Rewrite Experiments Css To Module Rules

Rewrite `experiments.css: true` for `@rspack/core@2`

@rspack/core@2 removed experiments.css and promoted CSS handling to a default-available feature — but it's now opt-in per file type via module.rules. Workspaces that set experiments.css: true on v1 will silently lose CSS processing on v2 unless module.rules declares a rule matching their CSS file extensions with a type of 'css', 'css/module', or 'css/auto'.

This change is workspace-specific (which test: regex, which type:, whether existing rules already cover it), so the migration ships as an AI-assisted instruction rather than a blind codemod.

What needs to change

For every rspack.config.{ts,js,mjs,cjs} in the workspace that has experiments.css: true:

Delete the experiments.css: true line. If experiments becomes empty after the deletion, delete the whole experiments: { ... } property too.
Ensure module.rules has a CSS rule using type: 'css/auto' (or 'css' / 'css/module' if you have a stronger preference). The rspack docs recommend 'css/auto' because it auto-detects CSS Modules (filenames matching *.module.css).
- If module.rules already has an entry that matches .css files — for example via css-loader / style-loader / MiniCssExtractPlugin — leave it alone. The user opted into a loader pipeline on v1 and that pipeline still works on v2.
- If module.rules has no CSS-related rule at all, append:
  ts
```
{
  test: /\.css$/,
  type: 'css/auto',
}
```
Do not touch experiments.css: false configs. Those are handled automatically by the deterministic codemod that runs alongside this prompt.

Sample Code Changes

Before

export default {
  // ...
  experiments: {
    css: true,
  },
};

After

export default {
  // ...
  module: {
    rules: [{ test: /\.css$/, type: 'css/auto' }],
  },
};

Before — workspace that already uses css-loader

export default {
  // ...
  experiments: {
    css: true,
  },
  module: {
    rules: [{ test: /\.css$/, use: ['style-loader', 'css-loader'] }],
  },
};

After — `experiments.css` removed, existing rule untouched

export default {
  // ...
  module: {
    rules: [{ test: /\.css$/, use: ['style-loader', 'css-loader'] }],
  },
};

Reference

@rspack/core@2 migration guide — Remove experiments.css

Rewrite experiments.css: true for @rspack/core@2