Sitemaps: Ensure entry for ‘page’ post type sitemap in index.

If there are no pages and no static homepage, there will still be one sitemap including the homepage URL.

This change ensures that this sitemap is correctly listed in the sitemap index.

Props Chouby, pacifika, elrae.
Fixes #50571.

git-svn-id: https://develop.svn.wordpress.org/trunk@48476 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php

@@ -174,7 +174,8 @@ class WP_Sitemaps_Posts extends WP_Sitemaps_Provider {
 
 		$query = new WP_Query( $args );
 
-		return isset( $query->max_num_pages ) ? $query->max_num_pages : 1;
+		$min_num_pages = ( 'page' === $post_type && 'posts' === get_option( 'show_on_front' ) ) ? 1 : 0;
+		return isset( $query->max_num_pages ) ? max( $min_num_pages, $query->max_num_pages ) : 1;
 	}
 
 	/**

tests/phpunit/tests/sitemaps/sitemaps-posts.php

@@ -4,6 +4,29 @@
  * @group sitemaps
  */
 class Test_WP_Sitemaps_Posts extends WP_UnitTestCase {
+	/**
+	 * Tests getting sitemap entries for post type page with 'posts' homepage.
+	 *
+	 * Ensures that an entry is added even if there are no pages.
+	 *
+	 * @ticket 50571
+	 */
+	public function test_get_sitemap_entries_homepage() {
+		update_option( 'show_on_front', 'posts' );
+
+		$posts_provider = new WP_Sitemaps_Posts();
+
+		$post_list = $posts_provider->get_sitemap_entries();
+
+		$expected = array(
+			array(
+				'loc' => home_url( '/?sitemap=posts&sitemap-subtype=page&paged=1' ),
+			),
+		);
+
+		$this->assertEquals( $expected, $post_list );
+	}
+
 	/**
 	 * Test ability to filter object subtypes.
 	 */