Solution to the E_COMPILE_ERROR in Declaration of Bootstrap_Walker_Nav_Menu

With one of the latest PHP updates, if you have a WordPress theme that uses the Bootstrap_Walker_Nav_Menu class from the Bootstrap framework, you might encounter an E_COMPILE_ERROR. This error occurs because the Bootstrap_Walker_Nav_Menu class does not follow the required method signature for start_lvl in its base class Walker_Nav_Menu. As mentioned, this happens due to changes in newer PHP versions, which are stricter about inherited method signatures.

Cause

The start_lvl method in your Bootstrap_Walker_Nav_Menu class is defined as:

start_lvl(&$output, $depth)

However, the base class Walker_Nav_Menu (from WordPress) defines the method as:

start_lvl(&$output, $depth = 0, $args = null)

The signature must match exactly, including default values and additional arguments.

Solution

Update the start_lvl method in your Bootstrap_Walker_Nav_Menu class to match the base class signature. Locate the method in one of your theme’s files (usually functions.php or functions-extra.php) and change it to:

public function start_lvl(&$output, $depth = 0, $args = null) {
    // Your custom code here
}

Compatibility Note

If you want your theme to remain compatible with older PHP versions, you can use a conditional approach. However, since PHP 7.4 and earlier versions are no longer officially supported, it is better to update all your code to comply with the newer versions.

Additional Steps

1. Check the rest of the class: Ensure that other methods like start_el, end_lvl, or end_el also comply with the required signatures.
2. Test the theme: After making this change, clear your site’s cache (if using plugins like W3 Total Cache or similar) and verify that the theme works correctly.
3. Plan for future updates: Ensure that your theme is compatible with the latest PHP and WordPress versions to avoid similar issues.