Fix server theme migration (#37810)

db/migrate/20260209142402_migrate_default_theme_setting.rb

@@ -7,15 +7,12 @@ class MigrateDefaultThemeSetting < ActiveRecord::Migration[8.0]
     Setting.reset_column_information
 
     setting = Setting.find_by(var: 'theme')
-    return unless setting.present? && setting.attributes['value'].present? && %w(mastodon-light contrast system).include?(setting.attributes['value'])
+    return unless setting.present? && setting.attributes['value'].present?
 
-    Setting.upsert(
-      {
-        var: 'theme',
-        value: "--- default\n",
-      },
-      unique_by: index_exists?(:settings, [:thing_type, :thing_id, :var]) ? [:thing_type, :thing_id, :var] : :var
-    )
+    theme = YAML.safe_load(setting.attributes['value'], permitted_classes: [ActiveSupport::HashWithIndifferentAccess, Symbol])
+    return unless %w(mastodon-light contrast system).include?(theme)
+
+    setting.update_column('value', "--- default\n")
   end
 
   def down; end

lib/tasks/tests.rake

@@ -154,6 +154,11 @@ namespace :tests do
         exit(1)
       end
 
+      unless Setting.theme == 'default'
+        puts 'Default theme setting not migrated as expected'
+        exit(1)
+      end
+
       puts 'No errors found. Database state is consistent with a successful migration process.'
     end
 
@@ -177,7 +182,8 @@ namespace :tests do
           (id, thing_type, thing_id, var, value, created_at, updated_at)
         VALUES
           (7, NULL, NULL, 'timeline_preview', E'--- false\n', now(), now()),
-          (8, NULL, NULL, 'trends_as_landing_page', E'--- false\n', now(), now());
+          (8, NULL, NULL, 'trends_as_landing_page', E'--- false\n', now(), now()),
+          (9, NULL, NULL, 'theme', E'--- system', now(), now());
 
         /* Doorkeeper records
            While the `read:me` scope was technically not valid in 3.3.0,