# class Gem::Ext::ExtConfBuilder

### Public Class Methods

build (extension, dest_path, results, args=[], lib_dir=nil, extension_dir=Dir.pwd, target_rbconfig=Gem.target_rbconfig)
Source

    # File lib/rubygems/ext/ext_conf_builder.rb, line 10
    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

get_relative_path (path, base)
Source

    # File lib/rubygems/ext/ext_conf_builder.rb, line 73
    def self.get_relative_path(path, base)
      path[0..base.length - 1] = "." if path.start_with?(base)
      path
    end