Gem::RequestSet#install_into

# File tmp/rubies/ruby-3.0.5/lib/rubygems/request_set.rb, line 256
def install_into(dir, force = true, options = {})
  gem_home, ENV['GEM_HOME'] = ENV['GEM_HOME'], dir

  existing = force ? [] : specs_in(dir)
  existing.delete_if {|s| @always_install.include? s }

  dir = File.expand_path dir

  installed = []

  options[:development] = false
  options[:install_dir] = dir
  options[:only_install_dir] = true
  @prerelease = options[:prerelease]

  sorted_requests.each do |request|
    spec = request.spec

    if existing.find {|s| s.full_name == spec.full_name }
      yield request, nil if block_given?
      next
    end

    spec.install options do |installer|
      yield request, installer if block_given?
    end

    installed << request
  end

  install_hooks installed, options

  installed
ensure
  ENV['GEM_HOME'] = gem_home
end