1// SPDX-License-Identifier: GPL-2.0 2 3use proc_macro::{Delimiter, Group, Ident, Spacing, Span, TokenTree}; 4 5fn concat(tokens: &[TokenTree], group_span: Span) -> TokenTree { 6 let mut tokens = tokens.iter(); 7 let mut segments = Vec::new(); 8 let mut span = None; 9 loop { 10 match tokens.next() { 11 None => break, 12 Some(TokenTree::Literal(lit)) => segments.push((lit.to_string(), lit.span())), 13 Some(TokenTree::Ident(ident)) => { 14 let mut value = ident.to_string(); 15 if value.starts_with("r#") { 16 value.replace_range(0..2, ""); 17 } 18 segments.push((value, ident.span())); 19 } 20 Some(TokenTree::Punct(p)) if p.as_char() == ':' => { 21 let Some(TokenTree::Ident(ident)) = tokens.next() else { 22 panic!("expected identifier as modifier"); 23 }; 24 25 let (mut value, sp) = segments.pop().expect("expected identifier before modifier"); 26 match ident.to_string().as_str() { 27 // Set the overall span of concatenated token as current span 28 "span" => { 29 assert!( 30 span.is_none(), 31 "span modifier should only appear at most once" 32 ); 33 span = Some(sp); 34 } 35 "lower" => value = value.to_lowercase(), 36 "upper" => value = value.to_uppercase(), 37 v => panic!("unknown modifier `{v}`"), 38 }; 39 segments.push((value, sp)); 40 } 41 _ => panic!("unexpected token in paste segments"), 42 }; 43 } 44 45 let pasted: String = segments.into_iter().map(|x| x.0).collect(); 46 TokenTree::Ident(Ident::new(&pasted, span.unwrap_or(group_span))) 47} 48 49pub(crate) fn expand(tokens: &mut Vec<TokenTree>) { 50 for token in tokens.iter_mut() { 51 if let TokenTree::Group(group) = token { 52 let delimiter = group.delimiter(); 53 let span = group.span(); 54 let mut stream: Vec<_> = group.stream().into_iter().collect(); 55 // Find groups that looks like `[< A B C D >]` 56 if delimiter == Delimiter::Bracket 57 && stream.len() >= 3 58 && matches!(&stream[0], TokenTree::Punct(p) if p.as_char() == '<') 59 && matches!(&stream[stream.len() - 1], TokenTree::Punct(p) if p.as_char() == '>') 60 { 61 // Replace the group with concatenated token 62 *token = concat(&stream[1..stream.len() - 1], span); 63 } else { 64 // Recursively expand tokens inside the group 65 expand(&mut stream); 66 let mut group = Group::new(delimiter, stream.into_iter().collect()); 67 group.set_span(span); 68 *token = TokenTree::Group(group); 69 } 70 } 71 } 72 73 // Path segments cannot contain invisible delimiter group, so remove them if any. 74 for i in (0..tokens.len().saturating_sub(3)).rev() { 75 // Looking for a double colon 76 if matches!( 77 (&tokens[i + 1], &tokens[i + 2]), 78 (TokenTree::Punct(a), TokenTree::Punct(b)) 79 if a.as_char() == ':' && a.spacing() == Spacing::Joint && b.as_char() == ':' 80 ) { 81 match &tokens[i + 3] { 82 TokenTree::Group(group) if group.delimiter() == Delimiter::None => { 83 tokens.splice(i + 3..i + 4, group.stream()); 84 } 85 _ => (), 86 } 87 88 match &tokens[i] { 89 TokenTree::Group(group) if group.delimiter() == Delimiter::None => { 90 tokens.splice(i..i + 1, group.stream()); 91 } 92 _ => (), 93 } 94 } 95 } 96} 97