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![Björn Roy Baron](/assets/img/avatar_default.png)
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>
23 lines
712 B
Rust
23 lines
712 B
Rust
// SPDX-License-Identifier: GPL-2.0
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use proc_macro::{token_stream, Ident, TokenStream, TokenTree};
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use crate::helpers::expect_punct;
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fn expect_ident(it: &mut token_stream::IntoIter) -> Ident {
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if let Some(TokenTree::Ident(ident)) = it.next() {
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ident
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} else {
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panic!("Expected Ident")
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}
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}
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pub(crate) fn concat_idents(ts: TokenStream) -> TokenStream {
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let mut it = ts.into_iter();
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let a = expect_ident(&mut it);
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assert_eq!(expect_punct(&mut it), ',');
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let b = expect_ident(&mut it);
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assert!(it.next().is_none(), "only two idents can be concatenated");
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let res = Ident::new(&format!("{a}{b}"), b.span());
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TokenStream::from_iter([TokenTree::Ident(res)])
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}
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