Scott Reilly

NOTE: WordPress 4.5 incorporated the functionality of this plugin and thus it is no longer needed unless you’re still running an older version of WP.
This plugin implements the belief that a trashed page or post should not in any way conflict with a new page or post when it comes to slugs. In essence, a new page or post should take precedence over anything in the trash. After all, the page/post is in the trash for a reason.
By default, WordPress takes into consideration posts and pages that have been trashed when deciding if the slug for a new post is already in use. Obviously, in general, WordPress should not allow duplicate slugs because that could interfere with permalinks. The thinking behind WordPress’s handling of the situation is that trashed posts/pages are still technically present, just inaccessible. It is possible that an author or admin would choose to restore a post from the trash, which WordPress feels should then occupy that same permalink as before it was trashed.
If what WordPress does is unclear, here’s an example to help clarify things:
<ul>
<li>WordPress ships with a page called “About” with the slug of “about”. The page’s URL would be http://yoursite/about/</li>
<li>Let’s say you trash that page and start a new page with the name “About”.</li>
<li>Due to a trashed page having the slug that would normally have been assigned to the new page (“about”), the new page gets the slug of “about-2”, resulting in the page’s URL being http://yoursite/about-2/</li>
</ul>
With this plugin, for this example, the new “About” page would get the slug “about” as one would hope.
That said, the plugin tries its best to restore untrashed posts to their original slug. The only time it fails to do so is if a new page or post has claimed the trashed post’s original slug, in which case the untrashed post is assigned a new slug.
See other sections of the documentation for more insight into the plugin’s functionality. See WP core <a href="https://core.trac.wordpress.org/ticket/11863" rel="nofollow ugc">ticket #11863</a> for discussion on the matter.
Links: <a href="http://coffee2code.com/wp-plugins/no-slug-conflicts-with-trash/" rel="nofollow ugc">Plugin Homepage</a> | <a href="https://wordpress.org/plugins/no-slug-conflicts-with-trash/" rel="ugc">Plugin Directory Page</a> | <a href="http://coffee2code.com" rel="nofollow ugc">Author Homepage</a>
<h3>The Solution Explained</h3>
An overview of the approach employed by the plugin to resolve the issue of slugs potentially conflicting with posts in the trash.
<h4>What WordPress does</h4>
In order to understand the crux of the implemented solution, a quick refresher on unique slug handling by WP:
Before published use, a desired slug is passed to <code>wp_unique_post_slug()</code> and a safe slug is returned. The safe slug may differ from the desired slug if any existing post (including a trashed post) has that slug (or, less likely, is invalid for permalink reasons such as feeds or date archives).
In order to prevent a trashed post’s slug from conflicting with a new post, this plugin takes an approach that is comprised of two primary tasks:
<h4>1. Permit a post to use a slug that conflicts with a trashed post.</h4>
The plugin hooks the ‘wp_unique_post_slug’ filter. If the desired slug matches the safe slug, the desired slug is unique and nothing needs to be done.
When the two slugs don’t match, it has to determine if the conflict is due to a trashed post or not, so it attempts to find a trashed post with the desired slug.
<ul>
<li>If no such trashed post is found, the conflict is with a live post (or was an otherwise unsuitable slug) so the safe slug must be used by the new post (so, again, nothing needs to be done).</li>
<li>If such a trashed post is found, then the plugin simply inverses the traditional behavior of <code>wp_unique_post_slug()</code>: give the trashed post the safe slug and return the desired slug for use by the new post (rather than having the trashed post retain its slug and forcing the new post to use the safe slug). In order to be able to restore a trashed post to its original slug, the trashed post’s original slug is stored in postmeta.</li>
</ul>
<h4>2. Restore a trashed post to its original slug, if necessary and possible.</h4>
For a post transitioning away from the ‘trash’ post status, check to see if its slug was rewritten (denoted by the presence of the postmeta field only assigned if the original slug was changed due to a conflict while the post was in the trash).
If there was no original slug, the slug was never changed and nothing more needs to happen.
When there is an original slug, check to see if that slug is still in use by a non-trashed post.
<ul>
<li>If not, restore the post slug to the original value.</li>
<li>If so, there is no recourse but to leave the post slug as-is (it is guaranteed to be unique already).</li>
</ul>
In either case, the postmeta field for the original slug value gets deleted since the now untrashed post is exposed in some fashion with its current slug and should abide by it going forward.

No Slug Conflicts with Trash

Lite and stable, no problems, does what it says!

works like a charm

NOTE: WordPress 4.5 incorporated the functionality of this plugin and thus it is no longer needed unless you're still running an older version of …

iropicci

In WordPress you can change the post name, which will impact its final URL and probably mess up the SEO on that article, since search engines will think both the previous and the new URL are different contents. You could fix this arranging some 301 redirects, but with this plugin active you just won’t be able to change that post name – hence its URL – unless the post is still in draft mode.

Published Posts Locked URL

Blocks URL modifications if post is already public. URL can still be modified if the article is a draft.

No Slug Conflicts with Trash vs Published Posts Locked URL