Rust: error[E0554]: `#![feature]` may not be used on the stable release channel

[Toon Moene]

I was eager to try the new rust updates ...

But I got this:

error[E0554]: `#![feature]` may not be used on the stable release channel
   --> src/lib.rs:19:1
    |
19 | #![feature(extern_types)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0554`.
error: could not compile `ffi-polonius` (lib) due to 1 previous error
[/home/toon/compilers/gcc/gcc/rust/Make-lang.in:506: 
rust/libffi_polonius.a] Error 101

...

and then the build died so hard that it couldn't even send an e-mail 
that the build aborted ...

Am I the only one seeing this ?

Kind regards,

-- 
Toon Moene - e-mail: toon@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands