Changeset 62650 for trunk/src/wp-includes/class-wp-theme-json.php

Timestamp:

07/07/2026 12:20:57 AM (8 weeks ago)

Author:

dmsnell

Message:

Editor: Skip parsing in prepend_to_selector() for simple selectors.

Splitting a CSS selector involves unnecessary computation and allocation when the selector could not possibly involve more than one selector. It was discovered in profiling that this function was being called 4000+ times in a single request, and adding a pre-condition before splitting saved meaningful time on a page render.

This patch adds the pre-condition to verify that any commas present in a selector string can only be “comma tokens,” which split selectors at the top level, making it safe to fall back to simpler parsing that’s more efficient than general separator splitting.

This commit synchronizes work from the following Gutenberg PRs:

• ​https://github.com/WordPress/gutenberg/pull/76556
• ​https://github.com/WordPress/gutenberg/pull/79499

Developed in: ​https://github.com/WordPress/wordpress-develop/pull/12306
Discussed in: https://core.trac.wordpress.org/ticket/65533

Follow-up to [62607].

Props dmsnell, josephscott.
See #65533.

File:

• trunk/src/wp-includes/class-wp-theme-json.php (modified) (2 diffs)

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

@@ -1297 +1297 @@
         protected static function append_to_selector( $selector, $to_append ) {
                 if ( ! str_contains( $selector, ',' ) ) {
-                        return $selector . $to_append;
-                }
+                        return trim( $selector, " \t\n" ) . $to_append;
+                }
+
+                /**
+                 * Check for an opportunity to skip the more-costly selector splitting.
+                 * This should be possible if there are no comments, strings, functions,
+                 * URLs, escapes, or comment declaration openers (CDOs).
+                 *
+                 * Note that this means the fast-path will not apply for selectors like
+                 * the following incomplete list:
+                 *
+                 *  - `[class ~= "wide"]`
+                 *  - `.wp-block:is(.is-style-a, .is-style-b)`
+                 *  - `:nth-child(1)`
+                 *
+                 * These syntax forms all present opportunities where a comma may not
+                 * separate selectors. If none of the start characters are present,
+                 * there should be no way for a comma to mean anything other than a
+                 * comma token. The exception are syntax errors, which are not handled here.
+                 *
+                 * @see https://www.w3.org/TR/css-syntax-3/#parse-comma-separated-list-of-component-values
+                 */
+                if ( strlen( $selector ) === strcspn( $selector, '/\'"(<\\' ) ) {
+                        return preg_replace( '~[ \t\n]*,[ \t\n]*~', "{$to_append}, ", trim( $selector, " \t\n" ) ) . $to_append;
+                }
+
                 $new_selectors = array();
                 $selectors     = static::split_selector_list( $selector );
@@ -1322 +1346 @@
         protected static function prepend_to_selector( $selector, $to_prepend ) {
                 if ( ! str_contains( $selector, ',' ) ) {
-                        return $to_prepend . $selector;
-                }
+                        return $to_prepend . trim( $selector, " \t\n" );
+                }
+
+                /**
+                 * Check for an opportunity to skip the more-costly selector splitting.
+                 * This should be possible if there are no comments, strings, functions,
+                 * URLs, escapes, or comment declaration openers (CDOs).
+                 *
+                 * Note that this means the fast-path will not apply for selectors like
+                 * the following incomplete list:
+                 *
+                 *  - `[class ~= "wide"]`
+                 *  - `.wp-block:is(.is-style-a, .is-style-b)`
+                 *  - `:nth-child(1)`
+                 *
+                 * These syntax forms all present opportunities where a comma may not
+                 * separate selectors. If none of the start characters are present,
+                 * there should be no way for a comma to mean anything other than a
+                 * comma token. The exception are syntax errors, which are not handled here.
+                 *
+                 * @see https://www.w3.org/TR/css-syntax-3/#parse-comma-separated-list-of-component-values
+                 */
+                if ( strlen( $selector ) === strcspn( $selector, '/\'"(<\\' ) ) {
+                        return $to_prepend . preg_replace( '~[ \t\n]*,[ \t\n]*~', ", {$to_prepend}", trim( $selector, " \t\n" ) );
+                }
+
                 $new_selectors = array();
                 $selectors     = static::split_selector_list( $selector );