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

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Message-ID: <20cc8581-0af2-47b3-9fdd-584ff0ef36ab@sedlak.dev>
Date: Wed, 30 Jul 2025 15:27:46 +0200
From: Daniel Sedlak <daniel@...lak.dev>
To: Daniel Almeida <daniel.almeida@...labora.com>,
 Benno Lossin <lossin@...nel.org>
Cc: 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>,
 Alice Ryhl <aliceryhl@...gle.com>, 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 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]

Thanks!
Daniel