Editing permalink allows duplicate permalinks

[synapsestudios]

I create and publish a post in uncategorized named Test, the permalink is:
​http://www.example.com/uncategorized/test/

I then create and publish an identical post, the permalink is:
​http://www.example.com/uncategorized/test-2/

So far, so good.

When I go to edit the second post, and try to edit the permalink such that the slug is simply "test", it allows me to Save that without providing any warning. It also shows the permalink as ​http://www.example.com/uncategorized/test/

Expected Result: When saving the duplicate slug, I would want it to notify me that it was unable to do so and then display the original permalink/slug.

Another scenario that relates to the functionality of the edit permalink's Save button is as follows:
Using the same scenario as above, but this time instead of changing test-2 to "test" I change it to "test-3" (a unique slug). I hit the Save button that is next to the Permalink and then leave the page. The changes, however, are not really saved at this point.

Expected Result: If it isn't actually saving anything, it shouldn't say "Save" or it should at least warn me that leaving the page would lose my changes.

I think if the Save button for the Permalink made an AJAX call, it could solve both of these problems. It could check if the slug was a duplicate and save it and the post right away if it was, otherwise it could trigger a notice to the user.

[pishmishy]

I'm splitting this ticket into two issues. Permalinks not being saved can be dealt with at #6925.

[ryan]

Milestone 2.5.2 deleted

[nbachiyski]

Here is a patch, which abstracts the logic of adding suffixes on duplicate slugs into wp_unique_slug(). Then the functions is used both on post saving and on generating sample permalinks.

[ryan]

(In [11071]) Add wp_unique_post_slug(). Apply it when getting sample permalinks. Props nbachiyski. fixes #6595