Re: [PATCH] rust: add `assert_sync` function

["Benno Lossin" <lossin@kernel.org>]

On Sat Jun 7, 2025 at 5:54 PM CEST, Christian Schrefl wrote:
> On 07.06.25 5:42 PM, Benno Lossin wrote:
>> On Sat Jun 7, 2025 at 3:02 PM CEST, Christian Schrefl wrote:
>>> - Add `assert_send` as well.
>> 
>> Sounds like a good idea.
>
> Should I already add this in V2 for this series?

If you want to then sure, but we can also wait until we have a use-case.
Also, let's finish the discussion about the macro idea below.

>>> +///     assert_sync::<i32>(); // Succeeds because `i32` is Sync
>>> +///     // assert_sync::<NotThreadSafe>(); // Fails because `NotThreadSafe` is not `Sync`.
>> 
>> Can you split this into two examples and mark the failing one with
>> `compile_fail`?
>
> I've tried it with `compile_fail` and it didn't work, I think
> that's not supported in (kernel) doc tests yet. 

Hmm, I thought that this worked... @Miguel any idea?

>> We also could provide a macro similar to [1].
>>
>> [1]: https://docs.rs/static_assertions/latest/static_assertions/
>
> You mean the `assert_impl_*!` macros?

Yes, but the others might also be useful from time to time.

> That might make sense, with macros we would not need to write
> a const block to ensure its not executed at runtime (although
> it's probably optimized out anyways).

It 100% will be optimized out.

> It would also mean that we won't need a assert for every Trait, which
> seems nice. So a macro sounds pretty good to me.

It depends, the macro impl needs to define its own function, which might
be inefficient if one uses it a lot. But there is no way to be generic
over traits, so there is no other way.

Let's see what the others think.

---
Cheers,
Benno