Copy navigation area infrastructure from Gutenberg

src/wp-admin/includes/post.php

@@ -2447,3 +2447,63 @@ function the_block_editor_meta_box_post_form_hidden_fields( $post ) {
 	 */
 	do_action( 'block_editor_meta_box_hidden_fields', $post );
 }
+
+/**
+ * Disable block editor for wp_navigation type posts so they can be managed via the UI.
+ *
+ * @since 5.9.0
+ * @access private
+ *
+ * @param bool   $value Whether the CPT supports block editor or not.
+ * @param string $post_type Post type.
+ *
+ * @return bool
+ */
+function _disable_block_editor_for_navigation_post_type( $value, $post_type ) {
+	if ( 'wp_navigation' === $post_type ) {
+		return false;
+	}
+
+	return $value;
+}
+
+/**
+ * This callback disables the content editor for wp_navigation type posts.
+ * Content editor cannot handle wp_navigation type posts correctly.
+ * We cannot disable the "editor" feature in the wp_navigation's CPT definition
+ * because it disables the ability to save navigation blocks via REST API.
+ *
+ * @since 5.9.0
+ * @access private
+ *
+ * @param WP_Post $post An instance of WP_Post class.
+ */
+function _disable_content_editor_for_navigation_post_type( $post ) {
+	$post_type = get_post_type( $post );
+	if ( 'wp_navigation' !== $post_type ) {
+		return;
+	}
+
+	remove_post_type_support( $post_type, 'editor' );
+}
+
+/**
+ * This callback enables content editor for wp_navigation type posts.
+ * We need to enable it back because we disable it to hide
+ * the content editor for wp_navigation type posts.
+ *
+ * @since 5.9.0
+ * @access private
+ *
+ * @see _disable_content_editor_for_navigation_post_type
+ *
+ * @param WP_Post $post An instance of WP_Post class.
+ */
+function _enable_content_editor_for_navigation_post_type( $post ) {
+	$post_type = get_post_type( $post );
+	if ( 'wp_navigation' !== $post_type ) {
+		return;
+	}
+
+	add_post_type_support( $post_type, 'editor' );
+}

src/wp-admin/site-editor.php

@@ -59,7 +59,17 @@ static function( $classes ) {
 	'/wp/v2/global-styles/' . $active_global_styles_id . '?context=edit',
 	'/wp/v2/global-styles/' . $active_global_styles_id,
 	'/wp/v2/themes/' . $active_theme . '/global-styles',
+	'/__experimental/block-navigation-areas?context=edit',
 );
+
+$areas        = get_option( 'fse_navigation_areas', array() );
+$active_areas = array_intersect_key( $areas, get_navigation_areas() );
+foreach ( $active_areas as $post_id ) {
+	if ( $post_id ) {
+		$preload_paths[] = "/wp/v2/navigation/$post_id?context=edit";
+	}
+}
+
 block_editor_rest_api_preload( $preload_paths, $block_editor_context );
 
 $editor_settings = get_block_editor_settings(

src/wp-includes/default-filters.php

@@ -583,6 +583,10 @@
 add_action( 'admin_footer-post-new.php', 'wp_add_iframed_editor_assets_html' );
 add_action( 'admin_footer-widgets.php', 'wp_add_iframed_editor_assets_html' );
 
+add_action( 'use_block_editor_for_post_type', '_disable_block_editor_for_navigation_post_type' );
+add_action( 'edit_form_after_title', '_disable_content_editor_for_navigation_post_type' );
+add_action( 'edit_form_after_editor', '_enable_content_editor_for_navigation_post_type' );
+
 // Taxonomy.
 add_action( 'init', 'create_initial_taxonomies', 0 ); // Highest priority.
 add_action( 'change_locale', 'create_initial_taxonomies' );
@@ -671,5 +675,6 @@
 
 // Navigation areas.
 add_action( 'setup_theme', '_register_default_navigation_areas' );
+add_action( 'switch_theme', '_migrate_menu_to_navigation_post', 200, 3 );
 
 unset( $filter, $action );

src/wp-includes/navigation-areas.php

@@ -50,3 +50,202 @@ function get_navigation_areas() {
 	global $navigation_areas;
 	return $navigation_areas;
 }
+
+/**
+ * Migrates classic menus to a block-based navigation post on theme switch.
+ * Assigns the created navigation post to the corresponding navigation area.
+ *
+ * @since 5.9.0
+ * @access private
+ *
+ * @param string   $new_name  Name of the new theme.
+ * @param WP_Theme $new_theme New theme.
+ * @param WP_Theme $old_theme Old theme.
+ */
+function _migrate_menu_to_navigation_post( $new_name, $new_theme, $old_theme ) {
+	// Do nothing when switching to a theme that does not support site editor.
+	if ( ! wp_is_block_template_theme() ) {
+		return;
+	}
+
+	// get_nav_menu_locations() calls get_theme_mod() which depends on the stylesheet option.
+	// At the same time, switch_theme runs only after the stylesheet option was updated to $new_theme.
+	// To retrieve theme mods of the old theme, the getter is hooked to get_option( 'stylesheet' ) so that we
+	// get the old theme, which causes the get_nav_menu_locations to get the locations of the old theme.
+	$get_old_theme_stylesheet = static function() use ( $old_theme ) {
+		return $old_theme->get_stylesheet();
+	};
+	add_filter( 'option_stylesheet', $get_old_theme_stylesheet );
+
+	$locations    = get_nav_menu_locations();
+	$area_mapping = get_option( 'fse_navigation_areas', array() );
+
+	foreach ( $locations as $location_name => $menu_id ) {
+		// Get the menu from the location, skipping if there is no
+		// menu or there was an error.
+		$menu = wp_get_nav_menu_object( $menu_id );
+		if ( ! $menu || is_wp_error( $menu ) ) {
+			continue;
+		}
+
+		$menu_items = _get_menu_items_at_location( $location_name );
+		if ( empty( $menu_items ) ) {
+			continue;
+		}
+
+		$post_name   = 'classic_menu_' . $menu_id;
+		$post_status = 'publish';
+
+		// Get or create to avoid creating too many wp_navigation posts.
+		$query          = new WP_Query;
+		$matching_posts = $query->query(
+			array(
+				'name'           => $post_name,
+				'post_status'    => $post_status,
+				'post_type'      => 'wp_navigation',
+				'posts_per_page' => 1,
+			)
+		);
+
+		if ( count( $matching_posts ) ) {
+			$navigation_post_id = $matching_posts[0]->ID;
+		} else {
+			$menu_items_by_parent_id = _sort_menu_items_by_parent_id( $menu_items );
+			$parsed_blocks           = _parse_blocks_from_menu_items( $menu_items_by_parent_id[0], $menu_items_by_parent_id );
+			$post_data               = array(
+				'post_type'    => 'wp_navigation',
+				'post_title'   => sprintf(
+					/* translators: %s: the name of the menu, e.g. "Main Menu". */
+					__( 'Classic menu: %s' ),
+					$menu->name
+				),
+				'post_name'    => $post_name,
+				'post_content' => serialize_blocks( $parsed_blocks ),
+				'post_status'  => $post_status,
+			);
+			$navigation_post_id      = wp_insert_post( $post_data );
+		}
+
+		$area_mapping[ $location_name ] = $navigation_post_id;
+	}
+	remove_filter( 'option_stylesheet', $get_old_theme_stylesheet );
+
+	update_option( 'fse_navigation_areas', $area_mapping );
+}
+
+/**
+ * Returns the menu items for a WordPress menu location.
+ *
+ * @since 5.9.0
+ * @access private
+ *
+ * @param string $location The menu location.
+ * @return array Menu items for the location.
+ */
+function _menu_items_at_location( $location ) {
+	if ( empty( $location ) ) {
+		return;
+	}
+
+	// Build menu data. The following approximates the code in `wp_nav_menu()`.
+
+	// Find the location in the list of locations, returning early if the
+	// location can't be found.
+	$locations = get_nav_menu_locations();
+	if ( ! isset( $locations[ $location ] ) ) {
+		return;
+	}
+
+	// Get the menu from the location, returning early if there is no
+	// menu or there was an error.
+	$menu = wp_get_nav_menu_object( $locations[ $location ] );
+	if ( ! $menu || is_wp_error( $menu ) ) {
+		return;
+	}
+
+	$menu_items = wp_get_nav_menu_items( $menu->term_id, array( 'update_post_term_cache' => false ) );
+	_wp_menu_item_classes_by_context( $menu_items );
+
+	return $menu_items;
+}
+
+/**
+ * Sorts a standard array of menu items into a nested structure keyed by the
+ * id of the parent menu.
+ *
+ * @since 5.9.0
+ * @access private
+ *
+ * @param array $menu_items Menu items to sort.
+ * @return array An array keyed by the id of the parent menu where each element
+ *               is an array of menu items that belong to that parent.
+ */
+function _sort_menu_items_by_parent_id( $menu_items ) {
+	$sorted_menu_items = array();
+	foreach ( (array) $menu_items as $menu_item ) {
+		$sorted_menu_items[ $menu_item->menu_order ] = $menu_item;
+	}
+	unset( $menu_items, $menu_item );
+
+	$menu_items_by_parent_id = array();
+	foreach ( $sorted_menu_items as $menu_item ) {
+		$menu_items_by_parent_id[ $menu_item->menu_item_parent ][] = $menu_item;
+	}
+
+	return $menu_items_by_parent_id;
+}
+
+/**
+ * Turns menu item data into a nested array of parsed blocks
+ *
+ * @since 5.9.0
+ * @access private
+ *
+ * @param array $menu_items               An array of menu items that represent
+ *                                        an individual level of a menu.
+ * @param array $menu_items_by_parent_id  An array keyed by the id of the
+ *                                        parent menu where each element is an
+ *                                        array of menu items that belong to
+ *                                        that parent.
+ * @return array An array of parsed block data.
+ */
+function _parse_blocks_from_menu_items( $menu_items, $menu_items_by_parent_id ) {
+	if ( empty( $menu_items ) ) {
+		return array();
+	}
+
+	$blocks = array();
+
+	foreach ( $menu_items as $menu_item ) {
+		$class_name       = ! empty( $menu_item->classes ) ? implode( ' ', (array) $menu_item->classes ) : null;
+		$id               = ( null !== $menu_item->object_id && 'custom' !== $menu_item->object ) ? $menu_item->object_id : null;
+		$opens_in_new_tab = null !== $menu_item->target && '_blank' === $menu_item->target;
+		$rel              = ( null !== $menu_item->xfn && '' !== $menu_item->xfn ) ? $menu_item->xfn : null;
+		$kind             = null !== $menu_item->type ? str_replace( '_', '-', $menu_item->type ) : 'custom';
+
+		$block = array(
+			'blockName' => isset( $menu_items_by_parent_id[ $menu_item->ID ] ) ? 'core/navigation-submenu' : 'core/navigation-link',
+			'attrs'     => array(
+				'className'     => $class_name,
+				'description'   => $menu_item->description,
+				'id'            => $id,
+				'kind'          => $kind,
+				'label'         => $menu_item->title,
+				'opensInNewTab' => $opens_in_new_tab,
+				'rel'           => $rel,
+				'title'         => $menu_item->attr_title,
+				'type'          => $menu_item->object,
+				'url'           => $menu_item->url,
+			),
+		);
+
+		$block['innerBlocks']  = isset( $menu_items_by_parent_id[ $menu_item->ID ] )
+			? _parse_blocks_from_menu_items( $menu_items_by_parent_id[ $menu_item->ID ], $menu_items_by_parent_id )
+			: array();
+		$block['innerContent'] = array_map( 'serialize_block', $block['innerBlocks'] );
+
+		$blocks[] = $block;
+	}
+
+	return $blocks;
+}

src/wp-includes/post.php

@@ -494,15 +494,15 @@ function create_initial_post_types() {
 				'archives'              => __( 'Navigation Menu archives' ),
 				'insert_into_item'      => __( 'Insert into Navigation Menu' ),
 				'uploaded_to_this_item' => __( 'Uploaded to this Navigation Menu' ),
-				// Some of these are a bit weird, what are they for?
 				'filter_items_list'     => __( 'Filter Navigation Menu list' ),
 				'items_list_navigation' => __( 'Navigation Menus list navigation' ),
 				'items_list'            => __( 'Navigation Menus list' ),
 			),
+			'description'           => __( 'Navigation menus that can be inserted into your site.' ),
 			'public'                => false,
 			'_builtin'              => true, /* internal use only. don't use this when registering your own post type. */
 			'has_archive'           => false,
-			'show_ui'               => false,
+			'show_ui'               => wp_is_block_template_theme(),
 			'show_in_menu'          => 'themes.php',
 			'show_in_admin_bar'     => false,
 			'show_in_rest'          => true,
@@ -2077,7 +2077,7 @@ function _add_post_type_submenus() {
 		if ( ! $ptype_obj->show_in_menu || true === $ptype_obj->show_in_menu ) {
 			continue;
 		}
-		add_submenu_page( $ptype_obj->show_in_menu, $ptype_obj->labels->name, $ptype_obj->labels->all_items, $ptype_obj->cap->edit_posts, "edit.php?post_type=$ptype" );
+		add_submenu_page( $ptype_obj->show_in_menu, $ptype_obj->labels->name, $ptype_obj->labels->menu_name, $ptype_obj->cap->edit_posts, "edit.php?post_type=$ptype" );
 	}
 }