Rewrite Rule for homepage not working correctly

Question

I am trying to setup rewrite rules for a custom homepage because we are planning on using full-screen slides and using a javascript pushstate to update the url instead of using formal WordPress pages. We decided using GET variables would be easiest in order to allow linking to a certain slide on the homepage, but it's not nice looking so I wanted to use rewrite rules in order to make everything slick and SEO friendly.

Here's a few examples of what we are trying to do ("slide" is not a page/post in WP):

Nice URL: example.com/slide/something/
Ugly URL: example.com/?slide=something

Nice URL: example.com/slide/videos/
Ugly URL: example.com/?slide=videos

Now, we have no problem with the ugly URLs, but my rewrite rule for this just isn't working. I have gone through several questions/answers on this but none of the accepted answers have been working. Here's what I have in functions.php:

add_action('init', 'add_rewrite_rules');
function add_rewrite_rules() {
    flush_rewrite_rules();
    add_rewrite_rule(
        '^slide/([^/]*)/?$',
        'index.php?slide=$matches[1]',
        'top'
    );
}

I'm flushing rewrite rules while I try to get this working; I realize I shouldn't have this in there, being called on every refresh if this was a production site.

If I try to go to example.com/slide/something/ I am redirected to the homepage.

Answer 1

Two problems I see- rewrite rules need to set query vars that will result in a successful main query. Setting just a custom var like slide doesn't parse to anything WordPress can load. Additionally, slide needs to be added to the recognized query vars for it to get parsed within a rule.

So, what would a rule look like that would load the front page posts in the main query? That's a good question- the posts page is a special case, the absence of any other query vars. I haven't found a way to do that with a rule, though it may exist.

An easier way to do this is with a rewrite endpoint:

function wpd_slide_endpoint(){
    add_rewrite_endpoint( 'slide', EP_ROOT );
}
add_action( 'init', 'wpd_slide_endpoint' );

Keep in mind that if you have code accessing values via $_GET, this still won't work, because WordPress doesn't put query vars there when rules are parsed. You can change the code to use get_query_var, or just assign it before the code tries to access it:

$_GET['slide'] = get_query_var('slide');

Answer 2

@Milo was two minutes faster, therefor I will just add to his answer, that using a CPT for slides might be the simplest way to get pretty urls for the slides, and in addition it will be much easier to SEO the slides.