feat: skip `__toESM` when not needed to reduce output size #6751

Copilot · 2025-10-29T14:16:26Z

Understand the issue: Rolldown uses __toESM for all external imports (except side-effect imports), while esbuild only uses it for namespace and default imports
Build rolldown and test current behavior
Compare with esbuild behavior
Identify the code locations that need modification
Implement the fix to align with esbuild behavior
Create or update tests to verify the fix
Run tests to ensure no regressions
Address code review feedback
- Extracted external_import_needs_interop to common utility
- Deduped external import handling in cjs.rs using .map()
- Renamed g_WRAP to g_nowrap in test (legacy __esModule artifact)
- Updated snapshots for content hash change
- Fixed clippy warning (map_or -> is_some_and)
Request code review

Original prompt

This section details on the original issue you should resolve

<issue_title>[Bug]: Align with esbuild external interop</issue_title>
<issue_description>### Reproduction link or steps

esbuild:
https://hyrious.me/esbuild-repl/?version=0.23.0&b=e%00main.js%00import+%27a%27%0Aimport+*+as+fs+from+%27b%27%0Aimport+defaultValue+from+%27c%27%0Aimport+%7BreadFileSync%7D+from+%27d%27%0Aconsole.log%28fs%2C+readFileSync%2C+defaultValue%29%0A&o=%7B%0A++treeShaking%3A+true%2C%0A++external%3A+%5B%22c%22%2C+%22a%22%2C+%22b%22%2C+%22d%22%5D%2C%0A%22bundle%22%3A+true%2C%0Aformat%3A+%22cjs%22%2C%0A%7D

rolldown:
https://repl.rolldown.rs/#eNptUcFOhDAQ/ZVJL+waJKs3SdaLiVeNJl6shy4MG0yZNqVd2RD+3UFAILtJD/P6Zl7fm7aiEGkrSsqxSXzd1yTSGcci62FljfMQqUjSWN+AqqHg40wF0WEmcixU0P5D6YAjm81s61Dlz6XG9zNl3cjnzGeGaqMx0ea4KeoYln3xSnQriW2hSL0L2MXCGa1z80MJSxTlcZHiCrPK488WoYW3se3F+pJdwGRrGo9A0mDQw6CUXszsoZUEYIK3wacDACiMqxRDKbLvWor+spPERxI2y22NuoLjWB2OJT0Z8qokdIs4V5hVnL8v6U0Hu1tECJbXOz53Ug5e/2Ww8Wz8c7OF/eM0+MXb7djGiXXvkl2yuz2gV8n9g+h+ARUUwNw=

What is expected?

just like esbuild

What is actually happening?

rolldown would always generate __toESM when interop with external

System Info
n/a
Any additional comments?

No response</issue_description>

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

Fixes [Bug]: Align with esbuild external interop #5434

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graphite-app · 2025-10-29T14:16:32Z

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sapphi-red · 2025-10-29T15:30:05Z

@copilot please continue

Copilot · 2025-10-29T16:04:41Z

@copilot please continue

I've completed the fix to align with esbuild's external interop behavior. The changes ensure that __toESM is only generated for namespace imports (import * as foo) and default imports (import foo), but not for named imports (import { bar }).

Changes made in commit 62eb628:

Updated reference_needed_symbols.rs to conditionally reference __toESM based on import type
Modified cjs.rs and utils/mod.rs to check if interop is needed before generating __toESM calls
Fixed compute_cross_chunk_links.rs to handle cases where __toESM is not needed
Updated test snapshots to reflect the new behavior

All tests pass successfully.

crates/rolldown/src/ecmascript/format/cjs.rs

crates/rolldown/src/stages/link_stage/reference_needed_symbols.rs

crates/rolldown/src/ecmascript/format/cjs.rs

crates/rolldown/tests/esbuild/default/to_esm_wrapper_omission/artifacts.snap

crates/rolldown/src/stages/link_stage/reference_needed_symbols.rs

github-actions · 2025-10-29T19:12:15Z

Benchmarks Rust

target: main(bcc6967)
pr: copilot/align-esbuild-external-interop(42a0cd9)

group                                                        pr                                     target
-----                                                        --                                     ------
bundle/bundle@multi-duplicated-top-level-symbol              1.00     70.4±2.26ms        ? ?/sec    1.06     74.5±4.32ms        ? ?/sec
bundle/bundle@multi-duplicated-top-level-symbol-sourcemap    1.00     77.5±2.68ms        ? ?/sec    1.07     83.1±2.27ms        ? ?/sec
bundle/bundle@rome_ts                                        1.00    112.8±2.50ms        ? ?/sec    1.04    116.8±2.58ms        ? ?/sec
bundle/bundle@rome_ts-sourcemap                              1.00    127.0±2.34ms        ? ?/sec    1.05    133.2±3.54ms        ? ?/sec
bundle/bundle@threejs                                        1.00     41.1±0.87ms        ? ?/sec    1.09     45.0±2.79ms        ? ?/sec
bundle/bundle@threejs-sourcemap                              1.00     46.0±1.46ms        ? ?/sec    1.01     46.5±0.76ms        ? ?/sec
bundle/bundle@threejs10x                                     1.00    411.7±6.18ms        ? ?/sec    1.00    412.3±6.72ms        ? ?/sec
bundle/bundle@threejs10x-sourcemap                           1.00    474.9±6.63ms        ? ?/sec    1.01    477.9±5.62ms        ? ?/sec
scan/scan@rome_ts                                            1.00     88.2±1.79ms        ? ?/sec    1.01     88.8±2.11ms        ? ?/sec
scan/scan@threejs                                            1.00     30.1±0.58ms        ? ?/sec    1.01     30.5±2.19ms        ? ?/sec
scan/scan@threejs10x                                         1.00    308.8±5.53ms        ? ?/sec    1.00    310.0±4.44ms        ? ?/sec

sapphi-red · 2025-10-30T02:20:46Z

@copilot update snapshot

Copilot · 2025-10-30T02:33:38Z

@copilot update snapshot

Done in commit 009a521. Updated the filename hash snapshot to reflect the content change from renaming g_WRAP to g_nowrap (hash changed from Cn6Q72T9 to C73CEcdw).

sapphi-red · 2025-10-30T02:36:34Z

@copilot fix CI error

Copilot · 2025-10-30T02:48:50Z

@copilot fix CI error

Fixed in commit 55967f3. The CI error was a clippy warning about using map_or(false, ...) instead of the more idiomatic is_some_and(...). Changed line 142 in cjs.rs to use is_some_and which resolves the clippy::unnecessary_map_or warning.

graphite-app · 2025-10-30T04:49:26Z

Merge activity

Oct 30, 4:49 AM UTC: sapphi-red added this pull request to the Graphite merge queue.
Oct 30, 4:55 AM UTC: The Graphite merge queue couldn't merge this PR because it was not satisfying all requirements (Failed CI: 'node-test (ubuntu-latest) / Node Test', 'node-test (macos-latest) / Node Test', 'node-test (windows-latest) / Node Test').

- [x] Understand the issue: Rolldown uses `__toESM` for all external imports (except side-effect imports), while esbuild only uses it for namespace and default imports - [x] Build rolldown and test current behavior - [x] Compare with esbuild behavior - [x] Identify the code locations that need modification - [x] Implement the fix to align with esbuild behavior - [x] Create or update tests to verify the fix - [x] Run tests to ensure no regressions - [x] Address code review feedback - Extracted `external_import_needs_interop` to common utility - Deduped external import handling in cjs.rs using .map() - Renamed g_WRAP to g_nowrap in test (legacy __esModule artifact) - Updated snapshots for content hash change - Fixed clippy warning (map_or -> is_some_and) - [x] Request code review Fixes #5434  <details> <summary>Original prompt</summary> > > ---- > > *This section details on the original issue you should resolve* > > <issue_title>[Bug]: Align with esbuild external interop</issue_title> > <issue_description>### Reproduction link or steps > > **esbuild**: > https://hyrious.me/esbuild-repl/?version=0.23.0&b=e%00main.js%00import+%27a%27%0Aimport+*+as+fs+from+%27b%27%0Aimport+defaultValue+from+%27c%27%0Aimport+%7BreadFileSync%7D+from+%27d%27%0Aconsole.log%28fs%2C+readFileSync%2C+defaultValue%29%0A&o=%7B%0A++treeShaking%3A+true%2C%0A++external%3A+%5B%22c%22%2C+%22a%22%2C+%22b%22%2C+%22d%22%5D%2C%0A%22bundle%22%3A+true%2C%0Aformat%3A+%22cjs%22%2C%0A%7D > > **rolldown**: > https://repl.rolldown.rs/#eNptUcFOhDAQ/ZVJL+waJKs3SdaLiVeNJl6shy4MG0yZNqVd2RD+3UFAILtJD/P6Zl7fm7aiEGkrSsqxSXzd1yTSGcci62FljfMQqUjSWN+AqqHg40wF0WEmcixU0P5D6YAjm81s61Dlz6XG9zNl3cjnzGeGaqMx0ea4KeoYln3xSnQriW2hSL0L2MXCGa1z80MJSxTlcZHiCrPK488WoYW3se3F+pJdwGRrGo9A0mDQw6CUXszsoZUEYIK3wacDACiMqxRDKbLvWor+spPERxI2y22NuoLjWB2OJT0Z8qokdIs4V5hVnL8v6U0Hu1tECJbXOz53Ug5e/2Ww8Wz8c7OF/eM0+MXb7djGiXXvkl2yuz2gV8n9g+h+ARUUwNw= > > > > > ### What is expected? > > just like esbuild > > ### What is actually happening? > > rolldown would always generate `__toESM` when interop with external > > ### System Info > > ```Shell > n/a > ``` > > ### Any additional comments? > > _No response_</issue_description> > > ## Comments on the Issue (you are @copilot in this section) > > <comments> > </comments> > </details> - Fixes #5434  --- 💬 We'd love your input! Share your thoughts on Copilot coding agent in our [2 minute survey](https://gh.io/copilot-coding-agent-survey).

IWANABETHATGUY · 2025-10-30T06:33:21Z

flaky test

@sapphi-red

## [1.0.0-beta.46] - 2025-11-03 ### 💥 BREAKING CHANGES - default `preserveEntrySignatures` to `'exports-only'` to align with Rollup (#6723) by @Copilot ### 🚀 Features - link to docs for commonjs prefer_builtin_feature diagnostic (#6793) by @sapphi-red - rolldown_plugin_build_import_analysis: align partial logic (#6789) by @shulaoda - improve `EVAL` warning message (#6776) by @sapphi-red - rolldown: oxc v0.96.0 (#6774) by @Boshen - rolldown_plugin_build_import_analysis: align partial logic (#6773) by @shulaoda - skip `__toESM` when not needed to reduce output size (#6751) by @Copilot - improve `EMPTY_IMPORT_META` warning message (#6761) by @sapphi-red - rolldown_plugin_build_import_analysis: align no preload logic (#6762) by @shulaoda - rolldown_plugin_vite_css_post: align `RemovedPureCSSFilesCache` logic (#6745) by @shulaoda - rolldown_plugin_build_import_analysis: initialize `generateBundle` logic (#6744) by @shulaoda - experimental: introduce `freeExternalMemory` to free external memory immediately (#6721) by @hyf0 ### 🐛 Bug Fixes - plugins: wrap replacePlugin with makeBuiltinPluginCallable (#6782) by @huang-julien - debug: make sure `this.resolve` is also tracked under corresponding session (#6798) by @hyf0 - legal comments above directives are not preserved (#6787) by @shulaoda - panic when rendering exports to other chunks (#6765) by @Copilot - transform/inject: escape special characters in import source (#6778) by @Copilot - handle default exports from CJS modules correctly (#6767) by @IWANABETHATGUY - rolldown_plugin_build_import_analysis: correct aligned logic (#6768) by @shulaoda - duplicate default export when using both import and require (#6764) by @Copilot - handle arbitrary module namespace identifiers in `preserveEntrySignatures: 'allow-extension'` (#6753) by @Copilot - TypeError when loading CJS files after bundling mixed CJS+TS project (#6743) by @IWANABETHATGUY - add warnings for import.meta.dirname/filename/url in UMD and IIFE formats (#6747) by @Copilot - rolldown_plugin_manifest: should keep `names` field (#6742) by @shulaoda - legal comments above import statements are not preserved (#6717) by @shulaoda - remove redundant node check in dynamic entry graph construction (#6730) by @IWANABETHATGUY ### 🚜 Refactor - remove unnecessary `#[napi(gettter)]`, use function call directly (#6694) by @hyf0 - explain the reason if memory doesn't get dropped by `freeExternalMemory` (#6781) by @hyf0 - pre compute exports (#6755) by @IWANABETHATGUY - dev: receive an interface for DevRuntime rather than WebSocket directly (#6734) by @sapphi-red - dev: fix types for the runtime file and expose it properly (#6731) by @sapphi-red ### 📚 Documentation - fix magicstring credit (#6812) by @TheAlexLichter - in-depth/bundling-cjs: wrap some sections with caveats section (#6796) by @sapphi-red - in-depth/bundling-cjs: add "Ambiguous `default` import from CJS modules" section (#6795) by @sapphi-red - in-depth/bundling-cjs: make `esmExternalRequirePlugin` link more prominent (#6792) by @sapphi-red - add explanation about direct eval (#6775) by @sapphi-red - add "Non-ESM Output Formats" page (#6760) by @sapphi-red - use oxc for benchmark comparison in native magic string doc (#6740) by @sapphi-red - polish `cleanDir` option (#6741) by @hyf0 - fix image in native magic string doc (#6739) by @sapphi-red - update description about `attachDebugInfo: 'none'` (#6738) by @IWANABETHATGUY - add warning about cleanDir behavior with multiple configs (#6735) by @Copilot ### 🧪 Testing - skip paths function test (#6771) by @IWANABETHATGUY - rust/dev: add test about recover from initial build error (#6567) by @hyf0 ### ⚙️ Miscellaneous Tasks - correct prepare release binding file (#6817) by @shulaoda - deps: update github-actions (#6806) by @renovate[bot] - deps: lock file maintenance npm packages (#6814) by @renovate[bot] - use correct node version (#6809) by @shulaoda - deps: lock file maintenance rust crates (#6815) by @renovate[bot] - deps: update npm packages (major) (#6813) by @renovate[bot] - deps: update dependency dprint-typescript to v0.95.12 (#6805) by @renovate[bot] - fix typo (#6801) by @iiio2 - fix typo in is_import_expr_ignored_by_comment method name (#6797) by @sapphi-red - deps: update crate-ci/typos action to v1.39.0 (#6794) by @renovate[bot] - deps: upgrade Rust to v1.91.0 and fix new clippy lints (#6785) by @Copilot - allow dprint to format `packages/rolldown/tests` except diagnostics directory (#6772) by @Copilot - deps: update dependency tsdown to v0.15.12 (#6759) by @renovate[bot] - deps: update dependency rolldown-plugin-dts to v0.17.3 (#6758) by @renovate[bot] - test/dev: collect multiple build outputs for each step (#6736) by @hyf0 - rolldown: change the NAPI-RS binding file to the cjs (#6688) by @Brooooooklyn - test: automatically run extra test with `preserve_entry_signatures: 'allow-extension'` (#6727) by @Copilot - deps: update dependency rolldown-plugin-dts to v0.17.2 (#6732) by @renovate[bot] - fix node validation (#6728) by @shulaoda - deps: lock file maintenance rust crates (#6636) by @renovate[bot] - deps: update dependency tsdown to v0.15.11 (#6725) by @renovate[bot] ### ❤️ New Contributors * @huang-julien made their first contribution in [#6782](#6782) Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

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release: v1.0.0-beta.46 #6818

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feat: skip __toESM when not needed to reduce output size #6751

feat: skip __toESM when not needed to reduce output size #6751

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feat: skip `__toESM` when not needed to reduce output size #6751

feat: skip `__toESM` when not needed to reduce output size #6751

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