Backport the global styles variations changes from Gutenberg

src/wp-includes/class-wp-theme-json-resolver.php

@@ -449,4 +449,32 @@ public static function clean_cached_data() {
 		static::$i18n_schema              = null;
 	}
 
+	/**
+	 * Returns the style variations defined by the theme.
+	 *
+	 * @since 6.0.0
+	 *
+	 * @return array
+	 */
+	public static function get_style_variations() {
+		$variations     = array();
+		$base_directory = get_stylesheet_directory() . '/styles';
+		if ( is_dir( $base_directory ) ) {
+			$nested_files      = new RecursiveIteratorIterator( new RecursiveDirectoryIterator( $base_directory ) );
+			$nested_html_files = iterator_to_array( new RegexIterator( $nested_files, '/^.+\.json$/i', RecursiveRegexIterator::GET_MATCH ) );
+			ksort( $nested_html_files );
+			foreach ( $nested_html_files as $path => $file ) {
+				$decoded_file = wp_json_file_decode( $path, array( 'associative' => true ) );
+				if ( is_array( $decoded_file ) ) {
+					$translated = static::translate( $decoded_file, wp_get_theme()->get( 'TextDomain' ) );
+					$variation  = ( new WP_Theme_JSON_Gutenberg( $translated ) )->get_raw_data();
+					if ( empty( $variation['title'] ) ) {
+						$variation['title'] = basename( $path, '.json' );
+					}
+					$variations[] = $variation;
+				}
+			}
+		}
+		return $variations;
+	}
 }

src/wp-includes/rest-api/endpoints/class-wp-rest-global-styles-controller.php

@@ -65,6 +65,24 @@ public function register_routes() {
 			)
 		);
 
+		register_rest_route(
+			$this->namespace,
+			'/' . $this->rest_base . '/themes/(?P<stylesheet>[\/\s%\w\.\(\)\[\]\@_\-]+)/variations',
+			array(
+				array(
+					'methods'             => WP_REST_Server::READABLE,
+					'callback'            => array( $this, 'get_theme_items' ),
+					'permission_callback' => array( $this, 'get_theme_items_permissions_check' ),
+					'args'                => array(
+						'stylesheet' => array(
+							'description' => __( 'The theme identifier', 'gutenberg' ),
+							'type'        => 'string',
+						),
+					),
+				),
+			)
+		);
+
 		// Lists/updates a single global style variation based on the given id.
 		register_rest_route(
 			$this->namespace,
@@ -585,4 +603,53 @@ public function get_theme_item( $request ) {
 
 		return $response;
 	}
+
+	/**
+	 * Checks if a given request has access to read a single theme global styles config.
+	 *
+	 * @since 6.0.0
+	 * 
+	 * @param WP_REST_Request $request Full details about the request.
+	 * @return true|WP_Error True if the request has read access for the item, WP_Error object otherwise.
+	 */
+	public function get_theme_items_permissions_check( $request ) { // phpcs:ignore VariableAnalysis.CodeAnalysis.VariableAnalysis.UnusedVariable
+		// Verify if the current user has edit_theme_options capability.
+		// This capability is required to edit/view/delete templates.
+		if ( ! current_user_can( 'edit_theme_options' ) ) {
+			return new WP_Error(
+				'rest_cannot_manage_global_styles',
+				__( 'Sorry, you are not allowed to access the global styles on this site.' ),
+				array(
+					'status' => rest_authorization_required_code(),
+				)
+			);
+		}
+
+		return true;
+	}
+
+	/**
+	 * Returns the given theme global styles variations.
+	 *
+	 * @since 6.0.0
+	 *
+	 * @param WP_REST_Request $request The request instance.
+	 *
+	 * @return WP_REST_Response|WP_Error
+	 */
+	public function get_theme_items( $request ) {
+		if ( wp_get_theme()->get_stylesheet() !== $request['stylesheet'] ) {
+			// This endpoint only supports the active theme for now.
+			return new WP_Error(
+				'rest_theme_not_found',
+				__( 'Theme not found.' ),
+				array( 'status' => 404 )
+			);
+		}
+
+		$variations = WP_Theme_JSON_Resolver::get_style_variations();
+		$response   = rest_ensure_response( $variations );
+
+		return $response;
+	}
 }

tests/phpunit/data/themedir1/theme1/styles/variation.json

@@ -0,0 +1,23 @@
+{
+    "version": 2,
+    "settings": {
+        "color": {
+            "palette": [
+                {
+                    "slug": "foreground",
+                    "color": "#3F67C6",
+                    "name": "Foreground"
+                }
+            ]
+        }
+    },
+    "styles": {
+        "blocks": {
+            "core/post-title": {
+                "typography": {
+                    "fontWeight": "700"
+                }
+            }
+        }
+    }
+}

tests/phpunit/tests/rest-api/rest-global-styles-controller.php

@@ -117,6 +117,11 @@ public function test_register_routes() {
 			$routes['/wp/v2/global-styles/themes/(?P<stylesheet>[^\/:<>\*\?"\|]+(?:\/[^\/:<>\*\?"\|]+)?)'],
 			'Theme global styles route does not have exactly one element'
 		);
+		$this->assertArrayHasKey(
+			'/wp/v2/global-styles/themes/(?P<stylesheet>[\/\s%\w\.\(\)\[\]\@_\-]+)/variations',
+			$routes,
+			'Theme global styles variations route does not exist'
+		);
 	}
 
 	public function test_context_param() {
@@ -455,4 +460,41 @@ public function test_get_item_schema() {
 		$this->assertArrayHasKey( 'settings', $properties, 'Schema properties array does not have "settings" key' );
 		$this->assertArrayHasKey( 'title', $properties, 'Schema properties array does not have "title" key' );
 	}
+
+
+	public function test_get_theme_items() {
+		wp_set_current_user( self::$admin_id );
+		switch_theme( 'theme1' );
+		$request  = new WP_REST_Request( 'GET', '/wp/v2/global-styles/themes/theme1/variations' );
+		$response = rest_get_server()->dispatch( $request );
+		$data     = $response->get_data();
+		$expected = array(
+			array(
+				'version'  => 2,
+				'settings' => array(
+					'color' => array(
+						'palette' => array(
+							'theme' => array(
+								array(
+									'slug'  => 'foreground',
+									'color' => '#3F67C6',
+									'name'  => 'Foreground',
+								),
+							),
+						),
+					),
+				),
+				'styles'   => array(
+					'blocks' => array(
+						'core/post-title' => array(
+							'typography' => array(
+								'fontWeight' => '700',
+							),
+						),
+					),
+				),
+			),
+		);
+		$this->assertSameSetsWithIndex( $data, $expected );
+	}
 }