[bastawhiz]

Paring down a rust compiler in rust to only use a subset of rust features might not be a big lift. Then you only need to build a rust compiler (in C) that implements the features used by the pared-down rust compiler rather than the full language.

Pypy, for instance, implements RPython, which is a valid subset of Python. The compiler is written in RPython. The compiler code is limited on features, but it only needs to implement what RPython includes.