Regression: Fix layout support to be compatible with enhanced pagination

[luisherranz]

This ticket tracks the merging of PHP files for the following Gutenberg changes:

​https://github.com/WordPress/gutenberg/pull/55416

This is fixing a regression introduced in 6.4 with the new enhanced pagination feature.

This is a backport PR for WordPress 6.4 that includes the following PHP Gutenberg changes:

• ​https://github.com/WordPress/gutenberg/pull/55416

Trac ticket: https://core.trac.wordpress.org/ticket/59681

Hi there!

I applied all changes requested. Thanks for the review @tellthemachines @costdev

Code updated with changes requested. Thanks for your reviews @tellthemachines , @costdev ! 🙇

This looks much better now. Thanks, @c4rl0sbr4v0 and @costdev! 🙏

[hellofromTonya]

This change is the 2nd half of fix for ​the Gutenberg issue 55230. The first half is in ticket #59694. Both tickets should be considered together for whether they should or shouldn't be backported to the 6.4 branch, as together they solve the issue with enhanced pagination in the Query block.

As I noted on #59694, for the bugfix to be backported to the 6.4 branch to ship in 6.4 RC2 or 3, it needs to resolve a regression or break/error introduced during the 6.4 cycle, i.e. ​per the commit guidelines during the release candidate phase:

Regressions: bugs that have been introduced during the WordPress 6.4 development cycle, either to existing or new features.

Some notes:

• The ​Gutenberg issue was punted to 6.4.1 last week ahead of 6.4 RC1.
• As @cbravobernal ​noted in Make/Core slack core channel, the bug did happen in 6.4, as the enhanced pagination is being introduced in 6.4.

  the layout support was working fine in 6.3. This is a compatibility fix with the new enhanced pagination of the Query block, which is being introduced in 6.4.
  

Patch Report

Patch tested: ​https://patch-diff.githubusercontent.com/raw/WordPress/wordpress-develop/pull/5528.diff

How to read this report:

🐞 <= Bug occurs.
✅ <= Behavior is expected.
❌ <= Behavior is NOT expected.

Environment

• OS: macOS 14.0
• Web Server: Nginx
• macOS 14.0
• PHP 8.2.11
• 6.4-RC1-56475-src
• Firefox 118.0.2

Steps to Reproduce

1. With WordPress 6.4 installed
2. Create 7 posts, configure to have 3 per page.
3. On the site editor, in home page, TT4, add pagination to the Query Loop, set it to inherit the template settings, activate "Enhanced Pagination feature). Make sure your layout is three posts in a row.
4. 🐞 Check that on page three, the last post layout is broken (full width instead of 1/3)

Steps to Test Patch

1. 🛠 Apply ​the patch.
2. Refresh the home page.
3. ✅ Check that the layout is correct when navigating to the last page.
4. ✅ Check that the navigation happened without a page reload.

Test Results

• ✅ Issue is reproducible.
• ✅ Issue resolved with patch.

Screenshots

Before patch:

After patch:

[hellofromTonya]

In discussions and reviews, this is fixing a 6.4 regression introduced with the new enhanced pagination feature. Thus it is okay to be fixed in the 6.4 RC cycle.

@aaronjorbin @costdev all feedback is now addressed. Can you re-review please?

[hellofromTonya]

Marking ​https://github.com/WordPress/wordpress-develop/pull/5528 for commit to trunk.

[jorbin]

This looks good. Marking as dev-reviewed to endorse committing to trunk and immediately backporting.

Thank you everyone! Luis has asked me to commit this, which I'll promptly do 😊

[Bernhard Reiter]

In 56994:

Blocks: Fix layout support to be compatible with enhanced pagination.

Make layout support compatible with enhanced pagination by ensuring that generated class names are stable across pagination, even when the number of rendered posts is different.

With the previous implementation of enhanced pagination, the CSS corresponding to each block was not detected. Therefore, for enhanced pagination to work correctly, the CSS of the blocks present in the Post Template must be stable on all pages.

The number of posts rendered by the Query block is always the same, except in the last page, where it can be only a fraction. If any of the blocks rendered by the Post Template used the wp_unique_id function, the ID (which is incremental) would have been different than in the previous pages and the class names would have varied.

This is remediated by this changeset by replacing the usage of wp_unique_id in the layout support (which is used by the Query block) with an implementation that uses IDs that are incremental only for that block. That way, the generated class names are never affected by the number of times wp_unique_id runs.

Props luisherranz, andrewserong, isabel_brison, costdev, mukesh27, cbravobernal, hellofromTonya, jorbin.
Fixes #59681.

[Bernhard Reiter]

Reopening for backporting to the 6.4 branch.

[Bernhard Reiter]

In 56995:

Blocks: Fix layout support to be compatible with enhanced pagination.

Make layout support compatible with enhanced pagination by ensuring that generated class names are stable across pagination, even when the number of rendered posts is different.

With the previous implementation of enhanced pagination, the CSS corresponding to each block was not detected. Therefore, for enhanced pagination to work correctly, the CSS of the blocks present in the Post Template must be stable on all pages.

The number of posts rendered by the Query block is always the same, except in the last page, where it can be only a fraction. If any of the blocks rendered by the Post Template used the wp_unique_id function, the ID (which is incremental) would have been different than in the previous pages and the class names would have varied.

This is remediated by this changeset by replacing the usage of wp_unique_id in the layout support (which is used by the Query block) with an implementation that uses IDs that are incremental only for that block. That way, the generated class names are never affected by the number of times wp_unique_id runs.

Props luisherranz, andrewserong, isabel_brison, costdev, mukesh27, cbravobernal, hellofromTonya, jorbin.
Merges [56994] to the 6.4 branch.
Fixes #59681.

Committed to Core trunk in `[56994] and to the 6.4 branch in [https://core.trac.wordpress.org/changeset/56995 [56995]`].

Thank you all for your help getting this to the finish line! @ockham, @c4rl0sbr4v0, @hellofromtonya, @aaronjorbin and @costdev 🙏