Add Style Engine support for nested CSS rules.

src/wp-includes/style-engine.php

@@ -113,11 +113,14 @@ function wp_style_engine_get_styles( $block_styles, $options = array() ) {
  *     .elephant-are-cool{color:gray;width:3em}
  *
  * @since 6.1.0
+ * @since 6.6.0 Added support for `$rules_group` in the `$css_rules` array.
  *
  * @param array $css_rules {
  *     Required. A collection of CSS rules.
  *
  *     @type array ...$0 {
+ *         @type string   $rules_group  A parent CSS selector in the case of nested CSS,
+ *                                      or a CSS nested @rule, such as `@media (min-width: 80rem)` or `@layer module`.
  *         @type string   $selector     A CSS selector.
  *         @type string[] $declarations An associative array of CSS definitions,
  *                                      e.g. `array( "$property" => "$value", "$property" => "$value" )`.
@@ -154,11 +157,12 @@ function wp_style_engine_get_stylesheet_from_css_rules( $css_rules, $options = a
 			continue;
 		}
 
+		$rules_group = $css_rule['rules_group'] ?? null;
 		if ( ! empty( $options['context'] ) ) {
-			WP_Style_Engine::store_css_rule( $options['context'], $css_rule['selector'], $css_rule['declarations'] );
+			WP_Style_Engine::store_css_rule( $options['context'], $css_rule['selector'], $css_rule['declarations'], $rules_group );
 		}
 
-		$css_rule_objects[] = new WP_Style_Engine_CSS_Rule( $css_rule['selector'], $css_rule['declarations'] );
+		$css_rule_objects[] = new WP_Style_Engine_CSS_Rule( $css_rule['selector'], $css_rule['declarations'], $rules_group );
 	}
 
 	if ( empty( $css_rule_objects ) ) {

src/wp-includes/style-engine/class-wp-style-engine-css-rule.php

@@ -35,20 +35,33 @@ class WP_Style_Engine_CSS_Rule {
 	 */
 	protected $declarations;
 
+	/**
+	 * A parent CSS selector in the case of nested CSS, or a CSS nested @rule,
+	 * such as `@media (min-width: 80rem)` or `@layer module`.
+	 *
+	 * @since 6.6.0
+	 * @var string
+	 */
+	protected $rules_group;
+
 	/**
 	 * Constructor.
 	 *
 	 * @since 6.1.0
+	 * @since 6.6.0 Added the `$rules_group` parameter.
 	 *
 	 * @param string                                    $selector     Optional. The CSS selector. Default empty string.
 	 * @param string[]|WP_Style_Engine_CSS_Declarations $declarations Optional. An associative array of CSS definitions,
 	 *                                                                e.g. `array( "$property" => "$value", "$property" => "$value" )`,
 	 *                                                                or a WP_Style_Engine_CSS_Declarations object.
 	 *                                                                Default empty array.
+	 * @param string                                    $rules_group  A parent CSS selector in the case of nested CSS, or a CSS nested @rule,
+	 *                                                                such as `@media (min-width: 80rem)` or `@layer module`.
 	 */
-	public function __construct( $selector = '', $declarations = array() ) {
+	public function __construct( $selector = '', $declarations = array(), $rules_group = '' ) {
 		$this->set_selector( $selector );
 		$this->add_declarations( $declarations );
+		$this->set_rules_group( $rules_group );
 	}
 
 	/**
@@ -89,6 +102,31 @@ public function add_declarations( $declarations ) {
 		return $this;
 	}
 
+	/**
+	 * Sets the rules group.
+	 *
+	 * @since 6.6.0
+	 *
+	 * @param string $rules_group A parent CSS selector in the case of nested CSS, or a CSS nested @rule,
+	 *                            such as `@media (min-width: 80rem)` or `@layer module`.
+	 * @return WP_Style_Engine_CSS_Rule Returns the object to allow chaining of methods.
+	 */
+	public function set_rules_group( $rules_group ) {
+		$this->rules_group = $rules_group;
+		return $this;
+	}
+
+	/**
+	 * Gets the rules group.
+	 *
+	 * @since 6.6.0
+	 *
+	 * @return string
+	 */
+	public function get_rules_group() {
+		return $this->rules_group;
+	}
+
 	/**
 	 * Gets the declarations object.
 	 *
@@ -115,6 +153,7 @@ public function get_selector() {
 	 * Gets the CSS.
 	 *
 	 * @since 6.1.0
+	 * @since 6.6.0 Added support for nested CSS with rules groups.
 	 *
 	 * @param bool $should_prettify Optional. Whether to add spacing, new lines and indents.
 	 *                              Default false.
@@ -123,17 +162,28 @@ public function get_selector() {
 	 * @return string
 	 */
 	public function get_css( $should_prettify = false, $indent_count = 0 ) {
-		$rule_indent         = $should_prettify ? str_repeat( "\t", $indent_count ) : '';
-		$declarations_indent = $should_prettify ? $indent_count + 1 : 0;
-		$suffix              = $should_prettify ? "\n" : '';
-		$spacer              = $should_prettify ? ' ' : '';
-		$selector            = $should_prettify ? str_replace( ',', ",\n", $this->get_selector() ) : $this->get_selector();
-		$css_declarations    = $this->declarations->get_declarations_string( $should_prettify, $declarations_indent );
+		$rule_indent                = $should_prettify ? str_repeat( "\t", $indent_count ) : '';
+		$nested_rule_indent         = $should_prettify ? str_repeat( "\t", $indent_count + 1 ) : '';
+		$declarations_indent        = $should_prettify ? $indent_count + 1 : 0;
+		$nested_declarations_indent = $should_prettify ? $indent_count + 2 : 0;
+		$suffix                     = $should_prettify ? "\n" : '';
+		$spacer                     = $should_prettify ? ' ' : '';
+		// Trims any multiple selectors strings.
+		$selector         = $should_prettify ? implode( ',', array_map( 'trim', explode( ',', $this->get_selector() ) ) ) : $this->get_selector();
+		$selector         = $should_prettify ? str_replace( array( ',' ), ",\n", $selector ) : $selector;
+		$rules_group      = $this->get_rules_group();
+		$has_rules_group  = ! empty( $rules_group );
+		$css_declarations = $this->declarations->get_declarations_string( $should_prettify, $has_rules_group ? $nested_declarations_indent : $declarations_indent );
 
 		if ( empty( $css_declarations ) ) {
 			return '';
 		}
 
+		if ( $has_rules_group ) {
+			$selector = "{$rule_indent}{$rules_group}{$spacer}{{$suffix}{$nested_rule_indent}{$selector}{$spacer}{{$suffix}{$css_declarations}{$suffix}{$nested_rule_indent}}{$suffix}{$rule_indent}}";
+			return $selector;
+		}
+
 		return "{$rule_indent}{$selector}{$spacer}{{$suffix}{$css_declarations}{$suffix}{$rule_indent}}";
 	}
 }

src/wp-includes/style-engine/class-wp-style-engine-css-rules-store.php

@@ -121,19 +121,30 @@ public function get_all_rules() {
 	 * If the rule does not exist, it will be created.
 	 *
 	 * @since 6.1.0
+	 * @since 6.6.0 Added the $rules_group parameter.
 	 *
 	 * @param string $selector The CSS selector.
+	 * @param string $rules_group A parent CSS selector in the case of nested CSS, or a CSS nested @rule,
+	 *                            such as `@media (min-width: 80rem)` or `@layer module`.
 	 * @return WP_Style_Engine_CSS_Rule|void Returns a WP_Style_Engine_CSS_Rule object,
 	 *                                       or void if the selector is empty.
 	 */
-	public function add_rule( $selector ) {
-		$selector = trim( $selector );
+	public function add_rule( $selector, $rules_group = '' ) {
+		$selector    = $selector ? trim( $selector ) : '';
+		$rules_group = $rules_group ? trim( $rules_group ) : '';
 
 		// Bail early if there is no selector.
 		if ( empty( $selector ) ) {
 			return;
 		}
 
+		if ( ! empty( $rules_group ) ) {
+			if ( empty( $this->rules[ "$rules_group $selector" ] ) ) {
+				$this->rules[ "$rules_group $selector" ] = new WP_Style_Engine_CSS_Rule( $selector, array(), $rules_group );
+			}
+			return $this->rules[ "$rules_group $selector" ];
+		}
+
 		// Create the rule if it doesn't exist.
 		if ( empty( $this->rules[ $selector ] ) ) {
 			$this->rules[ $selector ] = new WP_Style_Engine_CSS_Rule( $selector );

src/wp-includes/style-engine/class-wp-style-engine-processor.php

@@ -58,6 +58,7 @@ public function add_store( $store ) {
 	 * Adds rules to be processed.
 	 *
 	 * @since 6.1.0
+	 * @since 6.6.0 Added support for rules_group.
 	 *
 	 * @param WP_Style_Engine_CSS_Rule|WP_Style_Engine_CSS_Rule[] $css_rules A single, or an array of,
 	 *                                                                       WP_Style_Engine_CSS_Rule objects
@@ -70,7 +71,24 @@ public function add_rules( $css_rules ) {
 		}
 
 		foreach ( $css_rules as $rule ) {
-			$selector = $rule->get_selector();
+			$selector    = $rule->get_selector();
+			$rules_group = $rule->get_rules_group();
+
+			/**
+			 * If there is a rules_group and it already exists in the css_rules array,
+			 * add the rule to it.
+			 * Otherwise, create a new entry for the rules_group.
+			 */
+			if ( ! empty( $rules_group ) ) {
+				if ( isset( $this->css_rules[ "$rules_group $selector" ] ) ) {
+					$this->css_rules[ "$rules_group $selector" ]->add_declarations( $rule->get_declarations() );
+					continue;
+				}
+				$this->css_rules[ "$rules_group $selector" ] = $rule;
+				continue;
+			}
+
+			// If the selector already exists, add the declarations to it.
 			if ( isset( $this->css_rules[ $selector ] ) ) {
 				$this->css_rules[ $selector ]->add_declarations( $rule->get_declarations() );
 				continue;
@@ -117,6 +135,7 @@ public function get_css( $options = array() ) {
 		// Build the CSS.
 		$css = '';
 		foreach ( $this->css_rules as $rule ) {
+			// See class WP_Style_Engine_CSS_Rule for the get_css method.
 			$css .= $rule->get_css( $options['prettify'] );
 			$css .= $options['prettify'] ? "\n" : '';
 		}

src/wp-includes/style-engine/class-wp-style-engine.php

@@ -364,19 +364,22 @@ protected static function is_valid_style_value( $style_value ) {
 	 * Stores a CSS rule using the provided CSS selector and CSS declarations.
 	 *
 	 * @since 6.1.0
+	 * @since 6.6.0 Added the `$rules_group` parameter.
 	 *
 	 * @param string   $store_name       A valid store key.
 	 * @param string   $css_selector     When a selector is passed, the function will return
 	 *                                   a full CSS rule `$selector { ...rules }`
 	 *                                   otherwise a concatenated string of properties and values.
 	 * @param string[] $css_declarations An associative array of CSS definitions,
 	 *                                   e.g. `array( "$property" => "$value", "$property" => "$value" )`.
+	 * @param string $rules_group        Optional. A parent CSS selector in the case of nested CSS, or a CSS nested @rule,
+	 *                                   such as `@media (min-width: 80rem)` or `@layer module`.
 	 */
-	public static function store_css_rule( $store_name, $css_selector, $css_declarations ) {
+	public static function store_css_rule( $store_name, $css_selector, $css_declarations, $rules_group = '' ) {
 		if ( empty( $store_name ) || empty( $css_selector ) || empty( $css_declarations ) ) {
 			return;
 		}
-		static::get_store( $store_name )->add_rule( $css_selector )->add_declarations( $css_declarations );
+		static::get_store( $store_name )->add_rule( $css_selector, $rules_group )->add_declarations( $css_declarations );
 	}
 
 	/**

tests/phpunit/tests/style-engine/styleEngine.php

@@ -749,4 +749,68 @@ public function test_should_dedupe_and_merge_css_rules() {
 
 		$this->assertSame( '.gandalf{color:white;height:190px;border-style:dotted;padding:10px;margin-bottom:100px;}.dumbledore{color:grey;height:90px;border-style:dotted;}.rincewind{color:grey;height:90px;border-style:dotted;}', $compiled_stylesheet );
 	}
+
+	/**
+	 * Tests returning a generated stylesheet from a set of nested rules and merging their declarations.
+	 *
+	 * @ticket 61099
+	 *
+	 * @covers ::wp_style_engine_get_stylesheet_from_css_rules
+	 */
+	public function test_should_merge_declarations_for_rules_groups() {
+		$css_rules = array(
+			array(
+				'selector'     => '.saruman',
+				'rules_group'  => '@container (min-width: 700px)',
+				'declarations' => array(
+					'color'        => 'white',
+					'height'       => '100px',
+					'border-style' => 'solid',
+					'align-self'   => 'stretch',
+				),
+			),
+			array(
+				'selector'     => '.saruman',
+				'rules_group'  => '@container (min-width: 700px)',
+				'declarations' => array(
+					'color'       => 'black',
+					'font-family' => 'The-Great-Eye',
+				),
+			),
+		);
+
+		$compiled_stylesheet = wp_style_engine_get_stylesheet_from_css_rules( $css_rules, array( 'prettify' => false ) );
+
+		$this->assertSame( '@container (min-width: 700px){.saruman{color:black;height:100px;border-style:solid;align-self:stretch;font-family:The-Great-Eye;}}', $compiled_stylesheet );
+	}
+
+	/**
+	 * Tests returning a generated stylesheet from a set of nested rules.
+	 *
+	 * @ticket 61099
+	 *
+	 * @covers ::wp_style_engine_get_stylesheet_from_css_rules
+	 */
+	public function test_should_return_stylesheet_with_nested_rules() {
+		$css_rules = array(
+			array(
+				'rules_group'  => '.foo',
+				'selector'     => '@media (orientation: landscape)',
+				'declarations' => array(
+					'background-color' => 'blue',
+				),
+			),
+			array(
+				'rules_group'  => '.foo',
+				'selector'     => '@media (min-width > 1024px)',
+				'declarations' => array(
+					'background-color' => 'cotton-blue',
+				),
+			),
+		);
+
+		$compiled_stylesheet = wp_style_engine_get_stylesheet_from_css_rules( $css_rules, array( 'prettify' => false ) );
+
+		$this->assertSame( '.foo{@media (orientation: landscape){background-color:blue;}}.foo{@media (min-width > 1024px){background-color:cotton-blue;}}', $compiled_stylesheet );
+	}
 }

tests/phpunit/tests/style-engine/wpStyleEngineCssRule.php

@@ -37,6 +37,24 @@ public function test_should_instantiate_with_selector_and_rules() {
 		$this->assertSame( $expected, $css_rule->get_css(), 'Value returned by get_css() does not match expected declarations string.' );
 	}
 
+	/**
+	 * Tests setting and getting a rules group.
+	 *
+	 * @ticket 61099
+	 *
+	 * @covers ::set_rules_group
+	 * @covers ::get_rules_group
+	 */
+	public function test_should_set_rules_group() {
+		$rule = new WP_Style_Engine_CSS_Rule( '.heres-johnny', array(), '@layer state' );
+
+		$this->assertSame( '@layer state', $rule->get_rules_group(), 'Return value of get_rules_group() does not match value passed to constructor.' );
+
+		$rule->set_rules_group( '@layer pony' );
+
+		$this->assertSame( '@layer pony', $rule->get_rules_group(), 'Return value of get_rules_group() does not match value passed to set_rules_group().' );
+	}
+
 	/**
 	 * Tests that declaration properties are deduplicated.
 	 *

tests/phpunit/tests/style-engine/wpStyleEngineCssRulesStore.php

@@ -187,4 +187,22 @@ public function test_should_get_all_rule_objects_for_a_store() {
 
 		$this->assertSame( $expected, $new_pizza_store->get_all_rules(), 'Return value for get_all_rules() does not match expectations after adding new rules to store.' );
 	}
+
+	/**
+	 * Tests adding rules group keys to store.
+	 *
+	 * @ticket 61099
+	 *
+	 * @covers ::add_rule
+	 */
+	public function test_should_store_as_concatenated_rules_groups_and_selector() {
+		$store_one      = WP_Style_Engine_CSS_Rules_Store::get_store( 'one' );
+		$store_one_rule = $store_one->add_rule( '.tony', '.one' );
+
+		$this->assertSame(
+			'.one .tony',
+			"{$store_one_rule->get_rules_group()} {$store_one_rule->get_selector()}",
+			'add_rule() does not concatenate rules group and selector.'
+		);
+	}
 }