Add comprehensive --rspack documentation across all guides

## Documentation Updates

### 1. Generator Details (api-reference/generator-details.md)
- Added --rspack to generator options list
- Added Rspack section in generator description
- Created comprehensive "Rspack Support" section covering:
  - Benefits (~20x faster builds, unified config, easy switching)
  - What gets installed (packages and configuration)
  - Switching bundlers post-installation
  - Combining with other options (TypeScript, Redux)
  - Link to webpack configuration docs

### 2. Quick Start Guide (getting-started/quick-start.md)
- Added --rspack option example in installation step
- Added performance tip highlighting 20x improvement
- Mentioned bin/switch-bundler utility for later switching

### 3. Webpack Configuration (core-concepts/webpack-configuration.md)
- Added new "Rspack vs. Webpack" section covering:
  - Introduction to Rspack and performance benefits
  - Usage instructions (generation and switching)
  - Performance metrics (build times, SWC benefits)
  - Unified configuration approach with code examples
  - shakapacker.yml configuration details

## Documentation Structure

The documentation is now comprehensive and appears in all appropriate places:
- API Reference: Detailed generator option documentation
- Getting Started: Quick introduction for new users
- Core Concepts: Deep dive into configuration and usage

All docs follow existing formatting conventions and include:
- Clear code examples
- Performance metrics
- Cross-references between docs
- Practical usage instructions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

docs/api-reference/generator-details.md

@@ -10,6 +10,8 @@ Usage:
 
 Options:
   -R, [--redux], [--no-redux]                      # Install Redux package and Redux version of Hello World Example. Default: false
+  -T, [--typescript], [--no-typescript]            # Generate TypeScript files and install TypeScript dependencies. Default: false
+      [--rspack], [--no-rspack]                    # Use Rspack instead of Webpack as the bundler. Default: false
       [--ignore-warnings], [--no-ignore-warnings]  # Skip warnings. Default: false
 
 Runtime options:
@@ -29,6 +31,18 @@ can pass the redux option if you'd like to have redux setup for you automaticall
     to integrate the Redux state container framework. The necessary node modules
     will be automatically included for you.
 
+* TypeScript
+
+    Passing the --typescript generator option generates TypeScript files (.tsx)
+    instead of JavaScript files (.jsx) and sets up TypeScript configuration.
+
+* Rspack
+
+    Passing the --rspack generator option uses Rspack instead of Webpack as the
+    bundler, providing significantly faster builds (~20x improvement with SWC).
+    Includes unified configuration that works with both bundlers and a
+    bin/switch-bundler utility to switch between bundlers post-installation.
+
 *******************************************************************************
 
 
@@ -106,6 +120,57 @@ rails generate react_on_rails:install --typescript
 
 This creates `.tsx` files instead of `.jsx` and adds TypeScript configuration.
 
+### Rspack Support
+
+The generator supports a `--rspack` option for using Rspack instead of Webpack as the bundler:
+
+```bash
+rails generate react_on_rails:install --rspack
+```
+
+**Benefits:**
+
+- **~20x faster builds** with SWC transpilation (build times of ~53-270ms vs typical webpack builds)
+- **Unified configuration** - same webpack config files work for both bundlers
+- **Easy switching** - includes `bin/switch-bundler` utility to switch between bundlers post-installation
+
+**What gets installed:**
+
+- Rspack core packages (`@rspack/core`, `@rspack/cli`)
+- Rspack-specific plugins (`@rspack/plugin-react-refresh`, `rspack-manifest-plugin`)
+- Shakapacker configured with `assets_bundler: 'rspack'` and `webpack_loader: 'swc'`
+
+**Switching bundlers after installation:**
+
+```bash
+# Switch to Rspack
+bin/switch-bundler rspack
+
+# Switch back to Webpack
+bin/switch-bundler webpack
+```
+
+The switch-bundler script automatically:
+
+- Updates shakapacker.yml configuration
+- Installs/removes appropriate dependencies
+- Works with npm, yarn, and pnpm
+
+**Combining with other options:**
+
+```bash
+# Rspack with TypeScript
+rails generate react_on_rails:install --rspack --typescript
+
+# Rspack with Redux
+rails generate react_on_rails:install --rspack --redux
+
+# All options combined
+rails generate react_on_rails:install --rspack --typescript --redux
+```
+
+For more details on Rspack configuration, see the [Webpack Configuration](../core-concepts/webpack-configuration.md#rspack-vs-webpack) docs.
+
 ### Auto-Bundling and Component Registration
 
 Modern React on Rails uses auto-bundling to eliminate manual webpack configuration. Components placed in the configured `components_subdirectory` (default: `ror_components`) are automatically:

docs/core-concepts/webpack-configuration.md

@@ -11,6 +11,73 @@
 
 To get a deeper understanding of Shakapacker, watch [RailsConf 2020 CE - Webpacker, It-Just-Works, But How? by Justin Gordon](https://youtu.be/sJLoOpc5LD8).
 
+## Rspack vs. Webpack
+
+[Rspack](https://rspack.dev/) is a high-performance JavaScript bundler written in Rust that provides significantly faster builds than Webpack (~20x improvement). React on Rails supports both bundlers through unified configuration.
+
+### Using Rspack
+
+Generate a new app with Rspack:
+
+```bash
+rails generate react_on_rails:install --rspack
+```
+
+Or switch an existing app to Rspack:
+
+```bash
+bin/switch-bundler rspack
+```
+
+### Performance Benefits
+
+- **Build times**: ~53-270ms with Rspack vs typical webpack builds
+- **~20x faster transpilation** with SWC (used by Rspack)
+- **Faster development** builds and CI runs
+
+### Unified Configuration
+
+React on Rails generates unified webpack configuration files that work with both bundlers:
+
+**config/webpack/development.js** - Conditional plugin loading:
+
+```javascript
+const { config } = require('shakapacker');
+
+if (config.assets_bundler === 'rspack') {
+  // Rspack uses @rspack/plugin-react-refresh
+  const ReactRefreshPlugin = require('@rspack/plugin-react-refresh');
+  clientWebpackConfig.plugins.push(new ReactRefreshPlugin());
+} else {
+  // Webpack uses @pmmmwh/react-refresh-webpack-plugin
+  const ReactRefreshWebpackPlugin = require('@pmmmwh/react-refresh-webpack-plugin');
+  clientWebpackConfig.plugins.push(new ReactRefreshWebpackPlugin());
+}
+```
+
+**config/webpack/serverWebpackConfig.js** - Dynamic bundler detection:
+
+```javascript
+const { config } = require('shakapacker');
+
+const bundler = config.assets_bundler === 'rspack' ? require('@rspack/core') : require('webpack');
+
+// Use bundler-specific APIs
+serverWebpackConfig.plugins.unshift(new bundler.optimize.LimitChunkCountPlugin({ maxChunks: 1 }));
+```
+
+### Configuration in shakapacker.yml
+
+Rspack configuration is controlled via `config/shakapacker.yml`:
+
+```yaml
+default: &default
+  assets_bundler: 'rspack' # or 'webpack'
+  webpack_loader: 'swc' # Rspack works best with SWC
+```
+
+The `bin/switch-bundler` script automatically updates this configuration when switching bundlers.
+
 Per the example repo [shakacode/react_on_rails_demo_ssr_hmr](https://github.com/shakacode/react_on_rails_demo_ssr_hmr),
 you should consider keeping your codebase mostly consistent with the defaults for [Shakapacker](https://github.com/shakacode/shakapacker).
 

docs/getting-started/quick-start.md

@@ -31,6 +31,9 @@ git add . && git commit -m "Add react_on_rails gem"
 
 # Run the installer
 bin/rails generate react_on_rails:install
+
+# Optional: Use Rspack for ~20x faster builds
+# bin/rails generate react_on_rails:install --rspack
 ```
 
 Take a look at the files created by the generator.
@@ -41,6 +44,8 @@ Take a look at the files created by the generator.
 - A sample controller and view
 - Webpack configuration
 
+> 💡 **Performance Tip:** Add the `--rspack` flag for significantly faster builds (~20x improvement). You can also switch bundlers later with `bin/switch-bundler rspack`.
+
 ## 🎯 Step 2: Start the Development Server (1 minute)
 
 > **Note:** Ensure you have `overmind` or `foreman` installed to run `bin/dev`.