[zozbot234]

Doesn't Rust have a Reference manual already? A "spec" just wouldn't be very meaningful given the lack of independent implementations. But to the extent that the reference manual doesn't suffice for documenting the language, that's a defect which could and should be fixed.

[sheepshear]

The manual isn't directly consumable by formal processes. The compiler design doesn't have to be influenced by a specification, but it does have to be described by one.