Size limit not correctly applied for sitemaps index

[swissspidy]

Sitemaps have a few ​size restrictions:

• each Sitemap file that you provide must have no more than 50,000 URLs
• Sitemap index files may not list more than 50,000 Sitemaps

The latter is seemingly enforced in \WP_Sitemaps_Registry::get_sitemaps(), but actually this method only limits the number of sitemap providers, not the amount of sitemaps all providers add to the index in total.

Thus, this logic needs to be moved to \WP_Sitemaps_Index::get_sitemap_list()

[pbiron]

50666.diff​ works as expected, and all tests pass (existing and the new one).

However, I'd suggest one change to WP_Sitemaps_Index::get_sitemap_list(): for efficiency, break out of the loop as soon as count( $sitemaps ) >= $this->max_sitemaps, no need to have all providers generate entries if the max has already been reached.

I'd also structure the new test a little differently.

Updated patch coming shortly.

[pbiron]

50666.2.diff​ is the same as 50666.diff​ except for:

1. WP_Sitemaps_Index::get_sitemap_list(): break out of the loop as soon as count( $sitemaps ) >= $this->max_sitemaps
2. the new unit test is more explict about what it is testing
   • as part of that, the constructor for the new WP_Sitemaps_Large_Test_Provider class takes a parameter for how many entries the test provider should generate
   • this new parameter may also be useful in future uses of this test provider

[swissspidy]

In 48532:

Sitemaps: Correctly enforce maximum number of sitemaps in index.

Before this change, the limit of 50k entries was enforced for the number of providers, not the amount of sitemaps all providers add to the index in total.

Props pbiron, swissspidy.
Fixes #50666.