linux-kernel - Re: [PATCH v7 07/16] rust: add `io::{Io, IoRaw}` base types

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Message-ID: <CANiq72=gZhG8MOCqPi8F0yp3WR1oW77V+MXdLP=RK_R2Jzg-cw@mail.gmail.com>
Date: Fri, 21 Feb 2025 04:58:59 +0100
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Alistair Popple <apopple@...dia.com>
Cc: Danilo Krummrich <dakr@...nel.org>, gregkh@...uxfoundation.org, rafael@...nel.org, 
	bhelgaas@...gle.com, ojeda@...nel.org, alex.gaynor@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	benno.lossin@...ton.me, tmgross@...ch.edu, a.hindborg@...sung.com, 
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	fabien.parent@...aro.org, chrisi.schrefl@...il.com, paulmck@...nel.org, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: [PATCH v7 07/16] rust: add `io::{Io, IoRaw}` base types

Hi Alistair,

On Fri, Feb 21, 2025 at 2:20 AM Alistair Popple <apopple@...dia.com> wrote:
>
> Is this a known issue or limitation? Or is this a bug/rough edge that still
> needs fixing? Or alternatively am I just doing something wrong? Would appreciate
> any insights as figuring out what I'd done wrong here was a bit of a rough
> introduction!

Yeah, it is a result of our `build_assert!` machinery:

    https://rust.docs.kernel.org/kernel/macro.build_assert.html

which works by producing a build (link) error rather than the usual
compiler error and thus the bad error message.

`build_assert!` is really the biggest hammer we have to assert
something is true at build time, since it may rely on the optimizer.
For instance, if `static_assert!` is usable in that context, it should
be instead of `build_assert!`.

Ideally we would have a way to get the message propagated somehow,
because it is indeed confusing.

I hope that helps.

Cheers,
Miguel