users of the site at once.

Previous work

I saw that you tried to fix this issue 4 years ago, but it got reverted.

This fix

This is an attempt to have a quick fix for this, without trying to replicate all the logic in the PR merged 4 years ago.

I saw that in that attempt, they were filtering out users who did not have the capability to edit posts. See:

https://github.com/Automattic/Co-Authors-Plus/pull/544/files#diff-a3596cc30542e2cf428e6b5c295e6d757efda1539e9b3d2b8aaea5e818e3753dR45

Also, in our current code, we never return users who don't have this capability:

https://github.com/Automattic/Co-Authors-Plus/blob/e727fe75d432dda5e4ffea6799df85ff21a00531/co-authors-plus.php#L1351

So what I propose in this PR is just to run this filter earlier, and only fix terms for users who have this capability.

Can someone have a look at it?

Known issue: This will filter out users who have rights to edit other post types, but not posts. But this is already a limitation of the plugin. If we had a post_type in that context we could check for the right cap.

Question: In the comments I see that this is addressing something for people who were running CAP < 2.7. If that's only for this purpose and is not required for newer versions, do you think it has been there for long enough and this could be removed altogether?

[lkraav]

I can confirm, on our userbase of 50k, co-authors-plus request are timing out on post editor screens exactly as described.