fix to get_default_args(instance)

Summary:
Small config system fix. Allows get_default_args to work on an instance which has been created with a dict (instead of a DictConfig) as an args field. E.g.

```
gm = GenericModel(
        raysampler_AdaptiveRaySampler_args={"scene_extent": 4.0}
    )
    OmegaConf.structured(gm1)
```

Reviewed By: shapovalov

Differential Revision: D40341047

fbshipit-source-id: 587d0e8262e271df442a80858949a48e5d6db3df

pytorch3d/implicitron/tools/config.py

@@ -709,8 +709,8 @@ def expand_args_fields(
 
     with
 
-        x_Y_args : DictConfig = dataclasses.field(default_factory=lambda: get_default_args(Y))
-        x_Z_args : DictConfig = dataclasses.field(default_factory=lambda: get_default_args(Z))
+        x_Y_args: dict = dataclasses.field(default_factory=lambda: get_default_args(Y))
+        x_Z_args: dict = dataclasses.field(default_factory=lambda: get_default_args(Z))
         def create_x(self):
             args = self.getattr(f"x_{self.x_class_type}_args")
             self.create_x_impl(self.x_class_type, args)
@@ -733,8 +733,8 @@ def expand_args_fields(
 
     with
 
-        x_Y_args : DictConfig = dataclasses.field(default_factory=lambda: get_default_args(Y))
-        x_Z_args : DictConfig = dataclasses.field(default_factory=lambda: get_default_args(Z))
+        x_Y_args: dict = dataclasses.field(default_factory=lambda: get_default_args(Y))
+        x_Z_args: dict = dataclasses.field(default_factory=lambda: get_default_args(Z))
         def create_x(self):
             if self.x_class_type is None:
                 args = None
@@ -764,7 +764,7 @@ def expand_args_fields(
 
     will be replaced with
 
-        x_args : DictConfig = dataclasses.field(default_factory=lambda: get_default_args(X))
+        x_args: dict = dataclasses.field(default_factory=lambda: get_default_args(X))
         def create_x(self):
             self.create_x_impl(True, self.x_args)
 
@@ -786,7 +786,7 @@ def expand_args_fields(
 
     with
 
-        x_args : DictConfig = dataclasses.field(default_factory=lambda: get_default_args(X))
+        x_args: dict = dataclasses.field(default_factory=lambda: get_default_args(X))
         x_enabled: bool = False
         def create_x(self):
             self.create_x_impl(self.x_enabled, self.x_args)
@@ -818,6 +818,11 @@ def expand_args_fields(
     then the default_factory of x_args will also have a call to x_tweak_args(X, x_args) and
     the default_factory of x_Y_args will also have a call to x_tweak_args(Y, x_Y_args).
 
+    Note that although the *_args members are intended to have type DictConfig, they
+    are actually internally annotated as dicts. OmegaConf is happy to see a DictConfig
+    in place of a dict, but not vice-versa. Allowing dict lets a class user specify
+    x_args as an explicit dict without getting an incomprehensible error.
+
     Args:
         some_class: the class to be processed
         _do_not_process: Internal use for get_default_args: Because get_default_args calls
@@ -1040,7 +1045,7 @@ def _process_member(
                 raise ValueError(
                     f"Cannot generate {args_name} because it is already present."
                 )
-            some_class.__annotations__[args_name] = DictConfig
+            some_class.__annotations__[args_name] = dict
             if hook is not None:
                 hook_closed = partial(hook, derived_type)
             else:
@@ -1064,7 +1069,7 @@ def _process_member(
         if issubclass(type_, some_class) or type_ in _do_not_process:
             raise ValueError(f"Cannot process {type_} inside {some_class}")
 
-        some_class.__annotations__[args_name] = DictConfig
+        some_class.__annotations__[args_name] = dict
         if hook is not None:
             hook_closed = partial(hook, type_)
         else:

tests/implicitron/test_config.py

@@ -687,6 +687,34 @@ class TestConfig(unittest.TestCase):
         remove_unused_components(args)
         self.assertEqual(OmegaConf.to_yaml(args), "mt_enabled: false\n")
 
+    def test_get_instance_args(self):
+        mt1, mt2 = [
+            MainTest(
+                n_ids=0,
+                n_reps=909,
+                the_fruit_class_type="Pear",
+                the_second_fruit_class_type="Pear",
+                the_fruit_Pear_args=DictConfig({}),
+                the_second_fruit_Pear_args={},
+            )
+            for _ in range(2)
+        ]
+        # Two equivalent ways to get the DictConfig back out of an instance.
+        cfg1 = OmegaConf.structured(mt1)
+        cfg2 = get_default_args(mt2)
+        self.assertEqual(cfg1, cfg2)
+        self.assertEqual(len(cfg1.the_second_fruit_Pear_args), 0)
+        self.assertEqual(len(mt2.the_second_fruit_Pear_args), 0)
+
+        from_cfg = MainTest(**cfg2)
+        self.assertEqual(len(from_cfg.the_second_fruit_Pear_args), 0)
+
+        # If you want the complete args, merge with the defaults.
+        merged_args = OmegaConf.merge(get_default_args(MainTest), cfg2)
+        from_merged = MainTest(**merged_args)
+        self.assertEqual(len(from_merged.the_second_fruit_Pear_args), 1)
+        self.assertEqual(from_merged.n_reps, 909)
+
     def test_tweak_hook(self):
         class A(Configurable):
             n: int = 9