nightly-crimes

> This seems to favor c++, in which basically anything imaginable can be done with macros, and any other language can be implemented. Pfft. C++ macros can't even run a different compiler: https://github.com/m-ou-se/nightly-crimes/blob/main/yolo-rus...

More specifically, unsafe blocks may violate the compiler's security guarantees and procedural macros actually run inside the compiler process at build time. Declarative macros do this too, but they're far too restricted to allow shenanigans. Procmacros can disable Rust's stability guarantees[0]. [0] https://github.com/m-ou-se/nightly-crimes

> [ https://github.com/m-ou-se/nightly-crimes nightly-crimes! blows away your compiler, running it again in a new environment where it will allow nightly features even though you've got a stable compiler installed... ] That macros have access to the entire language including arbitrary IO is the defining feature of proc macros (not without controversy). The insanity here is the Rust compiler team adding the `RUSTC_BOOTSTRAP` env var which is a hack used to bootstrap rustc using a stable compiler despite the nightly features used by the codebase. All nightly-crimes does is use `std::process::Command` to rerun the compiler with the variable set [1], which tells rustc to throw all concepts of stability out the window. I haven't been following developments but one of the ideas (even has a PoC iirc) was to distribute and run proc macros as web

On the other hand, procedural macros are the big guns and as such if you aim them wrong you are going to blow both feet off. A declarative macro is only at worst going to spew nonsense into your post-processed source where it was used - which the Rust tools are quite happy to show you - but a sufficiently bad proc macro could cause unlimited mayhem with no diagnostics available. I don't know if somebody is collecting the worst mistakes they've seen with proc macros, but m-ou-se's nightly-crimes! shows what sort of insanity is possible. [ https://github.com/m-ou-se/nightly-crimes nightly-crimes! blows away your compiler, running it again in a new environment where it will allow nightly features even though you've got a stable compiler installed... ]