There are at least three separate things that rustc and cargo could do to significantly improve compilation speed, but they are complex engineering efforts that require time and engineers being paid to work on full-time. They are: doing what zig does to compile only items that arr reachable, which requires making rustc reentrant to stop after name resolution and cargo more complex to pass used paths through subsequently, leveraging an incremental linker and have rustc only codegen the binary patch instead of the whole binary and have the linker calculate the patch, and caching proc-macros and treat them as idempotent (likely as opt-in). There are of course others, like pre-compiled distribution, better intra-rustc parallelism or feature cfg handling, but those have more open questions and require additional design work before I could claim they're attainable.
Oh, I hadn't heard that you guys are looking at Zig-style "targeted" compilation (for lack of a better phrase). That sounds like it entails quite a bit of infrastructure work. Is there a GitHub issue I can follow to keep an eye on progress?
Out of curiosity, have there been any interesting pondered/proposed avenues for speedup that were rejected because they would result in too much breakage, violate a core tenant of Rust (e.g., require a runtime to be usable) or other reason that is "inherent" to Rust?
We discussed a lot of these last May in person. Haven't kept track of who's doing what on these fronts.
> have there been any interesting pondered/proposed avenues for speedup that were rejected because they would result in too much breakage, violate a core tenant of Rust (e.g., require a runtime to be usable) or other reason that is "inherent" to Rust?
Yes, but I haven't been part of all of them and can't ellaborate much here. Opening a thread in internals.rust-lang.org with that question might get some good info sooner that I could.
