Latest Posts block: Check priority of excerpt_length filter

[BinaryMoon]

Hi - the excerpt length setting in the latest posts block does not get used in all themes. This seems to be a common problem in themes that change the default excerpt length.

This appears to be a because of the excerpt_length filter in the render method.

gutenberg/packages/block-library/src/latest-posts/index.php

Line 48 in 97caf7b

add_filter( 'excerpt_length', 'block_core_latest_posts_get_excerpt_length', 20 );

In the method the filter has a priority of 20, however the official WordPress docs suggest a priority of 999 which I have found referenced on a number of sites and used in many themes.
https://developer.wordpress.org/reference/hooks/excerpt_length/#more-information

I started updating my 20+ themes to use a lower priority but then realised that it's used in so many other themes that it should probably be changed in core.

You can see how many public themes use it here:
https://wpdirectory.net/search/01F9927FX53NQ7AA33DS32YK38

If you expand the top 20 results on this page you will see that about 50% use the 999 priority.

My suggestion would be to use 9999 since some people (including myself) may go even higher in child themes.

[ramonjd]

I also noticed this while testing WordPress/wordpress-develop#5441 (comment)

I've tested using 99 and it seems to work.

Before

Editor	Frontend

After

Editor	Frontend

[ramonjd]

Testing if I can override in my theme also works.

I'm setting the priority to 999 in the latest posts block:

add_filter( 'excerpt_length', 'block_core_latest_posts_get_excerpt_length', 999 );

Then I add a hook in a function.php file for my theme:

function block_core_latest_posts_get_excerpt_length_again_totally( $length ) {
	return 4;
}

add_filter( 'excerpt_length', 'block_core_latest_posts_get_excerpt_length_again_totally', 9999 );

In the editor and frontend, the excerpt is trimmed to 4 words

[tomjn]

@ramonjd behaviour is different based on how the excerpt was acquired, what would be useful is a mapping of all the ways excerpts can be shown, and when/how/if they're truncated, making the point to distinguish between user defined excerpts and auto-generated excerpts. Perhaps a table?

[tomjn]

-	Truncated by default	Respects excerpt_length	Respects length block attribute
Excerpt block (auto)	✅	❌	✅
Excerpt block (manual)	?	?	?
the_excerpt() (auto)	✅	✅	❌
the_excerpt() (manual)	?	?	❌

There's a few gaps off the top of my head I'm unsure of their nuances, and I'm sure there are use cases I did not mention in the table, but it's a start

[ramonjd]

Thanks a lot for this @tomjn!

I find most of my confusion is reduced by bumping the priority of the filter to add_filter( 'excerpt_length', 'block_core_latest_posts_get_excerpt_length', 999 );

The only discrepancy I find is in the editor, which fetches the rendered excerpt from the post object (post.excerpt.rendered). It performs a bit of faffery to remove the outer HTML tags, which is fine, but only updates the excerpt after each save.

The discrepancy is most obvious when moving from a low word count to a higher one. Because the excerpt with a lower word count has been saved to the database, the editor cannot render the excerpt preview with a higher word count because those words are not available. Only after save are my changes reflected.

2023-10-11.12.31.00.mp4

[tomjn]

hmmm that's unusual and looks like a separate bug with the latest posts block, can you create an issue to track that? Note that this is a new place I did not expect so it does not appear in the table I posted earlier. Be sure to include the copy pasted blocks when you open the issue so that people can copy paste it into their editor to reproduce the problem.

[ramonjd]

It appears to be a side effect of bumping the priority of the excerpt_length filter in /latest-posts/index.php and not reproducible in trunk.

I think the post object (in the editor) is returning the 55 word limit by default, so I guess, with the priority at 20 it's not taking into account any subsequent hooks that are firing.

I'll keep an ear out on this issue and do a follow up issue if we come up with a fix.