fix: Handle merging lists in deep_merge_dicts

The deep_merge_dicts function will now extend lists when merging dictionaries, instead of overwriting them.

Co-authored-by: Vishwa Murugan <vishwamurugan@google.com>
PiperOrigin-RevId: 890531331

Author: vishwa180

src/google/adk/flows/llm_flows/functions.py

@@ -1151,10 +1151,12 @@ def __build_response_event(
 
 
 def deep_merge_dicts(d1: dict, d2: dict) -> dict:
-  """Recursively merges d2 into d1."""
+  """Recursively merges d2 into d1, extending lists where keys collide."""
   for key, value in d2.items():
     if key in d1 and isinstance(d1[key], dict) and isinstance(value, dict):
       d1[key] = deep_merge_dicts(d1[key], value)
+    elif key in d1 and isinstance(d1[key], list) and isinstance(value, list):
+      d1[key].extend(value)
     else:
       d1[key] = value
   return d1
@@ -1195,7 +1197,7 @@ def merge_parallel_function_response_events(
       author=base_event.author,
       branch=base_event.branch,
       content=types.Content(role='user', parts=merged_parts),
-      actions=merged_actions,  # Optionally merge actions if required
+      actions=merged_actions,  # Aggregated from all parallel events
   )
 
   # Use the base_event as the timestamp

tests/unittests/flows/llm_flows/test_functions_simple.py

@@ -18,6 +18,8 @@
 
 from google.adk.agents.llm_agent import Agent
 from google.adk.events.event import Event
+from google.adk.events.event_actions import EventActions
+from google.adk.events.ui_widget import UiWidget
 from google.adk.flows.llm_flows.functions import find_matching_function_call
 from google.adk.flows.llm_flows.functions import handle_function_calls_async
 from google.adk.flows.llm_flows.functions import handle_function_calls_live
@@ -1138,6 +1140,45 @@ async def yielding_async() -> dict:
   ]
 
 
+def test_merge_parallel_function_response_events_merges_ui_widgets():
+  """Test that merge_parallel_function_response_events merges render_ui_widgets."""
+  invocation_id = 'base_invocation_123'
+
+  widget1 = UiWidget(
+      id='widget_1', provider='mcp', payload={'resource_uri': 'ui://widget1'}
+  )
+  widget2 = UiWidget(
+      id='widget_2', provider='mcp', payload={'resource_uri': 'ui://widget2'}
+  )
+  widget3 = UiWidget(
+      id='widget_3', provider='mcp', payload={'resource_uri': 'ui://widget3'}
+  )
+
+  event1 = Event(
+      invocation_id=invocation_id,
+      author='test_agent',
+      actions=EventActions(render_ui_widgets=[widget1]),
+  )
+
+  event2 = Event(
+      invocation_id='different_invocation_456',
+      author='different_agent',
+      actions=EventActions(render_ui_widgets=[widget2, widget3]),
+  )
+
+  # Merge the events
+  merged_event = merge_parallel_function_response_events([event1, event2])
+
+  # Should contain all ui widgets
+  assert merged_event.actions.render_ui_widgets is not None
+  assert len(merged_event.actions.render_ui_widgets) == 3
+
+  widget_ids = {widget.id for widget in merged_event.actions.render_ui_widgets}
+  assert 'widget_1' in widget_ids
+  assert 'widget_2' in widget_ids
+  assert 'widget_3' in widget_ids
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
     'handle_function_calls',