Upstream Rust maintenance report (August-September 2026)

As noted in my previous report, I am currently working on the open source Rust toolchain as a Sovereign Tech Fellow. Every two months, I’m putting out a report of my open source work done in that period. This is the second installment of this series. Same as the last time, I’ll try to pick a few highlights, summarize the rest of the stuff that I worked on, and also provide contribution statistics and a raw list of opened PRs. This post details my open source Rust work done in August and September 2026. Here’s an index for simpler navigation: Reducing target directory size Compile time improvements Trying to optimize the Rust parser Making Polonius faster Shipping the parallel frontend Measuring compiler performance on ARM Investigating incremental recompilation Improving the Rust compiler merge queue Josh subtree migration Tracking rust-lang crates on crates.io Reviving unmaintained repositories thanks.rust-lang.org rustup-components-history Funding team activities Other things I…