linux/rust/macros/concat_idents.rs
Björn Roy Baron 60f18c225f rust: macros: add concat_idents! proc macro
This macro provides similar functionality to the unstable feature
`concat_idents` without having to rely on it.

For instance:

    let x_1 = 42;
    let x_2 = concat_idents!(x, _1);
    assert!(x_1 == x_2);

It has different behavior with respect to macro hygiene. Unlike
the unstable `concat_idents!` macro, it allows, for example,
referring to local variables by taking the span of the second
macro as span for the output identifier.

Signed-off-by: Björn Roy Baron <bjorn3_gh@protonmail.com>
Reviewed-by: Finn Behrens <me@kloenk.dev>
Reviewed-by: Gary Guo <gary@garyguo.net>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
2022-12-04 01:59:04 +01:00

24 lines
712 B
Rust

// SPDX-License-Identifier: GPL-2.0
use proc_macro::{token_stream, Ident, TokenStream, TokenTree};
use crate::helpers::expect_punct;
fn expect_ident(it: &mut token_stream::IntoIter) -> Ident {
if let Some(TokenTree::Ident(ident)) = it.next() {
ident
} else {
panic!("Expected 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), ',');
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)])
}