Use Rosetta header menu items instead of global

[iandunn]

The new header works on Rosetta sites, but it needs to have the local menu items (nav_menu_item posts).

Currently Rosetta sites use a homegrown API endpoint, e.g. https://de.wordpress.org/?fetch-custom-header=%2Fplugins%2F.

the Menu is generated on the "main localised site" and that menu (and therefor, all menu items) are then output on the sub-site. There's memcache involved in all that of course. The menu on Rosetta can't be built on a not-main/root-site as Nav Menu's (as used on Rosetta, rather than hard-coded links) can't be generated with a simple switch_to_site() correctly.
#38

If we want to take a different approach, then one workaround might be to have a cron job to generate the markup, and cache it in an option on each site. Then the global menu could switch_to_blog and retrieve it.

That may not even be necessary, though, since the Rosetta sites don't need to use the current homegrown REST API endpoint. It looks like they can just include the new block directly and it works fine. So, they could pull the menu items directly, without the need for a switch_to_blog, endpoint, etc.

[iandunn]

The menu on Rosetta can't be built on a not-main/root-site as Nav Menu's (as used on Rosetta, rather than hard-coded links) can't be generated with a simple switch_to_site() correctly.

@dd32 , switch_to_blog() seems to work works fine on /team, /support, /plugins, etc in my experiments. Do you remember what specifically didn't work?

function render_global_header() {
	remove_inner_group_container();

	if ( isset( $GLOBALS['rosetta'] ) ) {
		switch_to_blog( 82 ); // nl.w.org root site

		$rendered = wp_nav_menu( array(
			'menu' => get_nav_menu_locations()['rosetta_main'],
			'echo' => false,
			'theme_location' => 'rosetta_main'
		) );
		var_dump($rendered);

		restore_current_blog();
		wp_die();

wp_get_nav_menu_items( get_nav_menu_locations()['rosetta_main'] ) also works. I'm guessing we'll want to use that, and have the new header loop through them and generate block markup, rather that using the Classic markup that wp_nav_menu generates. That way it'll be consistent w/ the global menu items that non-rosetta sites use.

[iandunn]

FYI, i network-activated the Gutenberg plugin on Rosetta sites to support this.

cc @ocean90, @SergeyBiryukov, @dd32

[iandunn]

9a7ed8d and 51399a8 are the core of the solution, but I'm still planning to add some caching, fix a few edge cases, etc.

Some of this relies on changes to rosetta-sites.php, but I don't want to deploy those on a Friday afternoon, so I'll do it next week.

[iandunn]

I think this is all done now, except for things that have separate issues opened.