Remove reactions to a user when deleting the user (#15724)

* Remove reactions to a user when deleting the user

Fixes #15245

---

I have no idea why `create(:vomit_reaction, reactable: user)` gave a
validation error about category being invalid, but `build().save`
worked fine.

* Move relation details to reaction scope `for_user`

Add a user method to access this by passing self to reaction scope

* Create a moderator when flagging user in factory

This might be a missing requirement in the reactions factory - but
this suppresses an error about invalid category I was getting when
setting a privileged reaction on the user via

    create(:vomit_reaction, reactable: user)

Everywhere else it looks like we do this with `user: moderator` (where
there's a trusted user in the surrounding context).

* Move trusted user requirement into vomit_reaction factory

* Add a data update script to remove reactions to deleted users

This cleans up the remaining invalid references and should make the
change in #15249 obsolete (i.e. we don't need to limit the view to
exclude items that no longer exist).

app/models/reaction.rb

@@ -42,6 +42,7 @@ class Reaction < ApplicationRecord
       .or(user_vomits.where(user_id: user.id))
   }
   scope :privileged_category, -> { where(category: PRIVILEGED_CATEGORIES) }
+  scope :for_user, ->(user) { where(reactable: user) }
 
   validates :category, inclusion: { in: CATEGORIES }
   validates :reactable_type, inclusion: { in: REACTABLE_TYPES }

app/models/user.rb

@@ -536,6 +536,10 @@ class User < ApplicationRecord
     notification_setting.email_follower_notifications
   end
 
+  def reactions_to
+    Reaction.for_user(self)
+  end
+
   protected
 
   # Send emails asynchronously

app/services/users/delete_activity.rb

@@ -37,6 +37,7 @@ module Users
     def delete_profile_info(user)
       user.notifications.delete_all
       user.reactions.delete_all
+      user.reactions_to.delete_all
       user.follows.delete_all
       Follow.followable_user(user.id).delete_all
       user.mentions.delete_all

lib/data_update_scripts/20211209213849_remove_dangling_user_reactions.rb

@@ -0,0 +1,11 @@
+module DataUpdateScripts
+  class RemoveDanglingUserReactions
+    def run
+      # reactions to users who have been deleted should be removed:
+      Reaction
+        .where(reactable_type: "User")
+        .where.not(reactable_id: User.all.select(:id))
+        .delete_all
+    end
+  end
+end

spec/factories/reactions.rb

@@ -22,7 +22,7 @@ FactoryBot.define do
   end
 
   factory :vomit_reaction, class: "Reaction" do
-    user
+    user { create(:user, :trusted) }
     association :reactable, factory: :article
     category { "vomit" }
 

spec/lib/data_update_scripts/remove_dangling_user_reactions_spec.rb

@@ -0,0 +1,19 @@
+require "rails_helper"
+require Rails.root.join(
+  "lib/data_update_scripts/20211209213849_remove_dangling_user_reactions.rb",
+)
+
+describe DataUpdateScripts::RemoveDanglingUserReactions do
+  let(:user_to_delete) { create(:user) }
+
+  before do
+    create(:vomit_reaction, reactable: user_to_delete)
+
+    # there's no dependent callback on reactions_to so the reaction is not removed
+    user_to_delete.destroy
+  end
+
+  it "removes reactions to deleted users" do
+    expect { described_class.new.run }.to change(Reaction, :count).by(-1)
+  end
+end

spec/services/users/delete_spec.rb

@@ -68,6 +68,14 @@ RSpec.describe Users::Delete, type: :service do
     end.to change(FieldTest::Membership, :count).by(-1)
   end
 
+  it "deletes reactions to the user" do
+    create(:vomit_reaction, reactable: user)
+
+    expect do
+      described_class.call(user)
+    end.to change(Reaction, :count).by(-1)
+  end
+
   # check that all the associated records are being destroyed,
   # except for those that are kept explicitly (kept_associations)
   describe "deleting associations" do