def validate packaging = true
    require 'rubygems/user_interaction'
    extend Gem::UserInteraction
    normalize

    nil_attributes = self.class.non_nil_attributes.find_all do |name|
      instance_variable_get("@#{name}").nil?
    end

    unless nil_attributes.empty? then
      raise Gem::InvalidSpecificationException,
        "#{nil_attributes.join ', '} must not be nil"
    end

    if packaging and rubygems_version != Gem::VERSION then
      raise Gem::InvalidSpecificationException,
            "expected RubyGems version #{Gem::VERSION}, was #{rubygems_version}"
    end

    @@required_attributes.each do |symbol|
      unless self.send symbol then
        raise Gem::InvalidSpecificationException,
              "missing value for attribute #{symbol}"
      end
    end

    unless String === name then
      raise Gem::InvalidSpecificationException,
            "invalid value for attribute name: \"#{name.inspect}\""
    end

    if require_paths.empty? then
      raise Gem::InvalidSpecificationException,
            'specification must have at least one require_path'
    end

    @files.delete_if            { |x| File.directory?(x) }
    @test_files.delete_if       { |x| File.directory?(x) }
    @executables.delete_if      { |x| File.directory?(File.join(@bindir, x)) }
    @extra_rdoc_files.delete_if { |x| File.directory?(x) }
    @extensions.delete_if       { |x| File.directory?(x) }

    non_files = files.reject { |x| File.file?(x) }

    unless not packaging or non_files.empty? then
      raise Gem::InvalidSpecificationException,
            "[\"#{non_files.join "\", \""}\"] are not files"
    end

    unless specification_version.is_a?(Fixnum)
      raise Gem::InvalidSpecificationException,
            'specification_version must be a Fixnum (did you mean version?)'
    end

    case platform
    when Gem::Platform, Gem::Platform::RUBY then # ok
    else
      raise Gem::InvalidSpecificationException,
            "invalid platform #{platform.inspect}, see Gem::Platform"
    end

    self.class.array_attributes.each do |field|
      val = self.send field
      klass = case field
              when :dependencies
                Gem::Dependency
              else
                String
              end

      unless Array === val and val.all? { |x| x.kind_of?(klass) } then
        raise(Gem::InvalidSpecificationException,
              "#{field} must be an Array of #{klass}")
      end
    end

    [:authors].each do |field|
      val = self.send field
      raise Gem::InvalidSpecificationException, "#{field} may not be empty" if
        val.empty?
    end

    licenses.each { |license|
      if license.length > 64
        raise Gem::InvalidSpecificationException,
          "each license must be 64 characters or less"
      end
    }

    # reject lazy developers:

    lazy = '"FIxxxXME" or "TOxxxDO"'.gsub(/xxx/, '')

    unless authors.grep(/FI XME|TO DO/x).empty? then
      raise Gem::InvalidSpecificationException, "#{lazy} is not an author"
    end

    unless Array(email).grep(/FI XME|TO DO/x).empty? then
      raise Gem::InvalidSpecificationException, "#{lazy} is not an email"
    end

    if description =~ /FI XME|TO DO/x then
      raise Gem::InvalidSpecificationException, "#{lazy} is not a description"
    end

    if summary =~ /FI XME|TO DO/x then
      raise Gem::InvalidSpecificationException, "#{lazy} is not a summary"
    end

    if homepage and not homepage.empty? and
       homepage !~ /\A[a-z][a-z\d+.-]*:/i then
      raise Gem::InvalidSpecificationException,
            "\"#{homepage}\" is not a URI"
    end

    # Warnings

    %w[author description email homepage summary].each do |attribute|
      value = self.send attribute
      alert_warning "no #{attribute} specified" if value.nil? or value.empty?
    end

    if description == summary then
      alert_warning 'description and summary are identical'
    end

    # TODO: raise at some given date
    alert_warning "deprecated autorequire specified" if autorequire

    executables.each do |executable|
      executable_path = File.join(bindir, executable)
      shebang = File.read(executable_path, 2) == '#!'

      alert_warning "#{executable_path} is missing #! line" unless shebang
    end

    true
  end
#
Checks that the specification contains all required fields, and does a
very basic sanity check.

Raises InvalidSpecificationException if the spec does not pass the
checks..