Spooky Rust Compilation

An extremely quick prototype to demonstrate the possible optimization of avoiding unnecessary rebuilds of dependent crates.

Notably this brings incremental compile time down from 26.51s to 2.69s, on my 5950x linux workstation when developing on zed.

WARNING: The current implementation does no checking whatsoever on whether the optimization is safe to perform. Subtle changes can cause a rebuild to be necessary, so expect to see segfaults or worse. Using this is almost certainly going cause incremental compliation bugs and all sorts of pain but compile savings may be worth is.

Tested on Rust 1.81 on Linux.

Example Usage:

Say you're working on zed, and anticipate working on the internals of gpui.

Modify something in the internals of gpui (to ensure gpui gets rebuilt and collects the rustc invocations in the next step), then run:

spooky-rust-build gpui zed

Afterward, you can now run ./spooky_run.sh, which will rebuild only gpui, relink the final binary, and then run the zed binary.

Limitations

Currently, this only supports working on one crate at a time. Support could be expanded to more usecases that would only make it more dangerous this really just demo. Ideally, native & checked support lands in rustc itself.

See:

• Compiler Major Change Request
• Zulip Thread