check_primary_source_safety

# File lib/bundler/dsl.rb, line 470
    def check_primary_source_safety(source_list)
      return if source_list.rubygems_primary_remotes.empty? && source_list.global_rubygems_source.nil?

      if Bundler.feature_flag.disable_multisource?
        msg = "This Gemfile contains multiple primary sources. "            "Each source after the first must include a block to indicate which gems "            "should come from that source"
        unless Bundler.feature_flag.bundler_2_mode?
          msg += ". To downgrade this error to a warning, run "              "`bundle config --delete disable_multisource`"
        end
        raise GemfileEvalError, msg
      else
        Bundler::SharedHelpers.major_deprecation 2, "Your Gemfile contains multiple primary sources. "            "Using `source` more than once without a block is a security risk, and "            "may result in installing unexpected gems. To resolve this warning, use "            "a block to indicate which gems should come from the secondary source. "            "To upgrade this warning to an error, run `bundle config "            "disable_multisource true`."
      end
    end