Improvement in wp_parse_args for mutli-dimensional arrays

[Stachethemes]

I noticed the function doesn't work well when multi-dimensional arrays are present:

Example:

Consider having following default params and settings.

$defaults = array(
    'settings' => array(
        'option1' => 'default-value-1',
        'option2' => 'default-value-2'
    )
);

$settings = array(
    'settings' => array(
        'option1' => 'new-value-1',
    )
);

$return = wp_parse_args($settings, $defaults);

The above example will return:

Array
(
    [settings] => Array
        (
            [option1] => new-value-1
        )

)

It will completely ignore the option2 key.

My suggestion is to update wp_parse_args from:

if (is_array($defaults) && $defaults) {
    return array_merge($defaults, $parsed_args);
}

with:

if ( is_array( $defaults ) && $defaults ) {
    return array_replace_recursive($defaults, $parsed_args);
}

https://core.trac.wordpress.org/ticket/59330