Implement Engines support

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    tailwindcss-rails (4.2.2)
+    tailwindcss-rails (4.2.3)
       railties (>= 7.0.0)
       tailwindcss-ruby (~> 4.0)
 

README.md

@@ -400,6 +400,20 @@ Then you can use yarn or npm to install the dependencies.
 
 If you need to use a custom input or output file, you can run `bundle exec tailwindcss` to access the platform-specific executable, and give it your own build options.
 
+## Rails Engines support
+
+If you have Rails Engines in your application that use Tailwind CSS, they will be automatically included in the Tailwind build as long as they conform to next conventions:
+
+- The engine must have `tailwindcss-rails` as gem dependency.
+- The engine must have a `app/assets/tailwind/<engine_name>/application.css` file or your application must have overridden file in the same location of your application root.
+- The engine must register itself in Tailwindcss Rails:
+```ruby
+  initializer 'your_engine.tailwindcss' do |app|
+    ActiveSupport.on_load(:tailwindcss_rails) do
+      config.tailwindcss_rails.engines << Your::Engine.engine_name
+    end
+  end
+```
 
 ## Troubleshooting
 

lib/tailwindcss/commands.rb

@@ -3,13 +3,16 @@
 module Tailwindcss
   module Commands
     class << self
-      def compile_command(debug: false, **kwargs)
+      def rails_root
+        defined?(Rails) ? Rails.root : Pathname.new(Dir.pwd)
+      end
+
+      def compile_command(input = rails_root.join("app/assets/tailwind/application.css").to_s, debug: false, **kwargs)
         debug = ENV["TAILWINDCSS_DEBUG"].present? if ENV.key?("TAILWINDCSS_DEBUG")
-        rails_root = defined?(Rails) ? Rails.root : Pathname.new(Dir.pwd)
 
         command = [
           Tailwindcss::Ruby.executable(**kwargs),
-          "-i", rails_root.join("app/assets/tailwind/application.css").to_s,
+          "-i", input,
           "-o", rails_root.join("app/assets/builds/tailwind.css").to_s,
         ]
 
@@ -21,8 +24,8 @@ def compile_command(debug: false, **kwargs)
         command
       end
 
-      def watch_command(always: false, poll: false, **kwargs)
-        compile_command(**kwargs).tap do |command|
+      def watch_command(input = rails_root.join("app/assets/tailwind/application.css").to_s, always: false, poll: false, **kwargs)
+        compile_command(input, **kwargs).tap do |command|
           command << "-w"
           command << "always" if always
           command << "-p" if poll
@@ -38,6 +41,36 @@ def command_env(verbose:)
       def rails_css_compressor?
         defined?(Rails) && Rails&.application&.config&.assets&.css_compressor.present?
       end
+
+      def engines_roots
+        return [] unless defined?(Rails)
+        return [] unless Rails.application&.config&.tailwindcss_rails&.engines
+
+        Rails::Engine.descendants.select do |engine|
+          begin
+            engine.engine_name.in?(Rails.application.config.tailwindcss_rails.engines)
+          end
+        end.map do |engine|
+          [
+            Rails.root.join("app/assets/tailwind/#{engine.engine_name}/application.css"),
+            engine.root.join("app/assets/tailwind/#{engine.engine_name}/application.css")
+          ].select(&:exist?).compact.first.to_s
+        end.compact
+      end
+
+      def with_dynamic_input
+        engine_roots = Tailwindcss::Commands.engines_roots
+        if engine_roots.any?
+          Tempfile.create('tailwind.css') do |file|
+            file.write(engine_roots.map { |root| "@import \"#{root}\";" }.join("\n"))
+            file.write("\n@import \"#{Rails.root.join('app/assets/tailwind/application.css')}\";\n")
+            file.rewind
+            yield file.path if block_given?
+          end
+        else
+          yield rails_root.join("app/assets/tailwind/application.css").to_s if block_given?
+        end
+      end
     end
   end
 end

lib/tailwindcss/engine.rb

@@ -2,6 +2,13 @@
 
 module Tailwindcss
   class Engine < ::Rails::Engine
+    config.tailwindcss_rails = ActiveSupport::OrderedOptions.new
+    config.tailwindcss_rails.engines = []
+
+    initializer 'tailwindcss.load_hook' do |app|
+      ActiveSupport.run_load_hooks(:tailwindcss_rails, app)
+    end
+
     initializer "tailwindcss.disable_generator_stylesheets" do
       Rails.application.config.generators.stylesheets = false
     end

lib/tasks/build.rake

@@ -4,11 +4,13 @@ namespace :tailwindcss do
     debug = args.extras.include?("debug")
     verbose = args.extras.include?("verbose")
 
-    command = Tailwindcss::Commands.compile_command(debug: debug)
-    env = Tailwindcss::Commands.command_env(verbose: verbose)
-    puts "Running: #{Shellwords.join(command)}" if verbose
+    Tailwindcss::Commands.with_dynamic_input do |input|
+      command = Tailwindcss::Commands.compile_command(input, debug: debug)
+      env = Tailwindcss::Commands.command_env(verbose: verbose)
+      puts "Running: #{Shellwords.join(command)}" if verbose
 
-    system(env, *command, exception: true)
+      system(env, *command, exception: true)
+    end
   end
 
   desc "Watch and build your Tailwind CSS on file changes"
@@ -18,11 +20,13 @@ namespace :tailwindcss do
     always = args.extras.include?("always")
     verbose = args.extras.include?("verbose")
 
-    command = Tailwindcss::Commands.watch_command(always: always, debug: debug, poll: poll)
-    env = Tailwindcss::Commands.command_env(verbose: verbose)
-    puts "Running: #{Shellwords.join(command)}" if verbose
+    Tailwindcss::Commands.with_dynamic_input do |input|
+      command = Tailwindcss::Commands.watch_command(input, always: always, debug: debug, poll: poll)
+      env = Tailwindcss::Commands.command_env(verbose: verbose)
+      puts "Running: #{Shellwords.join(command)}" if verbose
 
-    system(env, *command)
+      system(env, *command)
+    end
   rescue Interrupt
     puts "Received interrupt, exiting tailwindcss:watch" if args.extras.include?("verbose")
   end

test/lib/tailwindcss/commands_test.rb

@@ -2,16 +2,23 @@
 require "minitest/mock"
 
 class Tailwindcss::CommandsTest < ActiveSupport::TestCase
-  attr_accessor :executable
+  attr_accessor :executable, :original_rails, :tmp_dir
 
-  def setup
-    super
+  setup do
+    @tmp_dir = Dir.mktmpdir
+    @original_rails = Object.const_get(:Rails) if Object.const_defined?(:Rails)
     @executable = Tailwindcss::Ruby.executable
   end
 
+  teardown do
+    FileUtils.rm_rf(@tmp_dir)
+    Tailwindcss::Commands.remove_tempfile! if Tailwindcss::Commands.class_variable_defined?(:@@tempfile)
+    restore_rails_constant
+  end
+
   test ".compile_command" do
     Rails.stub(:root, File) do # Rails.root won't work in this test suite
-      actual = Tailwindcss::Commands.compile_command
+      actual = Tailwindcss::Commands.compile_command("app/assets/tailwind/application.css")
       assert_kind_of(Array, actual)
       assert_equal(executable, actual.first)
       assert_includes(actual, "-i")
@@ -126,4 +133,175 @@ def setup
       assert_includes(actual, "always")
     end
   end
+
+  test ".engines_roots when Rails is not defined" do
+    Object.send(:remove_const, :Rails) if Object.const_defined?(:Rails)
+    assert_empty Tailwindcss::Commands.engines_roots
+  end
+
+  test ".engines_roots when no engines are configured" do
+    with_rails_app do
+      assert_empty Tailwindcss::Commands.engines_roots
+    end
+  end
+
+  test ".engines_roots when there are engines" do
+    within_engine_configs do |engine1, engine2, engine3|
+      roots = Tailwindcss::Commands.engines_roots
+
+      assert_equal 2, roots.size
+      assert_includes roots, engine1.css_path.to_s
+      assert_includes roots, engine2.css_path.to_s
+      refute_includes roots, engine3.css_path.to_s
+    end
+  end
+
+  test ".with_dynamic_input yields tempfile path when engines exist" do
+    within_engine_configs do |engine1, engine2|
+      Tailwindcss::Commands.with_dynamic_input do |css_path|
+        assert_match(/tailwind\.css/, css_path)
+        assert File.exist?(css_path)
+
+        content = File.read(css_path)
+        assert_match %r{@import "#{engine1.css_path}";}, content
+        assert_match %r{@import "#{engine2.css_path}";}, content
+        assert_match %r{@import "#{Rails.root.join('app/assets/tailwind/application.css')}";}, content
+      end
+    end
+  end
+
+  test ".with_dynamic_input yields application.css path when no engines" do
+    with_rails_app do
+      expected_path = Rails.root.join("app/assets/tailwind/application.css").to_s
+      Tailwindcss::Commands.with_dynamic_input do |css_path|
+        assert_equal expected_path, css_path
+      end
+    end
+  end
+
+  test "engines can be configured via tailwindcss_rails.engines" do
+    with_rails_app do
+      # Create a test engine
+      test_engine = Class.new(Rails::Engine) do
+        def self.engine_name
+          "test_engine"
+        end
+
+        def self.root
+          Pathname.new(Dir.mktmpdir)
+        end
+      end
+
+      # Create CSS file for the engine
+      engine_css_path = test_engine.root.join("app/assets/tailwind/test_engine/application.css")
+      FileUtils.mkdir_p(File.dirname(engine_css_path))
+      FileUtils.touch(engine_css_path)
+
+      # Create application-level CSS file
+      app_css_path = Rails.root.join("app/assets/tailwind/test_engine/application.css")
+      FileUtils.mkdir_p(File.dirname(app_css_path))
+      FileUtils.touch(app_css_path)
+
+      # Register the engine
+      Rails::Engine.descendants << test_engine
+
+      # Store the hook for later execution
+      hook = nil
+      ActiveSupport.on_load(:tailwindcss_rails) do
+        hook = self
+        Rails.application.config.tailwindcss_rails.engines << "test_engine"
+      end
+
+      # Trigger the hook manually
+      ActiveSupport.run_load_hooks(:tailwindcss_rails, hook)
+
+      # Verify the engine is included in roots
+      roots = Tailwindcss::Commands.engines_roots
+      assert_equal 1, roots.size
+      assert_includes roots, app_css_path.to_s
+    ensure
+      FileUtils.rm_rf(test_engine.root) if defined?(test_engine)
+      FileUtils.rm_rf(File.dirname(app_css_path)) if defined?(app_css_path)
+    end
+  end
+
+  private
+    # Define Structs outside of methods to avoid redefining them
+    ConfigStruct = Struct.new(:engines)
+    AssetsStruct = Struct.new(:css_compressor)
+    TailwindStruct = Struct.new(:tailwindcss_rails, :assets)
+    AppStruct = Struct.new(:config)
+    EngineStruct = Struct.new(:name, :root, :css_path)
+
+    def with_rails_app
+      Object.send(:remove_const, :Rails) if Object.const_defined?(:Rails)
+      Object.const_set(:Rails, setup_mock_rails)
+      yield
+    end
+
+    def setup_mock_rails
+      mock_engine = Class.new do
+        class << self
+          attr_accessor :engine_name, :root
+
+          def descendants
+            @descendants ||= []
+          end
+        end
+      end
+
+      mock_rails = Class.new do
+        class << self
+          attr_accessor :root, :application
+
+          def const_get(const_name)
+            return Engine if const_name == :Engine
+            super
+          end
+        end
+      end
+
+      mock_rails.const_set(:Engine, mock_engine)
+      mock_rails.root = Pathname.new(@tmp_dir)
+      tailwind_config = ConfigStruct.new([])
+      assets_config = AssetsStruct.new(nil)
+      app_config = TailwindStruct.new(tailwind_config, assets_config)
+      mock_rails.application = AppStruct.new(app_config)
+      mock_rails
+    end
+
+    def restore_rails_constant
+      Object.send(:remove_const, :Rails) if Object.const_defined?(:Rails)
+      Object.const_set(:Rails, @original_rails) if @original_rails
+    end
+
+    def within_engine_configs
+      engine_configs = create_test_engines
+      with_rails_app do
+        Rails.application.config.tailwindcss_rails.engines = %w[test_engine1 test_engine2]
+
+        # Create and register mock engine classes
+        engine_configs.each do |config|
+          engine_class = Class.new(Rails::Engine)
+          engine_class.engine_name = config.name
+          engine_class.root = Pathname.new(config.root)
+          Rails::Engine.descendants << engine_class
+        end
+
+        yield(*engine_configs)
+      end
+    end
+
+    def create_test_engines
+      [1, 2, 3].map do |i|
+        engine = EngineStruct.new(
+          "test_engine#{i}",
+          File.join(@tmp_dir, "engine#{i}"),
+          File.join(@tmp_dir, "app/assets/tailwind/test_engine#{i}/application.css")
+        )
+        FileUtils.mkdir_p(File.dirname(engine.css_path))
+        FileUtils.touch(engine.css_path)
+        engine
+      end
+    end
 end