accessed_attributes.rb

module AccessedAttributes
  def self.included(klass)
    association_proxy = Module.new do
      def accessed_associations
        @_accessed_associations ||= []
      end
    end

    klass.reflect_on_all_associations.each do |association|
      name = association.name

      association_proxy.define_method(name) do |*args, &block|
        accessed_associations << name
        super(*args, &block)
      end
    end

    klass.prepend(association_proxy)
  end
end

class MyModel < ApplicationRecord
  include AccessedAttributes
end

module AccessedAttributes
  def self.included(klass)
    association_proxy = Module.new do
      def accessed_associations
        @_accessed_associations ||= Set.new
      end

      def association(name)
        accessed_associations << name
        super(name)
      end
    end

    klass.prepend(association_proxy)
  end
end

Josh wins: https://twitter.com/josh_cheek/status/1588046756171890690