I recently started doing a bit of experimenting with unsafe rust, and I ended up encountering the warning unused_unsafe where I didn't expect it. Here is a simplified example.
The following function
unsafe fn testing() {
let i = 3;
let mut j = 1;
unsafe { copy(&i, &mut j, 1) };
}
raises the following warning:
warning: unnecessary `unsafe` block
--> src/main.rs:6:5
|
3 | unsafe fn testing() {
| ------------------- because it's nested under this `unsafe` fn
...
6 | unsafe { copy(&i, &mut j, 1) };
| ^^^^^^ unnecessary `unsafe` block
|
= note: `#[warn(unused_unsafe)]` on by default
warning: 1 warning emitted
I know that unsafe fn means that the entire body of the unsafe function is a unsafe block. However, I remember reading somewhere a discussion about this choice, and that it would be better to change it, and require developers to explicitly put the relevant parts of the body in unsafe blocks. I even thought that this change was planned, and that the above warning was not shown, and that there was already a warning in place (either in rustc or clippy) to warn developers that they should use redundant unsafe blocks in that case to have more granularity over where unsafe operations can be used.
It seems I remember wrong, but I haven't been able to find where I read about this. So, with the recent release of the Plan for the Rust 2021 Edition, I wonder why this change isn't a part of the 2021 edition.