linux-kernel - Re: [PATCH 2/3] rust: macros: concat_idents: Allow

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Message-ID: <20230225003156.4858d79e.gary@garyguo.net>
Date:   Sat, 25 Feb 2023 00:31:56 +0000
From:   Gary Guo <gary@...yguo.net>
To:     Asahi Lina <lina@...hilina.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>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        asahi@...ts.linux.dev
Subject: Re: [PATCH 2/3] rust: macros: concat_idents: Allow :: paths in the
 first argument

On Fri, 24 Feb 2023 16:25:56 +0900
Asahi Lina <lina@...hilina.net> wrote:

> This makes things like concat_idents!(bindings::foo, bar) work.
> Otherwise, there is no way to concatenate two idents and then use the
> result as part of a type path.

It seems weird to me that this is called `concat_idents` despite
working for more things than just idents.

How about just implement a simple version of the `paste` macro instead?

Best,
Gary

> 
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> ---
>  rust/macros/concat_idents.rs | 24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/rust/macros/concat_idents.rs b/rust/macros/concat_idents.rs
> index 6d955d65016e..d6614b900aa2 100644
> --- a/rust/macros/concat_idents.rs
> +++ b/rust/macros/concat_idents.rs
> @@ -14,10 +14,28 @@ fn expect_ident(it: &mut token_stream::IntoIter) -> Ident {
>  
>  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).as_char(), ',');
> +    let mut out = TokenStream::new();
> +    let a = loop {
> +        let ident = expect_ident(&mut it);
> +        let punct = expect_punct(&mut it);
> +        match punct.as_char() {
> +            ',' => break ident,
> +            ':' => {
> +                let punct2 = expect_punct(&mut it);
> +                assert_eq!(punct2.as_char(), ':');
> +                out.extend([
> +                    TokenTree::Ident(ident),
> +                    TokenTree::Punct(punct),
> +                    TokenTree::Punct(punct2),
> +                ]);
> +            }
> +            _ => panic!("Expected , or ::"),
> +        }
> +    };
> +
>      let b = expect_ident(&mut it);
>      assert!(it.next().is_none(), "only two idents can be concatenated");
>      let res = Ident::new(&format!("{a}{b}"), b.span());
> -    TokenStream::from_iter([TokenTree::Ident(res)])
> +    out.extend([TokenTree::Ident(res)]);
> +    out
>  }
>