resolve_layout

# File actionview/lib/action_view/renderer/template_renderer.rb, line 92
      def resolve_layout(layout, keys, formats)
        details = @details.dup
        details[:formats] = formats

        case layout
        when String
          begin
            if layout.start_with?("/")
              raise ArgumentError, "Rendering layouts from an absolute path is not supported."
            else
              @lookup_context.find_template(layout, nil, false, keys, details)
            end
          rescue ActionView::MissingTemplate
            all_details = @details.merge(formats: @lookup_context.default_formats)
            raise unless template_exists?(layout, nil, false, keys, **all_details)
          end
        when Proc
          resolve_layout(layout.call(@lookup_context, formats, keys), keys, formats)
        else
          layout
        end
      end