Specifically the expensive part is getting a C89 port of mrustc to compile rustc 1.90.0. mrustc needs C++ right now, bootstrapping via TCC by writing it in C89 would be the shorter chain.

Sounds pretty difficult (if not impossible, see cfront 4.0) to translate C++ code to C89. You have to keep track of all constructors and destructors and their progress along the body yourself, and I assume it must be fit for exceptions as well?

Yes, this isn't meant to be a complete port and I only started dipping into mrustc because the previous agents were going off the rails. I have mostly been throwing spare weekly quotas at this but deeper thought will be required to get an actual working Rust compiler in C. Rust is an enormously more complex language, so it might just be at the capability limit.

> Rust is an enormously more complex language

I have no doubt that a Rust compiler can be implemented in C. But it's a different project to write one in C from start than trying to migrate an existing C++14 based project to C. The former is likely "easier". An alternative approach could be to migrate the C++14 code back to C++98 and get rid of the exceptions, which makes it transpilable to C (using the cfront approach). Though the result might not be maintainable C, but still C.

Thanks, will look into this as another avenue!