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Improve CSS selector performance safeguards - #333818
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Justin Chen (justschen) merged 3 commits intoSep 2, 2026
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Replace non-codicon class substring selectors with stable markers, remove disconnected editor header styles, and prevent new high-cost selector patterns. Add a repeatable Modern UI CSS benchmark and document the observed results and limitations. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: aa457496-6844-4e4c-b182-07866a0a7506
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📬 CODENOTIFYThe following users are being notified based on files changed in this PR: Benjamin Christopher Simmonds (@benibenj)Matched files:
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Copilot review overview
Review tier: Balanced
Findings: 2
New issues introduced by this change (2)
| Severity | Finding |
|---|---|
 |
.github/skills/auto-perf-optimize/scripts/workbench-css-performance.mts — These setup steps run before both summary initialization and the try/catch. If transpilation… |
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build/stylelint.ts — This also classifies CSS under src/vs/**/test/** as production (for example, the… |
What changed in this PR
Improves CSS selector invalidation safeguards and adds repeatable performance measurement.
Changes:
- Replaces non-codicon class-substring selectors with stable or exact classes.
- Extends stylelint enforcement to core and extension CSS.
- Adds a Modern UI CSS benchmark and audit documentation.
| File | Description |
|---|---|
src/vs/workbench/services/decorations/common/decorations.ts |
Defines a stable badge marker. |
src/vs/workbench/contrib/modernUI/README.md |
Links performance documentation. |
src/vs/workbench/contrib/modernUI/CSS_PERFORMANCE.md |
Documents audit and benchmark results. |
src/vs/workbench/contrib/inlineChat/browser/media/inlineChat.css |
Uses an exact decoration class. |
src/vs/workbench/contrib/chat/browser/widget/media/chat.css |
Replaces placeholder substring matching. |
src/vs/workbench/browser/parts/views/media/views.css |
Uses stable decoration markers. |
src/vs/workbench/browser/parts/editor/media/editorgroupview.css |
Removes disconnected header styles. |
src/vs/workbench/browser/labels.ts |
Applies the badge marker. |
package.json |
Adds the CSS benchmark command. |
build/stylelint.ts |
Enforces the new selector restriction. |
build/lib/test/stylelint.test.ts |
Checks extension CSS filtering. |
build/lib/test/rootAnchoredHas.test.ts |
Tests substring-selector parsing. |
build/lib/stylelint/validateHasSelectors.ts |
Implements selector detection. |
build/filters.ts |
Includes production extension CSS. |
.github/skills/auto-perf-optimize/scripts/workbench-css-performance.mts |
Implements the benchmark runner. |
.github/skills/auto-perf-optimize/scratchpad/README.md |
Documents the runner. |
.github/instructions/css-best-practices.instructions.md |
Documents the codicon exception. |
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Move process-exit error propagation outside benchmark cleanup and use the repository's preferred string quoting in the selector regression test. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: aa457496-6844-4e4c-b182-07866a0a7506
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Author
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CI follow-up:
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Dmitriy Vasyura (dmitrivMS)
previously approved these changes
Sep 1, 2026
Justin Chen (justschen)
marked this pull request as draft
September 1, 2026 18:03
Ensure benchmark setup failures retain a diagnostic summary artifact and exclude test fixture paths from the production-only class substring selector safeguard. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: aa457496-6844-4e4c-b182-07866a0a7506
Lee Murray (mrleemurray)
approved these changes
Sep 2, 2026
Lee Murray (mrleemurray)
left a comment
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Awesome!
Justin Chen (justschen)
enabled auto-merge (squash)
September 2, 2026 09:25
Justin Chen (justschen)
deleted the
agents/css-performance-audit-and-fixes
branch
September 2, 2026 09:27
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Summary
:has()rule:has()inventory, correctness rationale, and measurement limitationsExisting codicon-family selectors are intentionally unchanged and grandfathered by the lint rule. The experimental transform shimmer work was fully reverted and is not part of this PR.
Performance
Bracketed before/after runs observed these median wall-time changes:
These are observed timings, not isolated causal gains. Generic style-recalculation counts did not materially decrease because codicon substring selectors remain, so the PR conservatively claims no broad proven speedup and focuses on targeted invalidation prevention.
Validation
npm run compilenpm run hygiene