Adding tags using #tag_ids= breaks when migrating from v5 to v6

[tatethurston]

When updating from v5 to v6, I noticed that setting tags using #tag_ids= has stopped working. The commit that broke this functionality is #887.

Repro:

class User < ActiveRecord::Base
  acts_as_taggable_on :tags
end

require "rails_helper"

RSpec.describe "these tests pass on v5 but fail after 887" do
  let!(:existing_tags) { FactoryBot.create_list(:tag, 3) }
  
  describe "create" do
    let(:create) do
      FactoryBot.create(:user, tag_ids: existing_tags.map(&:id))
    end

    it do
      expect { create }.to change { ActsAsTaggableOn::Tagging.count }.by(3)
    end

    it do
      user = create
      expect(user.reload.tag_list).to match_array(existing_tags.map(&:name))
    end
  end
  
  describe "update" do
    let!(:user) { FactoryBot.create(:user) }
    let(:update) do
      user.update(tag_ids: existing_tags.map(&:id))
    end
    
    it do
      expect { update }.to change { ActsAsTaggableOn::Tagging.count }.by(3)
    end

    it do
      update
      expect(user.reload.tag_list).to match_array(existing_tags.map(&:name))
    end
  end
end

[tatethurston]

duplicate of #914