Ok, yes, as long as you get into the existing gcc front-ends, you're fine. So hypothetically the rustlang compiler could be written in gfortran, because gcc happily compiles that up from scratch. That would be a bundle of fun.
Yes you have a better handle on (used more accurate words) how gcc bootstrapping works.
So, correction: either gcc or g++ could be used, thank you for spotting that, sanxiyn.
Jacob: if the frontend in gcc is written in rustlang, how do you get to bootstrap to gcc being able to compile that rustlang frontend in order to compile the frontend? (hint: answers do NOT involve use of rustlang-llvm )
It would be necessary to have a minimal subset rustlang compiler, written in c/c++, which could at least be used to compile a second stage compiler written ONLY in the subset of rust but providing full functionality, which FINALLY compiles the actual compiler which supports the FULL functionality of rustlang, wouldn't it?
This is the process that sanxiyn is referring to, and it's pretty awkward, but feasible.
To that end, actually, now that I think about it, there is no reason why redbrain's original work should not be considered the first stage bootstrap compiler!
It would mean that the second stage in the 3 stage bootstrap process could be written in rustlang, it would just have to be in the pre 1.0 rustlang, which may not appeal to a lot of people.
The final third stage could be written in the latest version of rustlang and be capable of both compiling itself and also the current rustlang-llvm compiler.
Later iterations could greatly improve on this.
The nice thing is that once crate is compilable it will be possible to start grabbing libraries and source that could accelerate the process of getting up and running. However a caveat is that great care needs to be taken to minimise the dependencies during the bootstrap process, and a full license audit would be needed on any libraries, if they were to become effectively critical build or runtime dependencies of gcc-rustlang.
Great feedback, very encouraging.