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
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
|
/// This module takes a (parsed) defenition of `macro_rules` invocation, a
/// `tt::TokenTree` representing an argument of macro invocation, and produces a
/// `tt::TokenTree` for the result of the expansion.
use rustc_hash::FxHashMap;
use ra_syntax::SmolStr;
use crate::tt_cursor::TtCursor;
pub(crate) fn exapnd(rules: &crate::MacroRules, input: &tt::Subtree) -> Option<tt::Subtree> {
rules.rules.iter().find_map(|it| expand_rule(it, input))
}
fn expand_rule(rule: &crate::Rule, input: &tt::Subtree) -> Option<tt::Subtree> {
let mut input = TtCursor::new(input);
let bindings = match_lhs(&rule.lhs, &mut input)?;
expand_subtree(&rule.rhs, &bindings, &mut Vec::new())
}
/// The actual algorithm for expansion is not too hard, but is pretty tricky.
/// `Bindings` structure is the key to understanding what we are doing here.
///
/// On the high level, it stores mapping from meta variables to the bits of
/// syntax it should be substituted with. For example, if `$e:expr` is matched
/// with `1 + 1` by macro_rules, the `Binding` will store `$e -> 1 + 1`.
///
/// The tricky bit is dealing with repetitions (`$()*`). Consider this example:
///
/// ```ignore
/// macro_rules! foo {
/// ($($ i:ident $($ e:expr),*);*) => {
/// $(fn $ i() { $($ e);*; })*
/// }
/// }
/// foo! { foo 1,2,3; bar 4,5,6 }
/// ```
///
/// Here, the `$i` meta variable is matched first with `foo` and then with
/// `bar`, and `$e` is matched in turn with `1`, `2`, `3`, `4`, `5`, `6`.
///
/// To represent such "multi-mappings", we use a recursive structures: we map
/// variables not to values, but to *lists* of values or other lists (that is,
/// to the trees).
///
/// For the above example, the bindings would store
///
/// ```ignore
/// i -> [foo, bar]
/// e -> [[1, 2, 3], [4, 5, 6]]
/// ```
///
/// We construct `Bindings` in the `match_lhs`. The interesting case is
/// `TokenTree::Repeat`, where we use `push_nested` to create the desired
/// nesting structure.
///
/// The other side of the puzzle is `expand_subtree`, where we use the bindings
/// to substitute meta variables in the output template. When expanding, we
/// maintain a `nesteing` stack of indicies whihc tells us which occurence from
/// the `Bindings` we should take. We push to the stack when we enter a
/// repetition.
///
/// In other words, `Bindings` is a *multi* mapping from `SmolStr` to
/// `tt::TokenTree`, where the index to select a particular `TokenTree` among
/// many is not a plain `usize`, but an `&[usize]`.
#[derive(Debug, Default)]
struct Bindings {
inner: FxHashMap<SmolStr, Binding>,
}
#[derive(Debug)]
enum Binding {
Simple(tt::TokenTree),
Nested(Vec<Binding>),
}
impl Bindings {
fn get(&self, name: &SmolStr, nesting: &[usize]) -> Option<&tt::TokenTree> {
let mut b = self.inner.get(name)?;
for &idx in nesting.iter() {
b = match b {
Binding::Simple(_) => break,
Binding::Nested(bs) => bs.get(idx)?,
};
}
match b {
Binding::Simple(it) => Some(it),
Binding::Nested(_) => None,
}
}
fn push_nested(&mut self, nested: Bindings) -> Option<()> {
for (key, value) in nested.inner {
if !self.inner.contains_key(&key) {
self.inner.insert(key.clone(), Binding::Nested(Vec::new()));
}
match self.inner.get_mut(&key) {
Some(Binding::Nested(it)) => it.push(value),
_ => return None,
}
}
Some(())
}
}
fn match_lhs(pattern: &crate::Subtree, input: &mut TtCursor) -> Option<Bindings> {
let mut res = Bindings::default();
for pat in pattern.token_trees.iter() {
match pat {
crate::TokenTree::Leaf(leaf) => match leaf {
crate::Leaf::Var(crate::Var { text, kind }) => {
let kind = kind.clone()?;
match kind.as_str() {
"ident" => {
let ident = input.eat_ident()?.clone();
res.inner.insert(
text.clone(),
Binding::Simple(tt::Leaf::from(ident).into()),
);
}
_ => return None,
}
}
crate::Leaf::Punct(punct) => {
if input.eat_punct()? != punct {
return None;
}
}
_ => return None,
},
crate::TokenTree::Repeat(crate::Repeat {
subtree,
kind: _,
separator,
}) => {
while let Some(nested) = match_lhs(subtree, input) {
res.push_nested(nested)?;
if separator.is_some() && !input.is_eof() {
input.eat_punct()?;
}
}
}
_ => {}
}
}
Some(res)
}
fn expand_subtree(
template: &crate::Subtree,
bindings: &Bindings,
nesting: &mut Vec<usize>,
) -> Option<tt::Subtree> {
let token_trees = template
.token_trees
.iter()
.map(|it| expand_tt(it, bindings, nesting))
.collect::<Option<Vec<_>>>()?;
Some(tt::Subtree {
token_trees,
delimiter: template.delimiter,
})
}
fn expand_tt(
template: &crate::TokenTree,
bindings: &Bindings,
nesting: &mut Vec<usize>,
) -> Option<tt::TokenTree> {
let res: tt::TokenTree = match template {
crate::TokenTree::Subtree(subtree) => expand_subtree(subtree, bindings, nesting)?.into(),
crate::TokenTree::Repeat(repeat) => {
let mut token_trees = Vec::new();
nesting.push(0);
while let Some(t) = expand_subtree(&repeat.subtree, bindings, nesting) {
let idx = nesting.pop().unwrap();
nesting.push(idx + 1);
token_trees.push(t.into())
}
nesting.pop().unwrap();
tt::Subtree {
token_trees,
delimiter: tt::Delimiter::None,
}
.into()
}
crate::TokenTree::Leaf(leaf) => match leaf {
crate::Leaf::Ident(ident) => tt::Leaf::from(tt::Ident {
text: ident.text.clone(),
})
.into(),
crate::Leaf::Punct(punct) => tt::Leaf::from(punct.clone()).into(),
crate::Leaf::Var(v) => bindings.get(&v.text, nesting)?.clone(),
crate::Leaf::Literal(l) => tt::Leaf::from(tt::Literal {
text: l.text.clone(),
})
.into(),
},
};
Some(res)
}
|
