Gem::Commands::SetupCommand#install_file

# File tmp/rubies/ruby-4.1.0-preview1/lib/rubygems/commands/setup_command.rb, line 619
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: 0o755
  end

  install file, dest_file, mode: options[:data_mode] || 0o644
end