Fix notification policy migration not preserving filter_private_mentions correctly (#29699)

db/post_migrate/20240321160706_migrate_interaction_settings_to_policy_again.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+class MigrateInteractionSettingsToPolicyAgain < ActiveRecord::Migration[7.1]
+  disable_ddl_transaction!
+
+  # Dummy classes, to make migration possible across version changes
+  class Account < ApplicationRecord
+    has_one :user, inverse_of: :account
+    has_one :notification_policy, inverse_of: :account
+  end
+
+  class User < ApplicationRecord
+    belongs_to :account
+  end
+
+  class NotificationPolicy < ApplicationRecord
+    belongs_to :account
+  end
+
+  def up
+    User.includes(account: :notification_policy).find_each do |user|
+      deserialized_settings = Oj.load(user.attributes_before_type_cast['settings'])
+
+      next if deserialized_settings.nil?
+
+      # If the user has configured a notification policy, don't override it
+      next if user.account.notification_policy.present?
+
+      policy = user.account.build_notification_policy
+      requires_new_policy = false
+
+      if deserialized_settings['interactions.must_be_follower']
+        policy.filter_not_followers = true
+        requires_new_policy = true
+      end
+
+      if deserialized_settings['interactions.must_be_following']
+        policy.filter_not_following = true
+        requires_new_policy = true
+      end
+
+      unless deserialized_settings['interactions.must_be_following_dm']
+        policy.filter_private_mentions = false
+        requires_new_policy = true
+      end
+
+      policy.save if requires_new_policy && policy.changed?
+    rescue ActiveRecord::RecordNotUnique
+      next
+    end
+  end
+
+  def down; end
+end