In langchain 0.2, vector stores were split out of the core langchain package into langchain-community. Imports from langchain.vectorstores still trigger a deprecation warning in 0.1.x and raise ImportError in 0.2+. You must install langchain-community and update the import path.
Install the community package if you haven't already, then update the import path. No other code changes required.
pip install langchain-community chromadb # Before (broken on 0.2+): # from langchain.vectorstores import Chroma # After: from langchain_community.vectorstores import Chroma