Allow separate config files for parameters with class type when LightningCLI is in subclass_mode=False (#10286)

CHANGELOG.md

@@ -179,6 +179,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Enabled `on_load_checkpoint` for `LightningDataModule` for all `trainer_fn` ([#10238](https://github.com/PyTorchLightning/pytorch-lightning/pull/10238))
 
 
+- Allow separate config files for parameters with class type when LightningCLI is in subclass_mode=False ([#10286](https://github.com/PyTorchLightning/pytorch-lightning/pull/10286))
+
+
 ### Deprecated
 
 - Deprecated Trainer argument `terminate_on_nan` in favor of `detect_anomaly`([#9175](https://github.com/PyTorchLightning/pytorch-lightning/pull/9175))

pytorch_lightning/utilities/cli.py

@@ -155,7 +155,11 @@ class LightningArgumentParser(ArgumentParser):
             if subclass_mode:
                 return self.add_subclass_arguments(lightning_class, nested_key, fail_untyped=False, required=required)
             return self.add_class_arguments(
-                lightning_class, nested_key, fail_untyped=False, instantiate=not issubclass(lightning_class, Trainer)
+                lightning_class,
+                nested_key,
+                fail_untyped=False,
+                instantiate=not issubclass(lightning_class, Trainer),
+                sub_configs=True,
             )
         raise MisconfigurationException(
             f"Cannot add arguments from: {lightning_class}. You should provide either a callable or a subclass of: "
@@ -184,7 +188,7 @@ class LightningArgumentParser(ArgumentParser):
             self.add_subclass_arguments(optimizer_class, nested_key, **kwargs)
             self.set_choices(nested_key, optimizer_class)
         else:
-            self.add_class_arguments(optimizer_class, nested_key, **kwargs)
+            self.add_class_arguments(optimizer_class, nested_key, sub_configs=True, **kwargs)
         self._optimizers[nested_key] = (optimizer_class, link_to)
 
     def add_lr_scheduler_args(
@@ -209,7 +213,7 @@ class LightningArgumentParser(ArgumentParser):
             self.add_subclass_arguments(lr_scheduler_class, nested_key, **kwargs)
             self.set_choices(nested_key, lr_scheduler_class)
         else:
-            self.add_class_arguments(lr_scheduler_class, nested_key, **kwargs)
+            self.add_class_arguments(lr_scheduler_class, nested_key, sub_configs=True, **kwargs)
         self._lr_schedulers[nested_key] = (lr_scheduler_class, link_to)
 
     def parse_args(self, *args: Any, **kwargs: Any) -> Dict[str, Any]: