#[ffi_returns_twice]
was used on something other than a foreign function declaration.
Erroneous code example:
#![feature(ffi_returns_twice)] #![crate_type = "lib"] #[ffi_returns_twice] // error! pub fn foo() {}
#[ffi_returns_twice]
can only be used on foreign function declarations. For example, we might correct the previous example by declaring the function inside of an extern
block.
#![feature(ffi_returns_twice)] extern "C" { #[ffi_returns_twice] // ok! pub fn foo(); }