Re: [RFC PATCH] rust: alloc: pass `old_layout` to `Allocator`

[Alice Ryhl]

On Sat, Sep 21, 2024 at 5:33 PM Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
> @@ -84,11 +92,18 @@ unsafe fn call(
>          &self,
>          ptr: Option<NonNull<u8>>,
>          layout: Layout,
> +        old_layout: Layout,
>          flags: Flags,
>      ) -> Result<NonNull<[u8]>, AllocError> {
>          let size = aligned_size(layout);
>          let ptr = match ptr {
> -            Some(ptr) => ptr.as_ptr(),
> +            Some(ptr) => {
> +                if old_layout.size() == 0 {
> +                    ptr::null()
> +                } else {
> +                    ptr.as_ptr()
> +                }
> +            }

This is making Allocator work with zero-sized types, which deviates
from std. We should not do that without a reason. What is the reason?

Alice