Headstart experiments with starting Rust dependencies sooner

Headstart patches rustc and Cargo so dependent crates can begin analysis before their dependencies finish checking function bodies. The compiler emits interface metadata early, while Cargo overlaps the remaining work. Code generation still waits for complete metadata. The aim is to use otherwise idle CPU cores, especially in projects whose dependency chains serialize compilation.

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Why it matters

The experiment explains a concrete source of build latency and a possible way to reduce it.

More context

Watch upstream progress, or try a separate experimental toolchain built from the repository’s patches. Compare the same project with the option enabled and disabled. No exact publication date was verified; this is a project discovery.

Keep in mind

This is a patch series intended for upstream review, not a stable Rust feature. Extra parallel work can consume more memory or be discarded after errors. Reported speedups are author measurements; 1min has not benchmarked it.

Original read