Merge pull request #46140 from ahoglund/ahoglund/nil-precision-option

Check for Existing but nil `:precision` Option

activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb

@@ -514,6 +514,10 @@ module ActiveRecord
       def timestamps(**options)
         options[:null] = false if options[:null].nil?
 
+        if !options.key?(:precision) && @conn.supports_datetime_with_precision?
+          options[:precision] = 6
+        end
+
         column(:created_at, :datetime, **options)
         column(:updated_at, :datetime, **options)
       end

activerecord/test/cases/migration/compatibility_test.rb

@@ -274,6 +274,23 @@ module ActiveRecord
         end
       end
 
+      def test_timestamps_sets_default_precision_on_create_table
+        migration = Class.new(ActiveRecord::Migration[6.1]) {
+          def migrate(x)
+            create_table :more_testings do |t|
+              t.timestamps
+            end
+          end
+        }.new
+
+        ActiveRecord::Migrator.new(:up, [migration], @schema_migration, @internal_metadata).migrate
+
+        assert connection.column_exists?(:more_testings, :created_at, **{ precision: 6 })
+        assert connection.column_exists?(:more_testings, :updated_at, **{ precision: 6 })
+      ensure
+        connection.drop_table :more_testings rescue nil
+      end
+
       def test_datetime_doesnt_set_precision_on_create_table
         migration = Class.new(ActiveRecord::Migration[6.1]) {
           def migrate(x)