We (the rust-analyzer team) have been aware of the slowness in Rowan for a while, but other things always took priority. Beyond allocation, Rowan is structured internally as a doubly-linked list to support mutating trees, but:
1. Mutation isn’t really worth it; the API isn’t user-friendly.
2. In most cases, it’s straight up faster to create a new parse tree and replace the existing one. Cache effects of a linked list vs. an arena!
In fairness, I don’t think we predicted just how large L1/L2 caches would get over the coming years.
In fairness, I don’t think we predicted just how large L1/L2 caches would get over the coming years.