Fix account migration not affecting followers on origin server (mastodon#11980)

Author: Gargron

app/controllers/settings/migrations_controller.rb

@@ -18,9 +18,7 @@ def create
     @migration = current_account.migrations.build(resource_params)
 
     if @migration.save_with_challenge(current_user)
-      current_account.update!(moved_to_account: @migration.target_account)
-      ActivityPub::UpdateDistributionWorker.perform_async(current_account.id)
-      ActivityPub::MoveDistributionWorker.perform_async(@migration.id)
+      MoveService.new.call(@migration)
       redirect_to settings_migration_path, notice: I18n.t('migrations.moved_msg', acct: current_account.moved_to_account.acct)
     else
       render :show

app/lib/activitypub/activity/move.rb

@@ -19,11 +19,7 @@ def perform
     origin_account.update(moved_to_account: target_account)
 
     # Initiate a re-follow for each follower
-    origin_account.followers.local.select(:id).find_in_batches do |follower_accounts|
-      UnfollowFollowWorker.push_bulk(follower_accounts.map(&:id)) do |follower_account_id|
-        [follower_account_id, origin_account.id, target_account.id]
-      end
-    end
+    MoveWorker.perform_async(origin_account.id, target_account.id)
   end
 
   private

app/services/move_service.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+class MoveService < BaseService
+  def call(migration)
+    @migration      = migration
+    @source_account = migration.account
+    @target_account = migration.target_account
+
+    update_redirect!
+    process_local_relationships!
+    distribute_update!
+    distribute_move!
+  end
+
+  private
+
+  def update_redirect!
+    @source_account.update!(moved_to_account: @target_account)
+  end
+
+  def process_local_relationships!
+    MoveWorker.perform_async(@source_account.id, @target_account.id)
+  end
+
+  def distribute_update!
+    ActivityPub::UpdateDistributionWorker.perform_async(@source_account.id)
+  end
+
+  def distribute_move!
+    ActivityPub::MoveDistributionWorker.perform_async(@migration.id)
+  end
+end

app/workers/move_worker.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+class MoveWorker
+  include Sidekiq::Worker
+
+  def perform(source_account_id, target_account_id)
+    @source_account = Account.find(source_account_id)
+    @target_account = Account.find(target_account_id)
+
+    if @target_account.local?
+      rewrite_follows!
+    else
+      queue_follow_unfollows!
+    end
+  rescue ActiveRecord::RecordNotFound
+    true
+  end
+
+  private
+
+  def rewrite_follows!
+    @source_account.passive_relationships
+                   .where(account: Account.local)
+                   .in_batches
+                   .update_all(target_account: @target_account)
+  end
+
+  def queue_follow_unfollows!
+    @source_account.followers.local.select(:id).find_in_batches do |accounts|
+      UnfollowFollowWorker.push_bulk(accounts.map(&:id)) { |follower_id| [follower_id, @source_account.id, @target_account.id] }
+    end
+  end
+end