Preserve optional defaults in ADK tool signatures

packages/nvidia_nat_adk/src/nat/plugins/adk/tool_wrapper.py

@@ -68,6 +68,21 @@ def google_adk_tool_wrapper(
     """
     import inspect
 
+    def _field_default(field: Any) -> Any:
+        """Return a Pydantic field's default for an inspect signature."""
+        is_required = getattr(field, "is_required", None)
+        if is_required is not None and is_required():
+            return inspect.Parameter.empty
+        if getattr(field, "required", False):
+            return inspect.Parameter.empty
+        default_factory = getattr(field, "default_factory", None)
+        if default_factory is not None:
+            try:
+                return default_factory()
+            except TypeError:
+                return None
+        return getattr(field, "default", inspect.Parameter.empty)
+
     async def callable_ainvoke(*args: Any, **kwargs: Any) -> Any:
         """Async function to invoke the NAT function.
 
@@ -137,16 +152,19 @@ def decorator(func_to_wrap: Callable[..., Any]) -> Callable[..., Any]:
             if input_schema is not None:
                 model_fields = getattr(input_schema, "model_fields", None)
                 if model_fields is not None:
-                    field_items = ((n, f.annotation) for n, f in model_fields.items())
+                    field_items = ((n, f.annotation, _field_default(f)) for n, f in model_fields.items())
                 else:
-                    field_items = getattr(input_schema, "__annotations__", {}).items()
-                for param_name, param_annotation in field_items:
+                    field_items = ((n, a, inspect.Parameter.empty)
+                                   for n, a in getattr(input_schema, "__annotations__", {}).items())
+                for param_name, param_annotation, default in field_items:
                     params.append(
                         inspect.Parameter(
                             param_name,
                             inspect.Parameter.POSITIONAL_OR_KEYWORD,
                             annotation=resolve_type(param_annotation),
+                            default=default,
                         ))
+            params.sort(key=lambda param: param.default is not inspect.Parameter.empty)
             setattr(func_to_wrap, "__signature__", inspect.Signature(parameters=params))
 
             return func_to_wrap

packages/nvidia_nat_adk/tests/test_adk_tool_wrapper.py

@@ -19,6 +19,7 @@
 
 import pytest
 from pydantic import BaseModel
+from pydantic import Field
 
 from nat.plugins.adk.tool_wrapper import google_adk_tool_wrapper
 from nat.plugins.adk.tool_wrapper import resolve_type
@@ -32,6 +33,11 @@ class DummyInput(BaseModel):
     value: int
 
 
+class OptionalInput(BaseModel):
+    optional_value: int = 42
+    required_value: str
+
+
 class DummyOutput(BaseModel):
     result: int
 
@@ -194,6 +200,58 @@ async def test_google_adk_tool_wrapper_nested_function(mock_function_tool):
     assert call_args.__doc__ == "Nested ADK function"
 
 
+@patch('google.adk.tools.function_tool.FunctionTool')
+def test_google_adk_tool_wrapper_preserves_field_defaults(mock_function_tool):
+    """Optional input fields must remain optional in the ADK signature."""
+    import inspect
+
+    class OptionalFunction:
+        description = "Optional ADK function"
+        has_single_output = True
+        has_streaming_output = False
+        input_schema = OptionalInput
+
+        async def acall_invoke(self, *_args, **_kwargs):
+            return None
+
+    google_adk_tool_wrapper("optional_adk_func", OptionalFunction(), MagicMock())
+
+    callable_tool = mock_function_tool.call_args[0][0]
+    signature = inspect.signature(callable_tool)
+
+    assert list(signature.parameters) == ["required_value", "optional_value"]
+    assert signature.parameters["required_value"].default is inspect.Parameter.empty
+    assert signature.parameters["optional_value"].default == 42
+
+
+@patch('google.adk.tools.function_tool.FunctionTool')
+def test_google_adk_tool_wrapper_handles_data_aware_default_factory(mock_function_tool):
+    """A default factory requiring validated data must not break signature creation."""
+    import inspect
+
+    class FactoryInput(BaseModel):
+        required_value: str
+        generated: list[str] = Field(default_factory=list)
+        derived: str = Field(default_factory=lambda data: data["required_value"])
+
+    class FactoryFunction:
+        description = "Factory ADK function"
+        has_single_output = True
+        has_streaming_output = False
+        input_schema = FactoryInput
+
+        async def acall_invoke(self, *_args, **_kwargs):
+            return None
+
+    google_adk_tool_wrapper("factory_adk_func", FactoryFunction(), MagicMock())
+
+    signature = inspect.signature(mock_function_tool.call_args[0][0])
+
+    assert list(signature.parameters) == ["required_value", "generated", "derived"]
+    assert signature.parameters["generated"].default == []
+    assert signature.parameters["derived"].default is None
+
+
 @patch('google.adk.tools.function_tool.FunctionTool')
 @pytest.mark.asyncio
 async def test_google_adk_tool_wrapper_streaming_function(mock_function_tool):