Adds the_excerpt filter in the core/post-excerpt block.

[CoderAbhinav]

What?

This PR adds missing the_excerpt filter. Allowing much more consistent usage.

Why?

The post excerpt block does not call the the_excerpt filter before rendering the block. In contrast, the post content block does call the the_content filter before rendering. (Ref. #28214). In order to add consistency this filter has been added.

How?

This PR adds filter in frontend (index.js) as well as in the edit.js of the block.
https://github.com/CoderAbhinav/gutenberg/blob/351c8fe74313d3f2f8eabbbcca1ac91224751347/packages/block-library/src/post-excerpt/index.php#L31-L38

https://github.com/CoderAbhinav/gutenberg/blob/756b5970d155feae8a45f23fd62473dacd6a89b6/packages/block-library/src/post-excerpt/edit.js#L149-L155

The implementation is done with reference to https://developer.wordpress.org/reference/functions/the_excerpt/#source this code.

Testing Instructions

Add a filter like this first.

function my_excerpt_filter( $excerpt ) {
	return "Filtered: $excerpt";
  }
add_filter( 'the_excerpt', 'my_excerpt_filter' );

1. Then create a new post.
2. Add excerpt to the post.
3. Add post excerpt block in the editor. Check if the content is updated.
4. Save the post and check the frontend, for same changes.

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[Mamaduka]

The function already has a filter - get_the_excerpt.

[CoderAbhinav]

Hey @Mamaduka, so in one of the issues #28214 it has been discussed already that, even though get_the_excerpt() function already uses the get_the_excerpt filter, It would be good to have the_excerpt filter for backwards compatibility.

[Mamaduka]

I got it. The issue concerns the PHP filter. There's no need to update the JS code. For various reasons, the blocks don't mirror PHP filters in their React components.

P.S. I would recommend using reserved GitHub keywords to reference issues. It makes clear what you're trying to solve.

[Mamaduka]

Thanks for contributing, @CoderAbhinav! What is PR is trying to solve?

The PHP rendered has the correct filters, and data on the client side is consumed via REST API, which also has excerpt filters.

There's no need to mimic PHP filters in client-side code (JS), as they serve a different purpose, and filters in JS can negatively affect performance.

[talldan]

@CoderAbhinav I think this will result in all the default filters being applied, so it'd be good to make everything still works correctly:
https://github.com/WordPress/wordpress-develop/blob/6106332617128820c0ee5132c34ff1cf6f785d1a/src/wp-includes/default-filters.php#L205-L211

I did some testing personally and couldn't see any issues. I think most of these filters like convert_smilies are already run on the content, so there's no change from trunk to this PR.

The change might also need a dev note, as some plugins might be working around the missing filter and reintroducing it could require plugins updating their code.

As long as everything works, then this change seems fine (apart from Mamaduka's request change). There's precedence in that the post content block also does this and has done for a long time:

gutenberg/packages/block-library/src/post-content/index.php

Line 50 in 8e048a8

$content = apply_filters( 'the_content', str_replace( ']]>', ']]>', $content ) );