linux-kernel - Re: [PATCH 2/2] rust: add `const

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Message-Id: <DG87KRN75MKZ.1O0TZI77MLIBT@garyguo.net>
Date: Fri, 06 Feb 2026 21:48:59 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Benno Lossin" <lossin@...nel.org>, "Gary Guo" <gary@...yguo.net>,
 "Miguel Ojeda" <ojeda@...nel.org>, "Boqun Feng" <boqun@...nel.org>,
 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>,
 "Alexandre Courbot" <acourbot@...dia.com>, "Yury Norov"
 <yury.norov@...il.com>, "Nathan Chancellor" <nathan@...nel.org>, "Nicolas
 Schier" <nsc@...nel.org>
Cc: <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
 <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH 2/2] rust: add `const_assert!` macro

On Fri Feb 6, 2026 at 9:30 PM GMT, Benno Lossin wrote:
> On Fri Feb 6, 2026 at 6:12 PM CET, Gary Guo wrote:
>> +/// Assertion during constant evaluation.
>> +///
>> +/// This is a more powerful version of `static_assert` that can refer to generics inside functions
>> +/// or implementation blocks. However, it also have a limitation where it can only appear in places
>> +/// where statements can appear; for example, you cannot use it as an item in the module.
>> +///
>> +/// [`static_assert!`] should be preferred where possible.
>> +///
>> +/// # Examples
>> +///
>> +/// When the condition refers to generic parameters [`static_assert!`] cannot be used.
>> +/// Use `const_assert!` in this scenario.
>> +/// ```
>> +/// fn foo<const N: usize>() {
>> +///     // `static_assert!(N > 1);` is not allowed
>> +///     const_assert!(N > 1); // Compile-time check
>> +///     build_assert!(N > 1); // Build-time check
>
> I think having "Build-time check" here is a bit confusing, how about we
> change it to "Link-time check"? Since a "Compile-time check" also is
> done at "Build-time"

This is the intentional phrasing that I used for `build_assert!` when I created
it, for the reason that `build_assert!` ensure that it will fire, at latest,
link time. However, if you actually use such methods with CTFE, it will error
earlier. So it is "at latest link-time check", so I decided to just use
"build-time".

Best,
Gary

>
> Cheers,
> Benno