Return posts sorted by hierarchy

lib/compat/wordpress-6.8/class-gutenberg-rest-posts-controller-6-8.php

@@ -0,0 +1,108 @@
+<?php
+/**
+ * A custom REST server for Gutenberg.
+ *
+ * @package gutenberg
+ * @since   6.8.0
+ */
+
+add_filter( 'rest_page_collection_params', function ( $params ) {
+	$params['orderby_hierarchy'] = array(
+		'description' => 'Sort pages by hierarchy.',
+		'type'        => 'boolean',
+		'default'     => false,
+	);
+	return $params;
+} );
+
+add_filter( 'rest_page_query', function ( $args, $request ) {
+	if ( $request['orderby_hierarchy'] ) {
+		// Build the list of post ids to be displayed.
+		$new_args = array_merge( $args, array(
+			'fields'         => 'id=>parent',
+			'posts_per_page' => -1,
+		) );
+		$query    = new WP_Query( $new_args );
+		$posts    = $query->posts;
+		$post_ids = sort_ids_by_hierarchy( $posts, $args );
+
+		// Reconfigure the args to display only the ids in the list.
+		$args['paged'] = 1;
+		$args['post__in'] = $post_ids;
+	}
+	return $args;
+}, 10, 2 );
+
+/**
+ * Sort the post ids by hierarchy.
+ *
+ * @param array $posts The posts to sort.
+ * @param array $args  The arguments to sort the posts by.
+ * @return array The sorted post ids.
+ */
+function sort_ids_by_hierarchy( $posts, $args = array() ) {
+	/**
+	 * $posts is:
+	 * [
+	 *   ['ID' => 2, 'post_parent' => 0],
+	 *   ['ID' => 3, 'post_parent' => 2],
+	 *   ['ID' => 4, 'post_parent' => 2],
+	 * ]
+	 *
+	 * $args is:
+	 * [
+	 *   'posts_per_page' => 20,
+	 *   'paged' => 1,
+	 * ]
+	 */
+	if ( isset( $args['posts_per_page'] ) && $args['posts_per_page'] === 0 ) {
+		return array();
+	}
+
+	$per_page = isset( $args['posts_per_page'] ) && is_int( $args['posts_per_page'] ) ? $args['posts_per_page'] : -1;
+	$page     = isset( $args['paged'] ) && is_int( $args['paged'] ) ? $args['paged'] : 1;
+	$start    = 0;
+	$end      = count( $posts );
+	if ( $per_page > 0 ) {
+		$start    = ( $page - 1 ) * $per_page;
+		$end      = $start + $per_page;
+	}
+
+	/*
+	 * Arrange pages in two arrays:
+	 *
+	 * - $top_level: posts whose parent is 0
+	 * - $parent_children: post ID as the key and an array of children post IDs as the value.
+	 *   Example: parent_children[10][] contains all sub-pages whose parent is 10.
+	 *
+	 */
+
+	$top_level       = array();
+	$parent_children = array();
+	foreach ( $posts as $post ) {
+		if ( $post->post_parent === 0 ) {
+			$top_level[] = $post->ID;
+		} else {
+			$parent_children[ $post->post_parent ][] = $post->ID;
+		}
+	}
+
+	$ids = array();
+	$count = 0;
+	add_hierarchical_ids( $ids, $top_level, $count, $start, $end, $parent_children );
+
+	return $ids;
+}
+
+function add_hierarchical_ids( &$ids, $to_process, &$count, $start, $end, $parent_children ) {
+	foreach ( $to_process as $id ) {
+		if ( $count >= $start && $count < $end ) {
+			$ids[] = $id;
+		}
+		$count++;
+
+		if ( isset( $parent_children[ $id ] ) ) {
+			add_hierarchical_ids( $ids, $parent_children[ $id ], $count, $start, $end, $parent_children );
+		}
+	}
+}

lib/load.php

@@ -45,6 +45,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 	require __DIR__ . '/compat/wordpress-6.8/block-comments.php';
 	require __DIR__ . '/compat/wordpress-6.8/class-gutenberg-rest-comment-controller-6-8.php';
 	require __DIR__ . '/compat/wordpress-6.8/class-gutenberg-rest-post-types-controller-6-8.php';
+	require __DIR__ . '/compat/wordpress-6.8/class-gutenberg-rest-posts-controller-6-8.php';
 	require __DIR__ . '/compat/wordpress-6.8/rest-api.php';
 
 	// Plugin specific code.

packages/edit-site/src/components/post-list/index.js

@@ -290,6 +290,7 @@ export default function PostList( { postType } ) {
 			_embed: 'author',
 			order: view.sort?.direction,
 			orderby: view.sort?.field,
+			orderby_hierarchy: true,
 			search: view.search,
 			...filters,
 		};

phpunit/build-post-ids-to-display-test.php

@@ -0,0 +1,81 @@
+<?php
+
+/**
+ * Test the build_post_ids_to_display function.
+ *
+ * @package Gutenberg
+ */
+class SortIdsByHierarchyTest extends WP_UnitTestCase {
+
+	/*
+	 * Keep this updated as the input array changes.
+	 * The sorted hierarchy would be as follows:
+	 *
+	 * 2
+	 * - 3
+	 * -- 5
+	 * -- 6
+	 * - 4
+	 * -- 7
+	 * 8
+	 * - 9
+	 * -- 11
+	 * - 10
+	 *
+	 */
+	private $input = array(
+		array(
+			'ID' => 11,
+			'post_parent' => 9,
+		),
+		array(
+			'ID' => 2,
+			'post_parent' => 0,
+		),
+		array(
+			'ID' => 8,
+			'post_parent' => 0,
+		),
+		array(
+			'ID' => 3,
+			'post_parent' => 2,
+		),
+		array(
+			'ID' => 5,
+			'post_parent' => 3,
+		),
+		array(
+			'ID' => 7,
+			'post_parent' => 4,
+		),
+		array(
+			'ID' => 9,
+			'post_parent' => 8,
+		),
+		array(
+			'ID' => 4,
+			'post_parent' => 2,
+		),
+		array(
+			'ID' => 6,
+			'post_parent' => 3,
+		),
+		array(
+			'ID' => 10,
+			'post_parent' => 8,
+		),
+	);
+
+	public function test_return_all_post_ids() {
+		$output = sort_ids_by_hierarchy( $this->input );
+		$this->assertEquals( array( 2, 3, 5, 6, 4, 7, 8, 9, 11, 10 ), $output );
+	}
+
+	public function test_return_first_page() {
+		$output = sort_ids_by_hierarchy( $this->input, array(
+			'posts_per_page' => 3,
+			'paged'          => 1,
+		) );
+		$this->assertEquals( array( 2, 3, 5 ), $output );
+	}
+}