find_gems_with_sources

# File lib/rubygems/dependency_installer.rb, line 198
  def find_gems_with_sources dep, best_only=false # :nodoc:
    set = Gem::AvailableSet.new

    if consider_local?
      sl = Gem::Source::Local.new

      if spec = sl.find_gem(dep.name)
        if dep.matches_spec? spec
          set.add spec, sl
        end
      end
    end

    if consider_remote?
      begin
        # TODO this is pulled from #spec_for_dependency to allow
        # us to filter tuples before fetching specs.
        #
        tuples, errors = Gem::SpecFetcher.fetcher.search_for_dependency dep

        if best_only && !tuples.empty?
          tuples.sort! { |a,b| b[0].version <=> a[0].version }
          tuples = [tuples.first]
        end

        specs = []
        tuples.each do |tup, source|
          begin
            spec = source.fetch_spec(tup)
          rescue Gem::RemoteFetcher::FetchError => e
            errors << Gem::SourceFetchProblem.new(source, e)
          else
            specs << [spec, source]
          end
        end

        if @errors
          @errors += errors
        else
          @errors = errors
        end

        set << specs

      rescue Gem::RemoteFetcher::FetchError => e
        # FIX if there is a problem talking to the network, we either need to always tell
        # the user (no really_verbose) or fail hard, not silently tell them that we just
        # couldn't find their requested gem.
        if Gem.configuration.really_verbose then
          say "Error fetching remote data:\t\t#{e.message}"
          say "Falling back to local-only install"
        end
        @domain = :local
      end
    end

    set
  end