ruby-grape/grape · error · ArgumentError

both :with option and block cannot be passed

Error message

both :with option and block cannot be passed

What it means

`rescue_from` lets you specify a handler either as an inline block or via the `with:` option (a method name or Proc), but not both - Grape would not know which one wins. `extract_handler` raises 'both :with option and block cannot be passed' when a block is given and `with:` is non-nil.

Source

Thrown at lib/grape/dsl/request_response.rb:145

      #   end
      #
      # Note that Grape will automatically go up the class ancestry to
      # try to find a representing entity, so if you, for example, define
      # an entity to represent `Object` then all presented objects will
      # bubble up and utilize the entity provided on that `represent` call.
      #
      # @param model_class [Class] The model class that will be represented.
      # @option options [Class] :with The entity class that will represent the model.
      def represent(model_class, with:)
        raise Grape::Exceptions::InvalidWithOptionForRepresent.new unless with.is_a?(Class)

        inheritable_setting.add_representation(model_class, with)
      end

      private

      def extract_handler(args, with:, block:)
        raise ArgumentError, 'both :with option and block cannot be passed' if block && with

        return args.pop if args.last.is_a?(Proc)
        return block if block
        return unless with

        case with
        when Proc, Symbol then with
        when String then with.to_sym
        else raise ArgumentError, "with: #{with.class}, expected Symbol, String or Proc"
        end
      end
    end
  end
end

View on GitHub (pinned to 22d7975629)

Solutions

1. Keep the block and drop `with:`.
2. Keep `with:` and delete the block, ensuring the named method or lambda is defined on the endpoint.

Example fix

# before
rescue_from ArgumentError, with: :render_error do |e|
  error!(e.message, 400)
end # raises

# after - handler method only
rescue_from ArgumentError, with: :render_error
def render_error(e); error!(e.message, 400); end

# or block only
rescue_from ArgumentError do |e|
  error!(e.message, 400)
end

# House rule: either an inline block XOR with: - never both
raise ArgumentError, 'pass either block or with:, not both' if handler_block && with_option

When it happens

Trigger: `rescue_from ArgumentError, with: :render_error do |e| ... end`. `rescue_from :all, with: ->(e) { ... } do |e| ... end` - a do/end block after a with: lambda.

Common situations: Refactoring a handler into a named method and forgetting to delete the old block. A stray multiline do/end sneaking in after a `with:` lambda. Merging two rescue_from declarations during conflict resolution.

Related errors

• with: #{with.class}, expected Symbol, String or Proc
• rescue_from #{meta_selector.inspect} does not accept additio
• Returning or throwing a Hash from a rescue handler is deprec
• Grape: rescue_from #{klass} was already registered in this s
• Grape: rescue_from #{klass} will never run — #{covered_by} w

AI-assisted analysis of ruby-grape/grape@22d7975629 (2026-08-21). Data as JSON: /api/errors/706e7547b97deafb. Report an issue: GitHub.