Gem::DependencyInstaller#install

# File tmp/rubies/ruby-3.1.3/lib/rubygems/dependency_installer.rb, line 227
def install(dep_or_name, version = Gem::Requirement.default)
  request_set = resolve_dependencies dep_or_name, version

  @installed_gems = []

  options = {
    :bin_dir             => @bin_dir,
    :build_args          => @build_args,
    :document            => @document,
    :env_shebang         => @env_shebang,
    :force               => @force,
    :format_executable   => @format_executable,
    :ignore_dependencies => @ignore_dependencies,
    :prerelease          => @prerelease,
    :security_policy     => @security_policy,
    :user_install        => @user_install,
    :wrappers            => @wrappers,
    :build_root          => @build_root,
    :install_as_default  => @install_as_default,
    :dir_mode            => @dir_mode,
    :data_mode           => @data_mode,
    :prog_mode           => @prog_mode,
  }
  options[:install_dir] = @install_dir if @only_install_dir

  request_set.install options do |_, installer|
    @installed_gems << installer.spec if installer
  end

  @installed_gems.sort!

  # Since this is currently only called for docs, we can be lazy and just say
  # it's documentation. Ideally the hook adder could decide whether to be in
  # the background or not, and what to call it.
  in_background "Installing documentation" do
    Gem.done_installing_hooks.each do |hook|
      hook.call self, @installed_gems
    end
  end unless Gem.done_installing_hooks.empty?

  @installed_gems
end