Reject existing Follows when suspending a remote account (#10230)

* Reject existing Follows when suspending a remote account

Partial fix to #10229

* Add tests

app/services/suspend_account_service.rb

@@ -41,6 +41,7 @@ class SuspendAccountService < BaseService
     @account = account
     @options = options
 
+    reject_follows!
     purge_user!
     purge_profile!
     purge_content!
@@ -48,6 +49,14 @@ class SuspendAccountService < BaseService
 
   private
 
+  def reject_follows!
+    return if @account.local? || !@account.activitypub?
+
+    ActivityPub::DeliveryWorker.push_bulk(Follow.where(account: @account)) do |follow|
+      [build_reject_json(follow), follow.target_account_id, follow.account.inbox_url]
+    end
+  end
+
   def purge_user!
     return if !@account.local? || @account.user.nil?
 
@@ -120,6 +129,14 @@ class SuspendAccountService < BaseService
     @delete_actor_json = Oj.dump(ActivityPub::LinkedDataSignature.new(payload).sign!(@account))
   end
 
+  def build_reject_json(follow)
+    ActiveModelSerializers::SerializableResource.new(
+      follow,
+      serializer: ActivityPub::RejectFollowSerializer,
+      adapter: ActivityPub::Adapter
+    ).to_json
+  end
+
   def delivery_inboxes
     @delivery_inboxes ||= @account.followers.inboxes + Relay.enabled.pluck(:inbox_url)
   end