[cwzwarich]

I don't mean a formal spec. Rust is much too complicated and asymmetric to have a formal spec of the kind that exists for other languages (e.g. Standard ML), at least using current specification methodology. It doesn't even have an informal spec, which would be required to have a real attempt at multiple compatible implementations.

[steveklabnik]

I hear what you're saying, but at the same time, mrustc is almost a counterexample of that. And we have real counterexamples in other languages too; Ruby and Python, for example.

(My understanding of mrustc and borrowck is that it's not implemented because the primary initial goal is bootstrapping rustc, not being a general rust compiler.)