# File lib/bundler/resolver.rb, line 188
    def relevant_sources_for_vertex(vertex)
      if vertex.root?
        [@source_requirements[vertex.name]]
      elsif @lockfile_uses_separate_rubygems_sources
        vertex.recursive_predecessors.map do |v|
          @source_requirements[v.name]
        end << @source_requirements[:default]
      end
    end