cpp-vs-rust VS quote

> They seem to have chosen to use mold for C++ and not for Rust after seeing that it gave little benefit for small projects, but I would expect that to change as the project scales.

The benchmarks show Mold for both Rust and C++. This wasn't explicitly stated in the article; sorry. https://github.com/quick-lint/cpp-vs-rust/blob/f8d31341f5cac...

Very well-researched article (in my uninformed opinion because I've done virtually no benchmarking). I'd summarize it as, Rust doesn't significantly improve build times over C++ for a project where you need to frequently recompile to test the logic of the code. I gather that the Rust code is pretty idiosyncratic (using raw pointers rather than slices and custom owned and borrowed string containers with i32 length and capacity fields), but I don't know why more idiomatic Rust code would be faster to compile, and it could be very different, so a worse comparison. The results aren't relevant for me because I use Rust mainly for the language features and don't have a project with terrible compile times or the need to often rerun tests, but there might be other C++ projects in the same boat as quick-lint-js that would consider moving to Rust if it compiled faster than C++. Hopefully the efforts of people like u/nnethercote will make that happen.

A surprising source of slow compile times can be declarative macros in Rust [0].

I believe the core of the problem is that it has to reparse the code to pattern match for the macro.

One egregious patter is tt-munchers [1] where your macro is implemented recursively, requiring it to reparse the source on each call [2].

In one of my projects, someone decided to wrap a lot of core functions in simple macros (ie nt tt-munchers) to simplify the signatures. Unlike most macros which are used occasionally and have small inputs, this was a lot of input. When I refactored the code, I suspect dropping the macros is the reason CI times were cut in half and a clean `cargo check` went from 3s to 0.5s.

[0]: https://nnethercote.github.io/2022/04/12/how-to-speed-up-the...

[1]: https://veykril.github.io/tlborm/decl-macros/patterns/tt-mun...

[2]: https://github.com/dtolnay/quote/blob/31c3be473d0457e29c4f47...

In the build.rs, call your code generation function (probably in a separate crate added in build-dependencies). This function will read your input files, and use something like quote to generate code.

Or you can pair them with crates like syn, and quote for quasi-quoting, and then it's easy to make transformations on the AST of Rust input code. A lot of libraries do this for code-generation and hiding away a lot of complexity (example wasm-bindgen).