Add Ability: core/get-active-theme - #2

What?

Adds a new core ability core/get-active-theme to the Abilities API.

The ability returns information about the currently active theme. By default it returns a full set of fields (stylesheet, template, name, version, description, author, author_uri, theme_uri, status, parent, screenshot, tags, requires_wp, requires_php, text_domain); callers can pass an optional fields array to project to a subset.

This PR also introduces shared theme schema helpers ($theme_properties, $theme_fields, $prepare_theme_data) that are reused by the follow-up theme abilities in this stack.

Why?

The Abilities API is the surface AI assistants and other automations use to inspect and operate on a WordPress site. Knowing which theme is currently active is a foundational read-only signal: it lets a model describe the site, decide whether a feature is supported (block themes vs classic themes, child themes, required PHP/WP versions, etc.), and reason about subsequent actions before performing them.

A dedicated, schema-driven ability gives that signal a stable, typed contract — instead of relying on REST endpoints with broader payloads or on raw wp_get_theme() access.

How?

• Registers core/get-active-theme with wp_register_ability() under the site category.
• permission_callback: current_user_can( 'switch_themes' ).
• execute_callback: calls wp_get_theme() and projects through the shared $prepare_theme_data helper.
• meta.annotations: readonly: true, destructive: false, idempotent: true.
• meta.show_in_rest: true so the ability is reachable via the Abilities REST namespace.
• Defines $theme_properties / $theme_fields / $prepare_theme_data once at the top of the theme-abilities block so the follow-up PRs (core/get-theme-info, core/get-themes, core/activate-theme) reuse the same schema and projection logic.

How to test

PHPUnit

The PR adds 3 new tests in tests/phpunit/tests/abilities-api/wpRegisterCoreAbilities.php:

• test_core_get_active_theme_ability_is_registered — verifies the ability is registered, exposed in REST, and that its input/output schemas declare every documented field.
• test_core_get_active_theme_executes — runs the ability as an administrator with no input (full payload) and with a fields projection (subset).
• test_core_get_active_theme_requires_switch_themes — runs the ability as a subscriber and asserts a ability_invalid_permissions WP_Error.

Run only this PR's tests:

npm run test:php -- --filter core_get_active_theme tests/phpunit/tests/abilities-api/wpRegisterCoreAbilities.php

Result on this branch:

OK (13 tests, 121 assertions)

Abilities Explorer

The new Abilities Explorer experiment shipped with the WordPress AI plugin can also be used to exercise this ability interactively:

1. Install the WordPress AI plugin from trunk and activate it.
2. Open the Abilities Explorer experiment from the plugin UI.
3. Find core/get-active-theme in the site category.
4. Run it with no input, then with { "fields": ["stylesheet", "name", "version"] }.

Testing evidence

Invoking the ability via wp eval-file against the dev-env:

Input (no arguments):

{}

Output:

{
    "stylesheet": "twentytwentyfive",
    "template": "twentytwentyfive",
    "name": "Twenty Twenty-Five",
    "version": "1.5",
    "description": "Twenty Twenty-Five emphasizes simplicity and adaptability. ...",
    "author": "the WordPress team",
    "author_uri": "https://wordpress.org",
    "theme_uri": "https://wordpress.org/themes/twentytwentyfive/",
    "status": "active",
    "parent": null,
    "screenshot": "http://localhost:8889/wp-content/themes/twentytwentyfive/screenshot.png",
    "tags": ["one-column", "custom-colors", "...", "news"],
    "requires_wp": "6.7",
    "requires_php": "7.2",
    "text_domain": "twentytwentyfive"
}

Input (field projection):

{ "fields": ["stylesheet", "name", "version"] }

Output:

{
    "stylesheet": "twentytwentyfive",
    "name": "Twenty Twenty-Five",
    "version": "1.5"
}

Input (called as a subscriber, no capability):

{}

Output (WP_Error):

code:    ability_invalid_permissions
message: Ability "core/get-active-theme" does not have necessary permission.

Stacked PRs

This PR is the base of a 4-PR stack that ships the theme abilities:

1. This PR — Add Ability: core/get-active-theme
2. Add Ability: core/get-theme-info — Add Ability: core/get-theme-info #3
3. Add Ability: core/get-themes — Add Ability: core/get-themes #4
4. Add Ability: core/activate-theme — Add Ability: core/activate-theme #5