A Turing-complete language can, in theory and assuming no real-world limitations like RAM, do any computation. You can use Rust traits to compile Rust, or run a JVM instance, or whatever. Input and output are limited to what the compiler has access to, but you could perhaps have input as source files and output as text strings in a Rust binary.
That doesn't mean that the OP's hack can be used today, or even tomorrow for compiling-Rust-in-Rust. But you could, in theory, do so.
