Compiling Rust with GCC: an update

While totally true: How will adding a gcc-based rust compiler change this?

The current process to improve Rust is to write an RFC and provide an implementation for rustc. This is then extensively tested, feedback on the implementation is collected, all available Rust projects will be built to see what breaks, etc. With this process gcc-based Rust will always have to catch up to the "real" rust and will never be a serious alternative! The only way to avoid this is to change the process and make that less code- and more paper-based. The process would need to produce a specifications for the compiler teams to implement later. This sounds like a huge step backwards to me! Just look at C++ to see how poorly that works: Compilers are always behind the specification and it is a huge pain for projects to agree on the exact features they can use in their code (without loosing too many users that need to stick with older compilers).

But in practice this will probably not be necessary: The gcc-based rust compiler plans to reuse parts of the original rust compiler as those are factored out and become available. E.g. Polonius, the library that should eventually contain the entire borrow checker. This will significantly reduce the costs to maintain the gcc-rust project and is thus obviously a good thing. So in the long-run all possible programs that work with rust code will converge towards a shared frontend, incl. rustc, rust-analyzer, a stand-alone gcc-based rust compiler and more. Many of the Rust features will be in this shared front-end code eventually, at which point we are back at having an implementation defined language. This also re-introduces the trusting-trust issues you bring up: If the shared front-end code produces malicious high-level code, then all non-malicious backend-implementations will faithfully produce malicious binaries from their inputs.