Pydantic ValidationError (extra_forbidden for properties.resource.$ref) when using LangchainTool with google-adk

[yakamazu]

Describe the bug
When running an agent using google-adk that utilizes tools wrapped by LangchainTool (specifically from GmailToolkit in this case), a pydantic_core._pydantic_core.ValidationError occurs related to properties.resource.$ref. This seems to happen during the function declaration building process for the LLM.

To Reproduce
Steps to reproduce the behavior:

1. Set up a project using google-adk.
2. Implement an agent that uses langchain_community.agent_toolkits.GmailToolkit wrapped with google.adk.tools.langchain_tool.LangchainTool. See the relevant code snippet below.
3. Run the agent using the ADK CLI or relevant execution method.
4. Observe the error during the agent's execution flow, specifically when the agent attempts to process the wrapped Langchain tools.

Relevant Code Snippet (gmail_agent/agent.py)

# ... (imports and other setup)
from google.adk import Agent
from google.adk.tools.langchain_tool import LangchainTool
from langchain_community.agent_toolkits import GmailToolkit
from langchain_community.tools.gmail.utils import (
    build_resource_service,
    get_gmail_credentials,
)
# ...

# Gmail setup
# Assuming credentials and api_resource are correctly set up
# credentials = get_gmail_credentials(...)
# api_resource = build_resource_service(credentials=credentials)
toolkit = GmailToolkit(api_resource=api_resource)

# Wrap with LangchainTool
gmail_tools = toolkit.get_tools()
adk_gmail_tools = [LangchainTool(tool=tool) for tool in gmail_tools]

try:
    # Define Agent with the wrapped tool
    gmail_root_agent = Agent(
        model="gemini-1.5-pro-latest", # Or your specific model
        # name=...,
        # description=...,
        # instruction=...,
        tools=adk_gmail_tools # Error seems to occur when processing these tools
    )

    # ... (Runner setup and execution)

except Exception as e:
    print(f"Error during agent initialization or execution: {e}")
    raise

Expected behavior
The agent should initialize and run without encountering the Pydantic validation error when processing LangchainTool-wrapped tools.

Error Message/Traceback

2025-04-21 12:24:29,847 - ERROR - fast_api.py:637 - Error in event_generator: 1 validation error for Schema
properties.resource.$ref
  Extra inputs are not permitted [type=extra_forbidden, input_value='#/$defs/Resource', input_type=str]
For further information visit https://errors.pydantic.dev/2.10/v/extra_forbidden
Traceback (most recent call last):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/cli/fast_api.py", line 626, in event_generator
    async for event in runner.run_async(
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/runners.py", line 197, in run_async
    async for event in invocation_context.agent.run_async(invocation_context):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/agents/base_agent.py", line 141, in run_async
    async for event in self._run_async_impl(ctx):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/agents/llm_agent.py", line 232, in _run_async_impl
    async for event in self._llm_flow.run_async(ctx):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 231, in run_async
    async for event in self._run_one_step_async(invocation_context):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 261, in _run_one_step_async
    async for event in self._postprocess_async(
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 329, in _postprocess_async
    async for event in self._postprocess_handle_function_calls_async(
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 419, in _postprocess_handle_function_calls_async
    async for event in agent_to_run.run_async(invocation_context):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/agents/base_agent.py", line 141, in run_async
    async for event in self._run_async_impl(ctx):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/agents/llm_agent.py", line 232, in _run_async_impl
    async for event in self._llm_flow.run_async(ctx):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 231, in run_async
    async for event in self._run_one_step_async(invocation_context):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 245, in _run_one_step_async
    async for event in self._preprocess_async(invocation_context, llm_request):
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 283, in _preprocess_async
    await tool.process_llm_request(
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/tools/base_tool.py", line 96, in process_llm_request
    if (function_declaration := self._get_declaration()) is None:
                                 ^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/tools/langchain_tool.py", line 69, in _get_declaration
    function_declaration = _automatic_function_calling_util.build_function_declaration_for_langchain(
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/tools/_automatic_function_calling_util.py", line 250, in build_function_declaration_for_langchain
    return build_function_declaration_util(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/user/home/.local/lib/python3.12/site-packages/google/adk/tools/_automatic_function_calling_util.py", line 273, in build_function_declaration_util
    parameters=types.Schema(
               ^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/pydantic/main.py", line 214, in __init__
    validated_self = self.pydantic_validator.validate_python(data, self_instance=self)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.ValidationError: 1 validation error for Schema
properties.resource.$ref
  Extra inputs are not permitted [type=extra_forbidden, input_value='#/$defs/Resource', input_type=str]
For further information visit https://errors.pydantic.dev/2.10/v/extra_forbidden

Environment (please complete the following information):

• OS: Linux 6.6
• Python version: 3.12
• google-adk version: 0.2.0
• langchain-community version: 0.3.21
• pydantic version: 2.11.3
• Other relevant libraries and versions from requirements.txt:

  google-adk>=0.2.0
  litellm>=1.67.0
  nest_asyncio>=1.6.0
  langchain_community>=0.3.21
  python-dotenv>=1.0.0
  google-generativeai>=0.4.0
  google-auth-oauthlib>=1.2.1
  

[Tahirc1]

i was getting a similiar error when i tried using GmailSearch tool from langchain

i was able to fix it by adding a pydantic model to the tools args_schema
i think something similiar can fix other tools

from google.adk.tools.langchain_tool import LangchainTool
from langchain_google_community.gmail.search import GmailSearch
from google.oauth2.credentials import Credentials
from pydantic import BaseModel, Field # Import BaseModel and Field

# Get unread Email
gmail_search_tool = GmailSearch(
    credentials=creds,
    # query="is:unread", # the input to the tool
    max_results=5,
    label_ids=["INBOX"],
    include_body=True,
    include_headers=False
)

#  Define the input schema for the GmailSearch tool 
class GmailSearchInput(BaseModel):
    query: str = Field(description="The Gmail search query. For example: 'is:unread', 'from:important@example.com', 'subject:urgent'")
    
# Assign the args_schema to the Langchain tool instance
gmail_search_tool.args_schema = GmailSearchInput

# Wrap it with LangchainTool for ADK
adk_gmail_search_tool = LangchainTool(tool=gmail_search_tool)

[seanzhou1023]

let's try reproduce it first.