hellorustc

This repository is a prototype for using rustc as a friendly compiler with R packages.

Essentially, there is an R build-system, which mainly consists of make, clang/gcc, and occasionally someone speaks of autoconf. On the other hand, Rust's build system is cargo. For now, people have tried to unify cargo with R's build system. This repository aims to join rustc and R's build system, instead.

Ultimately, the aim is to find a better way to work with R, Rust, cargo, and how to properly customize R-packages, such that they may build multiple native languages, not just single ones.

One goal here is to not use any C-files at all in this project, and simply lean on rustc for generating necessary C-ABI boilerplate. This is a contrived restriction, and may be abandoned later.

Currently, the src/Makevars currently builds any single Rust source file .rs as its own individual file, and links that to the R-package.

• One has to add the rust-file to the list of files in OBJECTS in Makevars. If there is a kewl makefile way to glob select files to do that, please let me know. For now, one also has to link the object .o together with the .rs file in the Makevars file. But invoking rustc is done for you.

This R package generates bindings for R's C-API on its own and stores it in the package itself. How to include these files is shown in src/hello.rs and src/rust_add.rs.

A major pre-requisite is to have bindgen installed, i.e.

cargo install bindgen-cli --force

And to use bindgen, one needs to install and configure clang. On a Mac, this is already setup.

Learnings

This was done as a means to learn more about what variables are available for us in Makevars, and how they could be used to accomplish various things.

Another is to learn about the inner workings of cargo, through investigating what it takes to make rustc produce the right artefact. I would not recommend this experience in "production".

Also, note that the way rust crates are linked here is not the usual staticlib way that is seen in extendr, savvy, roxido, etc.

_rust_eh_personality is missing. This is a sentence that comes up often. The issue is that Rust has a std, with which exception handling (eh) is implemented. This means if you use elaborate unwinding in your rustc, you'd somehow have to link or build std.

• Find a way to link to Rust's exception handling / unwinding. For now -Cpanic=abort, i.e. the C-way. This means that extern "C" is the only supported ABI, and that C-unwind cannot be supported by only calling rustc.

Acknowledgements

The name hellorustc is inspired by the hellorust.