class Gem::Ext::ExtConfBuilder

def self.build(extension, dest_path, results, args=[], lib_dir=nil, extension_dir=Dir.pwd,
  target_rbconfig=Gem.target_rbconfig)
  require "fileutils"
  require "tempfile"
  tmp_dest = Dir.mktmpdir(".gem.", extension_dir)
  # Some versions of `mktmpdir` return absolute paths, which will break make
  # if the paths contain spaces.
  #
  # As such, we convert to a relative path.
  tmp_dest_relative = get_relative_path(tmp_dest.clone, extension_dir)
  destdir = ENV["DESTDIR"]
  begin
    cmd = ruby << File.basename(extension)
    cmd << "--target-rbconfig=#{target_rbconfig.path}" if target_rbconfig.path
    cmd.push(*args)
    run(cmd, results, class_name, extension_dir) do |s, r|
      mkmf_log = File.join(extension_dir, "mkmf.log")
      if File.exist? mkmf_log
        unless s.success?
          r << "To see why this extension failed to compile, please check" \
            " the mkmf.log which can be found here:\n"
          r << "  " + File.join(dest_path, "mkmf.log") + "\n"
        end
        FileUtils.mv mkmf_log, dest_path
      end
    end
    ENV["DESTDIR"] = nil
    make dest_path, results, extension_dir, tmp_dest_relative, target_rbconfig: target_rbconfig
    full_tmp_dest = File.join(extension_dir, tmp_dest_relative)
    is_cross_compiling = target_rbconfig["platform"] != RbConfig::CONFIG["platform"]
    # Do not copy extension libraries by default when cross-compiling
    # not to conflict with the one already built for the host platform.
    if Gem.install_extension_in_lib && lib_dir && !is_cross_compiling
      FileUtils.mkdir_p lib_dir
      entries = Dir.entries(full_tmp_dest) - %w[. ..]
      entries = entries.map {|entry| File.join full_tmp_dest, entry }
      FileUtils.cp_r entries, lib_dir, remove_destination: true
    end
    FileUtils::Entry_.new(full_tmp_dest).traverse do |ent|
      destent = ent.class.new(dest_path, ent.rel)
      destent.exist? || FileUtils.mv(ent.path, destent.path)
    end
    make dest_path, results, extension_dir, tmp_dest_relative, ["clean"], target_rbconfig: target_rbconfig
  ensure
    ENV["DESTDIR"] = destdir
  end
  results
ensure
  FileUtils.rm_rf tmp_dest if tmp_dest
end

def self.get_relative_path(path, base)
  path[0..base.length - 1] = "." if path.start_with?(base)
  path
end