[steveklabnik]

Rust has not defined an ABI. You're misunderstanding how the edition mechanism works. Each compiler knows how to turn source code of any given edition into the same internal IR, but that's purely internal. You still cannot compile an rlib with Rust compiler version 1.X and use it in a program compiled with Rust compiler version 1.Y. You can compile an rlib with Rust compiler version 1.Z that uses edition 2015 and use it in a program compiled with Rust compiler version 1.Z that uses edition 2018.