Webpackerが提供しているコマンドの内部処理を追ってみた

#!/usr/bin/env ruby

ENV["RAILS_ENV"] ||= ENV["RACK_ENV"] || "development"
ENV["NODE_ENV"]  ||= "development"

require "pathname"
ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../../Gemfile",
  Pathname.new(__FILE__).realpath)

require "bundler/setup"

require "webpacker"
require "webpacker/webpack_runner"

APP_ROOT = File.expand_path("..", __dir__)
Dir.chdir(APP_ROOT) do
  Webpacker::WebpackRunner.run(ARGV)
end

require "shellwords"
require "webpacker/runner"

module Webpacker
  class WebpackRunner < Webpacker::Runner
    def run
      env = Webpacker::Compiler.env

      cmd = if node_modules_bin_exist?
        ["#{@node_modules_bin_path}/webpack"]
      else
        ["yarn", "webpack"]
      end

      if ARGV.include?("--debug")
        cmd = [ "node", "--inspect-brk"] + cmd
        ARGV.delete("--debug")
      end

      cmd += ["--config", @webpack_config] + @argv

      Dir.chdir(@app_path) do
        Kernel.exec env, *cmd
      end
    end

    private
      def node_modules_bin_exist?
        File.exist?("#{@node_modules_bin_path}/webpack")
      end
  end
end

****/app-root/node_modules/.bin/webpack --config ****/app-root/config/webpack/development.js

./node_modules/.bin/webpack --config ./config/webpack/development.js

yarn webpack --config ./config/webpack/development.js

#!/usr/bin/env ruby

ENV["RAILS_ENV"] ||= ENV["RACK_ENV"] || "development"
ENV["NODE_ENV"]  ||= "development"

require "pathname"
ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../../Gemfile",
  Pathname.new(__FILE__).realpath)

require "bundler/setup"

require "webpacker"
require "webpacker/dev_server_runner"

APP_ROOT = File.expand_path("..", __dir__)
Dir.chdir(APP_ROOT) do
  Webpacker::DevServerRunner.run(ARGV)
end

require "shellwords"
require "socket"
require "webpacker/configuration"
require "webpacker/dev_server"
require "webpacker/runner"

module Webpacker
  class DevServerRunner < Webpacker::Runner
    def run
      load_config
      detect_port!
      execute_cmd
    end

    private
      def load_config
        app_root = Pathname.new(@app_path)

        @config = Configuration.new(
          root_path: app_root,
          config_path: app_root.join("config/webpacker.yml"),
          env: ENV["RAILS_ENV"]
        )

        dev_server = DevServer.new(@config)

        @hostname          = dev_server.host
        @port              = dev_server.port
        @pretty            = dev_server.pretty?

      rescue Errno::ENOENT, NoMethodError
        $stdout.puts "webpack dev_server configuration not found in #{@config.config_path}[#{ENV["RAILS_ENV"]}]."
        $stdout.puts "Please run bundle exec rails webpacker:install to install Webpacker"
        exit!
      end

      def detect_port!
        server = TCPServer.new(@hostname, @port)
        server.close

      rescue Errno::EADDRINUSE
        $stdout.puts "Another program is running on port #{@port}. Set a new port in #{@config.config_path} for dev_server"
        exit!
      end

      def execute_cmd
        env = Webpacker::Compiler.env

        cmd = if node_modules_bin_exist?
          ["#{@node_modules_bin_path}/webpack-dev-server"]
        else
          ["yarn", "webpack-dev-server"]
        end

        if ARGV.include?("--debug")
          cmd = [ "node", "--inspect-brk"] + cmd
          ARGV.delete("--debug")
        end

        cmd += ["--config", @webpack_config]
        cmd += ["--progress", "--color"] if @pretty

        Dir.chdir(@app_path) do
          Kernel.exec env, *cmd
        end
      end

      def node_modules_bin_exist?
        File.exist?("#{@node_modules_bin_path}/webpack-dev-server")
      end
  end
end

****/app-root/node_modules/.bin/webpack-dev-server --config ****/app-root/config/webpack/development.js

./node_modules/.bin/webpack-dev-server --config ./config/webpack/development.js --port 3035

yarn webpack-dev-server --config ./config/webpack/development.js --port 3035

$stdout.sync = true

def yarn_install_available?
  rails_major = Rails::VERSION::MAJOR
  rails_minor = Rails::VERSION::MINOR

  rails_major > 5 || (rails_major == 5 && rails_minor >= 1)
end

def enhance_assets_precompile
  # yarn:install was added in Rails 5.1
  deps = yarn_install_available? ? [] : ["webpacker:yarn_install"]
  Rake::Task["assets:precompile"].enhance(deps) do
    Rake::Task["webpacker:compile"].invoke
  end
end

namespace :webpacker do
  desc "Compile JavaScript packs using webpack for production with digests"
  task compile: ["webpacker:verify_install", :environment] do
    Webpacker.with_node_env(ENV.fetch("NODE_ENV", "production")) do
      Webpacker.ensure_log_goes_to_stdout do
        if Webpacker.compile
          # Successful compilation!
        else
          # Failed compilation
          exit!
        end
      end
    end
  end
end

# Compile packs after we've compiled all other assets during precompilation
skip_webpacker_precompile = %w(no false n f).include?(ENV["WEBPACKER_PRECOMPILE"])

unless skip_webpacker_precompile
  if Rake::Task.task_defined?("assets:precompile")
    enhance_assets_precompile
  else
    Rake::Task.define_task("assets:precompile" => ["webpacker:yarn_install", "webpacker:compile"])
  end
end

    Webpacker.with_node_env(ENV.fetch("NODE_ENV", "production")) do
      Webpacker.ensure_log_goes_to_stdout do
        if Webpacker.compile
          # Successful compilation!
        else
          # Failed compilation
          exit!
        end
      end
    end

  def compile
    compiler.compile.tap do |success|
      manifest.refresh if success
    end
  end

  def compile
    if stale?
      run_webpack.tap do |success|
        # We used to only record the digest on success
        # However, the output file is still written on error, (at least with ts-loader), meaning that the
        # digest should still be updated. If it's not, you can end up in a situation where a recompile doesn't
        # take place when it should.
        # See https://github.com/rails/webpacker/issues/2113
        record_compilation_digest
      end
    else
      logger.info "Everything's up-to-date. Nothing to do"
      true
    end
  end

    def run_webpack
      logger.info "Compiling..."

      stdout, stderr, status = Open3.capture3(
        webpack_env,
        "#{RbConfig.ruby} ./bin/webpack",
        chdir: File.expand_path(config.root_path)
      )

      if status.success?
        logger.info "Compiled all packs in #{config.public_output_path}"
        logger.error "#{stderr}" unless stderr.empty?

        if config.webpack_compile_output?
          logger.info stdout
        end
      else
        non_empty_streams = [stdout, stderr].delete_if(&:empty?)
        logger.error "Compilation failed:\n#{non_empty_streams.join("\n\n")}"
      end

      status.success?
    end

NODE_ENV=production ./bin/webpack

./node_modules/.bin/webpack --config ./config/webpack/production.js

yarn webpack --config ./config/webpack/production.js