feat: support Langchain StructuredTool for Langchain tool

for fixing: https://github.com/google/adk-python/issues/707

PiperOrigin-RevId: 764781197

contributing/samples/langchain_structured_tool_agent/agent.py

@@ -0,0 +1,49 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+This agent aims to test the Langchain tool with Langchain's StructuredTool
+"""
+from google.adk.agents import Agent
+from google.adk.tools.langchain_tool import LangchainTool
+from langchain_core.tools.structured import StructuredTool
+from pydantic import BaseModel
+
+
+def add(x, y) -> int:
+  return x + y
+
+
+class AddSchema(BaseModel):
+  x: int
+  y: int
+
+
+test_langchain_tool = StructuredTool.from_function(
+    add,
+    name="add",
+    description="Adds two numbers",
+    args_schema=AddSchema,
+)
+
+root_agent = Agent(
+    model="gemini-2.0-flash-001",
+    name="test_app",
+    description="A helpful assistant for user questions.",
+    instruction=(
+        "You are a helpful assistant for user questions, you have access to a"
+        " tool that adds two numbers."
+    ),
+    tools=[LangchainTool(tool=test_langchain_tool)],
+)