linux-kernel - Re: [PATCH v2] rust: enable arbitrary_self

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Message-ID: <CAH5fLgihaSVg+=D_BfMxnt8VBO-r5LB4akus7EMvAfOyNv45FQ@mail.gmail.com>
Date: Wed, 2 Oct 2024 22:02:30 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Gary Guo <gary@...yguo.net>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>, 
	Trevor Gross <tmgross@...ch.edu>, Masahiro Yamada <masahiroy@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
	Danilo Krummrich <dakr@...hat.com>, FUJITA Tomonori <fujita.tomonori@...il.com>, 
	Valentin Obst <kernel@...entinobst.de>, Martin Rodriguez Reboredo <yakoyoku@...il.com>, 
	Alex Mantel <alexmantel93@...lbox.org>, Adrian Taylor <ade@...um.me.uk>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v2] rust: enable arbitrary_self_types and remove `Receiver`

On Sun, Sep 15, 2024 at 3:29 PM Gary Guo <gary@...yguo.net> wrote:
>
> The term "receiver" means that a type can be used as the type of `self`,
> and thus enables method call syntax `foo.bar()` instead of
> `Foo::bar(foo)`. Stable Rust as of today (1.81) enables a limited
> selection of types (primitives and types in std, e.g. `Box` and `Arc`)
> to be used as receivers, while custom types cannot.
>
> We want the kernel `Arc` type to have the same functionality as the Rust
> std `Arc`, so we use the `Receiver` trait (gated behind `receiver_trait`
> unstable feature) to gain the functionality.
>
> The `arbitrary_self_types` RFC [1] (tracking issue [2]) is accepted and
> it will allow all types that implement a new `Receiver` trait (different
> from today's unstable trait) to be used as receivers. This trait will be
> automatically implemented for all `Deref` types, which include our `Arc`
> type, so we no longer have to opt-in to be used as receiver. To prepare
> us for the change, remove the `Receiver` implementation and the
> associated feature. To still allow `Arc` and others to be used as method
> receivers, turn on `arbitrary_self_types` feature instead.
>
> This feature gate is introduced in 1.23.0. It used to enable both
> `Deref` types and raw pointer types to be used as receivers, but the
> latter is now split into a different feature gate in Rust 1.83 nightly.
> We do not need receivers on raw pointers so this change would not affect
> us and usage of `arbitrary_self_types` feature would work for all Rust
> versions that we support (>=1.78).
>
> Cc: Adrian Taylor <ade@...um.me.uk>
> Link: https://github.com/rust-lang/rfcs/pull/3519 [1]
> Link: https://github.com/rust-lang/rust/issues/44874 [2]
> Signed-off-by: Gary Guo <gary@...yguo.net>

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>