| The `ffi_pure` attribute was used on a non-foreign function. |
| |
| Erroneous code example: |
| |
| ```compile_fail,E0755 |
| #![feature(ffi_pure)] |
| |
| #[unsafe(ffi_pure)] // error! |
| pub fn foo() {} |
| # fn main() {} |
| ``` |
| |
| The `ffi_pure` attribute can only be used on foreign functions which do not have |
| side effects or infinite loops: |
| |
| ``` |
| #![feature(ffi_pure)] |
| |
| extern "C" { |
| #[unsafe(ffi_pure)] // ok! |
| pub fn strlen(s: *const i8) -> isize; |
| } |
| # fn main() {} |
| ``` |
| |
| You can find more information about it in the [unstable Rust Book]. |
| |
| [unstable Rust Book]: https://doc.rust-lang.org/unstable-book/language-features/ffi-pure.html |
