Background: add background attachment support to theme.json styles

[ramonjd]

Syncing changes from WordPress/gutenberg#61382

Note

This PR should be committed after #6836 to ensure a clean rebase 😄

Testing

Unit tests:

npm run test:php -- --filter Tests_Theme_wpThemeJson && npm run test:php -- --filter Tests_Block_Supports_WpRenderBackgroundSupport && npm run test:php -- --filter Tests_wpStyleEngine

This PR adds the backend functionality only, which means the editor UI isn't yet available.

To test, define a background image for the site in theme.json.

Here's an example using an image in src/wp-content/themes/twentytwentyfour/

{
	"$schema": "../../schemas/json/theme.json",
	"version": 3,
	"settings": {
		"appearanceTools": true
	},
	"styles": {
		"background": {
				"backgroundImage": {
					"url": "file:./assets/images/art-gallery.webp"
				},
				"backgroundAttachment": "fixed"
		},
		"blocks": {
			"core/verse": {
				"background": {
					"backgroundImage": {
						"url": "file:./assets/images/abstract-geometric-art.webp"
					}
				}
			}
        }
   	}
}

Now check the site:

2024-07-22.14.26.52.mp4

Trac ticket: https://core.trac.wordpress.org/ticket/61720

---

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props ramonopoly, mukesh27, andrewserong, noisysocks.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[mukeshpanchal27]

Add the property in docblock with @since

[andrewserong]

This code change looks good to me and is testing nicely in the site frontend 👍

For anyone else reviewing, some of the PHP changes in block-supports/background.php also include changes from #6836, as mentioned in the PR description, so it looks like that PR should land first. Factoring in #6836, the changes here match the expected changes from WordPress/gutenberg#61382 👍

LGTM!

[ramonjd]

I've rebased on top of #6836 and have added theme json block-level tests.

One thing to note is that #6836 opens up block-level global styles, so I've updated the theme.json test snippet in the description.

🍺

[noisysocks]

@ramonjd: Is this ready to commit?

[ramonjd]

Is this ready to commit?

Oh yes, please!!

[noisysocks]

I intended that as a nudge for you... 😂 You win this round, I was unclear.

[ramonjd]

I intended that as a nudge for you... 😂 You win this round, I was unclear.

Haha. No worries. I mistakenly assumed there was some rule about committing your own patches.

[ramonjd]

Merged in [58834]

c3e1d3a

[noisysocks]

Thanks!