linux-kernel - Re: [PATCH] rust: clk: use the type-state pattern

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Message-ID: <CAH5fLgjBQF+AGWQ-rKowViiL1kK47FZ80QfEa58Cx9bk11cjAw@mail.gmail.com>
Date: Wed, 30 Jul 2025 15:39:18 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Sedlak <daniel@...lak.dev>
Cc: Daniel Almeida <daniel.almeida@...labora.com>, Benno Lossin <lossin@...nel.org>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	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>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Viresh Kumar <viresh.kumar@...aro.org>, Alexandre Courbot <acourbot@...dia.com>, linux-clk@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org
Subject: Re: [PATCH] rust: clk: use the type-state pattern

On Wed, Jul 30, 2025 at 3:27 PM Daniel Sedlak <daniel@...lak.dev> wrote:
>
>
> On 7/30/25 2:59 PM, Daniel Almeida wrote:
> > […]
> >
> >> We essentially would like to have a `#[sealed]` attribute that we can
> >> put on a trait to avoid the `mod private { pub trait Sealed }` dance.
> >> (so a trait that cannot be implemented outside of the module declaring
> >> it)
> >>
> >> ---
> >> Cheers,
> >> Benno
> >
> > This is not exactly what you said, but how about a declarative macro? e.g.:
> >
> > macro_rules! sealed {
> >      ($($ty:ident),* $(,)?) => {
> >          mod private {
> >              pub trait Sealed {}
> >              $(impl Sealed for super::$ty {})*
> >          }
> >          use private::Sealed;
> >      };
> > }
> >
> > sealed!(Unprepared, Prepared, Enabled)
> >
> > Note that I am just brainstorming the general idea here, I did not test it yet.
>
> I think that API-wise it would be better to have a proc-macro #[sealed],
> something similar to [1], as it may provide better error messages, when
> used incorrectly. So the outcome could look like.
>
>         #[sealed]
>         pub trait ClkState {
>         …
>         }
>
> And then
>
>         #[sealed]
>         impl ClkState for XXX {
>         …
>         }
>
> If you are interested, I can try to look into that.
>
> Link: https://crates.io/crates/sealed [1]

It seems a bit much to have macros for everything.