FWIW, I've just published
It features what the OP asked for, implemented using a procedural macro with zero dependencies (for optimal compile times), and implements the "preprocessor pattern" (c.f.,
::paste) for enhanced usability.
No idea, the best usability I could come up with was to be able to evaluate the code inside doc comments, since it's the only plausible situation where one may encounter already stringified code
It's more of an educational crate than anything else, since it showcases:
a non trivial proc-macro (featuring well-spanned error reporting) with zero-dependencies;
the callback pattern;
an inlined implementation of
concat!, to support them being used in argument position.