REST API: Add missing options to the settings endpoint.

This adds the `show_on_front`, `page_on_front`, and `page_for_posts` options to the settings endpoint that were missed during WP 6.0 backports.

Related PR from Gutenberg repository:
* [https://github.com/WordPress/gutenberg/pull/38607 #38607 Page for Posts: Display notice in template panel]

Props Mamaduka, spacedmonkey, gziolo, jameskoster.
See #56058.

git-svn-id: https://develop.svn.wordpress.org/trunk@53588 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/option.php

@@ -2063,6 +2063,7 @@ function set_site_transient( $transient, $value, $expiration = 0 ) {
  * does not encompass all settings available in WordPress.
  *
  * @since 4.7.0
+ * @since 6.1.0 The `show_on_front`, `page_on_front`, and `page_for_posts` options were added.
  */
 function register_initial_settings() {
 	register_setting(
@@ -2220,6 +2221,36 @@ function register_initial_settings() {
 		)
 	);
 
+	register_setting(
+		'reading',
+		'show_on_front',
+		array(
+			'show_in_rest' => true,
+			'type'         => 'string',
+			'description'  => __( 'What to show on the front page' ),
+		)
+	);
+
+	register_setting(
+		'reading',
+		'page_on_front',
+		array(
+			'show_in_rest' => true,
+			'type'         => 'number',
+			'description'  => __( 'The ID of the page that should be displayed on the front page' ),
+		)
+	);
+
+	register_setting(
+		'reading',
+		'page_for_posts',
+		array(
+			'show_in_rest' => true,
+			'type'         => 'number',
+			'description'  => __( 'The ID of the page that should display the latest posts' ),
+		)
+	);
+
 	register_setting(
 		'discussion',
 		'default_ping_status',

tests/phpunit/tests/rest-api/rest-settings-controller.php

@@ -106,6 +106,9 @@ class WP_Test_REST_Settings_Controller extends WP_Test_REST_Controller_Testcase
 			'default_category',
 			'default_post_format',
 			'posts_per_page',
+			'show_on_front',
+			'page_on_front',
+			'page_for_posts',
 			'default_ping_status',
 			'default_comment_status',
 			'site_icon', // Registered in wp-includes/blocks/site-logo.php

tests/qunit/fixtures/wp-api-generated.js

@@ -9628,6 +9628,21 @@ mockedApiResponse.Schema = {
                             "type": "integer",
                             "required": false
                         },
+                        "show_on_front": {
+                            "description": "What to show on the front page",
+                            "type": "string",
+                            "required": false
+                        },
+                        "page_on_front": {
+                            "description": "The ID of the page that should be displayed on the front page",
+                            "type": "number",
+                            "required": false
+                        },
+                        "page_for_posts": {
+                            "description": "The ID of the page that should display the latest posts",
+                            "type": "number",
+                            "required": false
+                        },
                         "default_ping_status": {
                             "description": "Allow link notifications from other blogs (pingbacks and trackbacks) on new articles.",
                             "type": "string",
@@ -12283,6 +12298,9 @@ mockedApiResponse.settings = {
     "default_category": 1,
     "default_post_format": "0",
     "posts_per_page": 10,
+    "show_on_front": "posts",
+    "page_on_front": 0,
+    "page_for_posts": 0,
     "default_ping_status": "open",
     "default_comment_status": "open",
     "site_logo": null,