show?

# File actionpack/lib/action_dispatch/middleware/exception_wrapper.rb, line 177
    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")

      # Include true and false for backwards compatibility.
      case config
      when :none
        false
      when :rescuable
        rescue_response?
      when true
        ActionDispatch.deprecator.warn("Setting action_dispatch.show_exceptions to true is deprecated. Set to :all instead.")
        true
      when false
        ActionDispatch.deprecator.warn("Setting action_dispatch.show_exceptions to false is deprecated. Set to :none instead.")
        false
      else
        true
      end
    end