Add validation for ActiveRecord.default_timezone

activerecord/lib/active_record.rb

@@ -185,12 +185,19 @@ module ActiveRecord
   singleton_class.attr_accessor :legacy_connection_handling
   self.legacy_connection_handling = true
 
-  ##
-  # :singleton-method:
   # Determines whether to use Time.utc (using :utc) or Time.local (using :local) when pulling
   # dates and times from the database. This is set to :utc by default.
-  singleton_class.attr_accessor :default_timezone
-  self.default_timezone = :utc
+  def self.default_timezone=(default_timezone)
+    unless %i[local utc].include?(default_timezone)
+      raise ArgumentError, 'default_timezone must be either :utc (default) or :local'
+    end
+
+    @default_timezone = default_timezone
+  end
+
+  def self.default_timezone
+    @default_timezone ||= :utc
+  end
 
   singleton_class.attr_accessor :writing_role
   self.writing_role = :writing

activerecord/test/cases/date_time_test.rb

@@ -7,6 +7,16 @@ require "models/task"
 class DateTimeTest < ActiveRecord::TestCase
   include InTimeZone
 
+  def test_default_timezone_validation
+    assert_raises ArgumentError do
+      ActiveRecord.default_timezone = 'UTC'
+    end
+
+    # These values should not raise errors
+    ActiveRecord.default_timezone = :local
+    ActiveRecord.default_timezone = :utc
+  end
+
   def test_saves_both_date_and_time
     with_env_tz "America/New_York" do
       with_timezone_config default: :utc do