draft · 1 min read · open-source, langchain, python
The _get_last_messages bug in LangChain
Tracking down and fixing a subtle bug in a 120k-star codebase.
This essay is a draft. The outline below is a placeholder.
The symptom
What went wrong and how it showed up.
Finding the cause
Reading through _get_last_messages and reproducing the failure.
The fix
The change, the tests that cover it, and hardening default_tool_parser along the way.
Contributing to a large project
What I learned about getting a pull request merged in a busy repository.