Add frozen string literal comment into generated files in rails v5.1.0

add_frozen_string_literal_comment.rb

module AddFrozenStringLiteralComment
  def add_frozen_string_literal_comment(dist)
    if File.exist?(dist) && File.extname(dist) == '.rb'
      File.open(dist, 'r') do |f|
        body = f.read

        File.open(dist, 'w') do |new_f|
          new_f.write("# frozen_string_literal: true\n" + body)
        end
      end
    end
  end
end

module GeneratorPrepend
  include AddFrozenStringLiteralComment

  def invoke!
    res = super
    add_frozen_string_literal_comment(existing_migration)
    res
  end
end

module TemplatePrepend
  include AddFrozenStringLiteralComment

  def template(source, *args, &block)
    res = super
    add_frozen_string_literal_comment(args.first)
    res
  end
end

Rails::Generators::Migration
Rails::Generators::Actions::CreateMigration.send :prepend, GeneratorPrepend
Rails::Generators::NamedBase.send :prepend, TemplatePrepend

A simpler version of this might be

return unless defined?(::Rails::Generators)

module RailsGeneratorFrozenStringLiteralPrepend
  RUBY_EXTENSIONS = %w[.rb .rake]

  def render
    return super unless RUBY_EXTENSIONS.include? File.extname(self.destination)
    "# frozen_string_literal: true\n\n" + super
  end
end

Thor::Actions::CreateFile.prepend RailsGeneratorFrozenStringLiteralPrepend

A simpler version of this might be

return unless defined?(::Rails::Generators)

module RailsGeneratorFrozenStringLiteralPrepend
  RUBY_EXTENSIONS = %w[.rb .rake]

  def render
    return super unless RUBY_EXTENSIONS.include? File.extname(self.destination)
    "# frozen_string_literal: true\n\n" + super
  end
end

Thor::Actions::CreateFile.prepend RailsGeneratorFrozenStringLiteralPrepend

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