fix(vertex): ToolMessage is translated to function role which does not exist .
#1238
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RONAK-AI647
changed the title
ToolMessage is translated to function role which does not exist .ToolMessage is translated to function role which does not exist .
…ting chatmodel.py again to change the variable so the merging of messges happen to 6==6.
lkuligin
approved these changes
Oct 15, 2025
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Description
This PR resolves issue #1059 where the LangChain adapter for Google Gemini incorrectly translates the
ToolMessage(and the legacyFunctionMessage) into a GeminiContentobject using the role“function”.Whereas "according to gemini docs, "function" is not a valid role , only
userandmodelare accepted valid roles.Relevant issues
Fixes #1059
Type
🐛 Bug Fix
🧹 Refactoring
Changes(optional)
FunctionMessageandToolMessagefrom the invalid“function”to the API-compliant“user”and**model**prev_content.role == "user". This ensures that consecutive tool responses are correctly merged into a single“user”turn, maintaining the strict alternating sequence required by the Gemini chat models.Testing(optional)
Note(optional)
This ensures tool-calling flows are correctly translated and accepted by the Gemini API, especially when the agent is passing tool results back to the model for the final time.
This will not throw the
WARNING - langchain_core.language_models.llms - Retrying langchain_google_vertexai.chat_models._acompletion_with_retry.<locals>._completion_with_retry_inner in 4.0 seconds as it raised BadRequest: 400 POST https://.../models/gemini-2.5-flash:generateContent: Please use a valid role: user, model..now.