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Lukas Wirth
@lukaswirth.dev

Turns out the TokenStream implementation of rust-analyzer's proc-macro server is super slow when it comes to one of the most common proc-macro operations: concatenation. I noticed that in Zed's codebase, there were ~4 derives that just straight up together took 8 seconds to expand in rust-analyzer.

Lukas Wirth
@lukaswirth.dev

All that proc-macro was doing though is `quote!`ing a bunch, not much more. So I spent the day rewriting the implementation of TokenStream used by the server to make use of an immutable shared tree instead to get super cheap concatenations.

Nate Butler
@nate.rip

Err, I’m sorry, and thank you? I might be responsible for some of those 🤣 That is absolutely incredible though, great work.

Lukas Wirth
@lukaswirth.dev

Thanks! Funnily enough the macros in Zed themselves aren't really that problematic. They don't do a lot of quote!ing so they are mostly fine. Except for the `derive_inspector_reflection` which I straight up disabled for r-a's analysis because it took like 16 seconds alone github.com/zed-industri...

github.comReduce macro burden for rust-analyzer by Veykril · Pull Request #42871 · zed-industries/zedThis enables optimizations for our own proc-macros as well as some heavy hitters. Additionally this gates the derive_inspector_reflection to be skipped for rust-analyzer as it currently slows down...

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