Re: [PATCH v2] rust: check type of `$ptr` in `container_of!`

[Alice Ryhl <aliceryhl@google.com>]

On Sat, Apr 12, 2025 at 02:16:08PM -0400, Tamir Duberstein wrote:
> +    ($field_ptr:expr, $Container:ty, $($fields:tt)*) => {{
> +        let offset: usize = ::core::mem::offset_of!($Container, $($fields)*);
> +        let container_ptr = $field_ptr.byte_sub(offset).cast::<$Container>();
> +        if false {
> +            let field_ptr = ::core::ptr::addr_of!((*container_ptr).$($fields)*).cast_mut();
> +            [$field_ptr, field_ptr]; // typeof(`$ptr_to_field`) == typeof(`$Container.$($fields)*`)

This evaluates $field_ptr twice. The `if false` avoids bad stuff if the
expression has side-effects, but still seems sub-optimal.

Alice