Create a fallback navigation menu as one time operation on install and Theme switch

packages/block-library/src/navigation/edit/index.js

@@ -41,7 +41,6 @@ import {
 } from '@wordpress/components';
 import { __, sprintf } from '@wordpress/i18n';
 import { speak } from '@wordpress/a11y';
-import { createBlock, getBlockType } from '@wordpress/blocks';
 import { close, Icon } from '@wordpress/icons';
 
 /**
@@ -308,71 +307,6 @@ function Navigation( {
 	// that automatically saves the menu as an entity when changes are made to the inner blocks.
 	const hasUnsavedBlocks = hasUncontrolledInnerBlocks && ! isEntityAvailable;
 
-	useEffect( () => {
-		if (
-			ref ||
-			! hasResolvedNavigationMenus ||
-			isConvertingClassicMenu ||
-			fallbackNavigationMenus?.length > 0 ||
-			hasUnsavedBlocks
-		) {
-			return;
-		}
-
-		// If there's non fallback navigation menus and
-		// a classic menu with a `primary` location or slug,
-		// then create a new navigation menu based on it.
-		// Otherwise, use the most recently created classic menu.
-		if ( classicMenus?.length ) {
-			const primaryMenus = classicMenus.filter(
-				( classicMenu ) =>
-					classicMenu.locations.includes( 'primary' ) ||
-					classicMenu.slug === 'primary'
-			);
-
-			if ( primaryMenus.length ) {
-				convertClassicMenu(
-					primaryMenus[ 0 ].id,
-					primaryMenus[ 0 ].name,
-					'publish'
-				);
-			} else {
-				classicMenus.sort( ( a, b ) => {
-					return b.id - a.id;
-				} );
-				convertClassicMenu(
-					classicMenus[ 0 ].id,
-					classicMenus[ 0 ].name,
-					'publish'
-				);
-			}
-		} else {
-			// If there are no fallback navigation menus and no classic menus,
-			// then create a new navigation menu.
-
-			// Check that we have a page-list block type.
-			let defaultBlocks = [];
-			if ( getBlockType( 'core/page-list' ) ) {
-				defaultBlocks = [ createBlock( 'core/page-list' ) ];
-			}
-
-			createNavigationMenu(
-				'Navigation', // TODO - use the template slug in future
-				defaultBlocks,
-				'publish'
-			);
-		}
-	}, [
-		hasResolvedNavigationMenus,
-		hasUnsavedBlocks,
-		classicMenus,
-		convertClassicMenu,
-		createNavigationMenu,
-		fallbackNavigationMenus?.length,
-		isConvertingClassicMenu,
-		ref,
-	] );
-
 	const navRef = useRef();
 
 	// The standard HTML5 tag for the block wrapper.

packages/block-library/src/navigation/index.php

@@ -325,26 +325,31 @@ function block_core_navigation_get_classic_menu_fallback_blocks( $classic_nav_me
 }
 
 /**
- * If there's a the classic menu then use it as a fallback.
+ * Checks for a Classic Menu and attempts to convert into a block-based
+ * Navigation menu.
  *
- * @return array the normalized parsed blocks.
+ * @return int|WP_Error The Navigation menu post ID on success. A WP_Error on failure.
  */
-function block_core_navigation_maybe_use_classic_menu_fallback() {
-	// See if we have a classic menu.
+function block_core_navigation_create_classic_menu_fallback() {
+	// See if we have a Classic menu.
 	$classic_nav_menu = block_core_navigation_get_classic_menu_fallback();
 
+	// Exit early if one does not exist.
 	if ( ! $classic_nav_menu ) {
-		return;
+		return new WP_Error( 'no_classic_menu', __( 'No classic menu exists to convert to a block.' ) );
 	}
 
-	// If we have a classic menu then convert it to blocks.
+	// If we have a Classic menu then convert it to blocks.
 	$classic_nav_menu_blocks = block_core_navigation_get_classic_menu_fallback_blocks( $classic_nav_menu );
 
+	// If it's empty then exit early.
 	if ( empty( $classic_nav_menu_blocks ) ) {
-		return;
+		return new WP_Error( 'no_classic_menu', __( 'Classic menu is empty or could not be converted to blocks.' ) );
 	}
 
-	// Create a new navigation menu from the classic menu.
+	$return_errors = true;
+
+	// Create a new Navigation menu from the Classic menu blocks.
 	$wp_insert_post_result = wp_insert_post(
 		array(
 			'post_content' => $classic_nav_menu_blocks,
@@ -353,15 +358,10 @@ function block_core_navigation_maybe_use_classic_menu_fallback() {
 			'post_status'  => 'publish',
 			'post_type'    => 'wp_navigation',
 		),
-		true // So that we can check whether the result is an error.
+		$return_errors // So that we can check whether the result is an error.
 	);
 
-	if ( is_wp_error( $wp_insert_post_result ) ) {
-		return;
-	}
-
-	// Fetch the most recently published navigation which will be the classic one created above.
-	return block_core_navigation_get_most_recently_published_navigation();
+	return $wp_insert_post_result;
 }
 
 /**
@@ -432,11 +432,12 @@ function block_core_navigation_block_contains_core_navigation( $inner_blocks ) {
 }
 
 /**
- * Create and returns a navigation menu containing a page-list as a fallback.
+ * Creates a navigation menu containing default fallback content.
+ * (a page-list if registered).
  *
- * @return array the newly created navigation menu.
+ * @return int|WP_Error The post ID on success. A WP_Error on failure.
  */
-function block_core_navigation_get_default_pages_fallback() {
+function block_core_navigation_create_default_fallback() {
 	$registry = WP_Block_Type_Registry::get_instance();
 
 	// If `core/page-list` is not registered then use empty blocks.
@@ -454,13 +455,59 @@ function block_core_navigation_get_default_pages_fallback() {
 		true // So that we can check whether the result is an error.
 	);
 
-	if ( is_wp_error( $wp_insert_post_result ) ) {
+	return $wp_insert_post_result;
+}
+
+/**
+ * Creates an appropriate fallback Navigation Menu (`wp_navigation` Post)
+ * to be used by the Navigation block.
+ *
+ * Behaviour:
+ * 1. If there is a Navigation menu already then use it.
+ * 2. If there is a Classic menu then convert it to a Navigation menu.
+ * 3. If there is no Navigation menu and no Classic menu then create a default menu.
+ *
+ * The fallback menu is only created if the theme is a block theme.
+ *
+ * @return void
+ */
+function block_core_navigation_create_fallback() {
+	$should_skip = apply_filters( 'block_core_navigation_skip_fallback', false );
+
+	if ( $should_skip ) {
 		return;
 	}
 
-	// Fetch the most recently published navigation which will be the default one created above.
-	return block_core_navigation_get_most_recently_published_navigation();
+	// Don't create a fallback if the theme is not a block theme.
+	if ( ! wp_is_block_theme() ) {
+		return;
+	}
+
+	// Get the most recently published Navigation menu.
+	$existing_navigation_menu = block_core_navigation_get_most_recently_published_navigation();
+
+	// If there is already a Navigation menu then exit.
+	if ( $existing_navigation_menu ) {
+		return;
+	}
+
+	// If there are no Navigation menus then try to find a Classic menu
+	// and attempt to convert it into a Navigation menu.
+	$converted_classic_menu_id = block_core_navigation_create_classic_menu_fallback();
+
+	// If the conversion + creation was successful then exit.
+	if ( ! is_wp_error( $converted_classic_menu_id ) ) {
+		return;
+	}
+
+	// If the Classic menu process did not result in a post
+	// then default to creating a default fallback Navigaiton menu.
+	block_core_navigation_create_default_fallback();
 }
+// Run on switching Theme and when installing WP for the first time.
+add_action( 'switch_theme', 'block_core_navigation_create_fallback' );
+add_action( 'wp_install', 'block_core_navigation_create_fallback' );
+
 
 /**
  * Retrieves the appropriate fallback to be used on the front of the
@@ -475,17 +522,6 @@ function block_core_navigation_get_fallback_blocks() {
 	// Get the most recently published Navigation post.
 	$navigation_post = block_core_navigation_get_most_recently_published_navigation();
 
-	// If there are no navigation posts then try to find a classic menu
-	// and convert it into a block based navigation menu.
-	if ( ! $navigation_post ) {
-		$navigation_post = block_core_navigation_maybe_use_classic_menu_fallback();
-	}
-
-	// If there are no navigation posts then default to a list of Pages.
-	if ( ! $navigation_post ) {
-		$navigation_post = block_core_navigation_get_default_pages_fallback();
-	}
-
 	// Use the first non-empty Navigation as fallback, there should always be one.
 	if ( $navigation_post ) {
 		$parsed_blocks  = parse_blocks( $navigation_post->post_content );