linux-kernel - Re: [PATCH] rust: add `assert

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Message-Id: <DAGI57J7WBD0.2BOT553TRIXH8@kernel.org>
Date: Sat, 07 Jun 2025 20:11:21 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Christian Schrefl" <chrisi.schrefl@...il.com>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng"
 <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>,
 "Trevor Gross" <tmgross@...ch.edu>, "Danilo Krummrich" <dakr@...nel.org>
Cc: <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH] rust: add `assert_sync` function

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