index_for

# File lib/bundler/resolver.rb, line 149
    def index_for(dependency)
      source = @source_requirements[dependency.name]
      if source
        source.specs
      elsif @lockfile_uses_separate_rubygems_sources
        Index.build do |idx|
          if dependency.all_sources
            dependency.all_sources.each {|s| idx.add_source(s.specs) if s }
          else
            idx.add_source @source_requirements[:default].specs
          end
        end
      else
        @index
      end
    end