linux-kernel - Re: [PATCH] rust: allow `stable

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Message-ID: <ab399fac-4b10-4ed9-ac28-55797a17fff2@proton.me>
Date: Tue, 27 Aug 2024 11:29:43 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...sung.com>, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH] rust: allow `stable_features` lint

On 27.08.24 12:39, Alice Ryhl wrote:
> On Tue, Aug 27, 2024 at 12:04 PM Miguel Ojeda <ojeda@...nel.org> wrote:
>>
>> Support for several Rust compiler versions started in commit 63b27f4a0074
>> ("rust: start supporting several compiler versions"). Since we currently
>> need to use a number of unstable features in the kernel, it is a matter
>> of time until one gets stabilized and the `stable_features` lint warns.
>>
>> For instance, the `new_uninit` feature may become stable soon, which
>> would give us multiple warnings like the following:
>>
>>     warning: the feature `new_uninit` has been stable since 1.82.0-dev
>>     and no longer requires an attribute to enable
>>       --> rust/kernel/lib.rs:17:12
>>        |
>>     17 | #![feature(new_uninit)]
>>        |            ^^^^^^^^^^
>>        |
>>        = note: `#[warn(stable_features)]` on by default
>>
>> Thus allow the `stable_features` lint to avoid such warnings. This is
>> the simplest approach -- we do not have that many cases (and the goal
>> is to stop using unstable features anyway) and cleanups can be easily
>> done when we decide to update the minimum version.
>>
>> An alternative would be to conditionally enable them based on the
>> compiler version (with the upcoming `RUSTC_VERSION` or maybe with the
>> unstable `cfg(version(...))`, but that one apparently will not work for
>> the nightly case). However, doing so is more complex and may not work
>> well for different nightlies of the same version, unless we do not care
>> about older nightlies.
>>
>> Another alternative is using explicit tests of the feature calling
>> `rustc`, but that is also more complex and slower.
> 
> You mention a bunch of alternatives, but I agree that this is the best
> way forward. It's very simple. Only possible disadvantage could be if
> we forget to remove features when raising the MSRV, but I don't think
> that's a big risk.

What even are the risks associated with enabling an already stable
feature?

---
Cheers,
Benno