Related Posts: Remove the call to remove_filter( 'the_content', ...)

[kbrown9]

Fixes #13775

The filter filter_add_target_to_dom() removes itself from the the_content
hook when the site is in AMP mode. When a filter removes itself from a hook, a bug in Core causes the filter with the next highest priority to be skipped.

For more information on the Core bug see: https://core.trac.wordpress.org/ticket/9968

To avoid this bug, remove the call to remove_filter( 'the_content', array( $this, 'filter_add_target_to_dom'), ...). Instead, just rely on conditionals in the
filter_add_target_to_dom() method to control when related posts are added to the
content.

Related posts should not be added to the content when any of these three conditions are true:

1. The post contains a Related Posts block.
2. The post contains a jetpack-related-posts shortcode.
3. The get_the_excerpt hook is being executed. This hook is executed when the related
   posts are being generated, and related posts should not be added to the related post
   content.

These conditions are already handled by the filter_add_target_to_dom() method. However, when the call to remove_filter( 'the_content', array( $this, 'filter_add_target_to_dom'), ...)is removed, the legacy related posts are added to posts that contain a Related Posts block. Fix this by removing the $content parameter from has_block('jetpack/related-posts', $content). Then, the has_block() method will determine whether the global $post contains a Related Posts block.

Changes proposed in this Pull Request:

• Remove the call to remove_filter( 'the_content', array( $this, 'filter_add_target_to_dom'), ...).
• Remove the $content parameter from has_block('jetpack/related-posts', $content).

Is this a new feature or does it add/remove features to an existing part of Jetpack?

• Fixes an existing feature.

Testing instructions:

1. Set up the test site:

   • The Jetpack and AMP plugins must be installed and activated.
   • AMP should be set to Standard mode.
   • The Related Posts module must be activated.
   • The site must have enough posts with related content, tags, and categories that related post are generated.
   • At least one post must use legacy related posts.
   • At least one post must use a Related Posts block.

2. Add this code to a snipped plugin or your theme's functions.php:

add_filter( 'the_content', 'test_filter', 41 );

function test_filter( $content ) {
	return $content . ' TEST ';
}

3. Navigate to a post that uses legacy related posts. Note that the 'TEST' text (which should display after the related posts) is missing.

4. Apply this branch.

5. Refresh the post with legacy related posts. Verify that the 'TEST' text is now displayed under the related posts.

6. Navigate to a post that uses the Related Posts block. Verify that the legacy related posts are not displayed and that the 'TEST' text is displayed at the bottom of the post content.

Proposed changelog entry for your changes:

• Fix a bug in Related Posts that causes the filter with the next highest priority on the 'the_content' hook to be skipped while in AMP mode.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello kbrown9! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D34334-code before merging this PR. Thank you!

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: November 5, 2019.
Scheduled code freeze: October 29, 2019

Generated by 🚫 dangerJS against efc254c

[jeherve]

This seems to work well in my tests. Merging.

[mdawaffe]

When a filter removes itself from a hook, a bug in Core causes the filter with the next highest priority to be skipped.

Thanks for fixing! I thought this core issue had been addressed years ago… :)