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fix(javascript): stop the minifier hanging on type/interface and fold built-in calls on literals - #22398
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Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 6 remain after this review. 📝 WalkthroughWalkthroughThe JavaScript syntax printer now folds configured built-in calls on eligible literal inputs, using generated compatibility classifications and safeguards for rebinding, evaluation errors, Unicode behavior, and output size. Skipping TypeScript ChangesLiteral built-in folding
TypeScript statement skipping
Priority: ➖ Normal Change: Bug fix Merge Risk: ⚪ Minimal · up to No additional issue was established; merge after normal checks. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The change restricts evaluation to selected built-ins and literal inputs, limiting its authority. However, array joining can allocate a disproportionately large intermediate string before the size check rejects it. Exposure depends on who can supply source for minification; no remotely accessible minification service is established. Retained concerns
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Types CoverageCoverage after merging fix/minify-typescript-statement-hang into main will be
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #22398 +/- ##
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Coverage 96.00% 96.01%
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Files 772 772
Lines 121440 121543 +103
Branches 39330 39381 +51
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+ Hits 116592 116695 +103
Misses 4848 4848
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Inline comments:
Review comments at @lib/javascript/syntax-printer.js:
- Around line 19462-19485: Update foldBuiltInCall’s guard before invoking
builtIn.fn to detect relevant ordinary property writes, reusing or extending the
existing mutation analysis so global functions, static properties, and literal
prototype methods are not folded after they may have been modified. Preserve the
current behavior when no relevant mutation is possible.
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.changeset/025-javascript-minifier-corrections.md.changeset/047-javascript-minifier-unwrap-iife.mdAGENTS.mddocs/syntax.mdlib/javascript/syntax-printer-data.jslib/javascript/syntax-printer.jstest/helpers/oxcSmaller.jstest/helpers/swcSmaller.jstest/specCases/minify-corpora.spectest.jstest/unitCases/syntax-printer.unittest.jstooling/generate-js-data.js
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- test/helpers/swcSmaller.js
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Merging this PR will degrade performance by 9.11%
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| Mode | Benchmark | BASE |
HEAD |
Efficiency | |
|---|---|---|---|---|---|
| ❌ | Memory | unit benchmark "js-parser-unit", source 'lodash-es' |
108.3 KB | 305.1 KB | -64.51% |
| ❌ | Memory | benchmark "hmr", scenario '{"name":"mode-development","mode":"development"}' |
2.7 MB | 3.6 MB | -25.92% |
| ⚡ | Memory | benchmark "concatenate-modules", scenario '{"name":"mode-development-rebuild","mode":"development","watch":true}' |
2,826.9 KB | 990.1 KB | ×2.9 |
Tip
Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.
Comparing fix/minify-typescript-statement-hang (518f009) with main (7963bb8)
Footnotes
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6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩
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The improve phase now evaluates a call of an exactly specified built-in on
literal arguments, such as "abc".charAt(1), Math.max(1, 2) or
parseInt("ff", 16), and writes its value where that is no longer, taking
built-ins as the language defines them, as oxc and swc do. It leaves a
call alone under a with or direct eval, a shadowed global, case or white
space outside ASCII, and split, whose array gzips worse than its string.
400 OXC_SMALLER and 7 SWC_SMALLER entries are retired; the few test
programs a fold makes larger gzipped are listed in IMPROVED_YET_BIGGER.
The changesets fold into the pending minifier entries.
Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
…rowser-compat-data `tooling/generate-js-data.js` now writes the built-ins `improve` evaluates on literals into `syntax-printer-data.js`. Every member @mdn/browser-compat-data lists of `Math`, `Number`, `String`, `Array` and the global functions is placed as folded, or left out with a reason, and a bump that lists a new one fails generation until it is placed. A folded built-in must be in every Node `engines.node` allows, so `at` and `replaceAll` are no longer folded and output no longer depends on the build's Node; `fromCodePoint` and `normalize` (on ASCII) are now folded. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
… size A literal count or length such as `"a".repeat(2e8)` built the whole string, then printed it, before the size check refused it: 2.5 s and 443 MB for one call. Skip such calls before evaluating, and a longer string before printing. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
`at` is no longer folded, so its call never reached that branch. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
The size guard skipped any string method with a large number, so `"xy".charCodeAt(1e99)` stopped folding; it now covers `repeat`, `padStart` and `padEnd`, listed by the generator. Record the test262 sources whose folded calls gzip worse beside the text they repeat. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
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Summary
Three changes to the JavaScript minifier (
syntax-printer.js):Hang fix. A
type T = number;orinterface I {}statement looped forever in the ported terser parser (terser 5.51 hangs the same way). The TypeScript skippers now run only underexperimental_typescript. Otherwise the statement is a normal parse error.type T = number;Unexpected token: name (T)Built-in fold. The
improvephase now evaluates exactly specified built-ins called on literals, assuming built-ins are unmodified, as oxc and swc do:"abc".charAt(1)→"b",Math.max(1, 5, 2)→5,parseInt("ff", 16)→255,[1, 2].join("-")→"1-2". It is skipped for:withor next to a directeval;Generated tables.
tooling/generate-js-data.jswrites the folded built-ins intosyntax-printer-data.jsfrom@mdn/browser-compat-data. Every member BCD lists forMath,Number,String,Arrayand the global functions is either folded or left out with a reason. Generation fails if:engines.node. That rule keepsat/replaceAllout, so output doesn't depend on the build's Node.Real code, 56 swc/terser bench and project files, default minimizer options, against
main:3 files got smaller and none bigger. 400
OXC_SMALLERand 7SWC_SMALLERcorpus entries are retired. CPU is unchanged within noise (median 26,663 ms vs 26,535 ms withimproveoff; the fastest run favouredimproveon).What kind of change does this PR introduce?
fix
Did you add tests for your changes?
Yes.
test/unitCases/syntax-printer.unittest.js: the hang, plus folded and kept cases for each guard.test/specCases/minify-corpora.spectest.js: the ratchet lists intest/helpers/oxcSmaller.jsandtest/helpers/swcSmaller.js.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?
Documented in
docs/syntax.md: theimprovephase and the generated table, including its@mdn/browser-compat-datasource.Use of AI
Written with Claude Code. It wrote the code and tests, ran the corpus comparisons and measured size, all at the author's direction. The author reviewed the changes.
🤖 Generated with Claude Code
https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
Generated by Claude Code
Summary by CodeRabbit
New Features
typeandinterfacedeclarations are skipped only when the experimental TypeScript option is enabled.Documentation