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
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
|
//! This module provides a way to construct a `File`.
//! It is intended to be completely decoupled from the
//! parser, so as to allow to evolve the tree representation
//! and the parser algorithm independently.
//!
//! The `TreeSink` trait is the bridge between the parser and the
//! tree builder: the parser produces a stream of events like
//! `start node`, `finish node`, and `FileBuilder` converts
//! this stream to a real tree.
use std::mem;
use crate::{
output::Output,
SyntaxKind::{self, *},
};
/// `Parser` produces a flat list of `Event`s.
/// They are converted to a tree-structure in
/// a separate pass, via `TreeBuilder`.
#[derive(Debug)]
pub(crate) enum Event {
/// This event signifies the start of the node.
/// It should be either abandoned (in which case the
/// `kind` is `TOMBSTONE`, and the event is ignored),
/// or completed via a `Finish` event.
///
/// All tokens between a `Start` and a `Finish` would
/// become the children of the respective node.
///
/// For left-recursive syntactic constructs, the parser produces
/// a child node before it sees a parent. `forward_parent`
/// saves the position of current event's parent.
///
/// Consider this path
///
/// foo::bar
///
/// The events for it would look like this:
///
/// ```text
/// START(PATH) IDENT('foo') FINISH START(PATH) T![::] IDENT('bar') FINISH
/// | /\
/// | |
/// +------forward-parent------+
/// ```
///
/// And the tree would look like this
///
/// ```text
/// +--PATH---------+
/// | | |
/// | | |
/// | '::' 'bar'
/// |
/// PATH
/// |
/// 'foo'
/// ```
///
/// See also `CompletedMarker::precede`.
Start {
kind: SyntaxKind,
forward_parent: Option<u32>,
},
/// Complete the previous `Start` event
Finish,
/// Produce a single leaf-element.
/// `n_raw_tokens` is used to glue complex contextual tokens.
/// For example, lexer tokenizes `>>` as `>`, `>`, and
/// `n_raw_tokens = 2` is used to produced a single `>>`.
Token {
kind: SyntaxKind,
n_raw_tokens: u8,
},
/// When we parse `foo.0.0` or `foo. 0. 0` the lexer will hand us a float literal
/// instead of an integer literal followed by a dot as the lexer has no contextual knowledge.
/// This event instructs whatever consumes the events to split the float literal into
/// the corresponding parts.
FloatSplitHack {
ends_in_dot: bool,
},
Error {
msg: String,
},
}
impl Event {
pub(crate) fn tombstone() -> Self {
Event::Start { kind: TOMBSTONE, forward_parent: None }
}
}
/// Generate the syntax tree with the control of events.
pub(super) fn process(mut events: Vec<Event>) -> Output {
let mut res = Output::default();
let mut forward_parents = Vec::new();
for i in 0..events.len() {
match mem::replace(&mut events[i], Event::tombstone()) {
Event::Start { kind, forward_parent } => {
// For events[A, B, C], B is A's forward_parent, C is B's forward_parent,
// in the normal control flow, the parent-child relation: `A -> B -> C`,
// while with the magic forward_parent, it writes: `C <- B <- A`.
// append `A` into parents.
forward_parents.push(kind);
let mut idx = i;
let mut fp = forward_parent;
while let Some(fwd) = fp {
idx += fwd as usize;
// append `A`'s forward_parent `B`
fp = match mem::replace(&mut events[idx], Event::tombstone()) {
Event::Start { kind, forward_parent } => {
forward_parents.push(kind);
forward_parent
}
_ => unreachable!(),
};
// append `B`'s forward_parent `C` in the next stage.
}
for kind in forward_parents.drain(..).rev() {
if kind != TOMBSTONE {
res.enter_node(kind);
}
}
}
Event::Finish => res.leave_node(),
Event::Token { kind, n_raw_tokens } => {
res.token(kind, n_raw_tokens);
}
Event::FloatSplitHack { ends_in_dot } => {
res.float_split_hack(ends_in_dot);
let ev = mem::replace(&mut events[i + 1], Event::tombstone());
assert!(matches!(ev, Event::Finish), "{ev:?}");
}
Event::Error { msg } => res.error(msg),
}
}
res
}
|
