Improve preloading request code

[schlessera]

The attached patch removes the conditional branching based on the existence of the get_compact_response_links() method on the $server object, as that method was introduced with WordPress 4.5, and Gutenberg requires WordPress 4.9.8 or later.

Also, it turns the indirect and slow call through call_user_func() into a direct method call.

Note: The call would actually be more correct as a static call ($server::get_compact_response_links( $response)), but this notation is PHP 5.3+ only.

The patch is done against 5.0 branch.

Mirrors ​Gutenberg PR #11007 per request by @danielbachhuber.

[TimothyBlynJacobs]

If dropping the method exists check, I think it makes sense to drop it from WP_REST_Controller::prepare_response_for_collection() as well.

I wonder if this was included for BC because the server class is filterable, so theoretically someone could be using a server class without that method, though I think doing a completely custom class that doesn't extend WP_REST_Server is probably something that shouldn't/isn't supported anyways.

[danielbachhuber]

Replying to TimothyBlynJacobs:

If dropping the method exists check, I think it makes sense to drop it from WP_REST_Controller::prepare_response_for_collection() as well.

Yes, let's do.

I wonder if this was included for BC because the server class is filterable, so theoretically someone could be using a server class without that method, though I think doing a completely custom class that doesn't extend WP_REST_Server is probably something that shouldn't/isn't supported anyways.

There are a ton of WP_REST_Server methods in use so, if someone is filtering the server, they need to implement all methods that could be used. I'm not concerned about BC here.

[danielbachhuber]

In 43834:

REST API: Improve performance by avoiding call_user_func().

The get_compact_response_links() method was introduced in WP 4.5, and this conditional is no longer necessary.

Props schlessera, timothyblynjacobs.
Fixes #45189.

[danielbachhuber]

Reopening for merge to trunk.

[pento]

In 44173:

REST API: Improve performance by avoiding call_user_func().

The get_compact_response_links() method was introduced in WP 4.5, and this conditional is no longer necessary.

Merges [43834] from the 5.0 branch to trunk.

Props schlessera, timothyblynjacobs.
Fixes #45189.