* What is metadata_decode_entry_impl_trait_header and what does it have to do with proc macros? I suppose if a proc macro emitted code that used impl Trait a bunch then it might need to use this code, but I don't see why that would disproportionately affect compile times.
Back in the late 90s Geocities era, I did like surprise music on personal pages… but also I had bad taste in music at that point because I was an edgy goth teenager with limited experience.
None of us kids back then were any better.
The teachers were going to physically cut the speaker wires in each machine in the computer suite due to all the out-of-sync MIDI renditions of Beverly Hills Cop / Axel F theme before they figured out another solution.
It has to compile them; you can see the compiled binaries in your `target` directory. Rust doesn't have an interpreter for the full language, only for the `const` subset, so it can't interpret them.
There have been some proposals to compile the proc-macros to WASM and share those alongside the code in crates.io, but nothing substantial has come of it.
It does have an interpreter for the full language, that's what Miri uses [0]. In fact, Miri doesn't even have its own evaluator, it just adds additional features to the rustc const-evaluation. The big limitations are that it doesn't have much support for syscalls or other calls into non-Rust code, and it emulates all multithreaded code on a single thread.
> Rust doesn't have an interpreter for the full language
Ever since a while ago, rustc uses Miri for const evaluation. So there are a lot of things it can do that it used to not be able to do. But, yes, const evaluation is limited to things that are part of the `const` subset.
As far as I'm aware, it's always been the other way around: Miri adds some features on top of rustc's const-evaluation code. The limitations of the latter are mainly self-imposed, due to the issues of exposing the different runtime models to programs. (E.g., you don't want to create allocations in const code that get deallocated at runtime.) Indeed, since 2019, the full functionality can be exposed with the unstable -Zunleash-the-miri-inside-of-you flag [0].
* What is metadata_decode_entry_impl_trait_header and what does it have to do with proc macros? I suppose if a proc macro emitted code that used impl Trait a bunch then it might need to use this code, but I don't see why that would disproportionately affect compile times.
* What's the proposal for how to fix this?
You're linking to https://eveeifyeve.pages.dev/http://localhost:4321/blogs/car...
You meant to link to https://eveeifyeve.pages.dev/blogs/cargo-check-slow.mdx/
Also, ew, auto-playing music.
Either someone's edited that since then, or a weird auto-redirect on your server happened.
None of us kids back then were any better.
The teachers were going to physically cut the speaker wires in each machine in the computer suite due to all the out-of-sync MIDI renditions of Beverly Hills Cop / Axel F theme before they figured out another solution.
I use bacon with cargo-make to toggle between check, nextest+doctest, and a full series of pre-commit checks.
There have been some proposals to compile the proc-macros to WASM and share those alongside the code in crates.io, but nothing substantial has come of it.
[0] https://github.com/rust-lang/miri
Ever since a while ago, rustc uses Miri for const evaluation. So there are a lot of things it can do that it used to not be able to do. But, yes, const evaluation is limited to things that are part of the `const` subset.
[0] https://github.com/rust-lang/rust/pull/56123
We're starting to ban them from our Rust monorepo.