Gem::Commands::SetupCommand#install_file

# File tmp/rubies/ruby-3.2.0/lib/rubygems/commands/setup_command.rb, line 637
def install_file(file, dest_dir)
  dest_file = File.join dest_dir, file
  dest_dir = File.dirname dest_file
  unless File.directory? dest_dir
    mkdir_p dest_dir, :mode => 0755
  end

  install file, dest_file, :mode => options[:data_mode] || 0644
end