Gem::Installer#write_spec

# File tmp/rubies/ruby-4.1.0-preview1/lib/rubygems/installer.rb, line 425
def write_spec
  spec.installed_by_version = Gem.rubygems_version

  spec_file = self.spec_file
  spec_dir = File.dirname spec_file
  dir_mode = options[:dir_mode]
  content_addressed = Gem::ContentAddress.content_addressed?(spec)

  if File.directory? spec_dir
    if content_addressed && dir_mode && !File.writable?(spec_dir)
      File.chmod(0o755, spec_dir)
    end
  else
    ensure_writable_dir spec_dir
  end

  begin
    Gem.write_binary(spec_file, spec.to_ruby_for_cache)
  ensure
    File.chmod(dir_mode, spec_dir) if dir_mode && content_addressed
  end
end