Add filter to has_post_thumbnail() to override default thumbnail use

[rzen]

Similar to #23983, I have routinely run into issues with overriding standard thumbnail behavior because different plugins or themes are (properly) checking for has_post_thumbnail() before utilizing get_the_post_thumbnail() or get_the_post_thumbnail_url().

Adding a filter to get_post_thumbnail_id() does allow for a means of overriding this function indirectly (similar to how the filter in wp_get_attachment_image_scr() allows one to override get_the_post_thumbnail_url(), but it could also possibly lead to unintended outcomes.

For example, I want to override the post thumbnail output only when a post doesn't have an attached thumbnail (therefore, no thumbnail ID). If the theme is checking has_post_thumbnail() before calling the_post_thumbnail() nothing will be output because get_post_thumbnail_id() currently returns nothing and causes has_post_thumbnail() to present false.

Using the filter added in #23983, I can set an arbitrary, magic number (e.g. 1) to trigger a true response in has_post_thumbnail(). However, my own check in the function that filters post_thumbnail_html will also see a positive response from get_post_thumbnail_id(). This means my filter function will bail (because it sees the post does have a custom image set) or I need an extra condition to confirm the returned value does not match the magic number I used while overriding it previously.

This would work, but I think the code can be clearer and more expressive if its possible to override has_post_thumbnail() independently of overriding get_the_thumbnail_id().

[mukesh27]

@rzen Above patch is already committed in trunk version check this - https://core.trac.wordpress.org/browser/trunk/src/wp-includes/post-thumbnail-template.php#L25

[rzen]

Hi @mukesh27,

I think you are mistaken. There is nothing in trunk, nor any other trac tickets that I could find, that introduce a filter to the has_post_thumbnail() function. My patch was made fresh, straight from trunk, just yesterday. And your link points to has_post_thumbnail() as it currently exists (sans filter).

If I'm the one who is mistaken, though, please do correct me once again.

[mukesh27]

@rzen sorry for my misunderstanding.

[pento]

Bumping along with #23983.

[desrosj]

Thanks for this one, @rzen. I think a filter here is reasonable.

44859.2.diff​ has the following adjustments to 44859.diff​:

• Correctly pass a bool to the first parameter of the filter.
• Include the thumbnail image ID as an optional third parameter for the filter. This could be used to not show a post thumbnail that has a specific meta property.
• Improve the inline documentation. Previously, the $post param left out some potential types and had a typo in the variable name.
• Updated since to 5.1.0.

[desrosj]

Discussed this in ​#core-media. This can go in and be followed up with #23983 when it's ready.

[desrosj]

In 44542:

Media: Introduce the has_post_thumbnail filter.

Props rzen, desrosj.
Fixes #44859.