class Bundler::Resolver

def error_message
  output = errors.inject("") do |o, (conflict, (origin, requirement))|
    # origin is the SpecSet of specs from the Gemfile that is conflicted with
    if origin
      o << %{Bundler could not find compatible versions for gem "#{origin.name}":\n}
      o << "  In Gemfile:\n"
      o << gem_message(requirement)
      # If the origin is a LockfileParser, it does not respond_to :required_by
      unless origin.respond_to?(:required_by) && required_by = origin.required_by.first
        o << "  In snapshot (Gemfile.lock):\n"
      end
      o << gem_message(origin)
    # origin is nil if the required gem and version cannot be found in any of
    # the specified sources
    else
      # if the gem cannot be found because of a version conflict between lockfile and gemfile,
      # print a useful error that suggests running `bundle update`, which may fix things
      #
      # @base is a SpecSet of the gems in the lockfile
      # conflict is the name of the gem that could not be found
      if locked = @base[conflict].first
        o << "Bundler could not find compatible versions for gem #{conflict.inspect}:\n"
        o << "  In snapshot (Gemfile.lock):\n"
        o << "    #{clean_req(locked)}\n\n"
        o << "  In Gemfile:\n"
        o << gem_message(requirement)
        o << "Running `bundle update` will rebuild your snapshot from scratch, using only\n"
        o << "the gems in your Gemfile, which may resolve the conflict.\n"
      # the rest of the time, the gem cannot be found because it does not exist in the known sources
      else
        if requirement.required_by.first
          o << "Could not find gem '#{clean_req(requirement)}', required by '#{clean_req(requirement.required_by.first)}', in any of the sources\n"
        else
          o << "Could not find gem '#{clean_req(requirement)} in any of the sources\n"
        end
      end
    end
  end
end