Add --rspack generator option for faster builds

CHANGELOG.md

@@ -25,6 +25,8 @@ Changes since the last non-beta release.
 
 #### Added
 
+- **Rspack Support**: Added `--rspack` flag to `react_on_rails:install` generator for significantly faster builds (~20x improvement with SWC). Includes unified webpack/rspack configuration templates and `bin/switch-bundler` utility to switch between bundlers post-installation. [PR #1852](https://github.com/shakacode/react_on_rails/pull/1852) by [justin808](https://github.com/justin808).
+
 - **Attribution Comment**: Added HTML comment attribution to Rails views containing React on Rails functionality. The comment automatically displays which version is in use (open source React on Rails or React on Rails Pro) and, for Pro users, shows the license status. This helps identify React on Rails usage across your application. [PR #1857](https://github.com/shakacode/react_on_rails/pull/1857) by [AbanoubGhadban](https://github.com/AbanoubGhadban).
 
 - **Improved Error Messages**: Error messages for version mismatches and package configuration issues now include package-manager-specific installation commands (npm, yarn, pnpm, bun). [PR #1881](https://github.com/shakacode/react_on_rails/pull/1881) by [AbanoubGhadban](https://github.com/AbanoubGhadban).

RSPACK_IMPLEMENTATION.md

@@ -0,0 +1,160 @@
+# Rspack Generator Option Implementation
+
+This document summarizes the implementation of the `--rspack` option for the React on Rails generator, based on the patterns from [PR #20 in react_on_rails-demos](https://github.com/shakacode/react_on_rails-demos/pull/20).
+
+## Overview
+
+The `--rspack` flag allows users to generate a React on Rails application using Rspack instead of Webpack as the bundler. Rspack provides significantly faster build times (~53-270ms vs typical webpack builds).
+
+## Changes Made
+
+### 1. Install Generator (`lib/generators/react_on_rails/install_generator.rb`)
+
+- **Added `--rspack` class option** (line 31-35): Boolean flag to enable Rspack bundler
+- **Updated `invoke_generators`** (line 82-83): Pass rspack option to base generator
+- **Added `add_rspack_dependencies` method** (line 499-513): Installs Rspack core packages:
+  - `@rspack/core`
+  - `rspack-manifest-plugin`
+- **Updated `add_dev_dependencies`** (line 515-534): Conditionally installs rspack or webpack refresh plugins:
+  - Rspack: `@rspack/cli`, `@rspack/plugin-react-refresh`, `react-refresh`
+  - Webpack: `@pmmmwh/react-refresh-webpack-plugin`, `react-refresh`
+- **Updated `add_js_dependencies`** (line 433): Calls `add_rspack_dependencies` when rspack flag is set
+
+### 2. Base Generator (`lib/generators/react_on_rails/base_generator.rb`)
+
+- **Added `--rspack` class option** (line 22-26): Boolean flag (passed from install generator)
+- **Updated `copy_packer_config`** (line 85-100): Calls `configure_rspack_in_shakapacker` after copying config
+- **Added `configure_rspack_in_shakapacker` method** (line 404-426):
+  - Adds `assets_bundler: 'rspack'` to shakapacker.yml default section
+  - Changes `webpack_loader` to `'swc'` (Rspack works best with SWC transpiler)
+
+### 3. Webpack Configuration Templates
+
+Updated webpack configuration templates to support both webpack and rspack bundlers with unified config approach:
+
+**development.js.tt**:
+
+- Added `config` to shakapacker require to access `assets_bundler` setting
+- Conditional React Refresh plugin loading based on `config.assets_bundler`:
+  - Rspack: Uses `@rspack/plugin-react-refresh`
+  - Webpack: Uses `@pmmmwh/react-refresh-webpack-plugin`
+- Prevents "window not found" errors when using rspack
+
+**serverWebpackConfig.js.tt**:
+
+- Added `bundler` variable that conditionally requires `@rspack/core` or `webpack`
+- Changed `webpack.optimize.LimitChunkCountPlugin` to `bundler.optimize.LimitChunkCountPlugin`
+- Enables same config to work with both bundlers without warnings
+- Avoids hardcoding webpack-specific imports
+
+### 4. Bundler Switching Script (`lib/generators/react_on_rails/templates/base/base/bin/switch-bundler`)
+
+Created a new executable script that allows switching between webpack and rspack after installation:
+
+**Features:**
+
+- Updates `shakapacker.yml` with correct `assets_bundler` setting
+- Switches `webpack_loader` between 'swc' (rspack) and 'babel' (webpack)
+- Removes old bundler dependencies from package.json
+- Installs new bundler dependencies
+- Supports npm, yarn, and pnpm package managers
+- Auto-detects package manager from lock files
+
+**Usage:**
+
+```bash
+bin/switch-bundler rspack   # Switch to Rspack
+bin/switch-bundler webpack  # Switch to Webpack
+```
+
+**Dependencies managed:**
+
+- **Webpack**: webpack, webpack-cli, webpack-dev-server, webpack-assets-manifest, webpack-merge, @pmmmwh/react-refresh-webpack-plugin
+- **Rspack**: @rspack/core, @rspack/cli, @rspack/plugin-react-refresh, rspack-manifest-plugin
+
+## Usage
+
+### Generate new app with Rspack:
+
+```bash
+rails generate react_on_rails:install --rspack
+```
+
+### Generate with Rspack and TypeScript:
+
+```bash
+rails generate react_on_rails:install --rspack --typescript
+```
+
+### Generate with Rspack and Redux:
+
+```bash
+rails generate react_on_rails:install --rspack --redux
+```
+
+### Switch existing app to Rspack:
+
+```bash
+bin/switch-bundler rspack
+```
+
+## Configuration Changes
+
+When `--rspack` is used, the following configuration changes are applied to `config/shakapacker.yml`:
+
+```yaml
+default: &default
+  source_path: app/javascript
+  assets_bundler: 'rspack' # Added
+  # ... other settings
+  webpack_loader: 'swc' # Changed from 'babel'
+```
+
+## Dependencies
+
+### Rspack-specific packages installed:
+
+**Production:**
+
+- `@rspack/core` - Core Rspack bundler
+- `rspack-manifest-plugin` - Manifest generation for Rspack
+
+**Development:**
+
+- `@rspack/cli` - Rspack CLI tools
+- `@rspack/plugin-react-refresh` - React Fast Refresh for Rspack
+- `react-refresh` - React Fast Refresh runtime
+
+### Webpack packages NOT installed with --rspack:
+
+**Production:**
+
+- `webpack`
+- `webpack-assets-manifest`
+- `webpack-merge`
+
+**Development:**
+
+- `webpack-cli`
+- `webpack-dev-server`
+- `@pmmmwh/react-refresh-webpack-plugin`
+
+## Performance Benefits
+
+According to PR #20:
+
+- Build times: ~53-270ms with Rspack vs typical webpack builds
+- Approximately 20x faster transpilation with SWC (used by Rspack)
+- Faster development builds and CI runs
+
+## Testing
+
+The implementation follows existing generator patterns and passes RuboCop checks with zero offenses.
+
+## Compatibility
+
+- Works with existing webpack configuration files (unified config approach)
+- Compatible with TypeScript option (`--typescript`)
+- Compatible with Redux option (`--redux`)
+- Supports all package managers (npm, yarn, pnpm)
+- Reversible via `bin/switch-bundler` script

lib/generators/react_on_rails/base_generator.rb

@@ -19,6 +19,12 @@ class BaseGenerator < Rails::Generators::Base
                    desc: "Install Redux package and Redux version of Hello World Example",
                    aliases: "-R"
 
+      # --rspack
+      class_option :rspack,
+                   type: :boolean,
+                   default: false,
+                   desc: "Use Rspack instead of Webpack as the bundler"
+
       def add_hello_world_route
         route "get 'hello_world', to: 'hello_world#index'"
       end
@@ -82,13 +88,15 @@ def copy_packer_config
         if File.exist?(".shakapacker_just_installed")
           puts "Skipping Shakapacker config copy (already installed by Shakapacker installer)"
           File.delete(".shakapacker_just_installed") # Clean up marker
+          configure_rspack_in_shakapacker if options.rspack?
           return
         end
 
         puts "Adding Shakapacker #{ReactOnRails::PackerUtils.shakapacker_version} config"
         base_path = "base/base/"
         config = "config/shakapacker.yml"
         copy_file("#{base_path}#{config}", config)
+        configure_rspack_in_shakapacker if options.rspack?
       end
 
       def add_base_gems_to_gemfile
@@ -392,6 +400,25 @@ def add_configure_rspec_to_compile_assets(helper_file)
         search_str = "RSpec.configure do |config|"
         gsub_file(helper_file, search_str, CONFIGURE_RSPEC_TO_COMPILE_ASSETS)
       end
+
+      def configure_rspack_in_shakapacker
+        shakapacker_config_path = "config/shakapacker.yml"
+        return unless File.exist?(shakapacker_config_path)
+
+        puts Rainbow("🔧 Configuring Shakapacker for Rspack...").yellow
+
+        # Parse YAML config properly to avoid fragile regex manipulation
+        config = YAML.load_file(shakapacker_config_path)
+
+        # Update default section
+        config["default"] ||= {}
+        config["default"]["assets_bundler"] = "rspack"
+        config["default"]["webpack_loader"] = "swc"
+
+        # Write back as YAML
+        File.write(shakapacker_config_path, YAML.dump(config))
+        puts Rainbow("✅ Updated shakapacker.yml for Rspack").green
+      end
     end
   end
 end

lib/generators/react_on_rails/install_generator.rb

@@ -28,6 +28,12 @@ class InstallGenerator < Rails::Generators::Base
                    desc: "Generate TypeScript files and install TypeScript dependencies. Default: false",
                    aliases: "-T"
 
+      # --rspack
+      class_option :rspack,
+                   type: :boolean,
+                   default: false,
+                   desc: "Use Rspack instead of Webpack as the bundler. Default: false"
+
       # --ignore-warnings
       class_option :ignore_warnings,
                    type: :boolean,
@@ -96,7 +102,8 @@ def invoke_generators
           create_css_module_types
           create_typescript_config
         end
-        invoke "react_on_rails:base", [], { typescript: options.typescript?, redux: options.redux? }
+        invoke "react_on_rails:base", [],
+               { typescript: options.typescript?, redux: options.redux?, rspack: options.rspack? }
         if options.redux?
           invoke "react_on_rails:react_with_redux", [], { typescript: options.typescript? }
         else
@@ -447,6 +454,7 @@ def add_js_dependencies
         add_react_on_rails_package
         add_react_dependencies
         add_css_dependencies
+        add_rspack_dependencies if options.rspack?
         add_dev_dependencies
       end
 
@@ -512,12 +520,36 @@ def add_css_dependencies
         handle_npm_failure("CSS dependencies", css_deps) unless success
       end
 
+      def add_rspack_dependencies
+        puts "Installing Rspack core dependencies..."
+        rspack_deps = %w[
+          @rspack/core
+          rspack-manifest-plugin
+        ]
+        if add_npm_dependencies(rspack_deps)
+          @added_dependencies_to_package_json = true
+          return
+        end
+
+        success = system("npm", "install", *rspack_deps)
+        @ran_direct_installs = true if success
+        handle_npm_failure("Rspack dependencies", rspack_deps) unless success
+      end
+
       def add_dev_dependencies
         puts "Installing development dependencies..."
-        dev_deps = %w[
-          @pmmmwh/react-refresh-webpack-plugin
-          react-refresh
-        ]
+        dev_deps = if options.rspack?
+                     %w[
+                       @rspack/cli
+                       @rspack/plugin-react-refresh
+                       react-refresh
+                     ]
+                   else
+                     %w[
+                       @pmmmwh/react-refresh-webpack-plugin
+                       react-refresh
+                     ]
+                   end
         if add_npm_dependencies(dev_deps, dev: true)
           @added_dependencies_to_package_json = true
           return