Rspack 1.6 Release Plan

[JSerFeng]

Features

1. Stablize experiments.layers

#11593
#11819

Remove experiments.layers config @JSerFeng

2. Esm Library Plugin

#10350

Using brand-new esm output for library, more pretty and tree-shaking friendly output, supports manually code-splitting. @JSerFeng

3. output.charset is false by default

#11837

4. Improved dynamic import tree shaking

We have introduced many improvements for tree shaking dynamic import by @ahabhgk.

• fix: should walk call member chain args for dynamic import referenced #11661
• feat: static analyse import then for tree shaking #11665
• feat: static analyze destructuring assignment dynamic import variable for tree shaking #11731

5. Enable experiments.lazyBarrel by default

Rsbuild has already enabled it by default since v1.5, after a period of practicing on Rsbuild, we believe that lazyBarrel is close to being stable.

[chenjiahan]

Disable output.charset by default

Currently, Rspack injects the charset attribute into <script> tags for async chunks by default. However, this attribute is deprecated in the HTML specification and has no practical effect in modern browsers:

• All major browsers (Chrome, Firefox, Safari, Edge, and IE9+) ignore <script charset> since scripts are always parsed as UTF-8 or according to HTTP headers.
• The attribute was only relevant for IE8 and below when loading scripts encoded in non-UTF-8 charsets, which are no longer supported.
• Keeping this attribute increases output bundle size and may trigger deprecation warnings.

Proposal:

Change the default value of output.charset to false, so that Rspack no longer emits <script charset="utf-8"> by default. Users who still need this legacy behavior (very rare) can explicitly enable the option.

This would align Rspack’s default output with modern HTML best practices and simplify generated bundles.

Related:

• Deprecated <script charset="utf-8"> webpack/webpack#9327
• https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/script#deprecated_attributes

[JSerFeng]

EsmLibraryPlugin

Many of you already uses the modern-module library, which works based on ConcatenatedModule, can make more pretty esm output.

However it's implemented only for entries, it didn't change the way Rspack loads chunks, so if you have dynamic import, the imported chunk is not pretty as well, it looks like normal Rspack style chunk. 👇

exports.chunk_id = '467'
exports.modules = {
 'src/index.js': function() { ... }
}

Which is certainly not able to be statically analyzed, and statically analyzable is important for library.

So we change how chunk renders only for ESM library output, the output should be cleaner and more human-readable.

It can work with splitChunks, you can customize chunk creation.

import { foo } from './main-314.js'

const bar = () => foo

export { bar }

This is the experimental feature, if you encounter any problem, please contact us by issues

Related
#10350

[ahabhgk]

Improve dynamic import tree shaking

• fix: should walk call member chain args for dynamic import referenced #11661
• feat: static analyse import then for tree shaking #11665
• feat: static analyze destructuring assignment dynamic import variable for tree shaking #11731

[ahabhgk]

Enable experiments.lazyBarrel by default

Rsbuild has already enabled it by default since v1.5, after a period of practicing on Rsbuild, we believe that lazyBarrel is close to being stable.

[colinaaa]

Rule.extractSourceMap

Extracts existing source map data from files (from their //# sourceMappingURL comment), useful for preserving the source maps of third-party libraries.

export default {
  // ...
  module: {
    rules: [
      {
        test: /\.m?js$/,
        extractSourceMap: true,
      },
    ],
  },
};

This was introduced in Webpack v5.102.0 as a builtin replacement of source-map-loader.

Related:

• feat: implement extractSourceMap option #11814
• https://webpack.js.org/configuration/module/#ruleextractsourcemap