`wp_nav_menu()` throws undefined offset if a menu item's parent has a higher ID.

[peterwilsoncc]

Following [54478] for #28620, it's possible for wp_nav_menu() to throw an undefined offset notice if a menu item has a lower post ID than its parent.

This can occur if the menu items are created and then restructured/re-parented after they are initially created.

The following test demonstrates the problem.

<?php

// Add to tests/phpunit/tests/menu/wp-nav-menu.php

public function test_parent_with_higher_id_should_not_error() {
        // Create a new level zero menu item.
        $new_lvl0_menu_item = wp_update_nav_menu_item(
                self::$menu_id,
                0,
                array(
                        'menu-item-title'  => 'Root menu item with high ID',
                        'menu-item-url'    => '#',
                        'menu-item-status' => 'publish',
                )
        );

        // Reparent level 1 menu item to the new level zero menu item.
        self::$lvl1_menu_item = wp_update_nav_menu_item(
                self::$menu_id,
                self::$lvl1_menu_item,
                array(
                        'menu-item-parent-id' => $new_lvl0_menu_item,
                )
        );

        // Delete the old level zero menu item.
        wp_delete_post( self::$lvl0_menu_item, true );

        // Render the menu.
        $menu_html = wp_nav_menu(
                array(
                        'menu' => self::$menu_id,
                        'echo' => false,
                )
        );

        $this->assertStringContainsString(
                sprintf(
                        '<ul id="menu-test" class="menu"><li id="menu-item-%1$d" class="menu-item menu-item-type-custom menu-item-object-custom menu-item-has-children menu-item-%1$d">',
                        $new_lvl0_menu_item
                ),
                $menu_html,
                'The level zero menu item should appear as the first menu item.'
        );

}

Note: wp_get_nav_menu_items() queries by menu_order, so the sorting for items with a matching menu_order is somewhat undefined. Results may differ depending on the DB engine/version/phase of the moon.

This is the result on my local environment:

$ phpunit --filter test_parent_with_higher_id_should_not_throw
Installing...
Running as single site... To run multisite, use -c tests/phpunit/multisite.xml
Not running ajax tests. To execute these, use --group ajax.
Not running ms-files tests. To execute these, use --group ms-files.
Not running external-http tests. To execute these, use --group external-http.
PHPUnit 7.5.20 by Sebastian Bergmann and contributors.

E                                                                   1 / 1 (100%)

Time: 12.79 seconds, Memory: 242.05 MB

There was 1 error:

1) Tests_Menu_wpNavMenu::test_parent_with_higher_id_should_not_throw
Undefined offset: 5

/vagrant/wordpress-develop/src/wp-includes/nav-menu-template.php:210
/vagrant/wordpress-develop/tests/phpunit/tests/menu/wp-nav-menu.php:300

Just some tests initially.

https://core.trac.wordpress.org/ticket/57122

[peterwilsoncc]

I noticed this-morning my local environment was on an old commit when I tested this yesterday. It's possible it was fixed in [54801] for #56946.

I'll double check to make sure and close this if needs be.

[SergeyBiryukov]

#57160 was marked as a duplicate.

[peterwilsoncc]

#57333 was marked as a duplicate.

[peterwilsoncc]

Replying to peterwilsoncc:

I noticed this-morning my local environment was on an old commit when I tested this yesterday. It's possible it was fixed in [54801] for #56946.

I'll double check to make sure and close this if needs be.

This was indeed fixed in [54801] for WordPress 6.1.1

In the ​initial push the tests failed in the linked pull request. Rebasing against trunk has ​the tests passing.

I'll commit the additional test to close this ticket. I've moved this ticket to the 6.2 milestone for the tests commit.

[peterwilsoncc]

In 55328:

Menus: Test creating parent after a child doesn't throw an error.

As menus are re-arranged, it's possible a menu item was created prior to its parent.

This introduces a test to ensure the order in which menu items are created relevant to their parents does not trigger errors.

Props costdev, peterwilsoncc.
Fixes #57122.

Committed in ​https://github.com/WordPress/wordpress-develop/commit/c98ca19a20f3c59b8220681deebb5960a423758b / r55328