Both of these errors are reproducible with the 1.2 compiler, but not with the 1.17 compiler. Most likely this user believed they were compiling with 1.17 but they were compiling with 1.2.
Ah, in that case I can guess what happened. SliceConcatExt was probably not in the prelude back then. Well, we never guaranteed forward compatibility :)
How sure are you that this was compiled with Rust 1.2 and not some old rustc?
Here is a copy of the docs for Vec from June 2016: https://github.com/Manishearth/rust-internals-docs/blob/9419...
There is no join method there.
There is a join method on slices (which vectors dereference to). https://github.com/Manishearth/rust-internals-docs/blob/9419...
This method still exists. It used to take a delimeter argument, and works the same way today. https://play.rust-lang.org/?gist=13d19cd5dd33c1efb046cc69bec...
There have been various language tweaks, but Rust has not removed a (stable) API since 1.0.