Creating resource failes when association is polymorphic and singleton.

[ccfz]

Steps to reproduce

Given I have the following association:

class Comment < ApplicationRecord
  belongs_to :commentable, polymorphic: true, optional: true, inverse_of: :comments
end

class Post < ApplicationRecord
  has_one :comment, as: :commentable, inverse_of: :commentable
end

class Photo < ApplicationRecord
  has_many :comments, as: :commentable, inverse_of: :commentable
end

and the following controller:

  class CommentsController < ApplicationController

    load_and_authorize_resource :post
    load_and_authorize_resource through: :post, singleton: true

I ran into a problem when building the resource and assigning the attributes here.

def assign_attributes(resource)
  resource.send("#{parent_name}=", parent_resource) if @options[:singleton] && parent_resource
  initial_attributes.each do |attr_name, value|
    resource.send("#{attr_name}=", value)
  end
  resource
end

The line: resource.send("#{parent_name}=", parent_resource) if @options[:singleton] && parent_resource fails because the parent_resource in a polymorphic association is not post but commentable=. Therefore, we get the error:

 NoMethodError:
       undefined method `post=' for #<Comment

Expected behavior

I can instantiate a polymorphic association correctly.

Actual behavior

I get an undefined method error.

System configuration

Rails version:
7.0.7
Ruby version:
3.2.2.
CanCanCan version
3.5