Allow PluginRegistry to resolve fully qualified type names

draccus/choice_types.py

@@ -182,7 +182,33 @@ def __init_subclass__(cls, discover_packages_path: Optional[str] = None, **kwarg
     @classmethod
     def get_choice_class(cls, name: str) -> Any:
         cls._discover_packages()
-        return cls._choice_registry[name]
+        try:
+            return cls._choice_registry[name]
+        except KeyError:
+            if "." not in name:
+                raise
+
+        module_path, _, class_name = name.rpartition(".")
+        if not module_path:
+            # rpartition returns an empty string when no separator is found, so
+            # we shouldn't get here, but this keeps mypy happy and guards
+            # against malformed inputs.
+            raise KeyError(name)
+
+        try:
+            module = importlib.import_module(module_path)
+        except ModuleNotFoundError as e:
+            raise KeyError(name) from e
+
+        try:
+            choice_cls = getattr(module, class_name)
+        except AttributeError as e:
+            raise KeyError(name) from e
+
+        if not isinstance(choice_cls, type) or not issubclass(choice_cls, cls):
+            raise KeyError(name)
+
+        return choice_cls
 
     @classmethod
     def get_known_choices(cls) -> Dict[str, Any]:

tests/test_plugin_registry.py

@@ -0,0 +1,22 @@
+# SPDX-License-Identifier: MIT
+# Copyright 2025 The Board of Trustees of the Leland Stanford Junior University
+
+# SPDX-License-Identifier: MIT
+
+import draccus
+
+
+def test_plugin_registry_decode_fully_qualified_name():
+    from tests.draccus_choice_plugins.gpt import GptConfig
+    from tests.draccus_choice_plugins.model_config import ModelConfig
+
+    config = draccus.decode(
+        ModelConfig,
+        {
+            "type": "tests.draccus_choice_plugins.gpt.GptConfig",
+            "layers": 12,
+            "attn_pdrop": 0.2,
+        },
+    )
+
+    assert config == GptConfig(12, 0.2)