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