The Rust Reference is very far from being complete, or even correct in what it does cover.
If I have a question whose answer isn't obvious, it's far more likely that I have to go trawling around in RFCs than that there's an answer in the reference.
I think most languages of a similar age (eg Go, Swift) are doing better.
Re:GCC-Rust: Rust frontend for GCC
by littlestymaar on Sunday December 08, 2019 @05:09AM
(#21735185)
Rust is younger than Go (released in 2015 vs 2012) and way more ambitious, especially Rust 1.0 was released as kind of an MVP and many things have changed since then, which made the maintenance of such a reference an issue. The pace of change is slowing nowadays (that's especially visible if you look new and accepted RFCs), so I hope the reference will catch up eventually.
There are some people studying Rust with formal verification. For example in this paper https://plv.mpi-sws.org/rustbelt/rbrlx/paper.pdf However I do not know if the whole language is covered or only a core.
It really depends on how strictly you define the term specification. The Rust Reference is not required to be accurate. Though many other language compilers/implementations don’t fully implement their respective specs so, :shrug:.