Code for making scheduled posts available breaks preview in Wordpress

Question

Problem

There is a pice of code that makes scheduled posts available for outside users via URL. The code itself works just fine - however it seems to mess with the preview feature for the editor. What causes this problem and how can it be fixed?

The code

The code below is what I use for making schedulesd Posts available:

//this is inside the functions.php
function show_future_posts($posts)
{
    global $wp_query, $wpdb;

    if (is_single() && $wp_query->post_count == 0) {
        $posts = $wpdb->get_results($wp_query->request);
        for ($i = 0; $i < sizeof($posts); $i++) {
            if ($posts[$i]->post_status == 'trash') {
                unset($posts[$i]);
                $posts = array_values($posts);
            }
        }
    }
    return $posts;
}

add_filter('the_posts', 'show_future_posts');

Steps to reproduce

1. create new post
2. schedule post
3. edit somthing
4. hit preview

Some observations:

• as long as the post is marked as draft, the preview works fine.
• after updating/saving (ctrl + s) the preview is correct
• I dont think this is related to already known issues like this. When removing the code in question the autosave-feature works just fine
• published posts show the same behaviour as scheduled ones
• the editor (gutenberg/default) doesn`t seem to matter in this case

any help is much appreciated. Thanks!

Answer 1

I found a solution:
The problem was that $posts was overwritten inside the condition with a new posts array. The new posts array didd´t contain the recent changes for previewing. So I did a check, wather the post is in prview mode and then overwrite the post content in the new posts array.
The code below is what I came up with. It is not optimized yet but works. Feel free to share your optimizations in the comments. I`ll make sure to include them in this solution.

function show_future_posts($posts)
{
    global $wp_query, $wpdb;

    if (is_single() && $wp_query->post_count == 0) {

        $initial_posts = $posts; //save initial posts, in case we need to overwrite the new $posts content
        $posts = $wpdb->get_results($wp_query->request);
        /*
         * $initial_posts_exists_and_has_content is true when previewing scheduled posts.
         * We then can overwrite the post-content with the initial content
         * When viewing already published posts it is also true, but doesn`t contain the latest changes.
         * The content will still be overwritten, but this wont have any effect, since $initial_posts and $posts are
         * equal in this case.
         */
        $initial_posts_exists_and_has_content = !empty($initial_posts) && !is_null($initial_posts[0]->post_content);
        if($initial_posts_exists_and_has_content){
            $posts[0]->post_content = $initial_posts[0]->post_content;
        }

        for ($i = 0; $i < sizeof($posts); $i++) {
            if ($posts[$i]->post_status == 'trash') {
                unset($posts[$i]);
                $posts = array_values($posts);
            }
        }
    }
    return $posts;
}