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
|
//! As explained in [`crate::usefulness`], values and patterns are made from constructors applied to
//! fields. This file defines types that represent patterns in this way.
use std::cell::Cell;
use std::fmt;
use smallvec::{smallvec, SmallVec};
use crate::constructor::{Constructor, Slice, SliceKind};
use crate::usefulness::PlaceCtxt;
use crate::{Captures, TypeCx};
use self::Constructor::*;
/// Values and patterns can be represented as a constructor applied to some fields. This represents
/// a pattern in this form.
/// This also uses interior mutability to keep track of whether the pattern has been found reachable
/// during analysis. For this reason they cannot be cloned.
/// A `DeconstructedPat` will almost always come from user input; the only exception are some
/// `Wildcard`s introduced during specialization.
///
/// Note that the number of fields may not match the fields declared in the original struct/variant.
/// This happens if a private or `non_exhaustive` field is uninhabited, because the code mustn't
/// observe that it is uninhabited. In that case that field is not included in `fields`. Care must
/// be taken when converting to/from `thir::Pat`.
pub struct DeconstructedPat<'p, Cx: TypeCx> {
ctor: Constructor<Cx>,
fields: &'p [DeconstructedPat<'p, Cx>],
ty: Cx::Ty,
data: Cx::PatData,
/// Whether removing this arm would change the behavior of the match expression.
useful: Cell<bool>,
}
impl<'p, Cx: TypeCx> DeconstructedPat<'p, Cx> {
pub fn wildcard(ty: Cx::Ty, data: Cx::PatData) -> Self {
Self::new(Wildcard, &[], ty, data)
}
pub fn new(
ctor: Constructor<Cx>,
fields: &'p [DeconstructedPat<'p, Cx>],
ty: Cx::Ty,
data: Cx::PatData,
) -> Self {
DeconstructedPat { ctor, fields, ty, data, useful: Cell::new(false) }
}
pub(crate) fn is_or_pat(&self) -> bool {
matches!(self.ctor, Or)
}
/// Expand this (possibly-nested) or-pattern into its alternatives.
pub(crate) fn flatten_or_pat(&self) -> SmallVec<[&Self; 1]> {
if self.is_or_pat() {
self.iter_fields().flat_map(|p| p.flatten_or_pat()).collect()
} else {
smallvec![self]
}
}
pub fn ctor(&self) -> &Constructor<Cx> {
&self.ctor
}
pub fn ty(&self) -> Cx::Ty {
self.ty
}
pub fn data(&self) -> &Cx::PatData {
&self.data
}
pub fn iter_fields<'a>(
&'a self,
) -> impl Iterator<Item = &'p DeconstructedPat<'p, Cx>> + Captures<'a> {
self.fields.iter()
}
/// Specialize this pattern with a constructor.
/// `other_ctor` can be different from `self.ctor`, but must be covered by it.
pub(crate) fn specialize<'a>(
&self,
pcx: &PlaceCtxt<'a, 'p, Cx>,
other_ctor: &Constructor<Cx>,
) -> SmallVec<[&'a DeconstructedPat<'p, Cx>; 2]> {
let wildcard_sub_tys = || {
let tys = pcx.ctor_sub_tys(other_ctor);
tys.iter()
.map(|ty| DeconstructedPat::wildcard(*ty, Cx::PatData::default()))
.map(|pat| pcx.mcx.wildcard_arena.alloc(pat) as &_)
.collect()
};
match (&self.ctor, other_ctor) {
// Return a wildcard for each field of `other_ctor`.
(Wildcard, _) => wildcard_sub_tys(),
// The only non-trivial case: two slices of different arity. `other_slice` is
// guaranteed to have a larger arity, so we fill the middle part with enough
// wildcards to reach the length of the new, larger slice.
(
&Slice(self_slice @ Slice { kind: SliceKind::VarLen(prefix, suffix), .. }),
&Slice(other_slice),
) if self_slice.arity() != other_slice.arity() => {
// Start with a slice of wildcards of the appropriate length.
let mut fields: SmallVec<[_; 2]> = wildcard_sub_tys();
// Fill in the fields from both ends.
let new_arity = fields.len();
for i in 0..prefix {
fields[i] = &self.fields[i];
}
for i in 0..suffix {
fields[new_arity - 1 - i] = &self.fields[self.fields.len() - 1 - i];
}
fields
}
_ => self.fields.iter().collect(),
}
}
/// We keep track for each pattern if it was ever useful during the analysis. This is used with
/// `redundant_subpatterns` to report redundant subpatterns arising from or patterns.
pub(crate) fn set_useful(&self) {
self.useful.set(true)
}
pub(crate) fn is_useful(&self) -> bool {
if self.useful.get() {
true
} else if self.is_or_pat() && self.iter_fields().any(|f| f.is_useful()) {
// We always expand or patterns in the matrix, so we will never see the actual
// or-pattern (the one with constructor `Or`) in the column. As such, it will not be
// marked as useful itself, only its children will. We recover this information here.
self.set_useful();
true
} else {
false
}
}
/// Report the subpatterns that were not useful, if any.
pub(crate) fn redundant_subpatterns(&self) -> Vec<&Self> {
let mut subpats = Vec::new();
self.collect_redundant_subpatterns(&mut subpats);
subpats
}
fn collect_redundant_subpatterns<'a>(&'a self, subpats: &mut Vec<&'a Self>) {
// We don't look at subpatterns if we already reported the whole pattern as redundant.
if !self.is_useful() {
subpats.push(self);
} else {
for p in self.iter_fields() {
p.collect_redundant_subpatterns(subpats);
}
}
}
}
/// This is mostly copied from the `Pat` impl. This is best effort and not good enough for a
/// `Display` impl.
impl<'p, Cx: TypeCx> fmt::Debug for DeconstructedPat<'p, Cx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
Cx::debug_pat(f, self)
}
}
/// Same idea as `DeconstructedPat`, except this is a fictitious pattern built up for diagnostics
/// purposes. As such they don't use interning and can be cloned.
#[derive(Debug, Clone)]
pub struct WitnessPat<Cx: TypeCx> {
ctor: Constructor<Cx>,
pub(crate) fields: Vec<WitnessPat<Cx>>,
ty: Cx::Ty,
}
impl<Cx: TypeCx> WitnessPat<Cx> {
pub(crate) fn new(ctor: Constructor<Cx>, fields: Vec<Self>, ty: Cx::Ty) -> Self {
Self { ctor, fields, ty }
}
pub(crate) fn wildcard(ty: Cx::Ty) -> Self {
Self::new(Wildcard, Vec::new(), ty)
}
/// Construct a pattern that matches everything that starts with this constructor.
/// For example, if `ctor` is a `Constructor::Variant` for `Option::Some`, we get the pattern
/// `Some(_)`.
pub(crate) fn wild_from_ctor(pcx: &PlaceCtxt<'_, '_, Cx>, ctor: Constructor<Cx>) -> Self {
let field_tys = pcx.ctor_sub_tys(&ctor);
let fields = field_tys.iter().map(|ty| Self::wildcard(*ty)).collect();
Self::new(ctor, fields, pcx.ty)
}
pub fn ctor(&self) -> &Constructor<Cx> {
&self.ctor
}
pub fn ty(&self) -> Cx::Ty {
self.ty
}
pub fn iter_fields<'a>(&'a self) -> impl Iterator<Item = &'a WitnessPat<Cx>> {
self.fields.iter()
}
}
|
