Merge multiple WP_Error objects together

wp-error-merge.php

<?php

/**
 * Merge multiple WP_Error objects together
 *
 * @return WP_Error
 */
function wp_error_merge() {
	$wp_error_merged = new WP_Error();
	$wp_errors = func_get_args();
	foreach ( $wp_errors as $wp_error ) {
		if ( ! is_wp_error( $wp_error ) ) {
			continue;
		}
		/**
		 * @var WP_Error $wp_error
		 */
		$error_codes = $wp_error->get_error_codes();
		foreach( $error_codes as $error_code ) {
			// Merge error messages
			$error_messages = $wp_error->get_error_messages( $error_code );
			foreach( $error_messages as $error_message ) {
				$wp_error_merged->add( $error_code, $error_message );
			}
			// Merge error data
			$error_data = $wp_error->get_error_data( $error_code );
			if( $error_data ) {
				$prev_error_data = $wp_error_merged->get_error_data( $error_code );
				if( ! empty( $prev_error_data ) && is_array( $error_data ) && is_array( $prev_error_data ) ) {
					$wp_error_merged->add_data( array_merge( $prev_error_data, $error_data ), $error_code );
				} else {
					$wp_error_merged->add_data( $error_data, $error_code );
				}
			}
		}
	}
	return $wp_error_merged;
}

Inspired by: https://gist.github.com/mjangda/5871525

For anyone hitting this page, as of WordPress 5.6 WP_Error allows merging objects together. See https://core.trac.wordpress.org/ticket/38777