Add Shakapacker precompile hook support for auto pack generation

This change leverages Shakapacker's new precompile_hook feature to
automatically generate packs before webpack compilation, replacing the
need to manually modify assets:precompile tasks or bin/dev scripts.

Changes:
- Add bin/shakapacker-precompile-hook script to templates and spec/dummy
- Update shakapacker.yml to configure precompile_hook
- Add PackerUtils.shakapacker_precompile_hook_configured? method
- Skip generate_packs in configuration and PackGenerator when hook configured
- Update generator to copy hook script and make it executable

The precompile hook runs before webpack compilation and is properly
validated by Shakapacker to ensure it points to a file within the
project root.

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

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

Author: justin808

lib/generators/react_on_rails/base_generator.rb

@@ -37,12 +37,16 @@ def copy_base_files
                         app/views/layouts/hello_world.html.erb
                         Procfile.dev
                         Procfile.dev-static-assets
-                        Procfile.dev-prod-assets]
+                        Procfile.dev-prod-assets
+                        bin/shakapacker-precompile-hook]
         base_templates = %w[config/initializers/react_on_rails.rb]
         base_files.each { |file| copy_file("#{base_path}#{file}", file) }
         base_templates.each do |file|
           template("#{base_path}/#{file}.tt", file)
         end
+
+        # Make the hook script executable
+        File.chmod(0o755, "bin/shakapacker-precompile-hook") if File.exist?("bin/shakapacker-precompile-hook")
       end
 
       def copy_js_bundle_files

lib/generators/react_on_rails/templates/base/base/bin/shakapacker-precompile-hook

@@ -0,0 +1,20 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+# Shakapacker precompile hook for React on Rails
+#
+# This script runs before webpack compilation to generate pack files
+# for auto-bundled components. It's called automatically by Shakapacker
+# when configured in config/shakapacker.yml:
+#   precompile_hook: 'bin/shakapacker-precompile-hook'
+
+require_relative "../config/environment"
+
+begin
+  puts Rainbow("🔄 Running React on Rails precompile hook...").cyan
+  ReactOnRails::PacksGenerator.instance.generate_packs_if_stale
+rescue StandardError => e
+  warn Rainbow("❌ Error in precompile hook: #{e.message}").red
+  warn e.backtrace.first(5).join("\n")
+  exit 1
+end

lib/generators/react_on_rails/templates/base/base/config/shakapacker.yml

@@ -42,6 +42,11 @@ default: &default
   # Raises an error if there is a mismatch in the shakapacker gem and npm package being used
   ensure_consistent_versioning: true
 
+  # Hook to run before webpack compilation (e.g., for generating dynamic entry points)
+  # SECURITY: Only reference trusted scripts within your project. The hook command will be
+  # validated to ensure it points to a file within the project root.
+  precompile_hook: 'bin/shakapacker-precompile-hook'
+
   # Select whether the compiler will use SHA digest ('digest' option) or most recent modified timestamp ('mtime') to determine freshness
   compiler_strategy: digest
 

lib/react_on_rails/configuration.rb

@@ -238,7 +238,11 @@ def adjust_precompile_task
       raise(ReactOnRails::Error, compile_command_conflict_message) if ReactOnRails::PackerUtils.precompile?
 
       precompile_tasks = lambda {
-        Rake::Task["react_on_rails:generate_packs"].invoke
+        # Skip generate_packs if shakapacker has a precompile hook configured
+        unless ReactOnRails::PackerUtils.shakapacker_precompile_hook_configured?
+          Rake::Task["react_on_rails:generate_packs"].invoke
+        end
+
         Rake::Task["react_on_rails:assets:webpack"].invoke
 
         # VERSIONS is per the shakacode/shakapacker clean method definition.

lib/react_on_rails/dev/pack_generator.rb

@@ -8,6 +8,12 @@ module Dev
     class PackGenerator
       class << self
         def generate(verbose: false)
+          # Skip if shakapacker has a precompile hook configured
+          if ReactOnRails::PackerUtils.shakapacker_precompile_hook_configured?
+            puts "⏭️  Skipping pack generation (handled by shakapacker precompile hook)" if verbose
+            return
+          end
+
           if verbose
             puts "📦 Generating React on Rails packs..."
             success = run_pack_generation

lib/react_on_rails/dev/server_manager.rb

@@ -248,7 +248,7 @@ def help_mode_details
           <<~MODES
             #{Rainbow('🔥 HMR Development mode (default)').cyan.bold} - #{Rainbow('Procfile.dev').green}:
             #{Rainbow('•').yellow} #{Rainbow('Hot Module Replacement (HMR) enabled').white}
-            #{Rainbow('•').yellow} #{Rainbow('React on Rails pack generation before Procfile start').white}
+            #{Rainbow('•').yellow} #{Rainbow('React on Rails pack generation (via precompile hook or bin/dev)').white}
             #{Rainbow('•').yellow} #{Rainbow('Webpack dev server for fast recompilation').white}
             #{Rainbow('•').yellow} #{Rainbow('Source maps for debugging').white}
             #{Rainbow('•').yellow} #{Rainbow('May have Flash of Unstyled Content (FOUC)').white}
@@ -257,15 +257,15 @@ def help_mode_details
 
             #{Rainbow('📦 Static development mode').cyan.bold} - #{Rainbow('Procfile.dev-static-assets').green}:
             #{Rainbow('•').yellow} #{Rainbow('No HMR (static assets with auto-recompilation)').white}
-            #{Rainbow('•').yellow} #{Rainbow('React on Rails pack generation before Procfile start').white}
+            #{Rainbow('•').yellow} #{Rainbow('React on Rails pack generation (via precompile hook or bin/dev)').white}
             #{Rainbow('•').yellow} #{Rainbow('Webpack watch mode for auto-recompilation').white}
             #{Rainbow('•').yellow} #{Rainbow('CSS extracted to separate files (no FOUC)').white}
             #{Rainbow('•').yellow} #{Rainbow('Development environment (faster builds than production)').white}
             #{Rainbow('•').yellow} #{Rainbow('Source maps for debugging').white}
             #{Rainbow('•').yellow} #{Rainbow('Access at:').white} #{Rainbow('http://localhost:3000/<route>').cyan.underline}
 
             #{Rainbow('🏭 Production-assets mode').cyan.bold} - #{Rainbow('Procfile.dev-prod-assets').green}:
-            #{Rainbow('•').yellow} #{Rainbow('React on Rails pack generation before Procfile start').white}
+            #{Rainbow('•').yellow} #{Rainbow('React on Rails pack generation (via precompile hook or assets:precompile)').white}
             #{Rainbow('•').yellow} #{Rainbow('Asset precompilation with NODE_ENV=production (webpack optimizations)').white}
             #{Rainbow('•').yellow} #{Rainbow('RAILS_ENV=development by default for assets:precompile (avoids credentials)').white}
             #{Rainbow('•').yellow} #{Rainbow('Use --rails-env=production for assets:precompile only (not server processes)').white}
@@ -281,16 +281,20 @@ def help_mode_details
         def run_production_like(_verbose: false, route: nil, rails_env: nil)
           procfile = "Procfile.dev-prod-assets"
 
+          features = [
+            "Precompiling assets with production optimizations",
+            "Running Rails server on port 3001",
+            "No HMR (Hot Module Replacement)",
+            "CSS extracted to separate files (no FOUC)"
+          ]
+
+          # NOTE: Pack generation happens automatically during assets:precompile
+          # either via precompile hook or via the configuration.rb adjust_precompile_task
+
           print_procfile_info(procfile, route: route)
           print_server_info(
             "🏭 Starting production-like development server...",
-            [
-              "Generating React on Rails packs",
-              "Precompiling assets with production optimizations",
-              "Running Rails server on port 3001",
-              "No HMR (Hot Module Replacement)",
-              "CSS extracted to separate files (no FOUC)"
-            ],
+            features,
             3001,
             route: route
           )
@@ -409,15 +413,22 @@ def run_production_like(_verbose: false, route: nil, rails_env: nil)
 
         def run_static_development(procfile, verbose: false, route: nil)
           print_procfile_info(procfile, route: route)
+
+          features = [
+            "Using shakapacker --watch (no HMR)",
+            "CSS extracted to separate files (no FOUC)",
+            "Development environment (source maps, faster builds)",
+            "Auto-recompiles on file changes"
+          ]
+
+          # Add pack generation info if not using precompile hook
+          unless ReactOnRails::PackerUtils.shakapacker_precompile_hook_configured?
+            features.unshift("Generating React on Rails packs")
+          end
+
           print_server_info(
             "⚡ Starting development server with static assets...",
-            [
-              "Generating React on Rails packs",
-              "Using shakapacker --watch (no HMR)",
-              "CSS extracted to separate files (no FOUC)",
-              "Development environment (source maps, faster builds)",
-              "Auto-recompiles on file changes"
-            ],
+            features,
             route: route
           )
 

lib/react_on_rails/packer_utils.rb

@@ -166,5 +166,18 @@ def self.raise_shakapacker_version_incompatible_for_basic_pack_generation
 
       raise ReactOnRails::Error, msg
     end
+
+    # Check if shakapacker.yml has a precompile_hook configured
+    # This prevents react_on_rails from running generate_packs redundantly
+    def self.shakapacker_precompile_hook_configured?
+      return false unless defined?(::Shakapacker)
+
+      config_data = ::Shakapacker.config.send(:data)
+      hook = config_data[:precompile_hook]
+
+      hook.present?
+    rescue StandardError
+      false
+    end
   end
 end

spec/dummy/config/shakapacker.yml

@@ -25,6 +25,11 @@ default: &default
   cache_manifest: false
   nested_entries: true
 
+  # Hook to run before webpack compilation (e.g., for generating dynamic entry points)
+  # SECURITY: Only reference trusted scripts within your project. The hook command will be
+  # validated to ensure it points to a file within the project root.
+  precompile_hook: 'bin/shakapacker-precompile-hook'
+
 development:
   <<: *default
   # Turn this to true if you want to use the rails/shakapacker check that the test