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build(tooling): compare JavaScript parsers and printers, and widen the CSS and HTML fixtures - #22010
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…m to acorn The CSS and HTML comparisons already weigh what webpack's own parser and printer cost against the ecosystem's. This is the same three tables for JavaScript, over fourteen bundles as they ship — jQuery through the 8.9 MB TypeScript one, ES5 and modern, script and module. webpack owns a parser there and no printer, so it has a row in the parse table only, and that table's last column is what the comparison is for: every ESTree parser is held against acorn's tree and the first node where the two differ is named, so a divergence in `lib/javascript/syntax.js` is a line of output rather than a bug someone hits later. A parser answering in a dialect of its own reads as `own dialect` instead of as a disagreement.
Every fixture so far was source as its author wrote it, which is not the shape most of what a build reads is in. The JavaScript comparison gains minified bundles (jQuery, React DOM and Vue as they ship to production, plus Swagger UI's own bundle), a modern ESM one written in classes and private fields (pdf.js), the smallest module worth timing (Preact) and two more that dwarf the rest (ECharts, Immutable). CSS gains the shapes the framework sheets do not have: an icon font's thousands of one-declaration rules, a sheet that is custom properties and nothing else, and four more component and widget sheets. HTML gains the parts of §13.2 nothing there reached — a document that is all tables, one that leans on every recovery rule the spec writes down, one built out of templates and a declarative shadow root, and an inlined icon sprite for foreign content.
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This PR is packaged and the instant preview is available (af8bf0b). Install it locally:
npm i -D webpack@https://pkg.pr.new/webpack@af8bf0b
yarn add -D webpack@https://pkg.pr.new/webpack@af8bf0b
pnpm add -D webpack@https://pkg.pr.new/webpack@af8bf0b |
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Included review availability: Your plan provides up to 10 included reviews per hour; 7 remain after this review. 📝 WalkthroughWalkthroughThe pull request adds a JavaScript parser, printer, and minifier benchmark. It compares parser ASTs, measures tool resources, validates round trips, expands CSS and HTML fixtures, and wires the command into repository tooling. ChangesJavaScript benchmark tooling
Change: Other Merge Risk: ⚪ Minimal · up to This change adds internal JavaScript benchmarking and fixture coverage without altering library behavior. No current merge-blocking risk is identified. 🚥 Pre-merge checks | ✅ 3 | ❌ 1❌ Failed checks (1 inconclusive)
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #22010 +/- ##
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Coverage 95.31% 95.31%
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Branches 29541 29541
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In `@tooling/compare-js-tools.js`:
- Around line 233-234: Update the adapter’s `oxc.parseSync` call to inspect the
complete parse result and reject when `result.errors` contains parse errors
before returning `result.program`; preserve the existing `preserveParens: false`
option and successful AST return path.
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AGENTS.mdcspell.jsoneslint.config.mjspackage.jsontooling/compare-css-tools.jstooling/compare-html-tools.jstooling/compare-js-tools.js
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oxc does not throw on a file it cannot parse: it answers with whatever tree or text it salvaged and the diagnostics beside it. The parse row then read a refusal as a tree that merely disagreed with acorn's, and the minify row read one as an empty output — which is how `oxc-minify` first came out at 0.0 KB with every property name lost. Both rows raise the first diagnostic now, so a refusal reads as one.
Merging this PR will not alter performance
Comparing 
Footnotes
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Types CoverageCoverage after merging build/compare-js-tools into main will be
Coverage Report |
Summary
benchmark:css-toolsandbenchmark:html-toolsalready weigh webpack's own parser and printer against the ecosystem's; JavaScript had no equivalent, which is where webpack owns a parser and nothing was watching it.yarn benchmark:js-toolsadds the same three tables (parse, beautify, minify) over 22 bundles as they ship, from Preact's 11 KB to TypeScript's 8.9 MB, ES5 and modern, script and module. Since webpack owns a parser there and no printer, it has a row in the parse table only, and that table's last column is the point: every ESTree parser is held against acorn's tree and the first node where the two differ is named, so a divergence inlib/javascript/syntax.jsbecomes a line of output. It already reports that oxc reorders regexp flags, that meriyah and hermes omit ESTree fields acorn sets, and that webpack agrees with acorn on all 22 — while being the fastest in-process ESTree parser on every one (417 ms against acorn's 984 on the 8.9 MB file, at half the peak memory).The CSS and HTML fixture sets are widened in the same pass, because a comparison is only as good as what it runs over: an icon font's thousands of one-declaration rules, a sheet that is custom properties and nothing else, an all-tables document, a page that leans on every §13.2 recovery rule, a declarative shadow root, and an inlined SVG sprite. The tag-soup page pays for itself immediately — it separates the HTML minifiers, showing which ones drop the formatting elements the spec reopens.
What kind of change does this PR introduce?
build — repo-internal tooling only; nothing under
lib/changes.Did you add tests for your changes?
No new tests: the shared measuring harness these scripts run on is already covered by
test/CompareToolsHarness.unittest.js, and the scripts themselves are analysis tools nothing in the suite loads. Every fixture and every tool row was run before pushing.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 —
AGENTS.mddocuments the new comparison, itsagrees with acorncolumn and theFIXTURE=/TOOL=/STAGE=filters.Use of AI
AI (Claude Code) was used to write the comparison script and the fixture lists, and to draft this description. Every number quoted here was produced by running the tool in this branch, and each tool row and fixture path was verified by running it rather than assumed.
Generated by Claude Code
Summary by CodeRabbit
New Features
Documentation