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perf(css): cut CPU and allocation in the CSS minifier - #22868
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Types CoverageCoverage after merging perf/css-gc-pieces into main will be
Coverage Report |
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This PR is packaged and the instant preview of its latest commit is available. Install it locally:
npm i -D webpack@https://pkg.pr.new/webpack@22868
yarn add -D webpack@https://pkg.pr.new/webpack@22868
pnpm add -D webpack@https://pkg.pr.new/webpack@22868 |
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📝 Walkthrough
Priority: ⬇️ Low Change: Refactor Merge Risk: ⚪ Minimal · up to
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| Check name | Status | Explanation | Resolution |
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| Title check |  |
The title uses the required Conventional Commit format, perf(css): subject, and accurately describes the performance-focused changes. The branch prefix is not provided, so the required type-to-branc… |
Provide the branch name or branch prefix, or confirm that the branch prefix is perf. If it matches perf, the title passes this check. |
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
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Explanation
The title uses the required Conventional Commit format,
perf(css): subject, and accurately describes the performance-focused changes. The branch prefix is not provided, so the required type-to-branch-prefix match cannot be verified.Resolution
Provide the branch name or branch prefix, or confirm that the branch prefix is
perf. If it matchesperf, the title passes this check.
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Actionable comments posted: 1
- 🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @lib/css/syntax-parser.js:
- Around line 12951-12952: Update the `_unwrapLoneIs` JSDoc description to use
no more than two sentences by merging the caller-context sentence into the
existing description or removing it; preserve the relevant documentation without
changing implementation behavior.
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ℹ️ Review info
⚙️ Run configuration
- Source mode: Auto
- Repository: webpack/webpack
- Branch: perf/css-gc-pieces
- File: .coderabbit.yaml
- Commit: 68fba22
- Layers: Repository YAML
- Review profile: CHILL
- Plan: Advanced
- Run ID:
62bc267e-7c22-4975-b614-8fbb545b6406
📒 Files selected for processing: 3
lib/css/syntax-parser.jslib/css/syntax-printer.jslib/util/SourceProcessor.js
Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 9 remain after this review.
Generated code sizeComparing base (
Read No asset changed size. No runtime gained or lost a runtime module. Built |
Merging this PR will degrade performance by 24.78%2 warnings, 1 note
Warning Please fix the performance issues or acknowledge them on CodSpeed. Performance Changes
Tip Investigate this regression by commenting Comparing 
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Summary
Next round after #22830 of making the CSS minifier faster on the
benchmark:css-toolscorpus. Output is byte-identical:tooling/hash-css-outputs.jsmatches on all 6642 entries, source maps included.Maplookups per pair.:is()to unwrap during the pseudo-name fold, which already reads every part, and look for a*part natively before walking for an implied universal selector.pushreserved 17 slots for 1 span, which held 1.9 MB on Fomantic UI.printerwas recompiled 14 times in one 2-pass run, because rare branches kept deopting it.Measured against
main, all 77 fixtures:--predictable, 5-fixture subset)What kind of change does this PR introduce?
perf
Did you add tests for your changes?
No new tests: behavior is unchanged, which the output hashes check over the whole corpus. Existing
test/unitCases/css/syntaxand SourceProcessor tests pass (2719).Does this PR introduce a breaking change?
No.
If relevant, what needs to be documented once your changes are merged or what have you already documented?
n/a
Use of AI
Claude Code profiled the minifier, wrote the changes, and measured each one against
mainwith the hash check above; changes that did not measure as a win were dropped. The pending changeset300-faster-minifier-startup.mdalready covers faster CSS minification, so none is added.Generated by Claude Code
Summary by CodeRabbit