Support generating apps with npm instead of yarn (#122)

If you select options that require a JavaScript runtime (postcss, Vite,
ESLint, etc.), nextgen will now ask what package manager you'd like to
use:

```
Which JavaScript package manager will you use? 
‣ yarn (default)
  npm
```

If you choose npm, nextgen will scrub yarn references from the files
that Rails provides (Dockerfile, Procfile.dev) and replace them with
appropriate npm commands. The `bin/setup` script provided by nextgen now
autodetects yarn vs npm and runs the correct install command as well.

Yarn remains the default option.

Closes #118.

README.md

@@ -30,7 +30,7 @@ Nextgen generates apps using **Rails 7.2**.
 
 - **Ruby 3.1+** is required (Ruby 3.2 if you choose a Rails 8 pre-release)
 - **Rubygems 3.4.8+** is required (run `gem update --system` to get it)
-- **Node 18.12+ and Yarn** are required if you choose Vite or other Node-based options
+- **Node 18.12+ and Yarn** are required if you choose Vite or other Node-based options (see the [npm note](#yarn-or-npm) below)
 - Additional tools may be required depending on the options you select (e.g. PostgreSQL)
 
 Going forward, my goal is that Nextgen will always target the latest stable version of Rails and the next pre-release version. Support for Node LTS and Ruby versions will be dropped as soon as they reach EOL (see [Ruby](https://endoflife.date/ruby) and [Node](https://endoflife.date/nodejs) EOL schedules).
@@ -71,6 +71,13 @@ If you've opted into GitHub Actions, Nextgen will automatically add jobs to your
 
 Prefer RSpec? Nextgen can set you up with RSpec, plus the gems and configuration you need for system specs (browser testing). Or stick with the Rails Minitest defaults. In either case, Nextgen will set up a good default Rake task and appropriate CI job.
 
+### Yarn or npm
+
+Prefer npm? Nextgen allows you to choose Yarn or npm to manage your app's JavaScript dependencies. Your Dockerfile, CI jobs, `bin/setup` script, etc. will be adjusted appropriately.
+
+> [!NOTE]
+> As of Rails 8.0, `rails new` is still hard-coded to use Yarn in some places. Therefore you may still need Yarn installed on your system in order to generate a new app. Nextgen will remove these Yarn references from your generated project if you select the npm option.
+
 ### Opinionated RuboCop Config
 
 By default, Rails apps include RuboCop with a config defined by the [rubocop-rails-omakase](https://github.com/rails/rubocop-rails-omakase) gem. Nextgen allows you to opt out of RuboCop entirely, or use Nextgen's own custom RuboCop config. Nextgen's config will automatically include Capybara, FactoryBot, and RSpec rules, should your app include those frameworks.

config/generators.yml

@@ -21,7 +21,11 @@ rspec_github_actions:
   requires: rspec
 
 node:
-  description: "Set up Node and Yarn"
+  description: "Set up Node"
+
+npm:
+  description: "Use npm as JavaScript package manager"
+  requires: npm
 
 vite:
   description: "Replace the asset pipeline with Vite in app/frontend"

lib/nextgen/actions.rb

@@ -4,7 +4,7 @@ module Nextgen
   module Actions
     include Bundler
     include Git
-    include Yarn
+    include Javascript
 
     def with_nextgen_source_path
       path = Nextgen.template_path.to_s

lib/nextgen/actions/javascript.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module Nextgen
+  module Actions::Javascript
+    def add_js_packages(*packages, dev: false)
+      command = yarn? ? +"yarn add" : +"npm install --fund=false --audit-false"
+      command << " -D" if dev
+      run_js_command "#{command} #{packages.map(&:shellescape).join(" ")}"
+    end
+    alias add_js_package add_js_packages
+
+    def remove_js_packages(*packages, capture: false)
+      command = yarn? ? "yarn remove" : "npm uninstall"
+      run_js_command "#{command} #{packages.map(&:shellescape).join(" ")}", capture:
+    end
+    alias remove_js_package remove_js_packages
+
+    def add_package_json_scripts(scripts)
+      scripts.each do |name, script|
+        cmd = "npm pkg set scripts.#{name.to_s.shellescape}=#{script.shellescape}"
+        say_status :run, cmd.truncate(60), :green
+        run! cmd, verbose: false
+      end
+    end
+    alias add_package_json_script add_package_json_scripts
+
+    def remove_package_json_script(name)
+      cmd = "npm pkg delete scripts.#{name.to_s.shellescape}"
+      say_status :run, cmd.truncate(60), :green
+      run! cmd, verbose: false
+    end
+
+    def js_package_manager
+      File.exist?("yarn.lock") ? :yarn : :npm
+    end
+
+    def yarn?
+      js_package_manager == :yarn
+    end
+
+    def run_js_command(cmd, capture: false)
+      say_status(*cmd.split(" ", 2), :green)
+      output = run! cmd, capture: true, verbose: false
+      return output if capture
+      return puts(output) unless output.match?(/^success /)
+
+      puts output.lines.grep(/^(warning|success) /).join
+    end
+  end
+end

lib/nextgen/commands/create.rb

@@ -50,7 +50,10 @@ def run # rubocop:disable Metrics/MethodLength, Metrics/PerceivedComplexity
       ask_rails_frameworks
       ask_test_framework
       ask_system_testing if rails_opts.frontend? && rails_opts.test_framework?
+      reload_generators
       ask_optional_enhancements
+      ask_js_package_manager if node?
+      reload_generators
 
       say <<~SUMMARY
 
@@ -67,18 +70,19 @@ def run # rubocop:disable Metrics/MethodLength, Metrics/PerceivedComplexity
 
       if node?
         say <<~NODE
-          Based on the options you selected, your app will require Node and Yarn. For reference, you are using these versions:
+          Based on the options you selected, your app will require a JavaScript runtime. For reference, you are using:
 
-            Node: #{capture_version("node")}
-            Yarn: #{capture_version("yarn")}
+            node: #{capture_version("node")}
+            yarn: #{capture_version("yarn")}
+            npm:  #{capture_version("npm")}
 
         NODE
       end
 
       continue_if "Continue?"
 
       create_initial_commit_message
-      copy_package_json if node?
+      create_package_json if node?
       Nextgen::RailsCommand.run "new", *rails_new_args
       Dir.chdir(app_path) do
         Nextgen::RailsCommand.run "app:template", "LOCATION=#{write_generators_script}"
@@ -111,12 +115,13 @@ def continue_if(question)
       end
     end
 
-    def copy_package_json
+    def create_package_json
       FileUtils.mkdir_p(app_path)
       FileUtils.cp(
         Nextgen.template_path.join("package.json"),
         File.join(app_path, "package.json")
       )
+      FileUtils.touch(File.join(app_path, rails_opts.npm? ? "package-lock.json" : "yarn.lock"))
     end
 
     def ask_rails_version
@@ -240,16 +245,28 @@ def ask_system_testing
       rails_opts.skip_system_test! unless system_testing
     end
 
-    def ask_optional_enhancements
+    def reload_generators
+      selected = generators ? (generators.all_active & generators.optional.values) : []
       @generators = Generators.compatible_with(rails_opts:)
+      generators.activate(*(selected & generators.optional.values))
+    end
 
+    def ask_optional_enhancements
       answers = prompt.multi_select(
         "Which optional enhancements would you like to add?",
         generators.optional.sort_by { |label, _| label.downcase }.to_h
       )
       generators.activate(*answers)
     end
 
+    def ask_js_package_manager
+      options = {
+        "yarn (default)" => :yarn,
+        "npm" => :npm
+      }
+      rails_opts.js_package_manager = prompt_select("Which JavaScript package manager will you use?", options)
+    end
+
     def create_initial_commit_message
       path = File.join(app_path, "tmp", "initial_nextgen_commit")
       FileUtils.mkdir_p(File.dirname(path))

lib/nextgen/generators/eslint.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 say_git "Install eslint"
-add_yarn_packages(
+add_js_packages(
   "@eslint/js",
   "eslint@^9",
   "eslint-config-prettier",
@@ -21,7 +21,7 @@
 copy_file "eslint.config.js"
 
 say_git "Add eslint to default rake task"
-copy_file "lib/tasks/eslint.rake"
+template "lib/tasks/eslint.rake.tt"
 add_lint_task "eslint"
 
 if File.exist?(".github/workflows/ci.yml")
@@ -39,16 +39,16 @@
         uses: actions/setup-node@v4
         with:
           #{node_spec}
-          cache: yarn
+          cache: #{js_package_manager}
 
-      - name: Install Yarn packages
+      - name: Install #{js_package_manager} packages
         run: npx --yes ci
 
       - name: Lint JavaScript files with eslint
-        run: yarn lint:js
+        run: #{js_package_manager} run lint:js
 
   YAML
 end
 
 say_git "Auto-correct any existing issues"
-run "yarn fix:js", capture: true
+run "#{js_package_manager} run fix:js", capture: true

lib/nextgen/generators/node.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-say_git "Add Node and Yarn prerequisites"
 copy_file "package.json" unless File.exist?("package.json")
 inject_into_file "README.md", "\n- Node 18 (LTS) or newer\n- Yarn 1.x (classic)", after: /^- Ruby.*$/
 inject_into_file "README.md", "\nbrew install node\nbrew install yarn", after: /^brew install rbenv.*$/

lib/nextgen/generators/npm.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+remove_file "yarn.lock"
+run! "npm install --fund=false --audit=false"
+
+gsub_file "README.md", "\n- Yarn 1.x (classic)", ""
+gsub_file "README.md", "\nbrew install yarn", ""
+
+gsub_file "Procfile.dev", "yarn build", "npm run build --" if File.exist?("Procfile.dev")
+
+if File.exist?("Dockerfile")
+  gsub_file "Dockerfile", /^\s*ARG YARN_VERSION.*\n/, ""
+  gsub_file "Dockerfile", /^\s*npm install -g yarn.*\n/, ""
+  gsub_file "Dockerfile", "yarn.lock", "package-lock.json"
+  gsub_file "Dockerfile", /RUN yarn install.*/, "RUN npm ci"
+end

lib/nextgen/generators/stylelint.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 say_git "Install stylelint"
-add_yarn_packages(
+add_js_packages(
   "stylelint",
   "stylelint-config-standard",
   "stylelint-declaration-strict-value",
@@ -19,7 +19,7 @@
 copy_file ".stylelintrc.js"
 
 say_git "Add stylelint to default rake task"
-copy_file "lib/tasks/stylelint.rake"
+template "lib/tasks/stylelint.rake.tt"
 add_lint_task "stylelint"
 
 if File.exist?(".github/workflows/ci.yml")
@@ -37,16 +37,16 @@
         uses: actions/setup-node@v4
         with:
           #{node_spec}
-          cache: yarn
+          cache: #{js_package_manager}
 
-      - name: Install Yarn packages
+      - name: Install #{js_package_manager} packages
         run: npx --yes ci
 
       - name: Lint CSS files with stylelint
-        run: yarn lint:css
+        run: #{js_package_manager} run lint:css
 
   YAML
 end
 
 say_git "Auto-correct any existing issues"
-run "yarn fix:css", capture: true
+run "#{js_package_manager} run fix:css", capture: true