instance method show?

# File actionpack/lib/action_dispatch/middleware/exception_wrapper.rb, line 185
    def show?(request)
      # We're treating `nil` as "unset", and we want the default setting to be `:all`.
      # This logic should be extracted to `env_config` and calculated once.
      config = request.get_header("action_dispatch.show_exceptions")

      case config
      when :none
        false
      when :rescuable
        rescue_response?
      else
        true
      end
    end