MakeMakefile#pkg_config

# File tmp/rubies/ruby-3.0.5/lib/mkmf.rb, line 1821
def pkg_config(pkg, option=nil)
  if pkgconfig = with_config("#{pkg}-config") and find_executable0(pkgconfig)
    # iff package specific config command is given
  elsif ($PKGCONFIG ||=
         (pkgconfig = with_config("pkg-config", ("pkg-config" unless CROSS_COMPILING))) &&
         find_executable0(pkgconfig) && pkgconfig) and
      xsystem("#{$PKGCONFIG} --exists #{pkg}")
    # default to pkg-config command
    pkgconfig = $PKGCONFIG
    get = proc {|opt|
      opt = xpopen("#{$PKGCONFIG} --#{opt} #{pkg}", err:[:child, :out], &:read)
      Logging.open {puts opt.each_line.map{|s|"=> #{s.inspect}"}}
      opt.strip if $?.success?
    }
  elsif find_executable0(pkgconfig = "#{pkg}-config")
    # default to package specific config command, as a last resort.
  else
    pkgconfig = nil
  end
  if pkgconfig
    get ||= proc {|opt|
      opt = xpopen("#{pkgconfig} --#{opt}", err:[:child, :out], &:read)
      Logging.open {puts opt.each_line.map{|s|"=> #{s.inspect}"}}
      opt.strip if $?.success?
    }
  end
  orig_ldflags = $LDFLAGS
  if get and option
    get[option]
  elsif get and try_ldflags(ldflags = get['libs'])
    if incflags = get['cflags-only-I']
      $INCFLAGS << " " << incflags
      cflags = get['cflags-only-other']
    else
      cflags = get['cflags']
    end
    libs = get['libs-only-l']
    if cflags
      $CFLAGS += " " << cflags
      $CXXFLAGS += " " << cflags
    end
    if libs
      ldflags = (Shellwords.shellwords(ldflags) - Shellwords.shellwords(libs)).quote.join(" ")
    else
      libs, ldflags = Shellwords.shellwords(ldflags).partition {|s| s =~ /-l([^ ]+)/ }.map {|l|l.quote.join(" ")}
    end
    $libs += " " << libs

    $LDFLAGS = [orig_ldflags, ldflags].join(' ')
    Logging::message "package configuration for %s\n", pkg
    Logging::message "incflags: %s\ncflags: %s\nldflags: %s\nlibs: %s\n\n",
                     incflags, cflags, ldflags, libs
    [[incflags, cflags].join(' '), ldflags, libs]
  else
    Logging::message "package configuration for %s is not found\n", pkg
    nil
  end
end