Introduce prepend_to_selector() to avoid additional if checks and f…

…ollow single responsibility principle (#50266)

* Introduce prepend_to_selector() method to avoid additional if checks and follow single responsibility principle.

* Don't call append_to_selector() when selector is likely empty.

* Remove parameter completely instead of deprecating.

* Correct doc block.

lib/class-wp-theme-json-gutenberg.php

@@ -811,20 +811,45 @@ protected static function sanitize( $input, $valid_block_names, $valid_element_n
 	 *
 	 * @since 5.8.0
 	 * @since 6.1.0 Added append position.
+	 * @since 6.3.0 Removed append position parameter.
 	 *
 	 * @param string $selector  Original selector.
 	 * @param string $to_append Selector to append.
-	 * @param string $position  A position sub-selector should be appended. Default 'right'.
 	 * @return string The new selector.
 	 */
-	protected static function append_to_selector( $selector, $to_append, $position = 'right' ) {
+	protected static function append_to_selector( $selector, $to_append ) {
 		if ( ! str_contains( $selector, ',' ) ) {
-			return 'right' === $position ? $selector . $to_append : $to_append . $selector;
+			return $selector . $to_append;
 		}
 		$new_selectors = array();
 		$selectors     = explode( ',', $selector );
 		foreach ( $selectors as $sel ) {
-			$new_selectors[] = 'right' === $position ? $sel . $to_append : $to_append . $sel;
+			$new_selectors[] = $sel . $to_append;
+		}
+		return implode( ',', $new_selectors );
+	}
+
+	/**
+	 * Prepends a sub-selector to an existing one.
+	 *
+	 * Given the compounded $selector "h1, h2, h3"
+	 * and the $to_prepend selector ".some-class " the result will be
+	 * ".some-class h1, .some-class  h2, .some-class  h3".
+	 *
+	 * @since 6.3.0
+	 *
+	 * @param string $selector   Original selector.
+	 * @param string $to_prepend Selector to prepend.
+	 * @return string The new selector.
+	 */
+	protected static function prepend_to_selector( $selector, $to_prepend ) {
+		if ( ! str_contains( $selector, ',' ) ) {
+			return $to_prepend . $selector;
+		}
+		$new_selectors = array();
+		$selectors     = explode( ',', $selector );
+		foreach ( $selectors as $sel ) {
+			$new_selectors[] = $to_prepend . $sel;
 		}
 		return implode( ',', $new_selectors );
 	}
@@ -1530,10 +1555,13 @@ protected static function compute_preset_classes( $settings, $selector, $origins
 			$slugs = static::get_settings_slugs( $settings, $preset_metadata, $origins );
 			foreach ( $preset_metadata['classes'] as $class => $property ) {
 				foreach ( $slugs as $slug ) {
-					$css_var     = static::replace_slug_in_string( $preset_metadata['css_vars'], $slug );
-					$class_name  = static::replace_slug_in_string( $class, $slug );
-					$stylesheet .= static::to_ruleset(
-						static::append_to_selector( $selector, $class_name ),
+					$css_var    = static::replace_slug_in_string( $preset_metadata['css_vars'], $slug );
+					$class_name = static::replace_slug_in_string( $class, $slug );
+
+					// $selector is often empty, so we can save ourselves the `append_to_selector()` call then.
+					$new_selector = '' === $selector ? $class_name : static::append_to_selector( $selector, $class_name );
+					$stylesheet  .= static::to_ruleset(
+						$new_selector,
 						array(
 							array(
 								'name'  => $property,
@@ -3458,7 +3486,7 @@ protected static function get_block_element_selectors( $root_selector ) {
 					$element_selector = array( $el_selector );
 					break;
 				}
-				$element_selector[] = static::append_to_selector( $el_selector, $selector . ' ', 'left' );
+				$element_selector[] = static::prepend_to_selector( $el_selector, $selector . ' ' );
 			}
 			$element_selectors[ $el_name ] = implode( ',', $element_selector );
 		}