Filter logic has been put into the template loader while it not belongs there.

[hakre]

Some time ago, filter logic has been introduced in the template-loader. Looks like a fix for the inability to handle attachments propperly (WP misses more and more a strict request parsing so that newer features tend to introduce more and more bugs).

The code has not been removed yet. It should be removed there or put into a more appropriate location.

The code in question is:

remove_filter('the_content', 'prepend_attachment');

in /wp-inclueds/template-loader.php around line 30.

[hakre]

related: #6357 , code in question was introduced by ryan

[Ninos Ego]

Is it planned to remove this filter in one of the next releases? I think this hack should be removed from code, otherwise you'll see the attachments image on the attachment page if you're using the the_content filter for compiling shortcodes in widgets or somewhere else.
For theme developers it should be very easy to add a new line of code to their single-attachment.php (or use map the attachment image to the post_thumbnail function). If you want I can publish a patch...

Trac ticket: https://core.trac.wordpress.org/ticket/10275

[desrosj]

It's not exactly clear what problem this addresses. But I can't find a scenario where prepend_attachment() is actually utilized in Core as a filter anymore.

In the latest version of Core (currently 6.6), it's added as a default filter for the_content, and only removed when is_attachment is the template file. But when the filter is called when displaying non-attachment posts, the function returns early.

A ​brief check of the plugin directory shows that plugins are either calling prepend_attachment() directly or adding it as a filter for their own custom hooks. So I don't expect anything to break related to 3rd-party usage.

I've opened a PR and removed the related code and default filter, and no tests broke. I'm moving this to the 6.7 milestone for a second set of eyes before committing.

[sppramodh]

Test Report

This report validates that the changes in the patch do not introduce any issues and work as intended.

Patch tested: ​https://github.com/WordPress/wordpress-develop/pull/7321

Environments Tested

Environment 1

• WordPress Playground
• WordPress 6.7 (Patch applied)
• PHP: 7.4.29
• Browser: Google chrome 129.0.6668
• Theme: Twenty Twenty-Four (Version 1.2)
• Active Plugins:
  • Toggle wp_attachment_pages_enabled

Environment 2

• WordPress Playground
• PHP: 8.0
• WordPress: 6.6.2
• Browser: Google chrome 129.0.6668
• Theme: Twenty Twenty-Four (Version 1.2)
• Active Plugins:
  • Toggle wp_attachment_pages_enabled

Steps followed

1 Enable Attachment Pages:
Since attachment pages are fully disabled in WordPress 6.4 and later, the "Toggle wp_attachment_pages_enabled" plugin was used to enable attachment pages for testing.

2 Media Upload:
Uploaded an image to the Media Library.

3 View Attachment Page:

• On WordPress 6.6.2 (without the patch), the image was visible on the attachment page.
• On WordPress 6.7 (with the patch applied), the image did not appear on the attachment page.

screenshot from WordPress 6.7 patch applied

screenshot from WordPress 6.6.2

4 Behavior When Attachment Pages are Disabled (Default):
There was no change in how the images were displayed when viewing media items.

5 Custom Shortcode Testing:

• Created a custom shortcode that utilizes the the_content filter for compiling shortcodes.
• Developed a separate shortcode to display an attachment by ID.

6 Testing Shortcodes on the Header:
Added the custom shortcode and the attachment shortcode to the header, linking to a PDF (Download rates).

screenshot from WordPress 6.7 patch applied

screenshot from WordPress 6.6.2

7 Observations:

• On WordPress 6.6.2, the attachment was automatically added to the header, appearing multiple times due to the the_content filter's effect when using shortcodes.
• On WordPress 6.7 (with the patch), no such issue occurred on the attachment page. The attachment did not appear multiple times.

8 Compatibility Testing with WooCommerce:
Installed WooCommerce to verify if the shortcodes in the header caused any issues on WooCommerce pages.
No problems were found with WooCommerce active.

Actual Results

• ✅ Issue resolved with patch.

[desrosj]

6.7 RC1 is due out any moment. Unfortunately, this one missed the deadline so I'm going to punt this.