Performance: Follow-up fixes to prepend_to_selector() optimization. by dmsnell · Pull Request #79499 · WordPress/gutenberg

dmsnell · 2026-06-24T17:05:07Z

A recent optimization to theme.json code adds a fast-path to avoid attempting to split a selector list by commas, assuming that the absence of a parentheses means that all remaining commas are comma-tokens.

However, there are several other CSS syntax forms which are common in selectors which would present commas that are not comma tokens, and the new optimization will lead to CSS selector corruption.

This patch expands the list of potential syntax-form-openers to exclude the remaining domain of selector inputs which would be broken by the fast-path.

github-actions · 2026-06-24T17:05:17Z

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github-actions · 2026-06-26T22:50:01Z

Flaky tests detected in df325f7.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/28393619728
📝 Reported issues:

[Flaky Test] shows post-locked modal when document size limit is exceeded #78753 in /test/e2e/specs/editor/collaboration/http-only/collaboration-document-size-lock.spec.ts

westonruter

This is looking great.

westonruter · 2026-06-29T19:26:51Z

+	}
+
+	/**
+	 * @return array[]


Suggested change

* @return array[]

* @return array<string, array{selector: string, expected: string}>

added in 12f1e60

westonruter · 2026-06-29T19:27:53Z

+	}
+
+	/**
+	 * @return array[]


Suggested change

* @return array[]

* @return array<string, array{selector: string, expected: string}>

added in 12f1e60, but used the expected: string[] type

westonruter · 2026-06-29T19:31:10Z

-				$selectors[]      = $current_selector;
-				$current_selector = '';
+			/*
+			 * Start of a parenthesized expression, which maintains a stack of parenthesis.


Suggested change

* Start of a parenthesized expression, which maintains a stack of parenthesis.

* Start of a parenthesized expression, which maintains a stack of parentheses.

fixed in 12f1e60

westonruter · 2026-06-29T20:08:44Z

+	 *
+	 *     // Comments stay with the selector they follow.
+	 *     array( '.a /* a, the first *\/', '.b' ) === self::split_selector_list( '.a /* a, the first *\/,.b' );
+     *


Suggested change

*

*

transmogrified in 12f1e60

dmsnell · 2026-06-29T20:12:55Z

@westonruter I also auto-generated around 15 million selectors of varying counts (combined count), complexity, and syntax and found no cases where there were misparses. the testing may not be comprehensive and could have missed things, but I think it’s good

dmsnell · 2026-06-29T20:19:43Z

squashed in preparation to merge. former HEAD was 12f1e60

See #76556 A recent optimization to `theme.json` code adds a fast-path to avoid attempting to split a selector list by commas, assuming that the absence of a parentheses means that all remaining commas are comma-tokens. However, there are several other CSS syntax forms which are common in selectors which would present commas that are not comma tokens, and the new optimization will lead to CSS selector corruption. This patch expands the list of potential syntax-form-openers to exclude the remaining domain of selector inputs which would be broken by the fast-path, and applies fixes to `split_selector_list()` which would have left failing tests when applying the bug-fix to the earlier work. Co-Authored-By: Joseph Scott <josephscott@git.wordpress.org> Co-Authored-By: Weston Ruter <westonruter@git.wordpress.org>

Incorporated work from WordPress/gutenberg#79499

See WordPress/gutenberg#79499

Incorporated work from WordPress/gutenberg#79499

See WordPress/gutenberg#79499

In #79499 the `split_selector_list()` method was updated to avoid a number of mis-parsing cases with CSS selectors. The Core backport in WordPress/wordpress-develop#11857 includes a couple of updates not caught during review in Gutenberg, so this patch includes those updates: - the speedup from #76556 is added to `append_to_selector()` as well as `prepend_to_selector()`. - all selectors are trimmed, even single-selector selector lists and the last selector in a list. - callees no longer manually trim the results, improperly, leaning instead on the behavior in `split_selector_list()`.

Trac ticket: https://core.trac.wordpress.org/ticket/65533 This PR syncs the foloowing Gutenberg PRs: - WordPress/gutenberg#76556 - WordPress/gutenberg#79499 Opus 4.6 used in the initial patch creation in Gutenberg. Co-Authored-By: Dennis Snell <dmsnell@git.wordpress.org>

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: - WordPress/gutenberg#76556 - WordPress/gutenberg#79499 Developed in: #12306 Discussed in: https://core.trac.wordpress.org/ticket/65533 Follow-up to [62607]. Props dmsnell, josephscott. See #65533. git-svn-id: https://develop.svn.wordpress.org/trunk@62650 602fd350-edb4-49c9-b593-d223f7449a82

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: - WordPress/gutenberg#76556 - WordPress/gutenberg#79499 Developed in: WordPress/wordpress-develop#12306 Discussed in: https://core.trac.wordpress.org/ticket/65533 Follow-up to [62607]. Props dmsnell, josephscott. See #65533. Built from https://develop.svn.wordpress.org/trunk@62650 git-svn-id: http://core.svn.wordpress.org/trunk@61935 1a063a9b-81f0-0310-95a4-ce76da25c4cd

dmsnell requested a review from tellthemachines as a code owner June 24, 2026 17:05

westonruter reviewed Jun 29, 2026

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westonruter added the [Type] Performance Related to performance efforts label Jun 29, 2026

westonruter reviewed Jun 29, 2026

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westonruter approved these changes Jun 29, 2026

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dmsnell force-pushed the performance/prepent-for-the-selector-is-near branch from 12f1e60 to abaa8c3 Compare June 29, 2026 20:19

dmsnell force-pushed the performance/prepent-for-the-selector-is-near branch from abaa8c3 to 64f2669 Compare June 29, 2026 20:19

dmsnell merged commit 64f2669 into trunk Jun 29, 2026
41 checks passed

dmsnell deleted the performance/prepent-for-the-selector-is-near branch June 29, 2026 20:51

github-actions Bot mentioned this pull request Jun 29, 2026

PHP backports for WP 7.1 #79304

Open

dmsnell mentioned this pull request Jun 29, 2026

Editor: prepend_to_selector: optimized with str_replace() WordPress/wordpress-develop#12306

Closed

dmsnell added a commit to tellthemachines/wordpress-develop that referenced this pull request Jun 29, 2026

Expand selector parsing to avoid splitting on strings/comments/etc...

029d755

Incorporated work from WordPress/gutenberg#79499

dmsnell added a commit to tellthemachines/wordpress-develop that referenced this pull request Jun 29, 2026

Add tests for split_selector_list() from upstream PR

a42254d

See WordPress/gutenberg#79499

dmsnell mentioned this pull request Jun 29, 2026

fix inconsistencies in global styles feature selectors WordPress/wordpress-develop#11857

Closed

sirreal reviewed Jun 30, 2026

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

dmsnell mentioned this pull request Jun 30, 2026

CSS: Follow-up fixes to split_selector_list() #79723

Merged

tellthemachines pushed a commit to tellthemachines/wordpress-develop that referenced this pull request Jul 1, 2026

Expand selector parsing to avoid splitting on strings/comments/etc...

363b351

Incorporated work from WordPress/gutenberg#79499

tellthemachines pushed a commit to tellthemachines/wordpress-develop that referenced this pull request Jul 1, 2026

Add tests for split_selector_list() from upstream PR

4eb287d

See WordPress/gutenberg#79499

dmsnell mentioned this pull request Jul 1, 2026

Performance: Follow-up normalization in prepend_to_selector() and append_to_selector(). #79793

Open

	* @return array[]
	* @return array<string, array{selector: string, expected: string}>

	* Start of a parenthesized expression, which maintains a stack of parenthesis.
	* Start of a parenthesized expression, which maintains a stack of parentheses.

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dmsnell commented Jun 24, 2026

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dmsnell commented Jun 29, 2026

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