Feature attributes are only allowed on the nightly release channel. Stable or
beta compilers will not comply.

Erroneous code example:

`
#![feature(lang_items)] // error: `#![feature]` may not be used on the
                        //        stable release channel
`

If you need the feature, make sure to use a nightly release of the compiler
(but be warned that the feature may be removed or altered in the future).
(END)

In reply to @aktaboot:tchncs.de
does that mean that you can't put a package in nixpkgs that can only be built with the nightly rustc ?