| If an impl has a generic parameter with the `#[may_dangle]` attribute, then |
| that impl must be declared as an `unsafe impl`. |
| |
| Erroneous code example: |
| |
| ```compile_fail,E0569 |
| #![feature(dropck_eyepatch)] |
| |
| struct Foo<X>(X); |
| impl<#[may_dangle] X> Drop for Foo<X> { |
| fn drop(&mut self) { } |
| } |
| ``` |
| |
| In this example, we are asserting that the destructor for `Foo` will not |
| access any data of type `X`, and require this assertion to be true for |
| overall safety in our program. The compiler does not currently attempt to |
| verify this assertion; therefore we must tag this `impl` as unsafe. |
