Update child layout selector to match core.

[tellthemachines]

What?

Syncing a change that was made in the core sync PR for grid and column spans.

Using wp_unique_id to generate the child layout classname number means that number will vary depending on how many times wp_unique_id has been used on the page before. This was causing the results of the test added in #61392 to be unpredictable, and also the classname of any given block on a page to be unpredictable, which could affect things like dynamic loading (see #55416).

This PR changes the child layout classname to use wp_unique_prefixed_id instead.

Testing Instructions

Nothing should have visibly changed, but if you

1. Create a post with:
   • an Image block with a custom duotone filter applied (choose the colors yourself, don't use the preset);
   • a Row block with a few children, and set one of the children to "Fill" under Dimensions;
2. Create a custom template for that post that contains only the Post Content block;
3. Save and view on the front end. The classname for the Row child set to Fill should be wp-container-content-1 (in trunk it'll be wp-container-content-2 because the duotone filter also uses wp_unique_id).

Testing Instructions for Keyboard

Screenshots or screencast

[github-actions]

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Co-authored-by: tellthemachines <isabel_brison@git.wordpress.org>
Co-authored-by: andrewserong <andrewserong@git.wordpress.org>

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[github-actions]

This pull request has changed or added PHP files. Please confirm whether these changes need to be synced to WordPress Core, and therefore featured in the next release of WordPress.

If so, it is recommended to create a new Trac ticket and submit a pull request to the WordPress Core Github repository soon after this pull request is merged.

If you're unsure, you can always ask for help in the #core-editor channel in WordPress Slack.

Thank you! ❤️

View changed files

❔ lib/block-supports/layout.php
❔ phpunit/block-supports/layout-test.php

[andrewserong]

Working nicely. LGTM! 🚀