cross_check_for_errors

# File lib/bundler/injector.rb, line 224
    def cross_check_for_errors(gemfile_path, original_deps, removed_deps, initial_gemfile)
      # evalute the new gemfile to look for any failure cases
      builder = Dsl.new
      builder.eval_gemfile(gemfile_path)

      # record gems which were removed but not requested
      extra_removed_gems = original_deps - builder.dependencies

      # if some extra gems were removed then raise error
      # and revert Gemfile to original
      unless extra_removed_gems.empty?
        SharedHelpers.write_to_gemfile(gemfile_path, initial_gemfile.join)

        raise InvalidOption, "Gems could not be removed. #{extra_removed_gems.join(", ")} would also have been removed. Bundler cannot continue."
      end

      # record gems which could not be removed due to some reasons
      errored_deps = builder.dependencies.select {|d| d.gemfile == gemfile_path } & removed_deps.select {|d| d.gemfile == gemfile_path }

      show_warning "#{errored_deps.map(&:name).join(", ")} could not be removed." unless errored_deps.empty?

      # return actual removed dependencies
      removed_deps - errored_deps
    end