fix(minifier): preserve RegExp feature detection by Dunqing · Pull Request #24712 · oxc-project/oxc

Dunqing · 2026-07-20T09:42:00Z

PR stack (3 of 3)

refactor(ecmascript)!: gate analysis APIs #24739

refactor(ecmascript): expose engine targets to side effects #24742

fix(minifier): preserve RegExp feature detection #24712 (this PR)

Review #24739 and #24742 first. This PR is based on #24742, so GitHub shows only the RegExp behavior change.

Stacked on #24742, which exposes strict engine-target capabilities to side-effect analysis.

RegExp constructor calls used for engine feature detection were removed by DCE when their pattern was valid according to the current Oxc RegExp parser. A pattern can be valid at build time but still throw a SyntaxError on the configured runtime, so removing the call changes the result of surrounding try/catch checks.

RegExp purity now requires both syntactic validity and support from every configured target. Consumers without concrete targets remain conservative, while an explicit target allows the minifier to remove constructors known to be safe for those engines.

Target-independent flag validation and pattern compatibility checks now live in oxc_regular_expression; side-effect analysis only maps target support to unsupported flags and patterns. String patterns, modern flags, named groups, property escapes, lookbehind, modifiers, invalid flags, and lone-surrogate strings are covered. A RegExp literal with replacement flags is removable only when the target supports both those flags and the dedicated ES2015RegExpConstructorCanAlterFlags compatibility feature. Explicitly targeting esnext opts into current features.

Example

Input:

export function supportsUnicodeRegExp() {
  try {
    new RegExp("\\p{Ll}", "u");
    return true;
  } catch {
    return false;
  }
}

Before:

export function supportsUnicodeRegExp() {
  try {
    return true;
  } catch {
    return false;
  }
}

After:

export function supportsUnicodeRegExp() {
  try {
    new RegExp("\\p{Ll}", "u");
    return true;
  } catch {
    return false;
  }
}

Verified with all oxc_regular_expression, oxc_compat, oxc_ecmascript, and oxc_minifier tests; the no-feature/side_effects/constant_evaluation oxc_ecmascript matrix; affected-crate clippy; formatting; and diff checks.

Fixes rolldown/rolldown#10279.

Implemented with AI assistance (OpenAI Codex and Claude). The contributor remains responsible for reviewing, understanding, and submitting these changes under the repository AI usage policy.

codspeed-hq · 2026-07-20T09:49:50Z

Merging this PR will not alter performance

✅ 67 untouched benchmarks
⏩ 9 skipped benchmarks¹

_{Comparing codex/fix-regexp-feature-detection (2273082) with codex/side-effect-engine-targets (4994d9b)}

9 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. ↩

Dunqing · 2026-07-20T12:30:58Z

@codex review

chatgpt-codex-connector · 2026-07-20T12:36:59Z

Codex Review: Didn't find any major issues. 🎉

Reviewed commit: efb85e2315

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oxc-guard · 2026-07-20T13:37:22Z

Monitor Oxc

Commit: efb85e2315df

suite	result
Build	✅
Test262	❌
Uglify Corpus	✅
Isolated Declarations	✅
(compressor)	✅
(transformer)	✅
(mangler)	❌
(formatter_dcr)	✅
(whitespace)	✅
Runtime Bundles	✅
(formatter)	❌
(dce)	✅
(codegen)	✅
Runtime (es-toolkit)	✅
Runtime (svelte)	✅
Runtime (vue)	✅
Runtime (solid)	✅
Runtime (zod)	✅

Dunqing · 2026-07-21T03:35:46Z

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sapphi-red

LGTM!

Dunqing · 2026-07-21T14:13:47Z

Merge activity

Jul 21, 2:13 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
Jul 21, 2:14 PM UTC: Dunqing added this pull request to the Graphite merge queue.
Jul 21, 2:22 PM UTC: Merged by the Graphite merge queue.

> **PR stack (3 of 3)** > 1. #24739 > 2. #24742 > 3. **#24712 (this PR)** > > Review #24739 and #24742 first. This PR is based on #24742, so GitHub shows only the RegExp behavior change. Stacked on #24742, which exposes strict engine-target capabilities to side-effect analysis. RegExp constructor calls used for engine feature detection were removed by DCE when their pattern was valid according to the current Oxc RegExp parser. A pattern can be valid at build time but still throw a `SyntaxError` on the configured runtime, so removing the call changes the result of surrounding `try`/`catch` checks. RegExp purity now requires both syntactic validity and support from every configured target. Consumers without concrete targets remain conservative, while an explicit target allows the minifier to remove constructors known to be safe for those engines. Target-independent flag validation and pattern compatibility checks now live in `oxc_regular_expression`; side-effect analysis only maps target support to unsupported flags and patterns. String patterns, modern flags, named groups, property escapes, lookbehind, modifiers, invalid flags, and lone-surrogate strings are covered. A RegExp literal with replacement flags is removable only when the target supports both those flags and the dedicated `ES2015RegExpConstructorCanAlterFlags` compatibility feature. Explicitly targeting `esnext` opts into current features. ## Example Input: ```js export function supportsUnicodeRegExp() { try { new RegExp("\\p{Ll}", "u"); return true; } catch { return false; } } ``` Before: ```js export function supportsUnicodeRegExp() { try { return true; } catch { return false; } } ``` After: ```js export function supportsUnicodeRegExp() { try { new RegExp("\\p{Ll}", "u"); return true; } catch { return false; } } ``` Verified with all `oxc_regular_expression`, `oxc_compat`, `oxc_ecmascript`, and `oxc_minifier` tests; the no-feature/`side_effects`/`constant_evaluation` `oxc_ecmascript` matrix; affected-crate clippy; formatting; and diff checks. Fixes rolldown/rolldown#10279. Implemented with AI assistance (OpenAI Codex and Claude). The contributor remains responsible for reviewing, understanding, and submitting these changes under the repository AI usage policy.

> **PR stack (1 of 3)** > 1. **#24739 (this PR)** > 2. #24742 > 3. #24712 > > Review and merge in this order. The `oxc_ecmascript` crate currently compiles constant evaluation and side-effect analysis for every consumer, even when a consumer only needs the small shared ECMAScript value primitives. This makes optional analysis code and its dependencies part of unrelated builds. This introduces two explicit features: - `side_effects` enables side-effect analysis and its RegExp support. - `constant_evaluation` enables constant evaluation and implies `side_effects`, because side-effect analysis uses constant folding for several purity decisions. `ConstantValue`, `ValueType`, and `DetermineValueType` move to feature-independent root modules so `GlobalContext` remains available without either analysis feature. Existing paths through `constant_evaluation` remain re-exported when that feature is enabled. This is a prerequisite for #24742, which exposes engine targets to side-effect analysis without making compatibility data part of every `oxc_ecmascript` consumer. This is a breaking Cargo feature change for direct consumers of `oxc_ecmascript`: code using side-effect analysis or constant evaluation must enable the corresponding feature. Verified locally with the no-feature, `side_effects`, and `constant_evaluation` configurations, crate tests, dependent linter and minifier tests, rustdoc with warnings denied, and `just ready`. The release oxlint binary on this commit is 13,350,096 bytes. Implemented with AI assistance (OpenAI Codex and Claude). The contributor remains responsible for reviewing, understanding, and maintaining these changes.

> **PR stack (2 of 3)** > 1. #24739 > 2. **#24742 (this PR)** > 3. #24712 > > Review #24739 first. This PR is based on its branch, so GitHub shows only the engine-target plumbing. Stacked on #24739, which introduces the `side_effects` and `constant_evaluation` feature boundary for `oxc_ecmascript`. Side-effect analysis sometimes needs to know whether runtime syntax is supported by every configured engine. `MayHaveSideEffectsContext` currently has no access to target information, while `EngineTargets::has_feature` is intentionally permissive about missing compatibility data because it answers whether a transformation is needed. `MayHaveSideEffectsContext::engine_targets()` exposes the configured targets through a general-purpose accessor. Its default is `None`, so consumers without target information remain conservative, while the minifier supplies its existing `CompressOptions::target`. `EngineTargets::supports_es_feature` provides the corresponding strict capability query. Every configured engine must have compatibility data and meet the required version; empty targets and missing rows are not treated as proof of support. The existing transformation-oriented `has_feature` behavior remains unchanged. Because `oxc_linter` enables `side_effects`, this also adds `oxc_compat` to the oxlint and language-server build graphs. It does not change side-effect decisions by itself; #24712 consumes the new capability for target-aware RegExp validation. Verified with all `oxc_compat` tests, the no-feature/`side_effects`/`constant_evaluation` `oxc_ecmascript` matrix, a minifier check, formatting, and Clippy. Implemented with AI assistance (OpenAI Codex and Claude). The contributor remains responsible for reviewing, understanding, and maintaining these changes.

github-actions Bot added the A-minifier Area - Minifier label Jul 20, 2026

Dunqing force-pushed the codex/fix-regexp-feature-detection branch 2 times, most recently from e3c3f57 to efb85e2 Compare July 20, 2026 12:26

Dunqing added the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 20, 2026

oxc-guard Bot removed the run-monitor-oxc Add to a PR to dispatch oxc-project/monitor-oxc CI against it label Jul 20, 2026

Dunqing force-pushed the codex/fix-regexp-feature-detection branch 3 times, most recently from 53ced01 to 1a3ef05 Compare July 21, 2026 01:37

Dunqing mentioned this pull request Jul 21, 2026

refactor(ecmascript)!: gate analysis APIs #24739

Merged

Dunqing force-pushed the codex/fix-regexp-feature-detection branch from 1a3ef05 to 91d1240 Compare July 21, 2026 03:16

github-actions Bot added the A-linter Area - Linter label Jul 21, 2026

Dunqing changed the base branch from main to codex/ecmascript-analysis-features July 21, 2026 03:16

Dunqing force-pushed the codex/ecmascript-analysis-features branch from 0e7b2ae to 602e7f4 Compare July 21, 2026 03:35

Dunqing force-pushed the codex/fix-regexp-feature-detection branch from 91d1240 to 4490b5e Compare July 21, 2026 03:35

Dunqing changed the base branch from codex/ecmascript-analysis-features to graphite-base/24712 July 21, 2026 03:51

Dunqing force-pushed the codex/fix-regexp-feature-detection branch from 4490b5e to 32a4d45 Compare July 21, 2026 03:51

Dunqing changed the base branch from graphite-base/24712 to codex/side-effect-engine-targets July 21, 2026 03:52

Dunqing mentioned this pull request Jul 21, 2026

refactor(ecmascript): expose engine targets to side effects #24742

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Dunqing force-pushed the codex/fix-regexp-feature-detection branch from 03df362 to f51789f Compare July 21, 2026 03:57

Dunqing force-pushed the codex/side-effect-engine-targets branch 2 times, most recently from 9c04aa6 to 96987da Compare July 21, 2026 05:21

Dunqing force-pushed the codex/fix-regexp-feature-detection branch from f51789f to 3efd4d0 Compare July 21, 2026 05:21

Dunqing marked this pull request as ready for review July 21, 2026 05:32

Dunqing requested a review from sapphi-red July 21, 2026 05:45

sapphi-red reviewed Jul 21, 2026

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Dunqing force-pushed the codex/side-effect-engine-targets branch from 96987da to 4994d9b Compare July 21, 2026 08:07

Dunqing force-pushed the codex/fix-regexp-feature-detection branch 2 times, most recently from 27fd72e to a6ec664 Compare July 21, 2026 08:32

Dunqing requested a review from leaysgur as a code owner July 21, 2026 08:32

github-actions Bot added A-transformer Area - Transformer / Transpiler A-regular-expression Area - Regular Expression labels Jul 21, 2026

Dunqing requested a review from sapphi-red July 21, 2026 08:48

sapphi-red approved these changes Jul 21, 2026

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Comment thread crates/oxc_ecmascript/src/side_effects/known_globals.rs Outdated

Dunqing force-pushed the codex/fix-regexp-feature-detection branch from a6ec664 to 2273082 Compare July 21, 2026 14:02

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graphite-app Bot force-pushed the codex/side-effect-engine-targets branch from 4994d9b to 01c3611 Compare July 21, 2026 14:16

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Base automatically changed from codex/side-effect-engine-targets to main July 21, 2026 14:21

graphite-app Bot merged commit 79e6d77 into main Jul 21, 2026
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graphite-app Bot deleted the codex/fix-regexp-feature-detection branch July 21, 2026 14:22

Dunqing mentioned this pull request Jul 22, 2026

fix(minifier): respect targets when folding RegExp source #24790

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