docs(lazy-barrel): clarify default export behavior#8128
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Pull request overview
This PR enhances the lazy barrel optimization documentation by clarifying how default exports behave differently depending on whether they are re-exports or own exports. The key distinction is that re-exported defaults (using export { X as default } from './module') can be optimized, while own exports (using export default X where X is a local binding) cannot.
Changes:
- Added an example of re-exporting a named export as default
- Added a warning section explaining the non-equivalence of re-export vs own export for default exports
- Enhanced an existing example with clarifying comments about own exports
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Co-authored-by: 翠 <[email protected]> Signed-off-by: dalaoshu <[email protected]>
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Co-authored-by: Copilot <[email protected]> Signed-off-by: dalaoshu <[email protected]>
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Signed-off-by: 翠 <[email protected]>
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## [1.0.0-rc.3] - 2026-02-04
⚡ Remove Unnecessary Default Export Assignment
- Eliminates redundant variable assignments when exporting default values
- Reduces output bundle size and improves code clarity
```js
// index.js
var x = 42;
export default x;
// Before
var x = 42;
var entry_default = x;
export { entry_default as default };
// After
var x = 42;
export { x as default };
```
🐛 Avoid Unnecessary Facade Chunks
- Keep user-defined entry modules in their own chunks
- Reduces HTTP round trips and improves startup performance
```js
// main.js (entry module)
import { a } from './lib.js'
console.log(a)
// lib.js
export * from './counter.js'
// counter.js (entry module)
export const a = 100
// Before
dist/
├── main.js → import { a } from './counter-chunk.js'; console.log(a)
├── counter.js → export { a } from './counter-chunk.js' // ❌ facade chunk
└── counter-chunk.js → export const a = 100
// After
dist/
├── main.js → import { a } from './counter.js'; console.log(a)
└── counter.js → export const a = 100
```
### 🚀 Features
- expose `RUNTIME_MODULE_ID` constant for plugin authors (#8199) by @shulaoda
- warn unsupported combination of `preserveValueImports` and `importsNotUsedAsValues` in tsconfig.json (#8169) by @sapphi-red
- sophisticated watch tracking for load dependencies (#8092) by @sapphi-red
- add `inputMap` option to `minify` / `minifySync` functions (#8138) by @sapphi-red
- consolidate same tsconfig errors (#8119) by @sapphi-red
- include tsconfig file path in error messages (#8107) by @Copilot
- lazy-barrel: support incremental build mode (#8114) by @shulaoda
### 🐛 Bug Fixes
- rust: preserve dependencies added by `this.addWatchFile` (#8198) by @hyf0
- spawn `RuntimeModuleTask` after `build_start` to avoid race condition (#8182) by @shulaoda
- rust/dev: only close after the ongoing task finished (#8147) by @hyf0
- ensure `\0rolldown/runtime.js` will go through transform hook and add test (#8093) by @hyf0
- `[name]` in `assetFileNames` does not include the directory part (#8098) by @IWANABETHATGUY
- handle external module properties in namespace imports (#8124) by @IWANABETHATGUY
- keep user-defined entry modules in their own chunks (#8047) by @IWANABETHATGUY
- avoid `Unknown resolve error` error message (#8111) by @sapphi-red
### 💼 Other
- remove warnings for building rolldown with `not(feature = "experimental")` (#8110) by @coolreader18
### 🚜 Refactor
- move `VERSION` to `constants` directory (#8200) by @shulaoda
- simplify import symbol check using `SymbolFlags` (#8193) by @shulaoda
- extract tsconfig option and transform options merging logic (#8168) by @sapphi-red
- filter empty module_groups before sorting (#8149) by @ShroXd
- lazy-barrel: use single `remove` instead of `contains_key` + `remove` (#8123) by @shulaoda
- lazy-barrel: avoid redundant call and inline `get_barrel_normal_module` (#8122) by @shulaoda
- use logger instead of console.log for warnings (#8117) by @IWANABETHATGUY
- module-loader: remove intermediate ModuleTaskOwnerRef type (#8113) by @shulaoda
- rename ReExportExternalModule to ReExportDynamicExports (#8104) by @IWANABETHATGUY
### 📚 Documentation
- add dynamic OG image generation (#8192) by @sapphi-red
- add dynamic OG image generation (#8191) by @sapphi-red
- add dynamic OG image generation (#8179) by @Copilot
- apis: add links to option descriptions in JSDoc comments (#8167) by @sapphi-red
- apis: clarify parameters of `resolveDynamicImport` hook (#8137) by @sapphi-red
- lazy-barrel: clarify default export behavior (#8128) by @shulaoda
### ⚡ Performance
- remove unnecessary assignment for default export (#8127) by @shulaoda
### 🧪 Testing
- dev: `this.addWatchFile` dependency should be preserved after reload (#8165) by @sapphi-red
- mark flaky `transform_runtime_module` test as ignored (#8178) by @Copilot
- rolldown_sourcemap: add test for coarse segments (#8166) by @sapphi-red
- dev: correctly assert file change (#8164) by @sapphi-red
- rust: `transform_runtime_module` test shouldn't panic inside (#8151) by @hyf0
- rust: fix flakiness of rust tests (#8150) by @hyf0
- mark `output.dynamicImportInCjs` tests as passed (#8125) by @shulaoda
- lazy-barrel: add test cases for default export (#8129) by @shulaoda
- rolldown_plugin_vite_manifest: use relative path for outPath (#8101) by @shulaoda
### ⚙️ Miscellaneous Tasks
- deps: update crate-ci/typos action to v1.43.1 (#8188) by @renovate[bot]
- deps: update rust crate ts-rs to v12 (#8160) by @renovate[bot]
- deps: update crate-ci/typos action to v1.43.0 (#8175) by @renovate[bot]
- deps: update rust crates (#8157) by @renovate[bot]
- deps: update oxc to v0.112.0 (#8171) by @renovate[bot]
- deps: update rollup submodule for tests to v4.57.1 (#8176) by @sapphi-red
- deps: update test262 submodule for tests (#8177) by @sapphi-red
- deps: update dependency oxlint to v1.43.0 (#8173) by @renovate[bot]
- deps: update dependency oxfmt to ^0.28.0 (#8170) by @renovate[bot]
- deps: update dependency rolldown-plugin-dts to v0.21.8 (#8163) by @renovate[bot]
- deps: update dependency vue-router to v5 (#8159) by @renovate[bot]
- deps: update github-actions (#8158) by @renovate[bot]
- deps: update npm packages (#8156) by @renovate[bot]
- deps: update dependency oxlint-tsgolint to v0.11.4 (#8140) by @renovate[bot]
- fix clippy replacement typo (#8136) by @IWANABETHATGUY
- disallow `HashMap::new` and `HashSet::new` by clippy (#8135) by @sapphi-red
- deps: update dependency rolldown-plugin-dts to v0.21.7 (#8126) by @renovate[bot]
- deps: update oxc resolver to v11.17.0 (#8121) by @renovate[bot]
- deps: update dependency oxlint-tsgolint to v0.11.3 (#8109) by @renovate[bot]
### ❤️ New Contributors
* @coolreader18 made their first contribution in [#8110](#8110)
Co-authored-by: shulaoda <[email protected]>
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We should clarify the default export behavior:
export { Button as default } from './Button'andimport { Button } from './Button'; export default Buttonare not equivalent.