Easy way to document only declared params

I'm using Grape Entity Swagger to document all my parameters inside the Entities instead of the endpoints like this:

# my endpoint does not document any parameter...
params = params do
  requires :name, type: String
end
desc: 'Creates a product',
  success: { code: 201, model: Product },
  params: Product.params_doc(params)
post '/products' do
  # ...
end

And to achieve this I'm using a custom method params_doc that returns only the declared params' documentation.

class CustomEntity < Grape::Entity
  def self.params_doc(params)
    declared_params = params.instance_variable_get('@declared_params').flatten

    declared_params.reduce({}) do |memo, param|
      key = param.is_a?(Hash) ? param.keys.first : param
      memo[key] = documentation[key]
      memo
    end
  end
end

class Product < CustomEntity
  expose :id, documentation: { type: 'string', desc: 'The ID of the Product' }
  expose :name, documentation: { type: 'string', desc: 'foo bar' }
end

This works as expected and only documents the :name parameter for the endpoint. However this feels hacky and have caused some trouble if params block is not specified before the desc call. So I'm wondering if there's an easier way to achieve this.

Any help is appreciated.

Start by tracing how Grape Entity documentation is converted into Swagger parameters when an endpoint uses params and desc, using the Product and CustomEntity examples in the issue. Add a supported way to include only declared parameters without relying on params_doc or declaration order, then verify the generated documentation contains only :name for the example endpoint.