genai: Fix handling of optional arrays in tool input

libs/genai/langchain_google_genai/_function_utils.py

@@ -314,6 +314,14 @@
 
         if properties_item.get("type_") == glm.Type.ARRAY and v.get("items"):
             properties_item["items"] = _get_items_from_schema_any(v.get("items"))
+        elif properties_item.get("type_") == glm.Type.ARRAY and v.get("anyOf"):
+            types_with_items = [t for t in v.get("anyOf") if t.get("items")]
+            if len(types_with_items) > 1:
+                logger.warning(
+                    "Only first value for 'anyOf' key is supported in array types."
+                    f"Got {len(types_with_items)} types, using first one: {types_with_items[0]}"
+                )
+            properties_item["items"] = _get_items_from_schema_any(types_with_items[0]['items'])
 
         if properties_item.get("type_") == glm.Type.OBJECT and v.get("properties"):
             properties_item["properties"] = _get_properties_from_schema_any(

libs/genai/tests/unit_tests/test_function_utils.py

@@ -309,3 +309,12 @@
     gapic_tool = convert_to_genai_function_declarations([MyModel])
     tool_dict = tool_to_dict(gapic_tool)
     assert gapic_tool == convert_to_genai_function_declarations([tool_dict])
+
+
+def test_tool_input_can_have_optional_arrays() -> None:
+    class ExampleToolInput(BaseModel):
+        numbers: Optional[List[str]] = Field()
+
+    gapic_tool = convert_to_genai_function_declarations([ExampleToolInput])
+    assert gapic_tool.function_declarations[0].parameters.properties.get('numbers').items.type_ == 1
+