The C-variadic type ... has been nested inside another type.
Erroneous code example:
#![feature(c_variadic)]
fn foo2(x: u8, y: &...) {} // error!Only foreign functions can use the C-variadic type (...). In such functions,
... may only occur non-nested. That is, y: &'a ... is not allowed.
A C-variadic type is used to give an undefined number of parameters to a given
function (like printf in C). The equivalent in Rust would be to use macros
directly (like println! for example).