Backport: Navigation link: add support to style current menu item via theme.json

[MaggieCabrera]

What?

This backports the relevant changes from WordPress/gutenberg#75736, updated to match the current Gutenberg trunk state after:

• Style states: Use symbols for property keys to avoid clashes gutenberg#79210, which changed the custom state key from @current to -current.
• Add responsive global styles for blocks #11706, which backported responsive global block styles from Try responsive global block styles with states gutenberg#77513.

Why?

Theme authors need a way to style the active/current menu item differently from the rest of the navigation, including controlling its hover, focus, and active states.

How?

No UI changes are included; this is theme.json only.

A new VALID_BLOCK_CUSTOM_STATES constant whitelists --prefixed states per block in theme.json, playing the same role that VALID_BLOCK_PSEUDO_SELECTORS plays for CSS pseudo-selectors. The - prefix distinguishes these class-based custom states from real CSS pseudo-selectors and responsive breakpoint states.

Each block declares its state CSS selectors in block.json under selectors.states, following the existing Selectors API pattern, which get_blocks_metadata() reads into block metadata and get_block_nodes() uses to generate CSS.

Blocks listed in VALID_BLOCK_CUSTOM_STATES also inherit their VALID_BLOCK_PSEUDO_SELECTORS as valid sub-states, producing compound selectors like .wp-block-navigation-item.current-menu-item:hover.

The PHPUnit tests use get_styles_for_block() with explicit style nodes so they do not depend on block metadata that will arrive through the Gutenberg sync.

We've had initial discussions on how the UI for this scenario would look like over here.

Testing Instructions

Run the relevant PHP unit tests for WP_Theme_JSON, especially the custom-state tests added in this PR.

The following theme.json snippets show the intended public API once the corresponding selectors.states metadata for core/navigation-link is available in Core through the Gutenberg sync.

Current item base styles:

"core/navigation-link": {
  "-current": {
    "color": { "text": "#ff0000" }
  }
}

Current item hover:

"core/navigation-link": {
  "-current": {
    ":hover": {
      "color": { "text": "#0000ff" }
    }
  }
}

Current item focus:

"core/navigation-link": {
  "-current": {
    ":focus": {
      "color": { "text": "#00aa00" }
    }
  }
}

All combined:

"core/navigation-link": {
  "-current": {
    "color": { "text": "#ff0000" },
    "typography": { "fontWeight": "700" },
    ":hover": {
      "color": { "text": "#0000ff" }
    },
    ":focus": {
      "color": { "text": "#00aa00" }
    },
    ":active": {
      "color": { "text": "#ff6600" }
    }
  }
}

Test for navigation link items with and without submenus. Try other styles that aren't just the text color.

Testing Instructions for Keyboard

Screenshots or screencast

Trac ticket:
https://core.trac.wordpress.org/ticket/64806

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Props onemaggie, isabel_brison.

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[github-actions]

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[tellthemachines]

Aside from the submenu addition which I don't believe we should add here without adding first in Gutenberg, the rest of the changeset looks consistent with #75736.

The PHP unit tests are failing because they're testing get_stylesheet, which relies on data from the actual block attributes, and we won't get that in core until gutenberg is synced.

A good alternative would be to test get_styles_for_block instead and pass it the style nodes, so it's independent of the gutenberg sync and I think makes sense for this changeset because it's closer to where the changes actually are (we haven't changed get_stylesheet so we shouldn't have to test it). You can check the tests in #11706 for a similar approach.

[MaggieCabrera]

I updated this PR with the changes discussed plus rebased it and made it sure it was up to date with what is in Gutenberg right now. It should be ready for review

[tellthemachines]

The changes won't be testable in the core dev env until the editor files are updated to include the change from WordPress/gutenberg#79210.

The code mostly looks good, just a couple things I commented on below!

[tellthemachines]

Comparing with gutenberg we're missing 'elements' => $selectors[ $name ]['elements'] ?? array(), in this array as well as in the one from the loop below (those were added as part of WordPress/gutenberg#77513)

[MaggieCabrera]

good catch, thanks!