Ensure correct HTTP status when sitemaps are disabled

[swissspidy]

To reproduce:

Add add_filter( 'wp_sitemaps_enabled', '__return_false' ) in a plugin to disable sitemaps.

Expectation:

https://example.com/wp-sitemap.xml returns a 404 status and displays a 404 page.

Actual result:

https://example.com/wp-sitemap.xml returns a 200 status and displays the homepage.

This is because the rewrite rules are still there, but the sitemaps are actually disabled and wp_sitemaps_get_server() isn't initializing the sitemaps due to the filter

After flushing permalinks the result is as expected: a 404 status & page.

This inconsistent behavior should be fixed.

[kraftbj]

Tested this out and works as expected. Updating the patch with inline docs for the filter explaining the rewrites would still be present.

Return 404 on sitemap page without the need to flush permalinks. This PR is based on swissspidy's patch. I just added a unit test.

Trac ticket: https://core.trac.wordpress.org/ticket/50643

[donmhico]

The PR I attached - ​https://github.com/WordPress/wordpress-develop/pull/405 - includes Unit tests for @swissspidy's patch (thank you by the way).

[swissspidy]

Thanks all!

I extended the tests a little bit in the latest patch, and I think this is good to go now.

[swissspidy]

#50644 was marked as a duplicate.

[whyisjake]

In 48523:

Sitemaps: Ensure correct HTTP status when sitemaps are disabled

If sitemaps are disabled, previously there would be a rewrite rule for the sitemap endpoint. This endpoint would display the homepage since there was a rewrite rule. Now, Sitemaps are loaded, and the proper HTTP headers are returned.

Fixes #50643.
Props swissspidy, kraftbj, donmhico.

[swissspidy]

In 48540:

Sitemaps: Rename wp_get_sitemaps() to wp_get_sitemaps_providers()

Following [48536], rename the function to match the rest of the sitemaps logic.

Also eliminates some dead code after [48523].

Props pbiron.
See #50724. See #50643.