Fix streaming tools support for string annotations and serialization

src/google/adk/tools/_automatic_function_calling_util.py

@@ -394,6 +394,10 @@ def from_function_with_options(
 
   return_annotation = inspect.signature(func).return_annotation
 
+  # Resolve deferred type hints.
+  if 'return' in annotation_under_future:
+    return_annotation = annotation_under_future['return']
+
   # Handle AsyncGenerator and Generator return types (streaming tools)
   # AsyncGenerator[YieldType, SendType] -> use YieldType as response schema
   # Generator[YieldType, SendType, ReturnType] -> use YieldType as response schema

src/google/adk/tools/function_tool.py

@@ -222,6 +222,14 @@ async def _invoke_callable(
   ) -> Any:
     """Invokes a callable, handling both sync and async cases."""
 
+    # Handle async generator functions (streaming tools)
+    is_async_gen = inspect.isasyncgenfunction(target) or (
+        hasattr(target, '__call__')
+        and inspect.isasyncgenfunction(target.__call__)
+    )
+    if is_async_gen:
+      return [item async for item in target(**args_to_call)]
+
     # Functions are callable objects, but not all callable objects are functions
     # checking coroutine function is not enough. We also need to check whether
     # Callable's __call__ function is a coroutine function

tests/unittests/tools/test_build_function_declaration.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import collections.abc
 from enum import Enum
 
 from google.adk.features import FeatureName
@@ -661,3 +662,25 @@ def greet(name: str = 'World') -> str:
     schema = decl.parameters_json_schema
     assert schema['properties']['name']['default'] == 'World'
     assert 'name' not in schema.get('required', [])
+
+
+def test_schema_generation_for_streaming_tool_with_string_annotations():
+  """Test schema generation for AsyncGenerator with string annotations."""
+
+  # Simulate string annotation by using forward reference string
+  # This mimics "from __future__ import annotations" behavior
+  async def streaming_tool(
+      param: str,
+  ) -> 'collections.abc.AsyncGenerator[str, None]':
+    """A streaming tool."""
+    yield f'result {param}'
+
+  function_decl = _automatic_function_calling_util.build_function_declaration(
+      func=streaming_tool, variant=GoogleLLMVariant.VERTEX_AI
+  )
+
+  assert function_decl.name == 'streaming_tool'
+  assert function_decl.parameters.type == 'OBJECT'
+  # VERTEX_AI should have response schema for string return (yield type)
+  assert function_decl.response is not None
+  assert function_decl.response.type == types.Type.STRING

tests/unittests/tools/test_function_tool.py

@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import collections.abc
+from typing import AsyncGenerator
 from unittest.mock import MagicMock
 
 from google.adk.agents.invocation_context import InvocationContext
@@ -200,9 +202,11 @@ async def test_run_async_1_missing_arg_sync_func():
   args = {"arg1": "test_value_1"}
   result = await tool.run_async(args=args, tool_context=MagicMock())
   assert result == {
-      "error": """Invoking `function_for_testing_with_2_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
+      "error": (
+          """Invoking `function_for_testing_with_2_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
 arg2
 You could retry calling this tool, but it is IMPORTANT for you to provide all the mandatory parameters."""
+      )
   }
 
 
@@ -213,9 +217,11 @@ async def test_run_async_1_missing_arg_async_func():
   args = {"arg2": "test_value_1"}
   result = await tool.run_async(args=args, tool_context=MagicMock())
   assert result == {
-      "error": """Invoking `async_function_for_testing_with_2_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
+      "error": (
+          """Invoking `async_function_for_testing_with_2_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
 arg1
 You could retry calling this tool, but it is IMPORTANT for you to provide all the mandatory parameters."""
+      )
   }
 
 
@@ -226,11 +232,13 @@ async def test_run_async_3_missing_arg_sync_func():
   args = {"arg2": "test_value_1"}
   result = await tool.run_async(args=args, tool_context=MagicMock())
   assert result == {
-      "error": """Invoking `function_for_testing_with_4_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
+      "error": (
+          """Invoking `function_for_testing_with_4_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
 arg1
 arg3
 arg4
 You could retry calling this tool, but it is IMPORTANT for you to provide all the mandatory parameters."""
+      )
   }
 
 
@@ -241,11 +249,13 @@ async def test_run_async_3_missing_arg_async_func():
   args = {"arg3": "test_value_1"}
   result = await tool.run_async(args=args, tool_context=MagicMock())
   assert result == {
-      "error": """Invoking `async_function_for_testing_with_4_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
+      "error": (
+          """Invoking `async_function_for_testing_with_4_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
 arg1
 arg2
 arg4
 You could retry calling this tool, but it is IMPORTANT for you to provide all the mandatory parameters."""
+      )
   }
 
 
@@ -256,12 +266,14 @@ async def test_run_async_missing_all_arg_sync_func():
   args = {}
   result = await tool.run_async(args=args, tool_context=MagicMock())
   assert result == {
-      "error": """Invoking `function_for_testing_with_4_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
+      "error": (
+          """Invoking `function_for_testing_with_4_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
 arg1
 arg2
 arg3
 arg4
 You could retry calling this tool, but it is IMPORTANT for you to provide all the mandatory parameters."""
+      )
   }
 
 
@@ -272,12 +284,14 @@ async def test_run_async_missing_all_arg_async_func():
   args = {}
   result = await tool.run_async(args=args, tool_context=MagicMock())
   assert result == {
-      "error": """Invoking `async_function_for_testing_with_4_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
+      "error": (
+          """Invoking `async_function_for_testing_with_4_arg_and_no_tool_context()` failed as the following mandatory input parameters are not present:
 arg1
 arg2
 arg3
 arg4
 You could retry calling this tool, but it is IMPORTANT for you to provide all the mandatory parameters."""
+      )
   }
 
 
@@ -428,3 +442,19 @@ def explicit_params_func(arg1: str, arg2: int):
   assert result == {"arg1": "test", "arg2": 42}
   # Explicitly verify that unexpected_param was filtered out and not passed to the function
   assert "unexpected_param" not in result
+
+
+@pytest.mark.asyncio
+async def test_run_async_streaming_generator():
+  """Test that run_async consumes the async generator and returns a list."""
+
+  async def streaming_tool(param: str) -> AsyncGenerator[str, None]:
+    yield f"part 1 {param}"
+    yield f"part 2 {param}"
+
+  tool = FunctionTool(streaming_tool)
+
+  result = await tool.run_async(args={"param": "test"}, tool_context=MagicMock())
+
+  assert isinstance(result, list)
+  assert result == ["part 1 test", "part 2 test"]