macros/
paste.rs

1// SPDX-License-Identifier: GPL-2.0
2
3use proc_macro::{Delimiter, Group, Ident, Spacing, Span, TokenTree};
4
5fn concat_helper(tokens: &[TokenTree]) -> Vec<(String, Span)> {
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)) => {
13                // Allow us to concat string literals by stripping quotes
14                let mut value = lit.to_string();
15                if value.starts_with('"') && value.ends_with('"') {
16                    value.remove(0);
17                    value.pop();
18                }
19                segments.push((value, lit.span()));
20            }
21            Some(TokenTree::Ident(ident)) => {
22                let mut value = ident.to_string();
23                if value.starts_with("r#") {
24                    value.replace_range(0..2, "");
25                }
26                segments.push((value, ident.span()));
27            }
28            Some(TokenTree::Punct(p)) if p.as_char() == ':' => {
29                let Some(TokenTree::Ident(ident)) = tokens.next() else {
30                    panic!("expected identifier as modifier");
31                };
32
33                let (mut value, sp) = segments.pop().expect("expected identifier before modifier");
34                match ident.to_string().as_str() {
35                    // Set the overall span of concatenated token as current span
36                    "span" => {
37                        assert!(
38                            span.is_none(),
39                            "span modifier should only appear at most once"
40                        );
41                        span = Some(sp);
42                    }
43                    "lower" => value = value.to_lowercase(),
44                    "upper" => value = value.to_uppercase(),
45                    v => panic!("unknown modifier `{v}`"),
46                };
47                segments.push((value, sp));
48            }
49            Some(TokenTree::Group(group)) if group.delimiter() == Delimiter::None => {
50                let tokens = group.stream().into_iter().collect::<Vec<TokenTree>>();
51                segments.append(&mut concat_helper(tokens.as_slice()));
52            }
53            token => panic!("unexpected token in paste segments: {:?}", token),
54        };
55    }
56
57    segments
58}
59
60fn concat(tokens: &[TokenTree], group_span: Span) -> TokenTree {
61    let segments = concat_helper(tokens);
62    let pasted: String = segments.into_iter().map(|x| x.0).collect();
63    TokenTree::Ident(Ident::new(&pasted, group_span))
64}
65
66pub(crate) fn expand(tokens: &mut Vec<TokenTree>) {
67    for token in tokens.iter_mut() {
68        if let TokenTree::Group(group) = token {
69            let delimiter = group.delimiter();
70            let span = group.span();
71            let mut stream: Vec<_> = group.stream().into_iter().collect();
72            // Find groups that looks like `[< A B C D >]`
73            if delimiter == Delimiter::Bracket
74                && stream.len() >= 3
75                && matches!(&stream[0], TokenTree::Punct(p) if p.as_char() == '<')
76                && matches!(&stream[stream.len() - 1], TokenTree::Punct(p) if p.as_char() == '>')
77            {
78                // Replace the group with concatenated token
79                *token = concat(&stream[1..stream.len() - 1], span);
80            } else {
81                // Recursively expand tokens inside the group
82                expand(&mut stream);
83                let mut group = Group::new(delimiter, stream.into_iter().collect());
84                group.set_span(span);
85                *token = TokenTree::Group(group);
86            }
87        }
88    }
89
90    // Path segments cannot contain invisible delimiter group, so remove them if any.
91    for i in (0..tokens.len().saturating_sub(3)).rev() {
92        // Looking for a double colon
93        if matches!(
94            (&tokens[i + 1], &tokens[i + 2]),
95            (TokenTree::Punct(a), TokenTree::Punct(b))
96                if a.as_char() == ':' && a.spacing() == Spacing::Joint && b.as_char() == ':'
97        ) {
98            match &tokens[i + 3] {
99                TokenTree::Group(group) if group.delimiter() == Delimiter::None => {
100                    tokens.splice(i + 3..i + 4, group.stream());
101                }
102                _ => (),
103            }
104
105            match &tokens[i] {
106                TokenTree::Group(group) if group.delimiter() == Delimiter::None => {
107                    tokens.splice(i..i + 1, group.stream());
108                }
109                _ => (),
110            }
111        }
112    }
113}
macros/paste.rs

macros/
paste.rs
