Editor: Retain responsive styles in block style variation partials.

[guzel]

Trac ticket: https://core.trac.wordpress.org/ticket/65992

Problem

Responsive @tablet and @mobile styles are silently dropped from block style
variations declared in a standalone JSON partial in a theme's styles/
directory. The base rule is generated, but no media query CSS is emitted, and
nothing surfaces an error in the editor or on the front end.

The same variation declared inline in theme.json under
styles.blocks.<block>.variations.<slug> works correctly. Only the standalone
partial path is affected.

Cause

Partials declare their styles at the root of the styles object:

{
  "slug": "article-heading-xl",
  "blockTypes": [ "core/heading" ],
  "styles": {
    "typography": { "fontSize": "40px" },
    "@tablet": { "typography": { "fontSize": "28px" } }
  }
}

WP_Theme_JSON_Resolver::get_style_variations() sanitizes each partial by
running it through WP_Theme_JSON, so the partial is validated against the
top-level styles schema in WP_Theme_JSON::sanitize().

That schema was deliberately built to mirror the block style variation schema —
both are VALID_STYLES plus blocks and elements — which is what makes
partials sanitize correctly in the first place. The responsive breakpoint states
added in 7.1 were only added to the block, element, and variation branches, so
@tablet and @mobile at the top level are removed by
remove_keys_not_in_schema() as unknown keys.

The variation branch cannot cover this case: it validates
styles.blocks.<block>.variations.<slug>, a different location in the tree, and
its guard also requires the variation to already be present in
$valid_variations, which is derived from the block styles registry. Partials
are not registered until wp_register_block_style_variations_from_theme_json_partials()
runs, which happens after get_style_variations() returns.

The later, fully-correct sanitize pass in get_theme_data() cannot recover the
data either, because inject_variations_from_block_style_variation_files()
copies the already-stripped styles.

Fix

Add the responsive breakpoint states to the top-level styles schema, mirroring
what the block style variation branch already does. This restores the parity the
two schemas were written to have.

Testing instructions

1. On a block theme, create styles/article-heading-xl.json:

{
	"version": 3,
	"title": "Heading XL",
	"slug": "article-heading-xl",
	"blockTypes": [ "core/heading" ],
	"styles": {
		"typography": { "fontSize": "40px", "fontWeight": "700", "lineHeight": "1.3" },
		"@tablet": { "typography": { "fontSize": "28px" } },
		"@mobile": { "typography": { "fontSize": "16px", "lineHeight": "1.35" } }
	}
}

2. Add a Heading block to a page and apply the "Heading XL" style variation.
3. View the page on the front end and inspect the heading.

Before: only the base rule is generated; the heading keeps its desktop font
size at every viewport width.

After: the base rule plus tablet and mobile media query rules are generated,
and the font size steps down at each breakpoint.

Automated tests

• test_block_style_variation_partial_retains_responsive_styles — asserts the
  breakpoint keys survive WP_Theme_JSON_Resolver::get_style_variations().
• test_block_style_variation_partial_responsive_styles_generate_css — asserts
  the expected media queries appear in the generated CSS.

Both fail before the change and pass after. An existing expectation in
test_get_style_variations is updated to account for the new test fixture.

AI assistance

• AI assistance: Yes
• Tool(s): Claude Code (Claude Opus 5)
• Used for: Root cause analysis, drafting the fix, and the two regression tests.

The tests were written first and confirmed failing against unpatched trunk, then
confirmed passing after the change. The full PHPUnit suite was run locally
(31,037 tests, no regressions). All output was reviewed by me before submission.

[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 mitgiselle, ramonopoly, adamsilverstein.

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[github-actions]

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[adamsilverstein]

Hello @guzel is this PR ready for review? I see the upstream PR has not been merged.

Please note the RC for 7.1.1 is September 10th if we want it included in that version.

[guzel]

Thanks @adamsilverstein, yes, it's ready for review.
I've just pushed an update so this matches the current state of
WordPress/gutenberg#82403

That includes the review feedback from @talldan there: the states are now gated on the blockTypes property, so only block style variation partials are affected and regular theme.json files are unchanged. Pseudo-selectors in partials are supported alongside the responsive states, since they were dropped by the same root cause.

The Gutenberg PR is green and waiting on final sign-off. If anything changes there I'll mirror it here.

[adamsilverstein]

Thanks @guzel! I have requested some reviewers in GitHub.

[ramonjd]

Tested manually and did a fidelity check on the Gutenberg PR

This is a faithful backport that works the same as the original plugin PR, fixing the bug.

[ramonjd]

@adamsilverstein PR approved if there's still time for 7.1.1 RC 1

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 63610
GitHub commit: ce1aa14

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.