How to speed up the Rust compiler in September 2026
Learn how early metadata emission speeds up large Rust builds and what it means for your workflow.
A new private branch reduces Rust compile time by roughly 5% for deep‑nested projects like rust‑analyzer by emitting function type metadata earlier. The speedup appears even though the borrow checker was also improved, so the gain isn’t just a trade‑off.
The branch changes the compilation pipeline: after parsing, it generates meta data for function signatures and makes it available to downstream crates before the type checker finishes. Downstream crates can start their own compilation steps while the upstream crate is still being checked, overlapping work that normally runs sequentially.
Because downstream slots now have the type information they need, they no longer wait for the upstream crate’s full type‑checking pass. This parallelism reduces idle time in the build graph, especially in projects with many inter‑crate dependencies, which is why the effect shows up most strongly in rust‑analyzer’s codebase.
If you maintain a large Rust workspace, consider adjusting your build script to emit type metadata early, or test the branch to see if the overlap reduces your own compile latency. The approach works without changing existing code, only the compilation order, so it can be adopted incrementally.
TakeawayEmit type metadata early to let downstream crates compile in parallel and shave a few percent off Rust build times.