Re: [PATCH 1/2] rust: alloc: extend safety requirements of Vec::set_len()

[Danilo Krummrich <dakr@kernel.org>]

On Sun, Mar 16, 2025 at 07:59:34PM +0100, Danilo Krummrich wrote:
> But let's define it then; what about:
> 
> "[`Vec::set_len`] takes (or kepps) ownership of all elements within the range
> [0; `new_len`] and abandons ownership of all values outside of this range, if
> any."
> 
> The caller may take ownership of the abandoned elements."
> 
> I'd argue that giving up ownership, while offering someone else to take it means
> that it implies that otherwise we'll just end up forgetting about the value.

Btw. I'd still prefer if we could enforce that the caller has to document what
should happen to the abandoned value. But I acknowledge that the safety comment
isn't the scope for it.

It'd be great if e.g. clippy would give us a tool to do something analogous to
safety comments.

It think it would be useful to enfoce some additional safety documentation. For
instance, I think the kernel would much benefit if we could enforce that
mem::forget() must be justified with a comment, since as mentioned ina previous
mail, it can cause fatal bugs, for instance when used on lock guards.