Ignoring return value from `Box::from_raw` does not cause warning

[rhysd]

I tried this code:

#![allow(dead_code)]

unsafe fn free<T>(ptr: *mut T) {
    Box::from_raw(ptr);
}

fn main() {}

I expected to see this happen: explanation

The same as CString::from_raw, I expected the following warning:

warning: unused return value of `Box::<T>::from_raw` that must be used
 --> foo.rs:4:5
  |
4 |     Box::from_raw(ptr);
  |     ^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_must_use)]` on by default
  = note: call `drop(from_raw(ptr))` if you intend to drop the `Box`

Instead, this happened: explanation

No warning is reported.

Meta

rustc --version --verbose:

rustc 1.62.0 (a8314ef7d 2022-06-27)
binary: rustc
commit-hash: a8314ef7d0ec7b75c336af2c9857bfaf43002bfc
commit-date: 2022-06-27
host: x86_64-apple-darwin
release: 1.62.0
LLVM version: 14.0.5

Note that #[must_use] was added to CString::from_raw at #89753 following the activity tracked at #89692.

I'm creating this issue after discussion at rust-lang/regex#882.