Raise an explicit error if `decay` is set and new Keras optimizer is used.

PiperOrigin-RevId: 481980126

official/modeling/optimization/optimizer_factory.py

@@ -236,6 +236,11 @@ class OptimizerFactory:
     if use_legacy_optimizer:
       optimizer = LEGACY_OPTIMIZERS_CLS[self._optimizer_type](**optimizer_dict)
     else:
+      if 'decay' in optimizer_dict:
+        raise ValueError(
+            '`decay` is deprecated in new Keras optimizer, please reflect the '
+            'decay logic in `lr` or set `use_legacy_optimizer=True` to use the '
+            'legacy optimizer.')
       optimizer = NEW_OPTIMIZERS_CLS[self._optimizer_type](**optimizer_dict)
 
     if self._use_ema:

official/modeling/optimization/optimizer_factory_test.py

@@ -68,6 +68,9 @@ class OptimizerFactoryTest(tf.test.TestCase, parameterized.TestCase):
     expected_optimizer_config['learning_rate'] = 0.1
 
     opt_config = optimization_config.OptimizationConfig(params)
+    if optimizer_type == 'sgd':
+      # Delete unsupported arg `decay` from SGDConfig.
+      delattr(opt_config.optimizer.sgd, 'decay')
     opt_factory = optimizer_factory.OptimizerFactory(opt_config)
     lr = opt_factory.build_learning_rate()
     optimizer = opt_factory.build_optimizer(