[wp-trac] [WordPress Trac] #56171: Unexpected behaviour and data loss with a post type called 'link' and Link Manager plugin active

[WordPress Trac]

#56171: Unexpected behaviour and data loss with a post type called 'link' and Link
Manager plugin active
--------------------------+------------------------------
 Reporter:  manfcarlo     |       Owner:  (none)
     Type:  defect (bug)  |      Status:  new
 Priority:  normal        |   Milestone:  Awaiting Review
Component:  Taxonomy      |     Version:
 Severity:  critical      |  Resolution:
 Keywords:                |     Focuses:
--------------------------+------------------------------
Description changed by sabernhardt:

Old description:

> Steps to reproduce:
>
> 0. Install a fresh site (this will be easier to reproduce if the posts
> table has a low `auto_increment` value)
> 1. Install the Link Manager plugin (prior to version 3.5 this plugin was
> not required)
> 2. Register a post type called `link` (you can use the default args)
> **3. Observe that "Link Categories" is added under the newly registered
> post type in the admin menu**
> 4. Publish a post through the `link` post type and take note of its
> numeric ID
> 5. Add enough links through the Link Manager until you reach the same
> numeric ID observed in step 4
> 6. Assign a link category to the link with the same numeric ID observed
> in step 4 (if it's a fresh site it shouldn't be too many)
> **7. Go back to the `link` post type and observe that the published post
> has received the link category that was assigned to the link in step 6**
> 8. Now delete the post permanently
> **9. Go back to the Link Manager and observe that the link has lost its
> category that was assigned in step 6**
>
> This bug is caused because the taxonomy `link_category` is registered for
> the string `link`. [https://github.com/WordPress/WordPress/blob/6.0/wp-
> includes/taxonomy.php#L136 (See code)]
>
> Interestingly, the function `register_taxonomy_for_object_type`
> [https://github.com/WordPress/WordPress/blob/6.0/wp-
> includes/taxonomy.php#L734 rejects any string that is not registered as a
> post type.] Of course, if the same check were included for immediate
> registration through `register_taxonomy`, link categories could not exist
> at all.
>
> I discovered this while trying to get a clear answer on whether
> taxonomies were actually supported for non-post entities. I was nearly
> convinced they were not, until I noticed that link categories exist, and
> now it looks to me that no one knows the answer.

New description:

 Steps to reproduce:

 0. Install a fresh site (this will be easier to reproduce if the posts
 table has a low `auto_increment` value)
 1. Install the Link Manager plugin (prior to version 3.5 this plugin was
 not required)
 2. Register a post type called `link` (you can use the default args)
 **3. Observe that "Link Categories" is added under the newly registered
 post type in the admin menu**
 4. Publish a post through the `link` post type and take note of its
 numeric ID
 5. Add enough links through the Link Manager until you reach the same
 numeric ID observed in step 4 (if it's a fresh site it shouldn't be too
 many)
 6. Assign a link category to the link with the same numeric ID observed in
 step 4
 **7. Go back to the `link` post type and observe that the published post
 has received the link category that was assigned to the link in step 6**
 8. Now delete the post permanently
 **9. Go back to the Link Manager and observe that the link has lost its
 category that was assigned in step 6**

 This bug is caused because the taxonomy `link_category` is registered for
 the string `link`. [https://github.com/WordPress/WordPress/blob/6.0/wp-
 includes/taxonomy.php#L136 (See code)]

 Interestingly, the function `register_taxonomy_for_object_type`
 [https://github.com/WordPress/WordPress/blob/6.0/wp-
 includes/taxonomy.php#L734 rejects any string that is not registered as a
 post type.] Of course, if the same check were included for immediate
 registration through `register_taxonomy`, link categories could not exist
 at all.

 I discovered this while trying to get a clear answer on whether taxonomies
 were actually supported for non-post entities. I was nearly convinced they
 were not, until I noticed that link categories exist, and now it looks to
 me that no one knows the answer.

--

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/56171#comment:2>
WordPress Trac <https://core.trac.wordpress.org/>
WordPress publishing platform