Add --rspack generator option for faster builds

justin808 · claude · justin808 · commit 8275cac67228 · 2025-11-04T16:23:12.000-10:00
Implements --rspack flag for react_on_rails:install generator to use Rspack bundler instead of Webpack, providing ~20x faster builds. ## Changes - Added --rspack option to install_generator.rb and base_generator.rb - Conditional dependency installation (rspack vs webpack packages) - Auto-configures shakapacker.yml for rspack with SWC transpiler - Created bin/switch-bundler utility to switch bundlers post-install ## Key Features - Rspack packages: @rspack/core, @rspack/cli, @rspack/plugin-react-refresh - Compatible with --typescript and --redux options - Reversible via bin/switch-bundler script - Supports npm, yarn, and pnpm package managers ## Usage rails generate react_on_rails:install --rspack bin/switch-bundler rspack # Switch existing app Based on patterns from react_on_rails-demos PR #20 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
diff --git a/RSPACK_IMPLEMENTATION.md b/RSPACK_IMPLEMENTATION.md
@@ -0,0 +1,141 @@
+# 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. 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
diff --git a/lib/generators/react_on_rails/base_generator.rb b/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 +400,30 @@ 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
+
+        # Read the current config
+        config_content = File.read(shakapacker_config_path)
+
+        # Update assets_bundler to rspack in default section
+        unless config_content.include?("assets_bundler:")
+          # Add assets_bundler after source_path in default section
+          config_content.gsub!(/^default: &default\n(\s+source_path:.*\n)/) do
+            "default: &default\n#{Regexp.last_match(1)}  assets_bundler: 'rspack'\n"
+          end
+        end
+
+        # Update webpack_loader to swc (rspack works best with SWC)
+        config_content.gsub!(/^\s*webpack_loader:.*$/, "  webpack_loader: 'swc'")
+
+        File.write(shakapacker_config_path, config_content)
+        puts Rainbow("✅ Updated shakapacker.yml for Rspack").green
+      end
     end
   end
 end
diff --git a/lib/generators/react_on_rails/install_generator.rb b/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,
@@ -73,7 +79,8 @@ 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
@@ -424,6 +431,7 @@ 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
 
@@ -489,12 +497,36 @@ 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
diff --git a/lib/generators/react_on_rails/templates/base/base/bin/switch-bundler b/lib/generators/react_on_rails/templates/base/base/bin/switch-bundler
