Is it possible to replace a function within a PHP class of a WordPress plugin?

Question

I read that "unless the original function is meant to be overridden, no. This is basic PHP."

But I am trying to edit the WooCommerce plugin without editing the plugin files, so that the plugin can be updated without losing changes.

I have set up a child theme and done the following in the functions.php but it does not work...

functions.php - child theme

<?php
require_once(WP_PLUGIN_DIR . '/woocommerce/includes/class-wc-form-handler.php');

class child_WC_Form_Handler extends WC_Form_Handler {

    public function process_login() {

        parent::process_login();
       .
       .
       .
       if ( is_email( $_POST['username'] ) && apply_filters( 'woocommerce_get_username_from_email', true ) ) {
           $user = get_user_by( 'email', $_POST['username'] );

           if ( isset( $user->user_login ) ) {
               $creds['user_login']     = $user->user_login;
           } else {
               throw new Exception( '<strong>' . __( 'Error', 'woocommerce' ) . ':</strong> ' . __( 'MESSAGE TO BE REPLACED', 'woocommerce' ) );
           }

       } else {
           $creds['user_login']     = $_POST['username'];
       }
       .
       .
       .
    }

}
?>

class-wc-form-handler.php - where the original function lies

<?php
class WC_Form_Handler {
.
.
.
    public function process_login() {
       .
       .
       .
       if ( is_email( $_POST['username'] ) && apply_filters( 'woocommerce_get_username_from_email', true ) ) {
           $user = get_user_by( 'email', $_POST['username'] );

           if ( isset( $user->user_login ) ) {
               $creds['user_login']     = $user->user_login;
           } else {
               throw new Exception( '<strong>' . __( 'Error', 'woocommerce' ) . ':</strong> ' . __( 'A user could not be found with this email address.', 'woocommerce' ) );
           }

       } else {
           $creds['user_login']     = $_POST['username'];
       }
       .
       .
       .
    }
.
.
.
}
?>

Is there any way around this? I want to change the exception message of a login error. I have highlighted the message I want to change with 'MESSAGE TO BE REPLACED'.

Answer 1

Inside the process_login function, you should be able to see a try {} catch {} block which then calls wc_add_notice like this:

...
wc_add_notice( apply_filters('login_errors', $e->getMessage() ), 'error' );
...

So, we should be able to add a filter and intercept just that message:

function replace_email_error($message) {

    $emailError = '<strong>' . __( 'Error', 'woocommerce' ) . ':</strong> ' . __( 'A user could not be found with this email address.', 'woocommerce');

    if ($message == $emailError) {
        $message = 'MESSAGE TO BE REPLACED';
    }

    return $message;

}

add_filter('login_errors', 'replace_email_error');

I have not tested this - please try it out, if you have any problems with it I am happy to debug.

Alternatively, you should be able to see that the error message is passed to Wordpress's localization functions - so you can also add a filter to the gettext function and then check the domain and the text and return a different value if they match.

Answer 2

Even though you have your answer this could come in handy down the track.

According to the following Github thread it hasn't been implemented in WooCommerce directly: https://github.com/woothemes/woocommerce/issues/3687

You can however still extend their core classes but most likely will have to do cleanup behind them which can be annoying. Here is an example of the WC_Form_Handler that I had extended for my own needs:

class WC_BI_Form_Handler extends WC_Form_Handler {
    public function __construct() {
        parent::__construct();

        remove_filters_for_anonymous_class( 'init', 'WC_Form_Handler', 'process_login', 10 );
        add_action( 'init', array( $this, 'process_login' ) );
    }

    public function process_login() {
        if ( ! empty( $_POST['login'] ) && ! empty( $_POST['_wpnonce'] ) ) {
            # code
        }
    }
}

new WC_BI_Form_Handler;

I've used the following plugin which gave me access to the remove_filters_for_anonymous_class function. This allowed me to unhook class specific actions which wouldn't be otherwise possible: https://github.com/herewithme/wp-filters-extras/blob/master/wp-filters-extras.php