Re: [PATCH 07/11] rust: macros: convert `concat_idents!` to use `syn`

[Gary Guo]

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

> On Thu Dec 11, 2025 at 7:56 PM CET, Gary Guo wrote:
> > From: Gary Guo <gary@xxxxxxxxxxx>
> >
> > This eliminates the need for `expect_punct` helper.  
> 
> This commit message could use some more details :)
> 
> > Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>  
> 
> Reviewed-by: Benno Lossin <lossin@xxxxxxxxxx>
> 
> > ---
> >  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)])
> >  }