/
mod.rs
215 lines (200 loc) · 6.79 KB
/
mod.rs
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
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
use crate::ty::context::TyCtxt;
use crate::ty::{AdtDef, VariantDef, FieldDef, Ty, TyS};
use crate::ty::{DefId, SubstsRef};
use crate::ty::{AdtKind, Visibility};
use crate::ty::TyKind::*;
pub use self::def_id_forest::DefIdForest;
mod def_id_forest;
// The methods in this module calculate DefIdForests of modules in which a
// AdtDef/VariantDef/FieldDef is visibly uninhabited.
//
// # Example
// ```rust
// enum Void {}
// mod a {
// pub mod b {
// pub struct SecretlyUninhabited {
// _priv: !,
// }
// }
// }
//
// mod c {
// pub struct AlsoSecretlyUninhabited {
// _priv: Void,
// }
// mod d {
// }
// }
//
// struct Foo {
// x: a::b::SecretlyUninhabited,
// y: c::AlsoSecretlyUninhabited,
// }
// ```
// In this code, the type Foo will only be visibly uninhabited inside the
// modules b, c and d. Calling uninhabited_from on Foo or its AdtDef will
// return the forest of modules {b, c->d} (represented in a DefIdForest by the
// set {b, c})
//
// We need this information for pattern-matching on Foo or types that contain
// Foo.
//
// # Example
// ```rust
// let foo_result: Result<T, Foo> = ... ;
// let Ok(t) = foo_result;
// ```
// This code should only compile in modules where the uninhabitedness of Foo is
// visible.
impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
/// Checks whether a type is visibly uninhabited from a particular module.
/// # Example
/// ```rust
/// enum Void {}
/// mod a {
/// pub mod b {
/// pub struct SecretlyUninhabited {
/// _priv: !,
/// }
/// }
/// }
///
/// mod c {
/// pub struct AlsoSecretlyUninhabited {
/// _priv: Void,
/// }
/// mod d {
/// }
/// }
///
/// struct Foo {
/// x: a::b::SecretlyUninhabited,
/// y: c::AlsoSecretlyUninhabited,
/// }
/// ```
/// In this code, the type `Foo` will only be visibly uninhabited inside the
/// modules b, c and d. This effects pattern-matching on `Foo` or types that
/// contain `Foo`.
///
/// # Example
/// ```rust
/// let foo_result: Result<T, Foo> = ... ;
/// let Ok(t) = foo_result;
/// ```
/// This code should only compile in modules where the uninhabitedness of Foo is
/// visible.
pub fn is_ty_uninhabited_from(self, module: DefId, ty: Ty<'tcx>) -> bool {
// To check whether this type is uninhabited at all (not just from the
// given node) you could check whether the forest is empty.
// ```
// forest.is_empty()
// ```
self.ty_inhabitedness_forest(ty).contains(self, module)
}
pub fn is_ty_uninhabited_from_all_modules(self, ty: Ty<'tcx>) -> bool {
!self.ty_inhabitedness_forest(ty).is_empty()
}
fn ty_inhabitedness_forest(self, ty: Ty<'tcx>) -> DefIdForest {
ty.uninhabited_from(self)
}
}
impl<'a, 'gcx, 'tcx> AdtDef {
/// Calculate the forest of DefIds from which this adt is visibly uninhabited.
fn uninhabited_from(
&self,
tcx: TyCtxt<'a, 'gcx, 'tcx>,
substs: SubstsRef<'tcx>) -> DefIdForest
{
// Non-exhaustive ADTs from other crates are always considered inhabited.
if self.is_variant_list_non_exhaustive() && !self.did.is_local() {
DefIdForest::empty()
} else {
DefIdForest::intersection(tcx, self.variants.iter().map(|v| {
v.uninhabited_from(tcx, substs, self.adt_kind())
}))
}
}
}
impl<'a, 'gcx, 'tcx> VariantDef {
/// Calculate the forest of DefIds from which this variant is visibly uninhabited.
pub fn uninhabited_from(
&self,
tcx: TyCtxt<'a, 'gcx, 'tcx>,
substs: SubstsRef<'tcx>,
adt_kind: AdtKind) -> DefIdForest
{
let is_enum = match adt_kind {
// For now, `union`s are never considered uninhabited.
// The precise semantics of inhabitedness with respect to unions is currently undecided.
AdtKind::Union => return DefIdForest::empty(),
AdtKind::Enum => true,
AdtKind::Struct => false,
};
// Non-exhaustive variants from other crates are always considered inhabited.
if self.is_field_list_non_exhaustive() && !self.def_id.is_local() {
DefIdForest::empty()
} else {
DefIdForest::union(tcx, self.fields.iter().map(|f| {
f.uninhabited_from(tcx, substs, is_enum)
}))
}
}
}
impl<'a, 'gcx, 'tcx> FieldDef {
/// Calculate the forest of DefIds from which this field is visibly uninhabited.
fn uninhabited_from(
&self,
tcx: TyCtxt<'a, 'gcx, 'tcx>,
substs: SubstsRef<'tcx>,
is_enum: bool,
) -> DefIdForest {
let data_uninhabitedness = move || {
self.ty(tcx, substs).uninhabited_from(tcx)
};
// FIXME(canndrew): Currently enum fields are (incorrectly) stored with
// Visibility::Invisible so we need to override self.vis if we're
// dealing with an enum.
if is_enum {
data_uninhabitedness()
} else {
match self.vis {
Visibility::Invisible => DefIdForest::empty(),
Visibility::Restricted(from) => {
let forest = DefIdForest::from_id(from);
let iter = Some(forest).into_iter().chain(Some(data_uninhabitedness()));
DefIdForest::intersection(tcx, iter)
},
Visibility::Public => data_uninhabitedness(),
}
}
}
}
impl<'a, 'gcx, 'tcx> TyS<'tcx> {
/// Calculate the forest of DefIds from which this type is visibly uninhabited.
fn uninhabited_from(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> DefIdForest
{
match self.sty {
Adt(def, substs) => def.uninhabited_from(tcx, substs),
Never => DefIdForest::full(tcx),
Tuple(ref tys) => {
DefIdForest::union(tcx, tys.iter().map(|ty| {
ty.expect_ty().uninhabited_from(tcx)
}))
}
Array(ty, len) => match len.assert_usize(tcx) {
// If the array is definitely non-empty, it's uninhabited if
// the type of its elements is uninhabited.
Some(n) if n != 0 => ty.uninhabited_from(tcx),
_ => DefIdForest::empty()
},
// References to uninitialised memory is valid for any type, including
// uninhabited types, in unsafe code, so we treat all references as
// inhabited.
// The precise semantics of inhabitedness with respect to references is currently
// undecided.
Ref(..) => DefIdForest::empty(),
_ => DefIdForest::empty(),
}
}
}