linux-kernel - Re: [PATCH 07/11] rust: macros: convert `concat

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Message-ID: <20251222115956.62c7a4e5.gary@garyguo.net>
Date: Mon, 22 Dec 2025 11:59:56 +0000
From: Gary Guo <gary@...yguo.net>
To: "Benno Lossin" <lossin@...nel.org>
Cc: "Miguel Ojeda" <ojeda@...nel.org>, "Boqun Feng" <boqun.feng@...il.com>,
 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>,
 "Fiona Behrens" <me@...enk.dev>, "Guilherme Giacomo Simoes"
 <trintaeoitogc@...il.com>, José Expósito
 <jose.exposito89@...il.com>, "Tamir Duberstein" <tamird@...il.com>,
 <rust-for-linux@...r.kernel.org>, "David Gow" <davidgow@...gle.com>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/11] rust: macros: convert `concat_idents!` to use
 `syn`

On Mon, 22 Dec 2025 07:34:24 +0100
"Benno Lossin" <lossin@...nel.org> wrote:

> On Thu Dec 11, 2025 at 7:56 PM CET, Gary Guo wrote:
> > From: Gary Guo <gary@...yguo.net>
> >
> > This eliminates the need for `expect_punct` helper.  
> 
> This commit message could use some more details :)
> 
> > Signed-off-by: Gary Guo <gary@...yguo.net>  
> 
> Reviewed-by: Benno Lossin <lossin@...nel.org>
> 
> > ---
> >  rust/macros/concat_idents.rs | 39 ++++++++++++++++++++++++------------
> >  rust/macros/helpers.rs       | 14 +------------
> >  rust/macros/lib.rs           |  4 ++--
> >  3 files changed, 29 insertions(+), 28 deletions(-)  
> 
> > -pub(crate) fn concat_idents(ts: TokenStream) -> TokenStream {
> > -    let mut it = ts.into_iter();
> > -    let a = expect_ident(&mut it);
> > -    assert_eq!(expect_punct(&mut it), ',');
> > -    let b = expect_ident(&mut it);
> > -    assert!(it.next().is_none(), "only two idents can be concatenated");
> > +pub(crate) fn concat_idents(Input { a, b, .. }: Input) -> TokenStream {
> >      let res = Ident::new(&format!("{a}{b}"), b.span());  
> 
> There is `quote::format_ident!`, which directly returns an identifier,
> but with the span of the first of the two. Not sure if that is better.

All our use cases have a prefix concatenated to a changing identifier,
hence the existing implementation use b's span.

Best,
Gary

> 
> Cheers,
> Benno
> 
> >      TokenStream::from_iter([TokenTree::Ident(res)])
> >  }