Gem::Installer#windows_stub_script

# File tmp/rubies/ruby-4.0.0/lib/rubygems/installer.rb, line 770
  def windows_stub_script(bindir, bin_file_name)
    rb_topdir = RbConfig::TOPDIR || File.dirname(rb_config["bindir"])

    # get ruby executable file name from RbConfig
    ruby_exe = "#{rb_config["RUBY_INSTALL_NAME"]}#{rb_config["EXEEXT"]}"
    ruby_exe = "ruby.exe" if ruby_exe.empty?

    if File.exist?(File.join(bindir, ruby_exe))
      # stub & ruby.exe within same folder.  Portable
      <<~TEXT
        @ECHO OFF
        @"%~dp0#{ruby_exe}" "%~dpn0" %*
      TEXT
    elsif bindir.downcase.start_with? rb_topdir.downcase
      # stub within ruby folder, but not standard bin.  Portable
      require "pathname"
      from = Pathname.new bindir
      to   = Pathname.new "#{rb_topdir}/bin"
      rel  = to.relative_path_from from
      <<~TEXT
        @ECHO OFF
        @"%~dp0#{rel}/#{ruby_exe}" "%~dpn0" %*
      TEXT
    else
      # outside ruby folder, maybe -user-install or bundler.  Portable, but ruby
      # is dependent on PATH
      <<~TEXT
        @ECHO OFF
        @#{ruby_exe} "%~dpn0" %*
      TEXT
    end
  end