Policy lookup does not work with SimpleDelegator

[pcriv]

Tell us about your environment

Ruby Version:

2.6.3

Framework Version (Rails, whatever):

None.

Action Policy Version:

0.3.1

What did you do?

Used SimpleDelegator to decorate an object and send it to the policy.

What did you expect to happen?

Expect the correct policy to be resolved.

What actually happened?

~/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/action_policy-0.3.1/lib/action_policy.rb:32:in `lookup': Couldn't find policy class for #<Post:0x00007fe5234431c0> (ActionPolicy::NotFound)

How to reproduce?

#!/usr/bin/env ruby

require "bundler/inline"

gemfile true do
  source "https://rubygems.org"

  gem "action_policy"
end

require "action_policy"

class User
end

class Post
end

class PostPolicy < ActionPolicy::Base
  def update?
    true
  end
end

class PostDecorator < SimpleDelegator
end

class PostUpdateAction
  include ActionPolicy::Behaviour

  # provide authorization subject (performer)
  authorize :user

  attr_reader :user

  def initialize(user)
    @user = user
  end

  def call(post)
    authorize! post, to: :update?
  end
end

user = User.new
post = Post.new

puts PostUpdateAction.new(user).call(post)

post_decorator = PostDecorator.new(post)

puts PostUpdateAction.new(user).call(post_decorator)

[palkan]

Hey @pablocrivella,

This is not the expected behaviour: policy lookup relies on the object class (it's name or .policy_name / .policy_class methods, see docs).

In your case, the class of the object is PostDecorator (not Post) and we can only infer from it the PostDecoratorPolicy, which doesn't exist—and we fail.

We (from the library perspective) cannot know beforehand, whether you wan to use PostDecoratorPolicy or PostPolicy, that should be decide by the developer.

One workaround is to pass the underlying object to the lookup chain instead of a decorator. See, for example, the Draper use-case: https://actionpolicy.evilmartians.io/#/./decorators.

Another workaround is to specify the policy name explicitly:

class PostDecorator < SimpleDelegator
  def self.policy_name
    "PostPolicy"
  end
end

[pcriv]

Understood! Thanks for your explanation @palkan :)