feat: add `output.strict` option to control `"use strict"` directive emission by Copilot · Pull Request #8489 · rolldown/rolldown

Copilot · 2026-02-27T10:01:15Z

Original prompt

This section details on the original issue you should resolve

<issue_title>"use strict" is not injected for CJS builds</issue_title>
<issue_description>I've seen #4607, but I feel it's important to bring this up again.

I think this decision is quite unfortunate.

Is the expectation that developers will add 'use strict' to their ESM/TS source code when dual-bundling as ESM/CJS? Including 'use strict' in ESM code seems counterproductive.

An alternative might be to add 'use strict' to CJS files by default when "type": "module" is used and bundling for CJS.</issue_description>

Comments on the Issue (you are @copilot in this section)
@sapphi-red We are going to follow esbuild's behavior, which is to respect tsconfig.json's `strict` (`alwaysStrict`) option. When that is implemented, you should be able to output `"use strict"` by setting `"alwaysStrict": true` in tsconfig.json. If the tsconfig.json has `include` & `exclude`, the entrypoint should be included in them.

For now, if you add `"use strict"` to all entrypoints manually, Rolldown should emit `"use strict"`. @shulaoda I’d like to clarify a few points: 1. Should this only apply when the output format is CJS? 2. Should this behavior only take effect when `tsconfig` is enabled? If the user does not enable `tsconfig`, should we avoid emitting `"use strict"`? 3. If the user enables `tsconfig: 'auto'` and we resolve the `tsconfig.json` from the current working directory, or if they explicitly specify `tsconfig: '..'`, and the `include` / `exclude` configuration excludes the entry file, should we still respect the `alwaysStrict` setting from that `tsconfig.json`? @sapphi-red > 1. Should this only apply when the output format is CJS?
This should apply to all formats (other than ESM as it already enables strict mode).

Should this behavior only take effect when tsconfig is enabled? If the user does not enable tsconfig, should we avoid emitting "use strict"?

Yes. This behavior should only take effect when tsconfig is enabled.

If the user enables tsconfig: 'auto' and we resolve the tsconfig.json from the current working directory, or if they explicitly specify tsconfig: '..', and the include / exclude configuration excludes the entry file, should we still respect the alwaysStrict setting from that tsconfig.json?

No. It should apply the alwaysStrict setting only when the other settings are respected. In other words, we should respect the include / exclude options.
@sapphi-red I noticed that TS 6.0 will deprecate `"alwaysStrict": false`. https://devblogs.microsoft.com/typescript/announcing-typescript-6-0-beta/#deprecated:---alwaysstrict-false This means we should be treating any TS files as if they have `"use strict"` at the top of the file. @sapphi-red Maybe we should add [`output.strict`](https://rollupjs.org/configuration-options/#output-strict) option with `'auto' | boolean` instead. `'auto'` does not exist in Rollup and is the current behavior.

Fixes "use strict" is not injected for CJS builds #5865

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.

netlify · 2026-02-27T10:01:32Z

✅ Deploy Preview for rolldown-rs ready!

Name	Link
🔨 Latest commit	`ea8a2f8`
🔍 Latest deploy log	https://app.netlify.com/projects/rolldown-rs/deploys/69a69590bf5f3c00084887c4
😎 Deploy Preview	https://deploy-preview-8489--rolldown-rs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

To edit notification comments on pull requests, go to your Netlify project configuration.

crates/rolldown/tests/rolldown/misc/use_strict/strict_always_cjs/main.js

Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

… source Co-authored-by: IWANABETHATGUY <17974631+IWANABETHATGUY@users.noreply.github.com>

shulaoda

I think we should move node test cases to rust side, I will do it later

Copilot

Pull request overview

This PR adds a new output.strict option to control whether "use strict" directives are emitted in generated output (primarily affecting non-ESM formats), threading the option through TypeScript options, NAPI bindings, Rust options normalization, and code generation, with new integration tests and snapshot updates.

Changes:

Introduce StrictMode in rolldown_common and plumb strict through BundlerOptions → NormalizedBundlerOptions → build context preparation.
Expose strict in TypeScript OutputOptions, validator schema, and NAPI binding types/normalization.
Update code generation to apply strict behavior and reuse a shared is_use_strict_directive helper; add/refresh tests & snapshots.

Reviewed changes

Copilot reviewed 31 out of 31 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/rolldown/tests/cli/snapshots/cli-e2e.test.ts.snap	Updates CLI help snapshot to include `--strict`.
packages/rolldown/src/utils/validator.ts	Adds `strict` validation (`boolean
packages/rolldown/src/utils/bindingify-output-options.ts	Passes `outputOptions.strict` into binding output options.
packages/rolldown/src/options/output-options.ts	Adds `strict?: boolean
packages/rolldown/src/binding.d.cts	Regenerates binding types to include `strict`.
crates/rolldown_testing_config/src/config_variant.rs	Adds `strict` to test config variants and formatting.
crates/rolldown_testing/_config.schema.json	Extends test config JSON schema with `StrictMode` and `strict` fields.
crates/rolldown_common/src/lib.rs	Re-exports `StrictMode` from bundler options types.
crates/rolldown_common/src/inner_bundler_options/types/strict_mode.rs	Introduces `StrictMode` enum and conversions.
crates/rolldown_common/src/inner_bundler_options/types/normalized_bundler_options.rs	Adds normalized `strict: StrictMode` field + default.
crates/rolldown_common/src/inner_bundler_options/types/mod.rs	Registers the new `strict_mode` module.
crates/rolldown_common/src/inner_bundler_options/mod.rs	Adds `strict: Option<StrictMode>` to `BundlerOptions`.
crates/rolldown_binding/src/utils/normalize_binding_options.rs	Maps NAPI `strict` into Rust `StrictMode`.
crates/rolldown_binding/src/options/binding_output_options/mod.rs	Exposes `strict` in NAPI output options (`boolean
crates/rolldown/tests/snapshots/integration_rolldown__filename_with_hash.snap	Snapshot updates for new strict-mode test fixtures.
crates/rolldown/tests/rolldown/misc/use_strict/strict_never_cjs/main.js	Adds integration test input for `strict: never` (CJS).
crates/rolldown/tests/rolldown/misc/use_strict/strict_never_cjs/artifacts.snap	Adds expected output snapshot for `strict: never` (CJS).
crates/rolldown/tests/rolldown/misc/use_strict/strict_never_cjs/_config.json	Adds test config for `strict: never` (CJS).
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_esm/main.js	Adds integration test input for `strict: always` (ESM).
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_esm/artifacts.snap	Adds expected output snapshot for `strict: always` (ESM).
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_esm/_config.json	Adds test config for `strict: always` (ESM).
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_cjs_dedup/main.js	Adds dedup integration test input (entry already has `'use strict'`).
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_cjs_dedup/artifacts.snap	Adds expected output snapshot for dedup behavior.
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_cjs_dedup/_config.json	Adds test config for dedup case (`strict: always`, CJS).
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_cjs/main.js	Adds integration test input for `strict: always` (CJS).
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_cjs/artifacts.snap	Adds expected output snapshot for `strict: always` (CJS).
crates/rolldown/tests/rolldown/misc/use_strict/strict_always_cjs/_config.json	Adds test config for `strict: always` (CJS).
crates/rolldown/src/utils/prepare_build_context.rs	Threads `strict` into `NormalizedBundlerOptions`.
crates/rolldown/src/ecmascript/format/utils/mod.rs	Adds shared `is_use_strict_directive` helper.
crates/rolldown/src/ecmascript/format/esm.rs	Uses shared helper to filter `"use strict"` from ESM directives.
crates/rolldown/src/ecmascript/ecma_generator.rs	Applies `output.strict` policy to directives during chunk instantiation.

crates/rolldown_common/src/inner_bundler_options/types/strict_mode.rs

Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

github-actions · 2026-03-03T03:45:11Z

Benchmarks Rust

target: main(8fc5471)
pr: copilot/add-use-strict-to-cjs-builds(ea8a2f8)

group                                                        pr                                     target
-----                                                        --                                     ------
bundle/bundle@multi-duplicated-top-level-symbol              1.01     80.0±3.95ms        ? ?/sec    1.00     79.4±2.57ms        ? ?/sec
bundle/bundle@multi-duplicated-top-level-symbol-sourcemap    1.00     87.0±2.47ms        ? ?/sec    1.00     87.1±2.76ms        ? ?/sec
bundle/bundle@rome_ts                                        1.00    163.3±4.50ms        ? ?/sec    1.02    165.8±6.74ms        ? ?/sec
bundle/bundle@rome_ts-sourcemap                              1.00    183.8±8.10ms        ? ?/sec    1.01    186.5±3.86ms        ? ?/sec
bundle/bundle@threejs                                        1.00     74.7±2.71ms        ? ?/sec    1.03     76.6±2.28ms        ? ?/sec
bundle/bundle@threejs-sourcemap                              1.00     85.1±2.58ms        ? ?/sec    1.02     86.8±2.40ms        ? ?/sec
bundle/bundle@threejs10x                                     1.00   754.1±12.15ms        ? ?/sec    1.00   752.0±12.51ms        ? ?/sec
bundle/bundle@threejs10x-sourcemap                           1.02   885.9±12.46ms        ? ?/sec    1.00   870.4±13.32ms        ? ?/sec
scan/scan@rome_ts                                            1.03     73.1±1.54ms        ? ?/sec    1.00     71.1±1.46ms        ? ?/sec
scan/scan@threejs                                            1.04     26.6±1.72ms        ? ?/sec    1.00     25.6±0.48ms        ? ?/sec
scan/scan@threejs10x                                         1.01    256.4±4.44ms        ? ?/sec    1.00    254.4±3.38ms        ? ?/sec

Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

sapphi-red

LGTM. We should update https://rolldown.rs/in-depth/directives as well

packages/rolldown/src/options/output-options.ts

Co-authored-by: 翠 <green@sapphi.red> Signed-off-by: dalaoshu <165626830+shulaoda@users.noreply.github.com>

shulaoda · 2026-03-03T08:04:19Z

LGTM. We should update https://rolldown.rs/in-depth/directives as well

Do you mean we should update it for output.strict option?

minsoo-web · 2026-03-03T22:24:51Z

As a follow-up to this PR discussion, I opened #8535 to update docs/in-depth/directives for output.strict (#8532).

@IWANABETHATGUY

## [1.0.0-rc.7] - 2026-03-05 ⚡ Smarter Code Generation Defaults - DCE-only minification and smart constant inlining are now enabled by default - Produces cleaner, smaller output bundles without requiring explicit configuration 💡 LLM-Friendly Bundle Analyzer Reports - New markdown output format for the bundle analyzer plugin with bundle summaries, module graphs, dependency chains, and optimization suggestions - Optimization suggestions now also recommend using the entriesAware option when common chunks contain modules only reachable from specific entries ### 💥 BREAKING CHANGES - enable minify: 'dce-only' by default (#8465) by @IWANABETHATGUY - settings `inlineConst: { mode: 'smart', pass: 1}` by default (#8444) by @IWANABETHATGUY ### 🚀 Features - binding: add original getter to BindingMagicString (#8533) by @IWANABETHATGUY - native-magic-string: add `offset` property support (#8531) by @IWANABETHATGUY - add `output.strict` option to control `"use strict"` directive emission (#8489) by @Copilot - watch: expose `watcher.compareContentsForPolling` (#8526) by @hyf0 - watch: use new watcher to support watch mode (#8475) by @hyf0 - rust/watch: handle bulk-change (#8466) by @hyf0 - add LLM-friendly markdown output format to bundle analyzer plugin (#8242) by @IWANABETHATGUY ### 🐛 Bug Fixes - expose `plugins` on `NormalizedInputOptions` for `buildStart` hook (#8521) by @Copilot - only uppercase facade symbols in JSX preserve mode (#8519) by @IWANABETHATGUY - binding: export BindingResult in generated dts header (#8537) by @minsoo-web - pre-resolve paths option to avoid `invoke_sync` deadlock (#8518) by @IWANABETHATGUY - remove debug-only jsx_preset and UntranspiledSyntaxError (#8511) by @IWANABETHATGUY - apply `topLevelVar` to exported `const`/`let` declarations (#8507) by @IWANABETHATGUY - rolldown_plugin_vite_web_worker_post: avoid replacing `new.target` (#8488) by @sapphi-red - update copyright year to 2026 (#8486) by @maciekzygmunt ### 🚜 Refactor - rust: use Oxc's SymbolFlags::ConstVariable instead of custom IsConst flag (#8543) by @Dunqing - rust: remove FacadeScoping, use Scoping::create_symbol for facade symbols (#8540) by @Dunqing - rust/watch: remove hacky `reset_closed_for_watch_mode` (#8530) by @hyf0 - binding: return &str instead of String in filename() getter (#8534) by @IWANABETHATGUY - rust: remove old watch mode implementation (#8525) by @hyf0 - rust/watch: simply watch logic in the binding layer (#8516) by @hyf0 - rust/watch: tweak struct/function names (#8464) by @hyf0 ### 📚 Documentation - explain how external modules work in rolldown (#8457) by @sapphi-red - add some diagrams using graphviz (#8499) by @sapphi-red - use `vitepress-plugin-graphviz` (#8498) by @sapphi-red - list s390x/ppc64le prebuilt binaries (#8495) by @crusty-voidzero - fix error type for `RolldownBuild.generate` and others (#8490) by @sapphi-red ### ⚡ Performance - string_wizard: reduce allocations and add ASCII fast paths (#8541) by @IWANABETHATGUY - use IndexBitSet to replace IndexVec<XXXIdx, bool> for module/stmt inclusion tracking (#8503) by @IWANABETHATGUY - plugin: use IndexBitSet to optimize skipped plugins checking (#8497) by @ShroXd - rust/tla: skip compute_tla if there is no module use TLA (#8487) by @ShroXd ### 🧪 Testing - node/watch: make watch tests run in concurrent and retry-able (#8512) by @hyf0 - add test case for static flag tree-shaking (#8476) by @IWANABETHATGUY - migrate post-banner sourcemap-with-shebang to Rust (#8477) by @Copilot ### ⚙️ Miscellaneous Tasks - vscode: `formatOnSave` for markdown files using oxc formatter (#8536) by @minsoo-web - deps: update test262 submodule for tests (#8528) by @sapphi-red - remove `retry` workaround from output paths test fixtures (#8520) by @Copilot - docs: add Shuyuan Wang (h-a-n-a) and remove from acknowledgements (#8509) by @Copilot - consolidate top_level_var test cases using configVariants (#8508) by @IWANABETHATGUY - add s390x and ppc64le linux gnu targets (#8493) by @Brooooooklyn ### ◀️ Revert - fix(rolldown): increase tokio blocking threads size for watch mode (#8517) by @hyf0 ### ❤️ New Contributors * @minsoo-web made their first contribution in [#8536](#8536) * @crusty-voidzero made their first contribution in [#8495](#8495) * @maciekzygmunt made their first contribution in [#8486](#8486) Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

Copilot AI assigned Copilot and shulaoda Feb 27, 2026

Copilot started work on behalf of shulaoda February 27, 2026 10:01 View session

Copilot AI changed the title ~~[WIP] Add 'use strict' injection for CJS builds~~ Add output.strict option to control "use strict" directive emission Feb 27, 2026

Copilot finished work on behalf of shulaoda February 27, 2026 10:39

hyf0 assigned IWANABETHATGUY and unassigned shulaoda and Copilot Feb 27, 2026

IWANABETHATGUY reviewed Mar 2, 2026

View reviewed changes

crates/rolldown/tests/rolldown/misc/use_strict/strict_always_cjs/main.js Show resolved Hide resolved

Copilot started work on behalf of IWANABETHATGUY March 2, 2026 12:11 View session

Copilot finished work on behalf of IWANABETHATGUY March 2, 2026 12:16

Copilot AI and others added 3 commits March 3, 2026 10:56

Initial plan

69b8971

Add output.strict option to control use strict directive emission

98ff79c

Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

Add deduplication test for strict: always with existing use strict in…

092b4a1

… source Co-authored-by: IWANABETHATGUY <17974631+IWANABETHATGUY@users.noreply.github.com>

shulaoda force-pushed the copilot/add-use-strict-to-cjs-builds branch from 54e010d to 092b4a1 Compare March 3, 2026 02:57

u

828b684

shulaoda force-pushed the copilot/add-use-strict-to-cjs-builds branch from ffaa3eb to 828b684 Compare March 3, 2026 03:17

shulaoda changed the title ~~Add output.strict option to control "use strict" directive emission~~ feat: add output.strict option to control "use strict" directive emission Mar 3, 2026

shulaoda reviewed Mar 3, 2026

View reviewed changes

shulaoda requested review from Copilot and sapphi-red March 3, 2026 03:26

shulaoda marked this pull request as ready for review March 3, 2026 03:26

Copilot started reviewing on behalf of shulaoda March 3, 2026 03:27 View session

Copilot AI reviewed Mar 3, 2026

View reviewed changes

crates/rolldown_common/src/inner_bundler_options/types/strict_mode.rs Outdated Show resolved Hide resolved

Copilot started work on behalf of shulaoda March 3, 2026 03:36 View session

fix: handle all valid string values in StrictMode::from(String)

90a4516

Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

Copilot finished work on behalf of shulaoda March 3, 2026 03:43

Copilot started work on behalf of shulaoda March 3, 2026 03:45 View session

IWANABETHATGUY approved these changes Mar 3, 2026

View reviewed changes

refactor: use TryFrom<&str> for StrictMode instead of From<String>

f5f1e13

Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

Copilot finished work on behalf of shulaoda March 3, 2026 03:51

u

f494711

shulaoda assigned sapphi-red and unassigned IWANABETHATGUY Mar 3, 2026

sapphi-red approved these changes Mar 3, 2026

View reviewed changes

packages/rolldown/src/options/output-options.ts Show resolved Hide resolved

Update packages/rolldown/src/options/output-options.ts

ea8a2f8

Co-authored-by: 翠 <green@sapphi.red> Signed-off-by: dalaoshu <165626830+shulaoda@users.noreply.github.com>

shulaoda mentioned this pull request Mar 3, 2026

Update in-depth/directives for output.strict option #8532

Closed

shulaoda merged commit e9ddfbb into main Mar 3, 2026
34 checks passed

shulaoda deleted the copilot/add-use-strict-to-cjs-builds branch March 3, 2026 08:11

This was referenced Mar 4, 2026

release: v1.0.0-rc.7 #8539

Closed

release: v1.0.0-rc.7 #8547

Merged

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

feat: add `output.strict` option to control `"use strict"` directive emission#8489

feat: add `output.strict` option to control `"use strict"` directive emission#8489
shulaoda merged 8 commits intomainfrom
copilot/add-use-strict-to-cjs-builds

Copilot AI commented Feb 27, 2026 •

edited

Loading

Uh oh!

netlify bot commented Feb 27, 2026 •

edited

Loading

Uh oh!

Uh oh!

shulaoda left a comment •

edited

Loading

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

github-actions bot commented Mar 3, 2026 •

edited

Loading

Uh oh!

sapphi-red left a comment •

edited

Loading

Uh oh!

Uh oh!

shulaoda commented Mar 3, 2026 •

edited

Loading

Uh oh!

Uh oh!

minsoo-web commented Mar 3, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

Conversation

Copilot AI commented Feb 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Comments on the Issue (you are @copilot in this section)

Uh oh!

netlify bot commented Feb 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

✅ Deploy Preview for rolldown-rs ready!

Uh oh!

Uh oh!

shulaoda left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

github-actions bot commented Mar 3, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Benchmarks Rust

Uh oh!

sapphi-red left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

shulaoda commented Mar 3, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

minsoo-web commented Mar 3, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

Copilot AI commented Feb 27, 2026 •

edited

Loading

netlify bot commented Feb 27, 2026 •

edited

Loading

shulaoda left a comment •

edited

Loading

github-actions bot commented Mar 3, 2026 •

edited

Loading

sapphi-red left a comment •

edited

Loading

shulaoda commented Mar 3, 2026 •

edited

Loading