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# tools.sass

- **Type:** `Object | Function`
- **Default:**

```js
const defaultOptions = {
  sassLoaderOptions: {
    // CSS Source Map enabled by default in development environment
    sourceMap: isDev,
  },
};
```

`tools.sass` modifies the options of [@rsbuild/plugin-sass](https://rsbuild.rs/plugins/list/plugin-sass). It accepts the full plugin options:

| Option              | Description                                                                                         |
| ------------------- | --------------------------------------------------------------------------------------------------- |
| `sassLoaderOptions` | Options passed to [sass-loader](https://github.com/webpack-contrib/sass-loader), object or function |
| `include`           | Files handled by sass-loader, defaults to `/\.s(?:a\|c)ss$/`                                        |
| `exclude`           | Files that sass-loader should skip                                                                  |
| `rewriteUrls`       | Whether to rewrite relative URLs in Sass files with resolve-url-loader, defaults to `true`          |

### Modifying sass-loader options

When `sassLoaderOptions` is an `Object`, it is merged with the default config through Object.assign in a shallow way. It should be noted that `sassOptions` is merged through deepMerge in a deep way. For example:

```js
export default {
  tools: {
    sass: {
      sassLoaderOptions: {
        sourceMap: true,
      },
    },
  },
};
```

When `sassLoaderOptions` is a `Function`, the default config is passed as the first parameter, which can be directly modified or returned as the final result. The second parameter provides some utility functions that can be called directly. For example:

```js
export default {
  tools: {
    sass: {
      sassLoaderOptions(config) {
        // Modify the additionalData config
        config.additionalData = async (content, loaderContext) => {
          // ...
        };
      },
    },
  },
};
```

### Disabling URL rewriting

By default, relative URLs in Sass files are rewritten by resolve-url-loader so that they resolve relative to the source file. If your project does not rely on this, turn it off to drop one loader from the chain:

```js
export default {
  tools: {
    sass: {
      rewriteUrls: false,
    },
  },
};
```

### Modifying Sass Version

In some scenarios, if you need to use a specific version of Sass instead of the built-in Dart Sass v1 in Modern.js, you can install the desired Sass version in your project and set it up using the `implementation` option of the `sass-loader`.

```js
export default {
  tools: {
    sass: {
      sassLoaderOptions: {
        implementation: require('sass'),
      },
    },
  },
};
```

### Util Function

#### addExcludes

- **Type:** `(excludes: RegExp | RegExp[]) => void`

Used to specify which files `sass-loader` does not compile, You can pass in one or more regular expressions to match the path of sass files, for example:

```js
export default {
  tools: {
    sass: {
      sassLoaderOptions(config, { addExcludes }) {
        addExcludes(/node_modules/);
      },
    },
  },
};
```

The plugin's `exclude` option is the recommended equivalent:

```js
export default {
  tools: {
    sass: {
      exclude: /node_modules/,
    },
  },
};
```

### Legacy form

:::warning Do not mix the two layers
As soon as an object contains a plugin-level key (`sassLoaderOptions`, `include`, `exclude`, ...), the whole object is parsed as plugin options and any loader option in it has no effect. For example, `sassOptions` in `tools.sass: { rewriteUrls: false, sassOptions: { ... } }` is ignored and must be moved under `sassLoaderOptions`; a hint is printed in development.
:::

In earlier versions, `tools.sass` took the sass-loader options directly, e.g. `tools.sass: { sassOptions: {} }` or `tools.sass(config, { addExcludes }) {}`. This form still works: Modern.js wraps it into `sassLoaderOptions` and produces exactly the same config as before. A migration hint is printed in development, and the legacy form will be removed in the next major version.

```js
// legacy
export default {
  tools: {
    sass: {
      sourceMap: true,
    },
  },
};

// current
export default {
  tools: {
    sass: {
      sassLoaderOptions: {
        sourceMap: true,
      },
    },
  },
};
```