resolve_for

# File lib/rubygems/resolver.rb, line 294
  def resolve_for needed, specs # :nodoc:
    # The State objects that are used to attempt the activation tree.
    states = []

    while !needed.empty?
      @stats.iteration!

      dep = needed.remove
      explain :try, [dep, dep.requester ? dep.requester.request : :toplevel]
      explain_list(:next5) { needed.next5 }
      explain_list(:specs) { Array(specs).map { |x| x.full_name }.sort }

      # If there is already a spec activated for the requested name...
      if specs && existing = specs.find { |s| dep.name == s.name }
        # then we're done since this new dep matches the existing spec.
        next if dep.matches_spec? existing

        conflict = handle_conflict dep, existing

        return conflict unless dep.requester

        explain :conflict, dep, :existing, existing.full_name

        depreq = dep.requester.request

        state = nil
        until states.empty?
          x = states.pop

          i = existing.request.requester
          explain :consider, x.spec.full_name, [depreq.name, dep.name, i ? i.name : :top]

          if x.spec.name == depreq.name or
              x.spec.name == dep.name or
              (i && (i.name == x.spec.name))
            explain :found, x.spec.full_name
            state = x
            break
          end
        end

        return conflict unless state

        @stats.backtracking!

        needed, specs = resolve_for_conflict needed, specs, state

        states << state unless state.possibles.empty?

        next
      end

      matching, all = find_possible dep

      case matching.size
      when 0
        resolve_for_zero dep, all
      when 1
        needed, specs =
          resolve_for_single needed, specs, dep, matching
      else
        needed, specs =
          resolve_for_multiple needed, specs, states, dep, matching
      end
    end

    specs
  end