tt/
buffer.rs

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1//! Stateful iteration over token trees.
2//!
3//! We use this as the source of tokens for parser.
4use crate::{Leaf, Subtree, TokenTree, TokenTreesView};
5
6pub struct Cursor<'a, Span> {
7    buffer: &'a [TokenTree<Span>],
8    index: usize,
9    subtrees_stack: Vec<usize>,
10}
11
12impl<'a, Span: Copy> Cursor<'a, Span> {
13    pub fn new(buffer: &'a [TokenTree<Span>]) -> Self {
14        Self { buffer, index: 0, subtrees_stack: Vec::new() }
15    }
16
17    /// Check whether it is eof
18    pub fn eof(&self) -> bool {
19        self.index == self.buffer.len() && self.subtrees_stack.is_empty()
20    }
21
22    pub fn is_root(&self) -> bool {
23        self.subtrees_stack.is_empty()
24    }
25
26    fn last_subtree(&self) -> Option<(usize, &'a Subtree<Span>)> {
27        self.subtrees_stack.last().map(|&subtree_idx| {
28            let TokenTree::Subtree(subtree) = &self.buffer[subtree_idx] else {
29                panic!("subtree pointing to non-subtree");
30            };
31            (subtree_idx, subtree)
32        })
33    }
34
35    pub fn end(&mut self) -> &'a Subtree<Span> {
36        let (last_subtree_idx, last_subtree) =
37            self.last_subtree().expect("called `Cursor::end()` without an open subtree");
38        // +1 because `Subtree.len` excludes the subtree itself.
39        assert_eq!(
40            last_subtree_idx + last_subtree.usize_len() + 1,
41            self.index,
42            "called `Cursor::end()` without finishing a subtree"
43        );
44        self.subtrees_stack.pop();
45        last_subtree
46    }
47
48    /// Returns the `TokenTree` at the cursor if it is not at the end of a subtree.
49    pub fn token_tree(&self) -> Option<&'a TokenTree<Span>> {
50        if let Some((last_subtree_idx, last_subtree)) = self.last_subtree() {
51            // +1 because `Subtree.len` excludes the subtree itself.
52            if last_subtree_idx + last_subtree.usize_len() + 1 == self.index {
53                return None;
54            }
55        }
56        self.buffer.get(self.index)
57    }
58
59    /// Bump the cursor, and enters a subtree if it is on one.
60    pub fn bump(&mut self) {
61        if let Some((last_subtree_idx, last_subtree)) = self.last_subtree() {
62            // +1 because `Subtree.len` excludes the subtree itself.
63            assert_ne!(
64                last_subtree_idx + last_subtree.usize_len() + 1,
65                self.index,
66                "called `Cursor::bump()` when at the end of a subtree"
67            );
68        }
69        if let TokenTree::Subtree(_) = self.buffer[self.index] {
70            self.subtrees_stack.push(self.index);
71        }
72        self.index += 1;
73    }
74
75    pub fn bump_or_end(&mut self) {
76        if let Some((last_subtree_idx, last_subtree)) = self.last_subtree() {
77            // +1 because `Subtree.len` excludes the subtree itself.
78            if last_subtree_idx + last_subtree.usize_len() + 1 == self.index {
79                self.subtrees_stack.pop();
80                return;
81            }
82        }
83        // +1 because `Subtree.len` excludes the subtree itself.
84        if let TokenTree::Subtree(_) = self.buffer[self.index] {
85            self.subtrees_stack.push(self.index);
86        }
87        self.index += 1;
88    }
89
90    pub fn peek_two_leaves(&self) -> Option<[&'a Leaf<Span>; 2]> {
91        if let Some((last_subtree_idx, last_subtree)) = self.last_subtree() {
92            // +1 because `Subtree.len` excludes the subtree itself.
93            let last_end = last_subtree_idx + last_subtree.usize_len() + 1;
94            if last_end == self.index || last_end == self.index + 1 {
95                return None;
96            }
97        }
98        self.buffer.get(self.index..self.index + 2).and_then(|it| match it {
99            [TokenTree::Leaf(a), TokenTree::Leaf(b)] => Some([a, b]),
100            _ => None,
101        })
102    }
103
104    pub fn crossed(&self) -> TokenTreesView<'a, Span> {
105        assert!(self.is_root());
106        TokenTreesView::new(&self.buffer[..self.index])
107    }
108}
tt/buffer.rs

tt/
buffer.rs
