1 pub use self::def_id_forest::DefIdForest;
4 use crate::ty::context::TyCtxt;
5 use crate::ty::TyKind::*;
6 use crate::ty::{AdtDef, FieldDef, Ty, TyS, VariantDef};
7 use crate::ty::{AdtKind, Visibility};
8 use crate::ty::{DefId, SubstsRef};
9 use rustc_data_structures::stack::ensure_sufficient_stack;
13 // The methods in this module calculate `DefIdForest`s of modules in which a
14 // `AdtDef`/`VariantDef`/`FieldDef` is visibly uninhabited.
21 // pub struct SecretlyUninhabited {
28 // pub struct AlsoSecretlyUninhabited {
36 // x: a::b::SecretlyUninhabited,
37 // y: c::AlsoSecretlyUninhabited,
40 // In this code, the type `Foo` will only be visibly uninhabited inside the
41 // modules `b`, `c` and `d`. Calling `uninhabited_from` on `Foo` or its `AdtDef` will
42 // return the forest of modules {`b`, `c`->`d`} (represented in a `DefIdForest` by the
45 // We need this information for pattern-matching on `Foo` or types that contain
50 // let foo_result: Result<T, Foo> = ... ;
51 // let Ok(t) = foo_result;
53 // This code should only compile in modules where the uninhabitedness of `Foo` is
56 impl<'tcx> TyCtxt<'tcx> {
57 /// Checks whether a type is visibly uninhabited from a particular module.
64 /// pub struct SecretlyUninhabited {
71 /// pub struct AlsoSecretlyUninhabited {
79 /// x: a::b::SecretlyUninhabited,
80 /// y: c::AlsoSecretlyUninhabited,
83 /// In this code, the type `Foo` will only be visibly uninhabited inside the
84 /// modules b, c and d. This effects pattern-matching on `Foo` or types that
89 /// let foo_result: Result<T, Foo> = ... ;
90 /// let Ok(t) = foo_result;
92 /// This code should only compile in modules where the uninhabitedness of Foo is
94 pub fn is_ty_uninhabited_from(
98 param_env: ty::ParamEnv<'tcx>,
100 // To check whether this type is uninhabited at all (not just from the
101 // given node), you could check whether the forest is empty.
105 ty.uninhabited_from(self, param_env).contains(self, module)
108 pub fn is_ty_uninhabited_from_any_module(
111 param_env: ty::ParamEnv<'tcx>,
113 !ty.uninhabited_from(self, param_env).is_empty()
118 /// Calculates the forest of `DefId`s from which this ADT is visibly uninhabited.
122 substs: SubstsRef<'tcx>,
123 param_env: ty::ParamEnv<'tcx>,
125 // Non-exhaustive ADTs from other crates are always considered inhabited.
126 if self.is_variant_list_non_exhaustive() && !self.did.is_local() {
129 DefIdForest::intersection(
133 .map(|v| v.uninhabited_from(tcx, substs, self.adt_kind(), param_env)),
139 impl<'tcx> VariantDef {
140 /// Calculates the forest of `DefId`s from which this variant is visibly uninhabited.
141 pub fn uninhabited_from(
144 substs: SubstsRef<'tcx>,
146 param_env: ty::ParamEnv<'tcx>,
148 let is_enum = match adt_kind {
149 // For now, `union`s are never considered uninhabited.
150 // The precise semantics of inhabitedness with respect to unions is currently undecided.
151 AdtKind::Union => return DefIdForest::empty(),
152 AdtKind::Enum => true,
153 AdtKind::Struct => false,
155 // Non-exhaustive variants from other crates are always considered inhabited.
156 if self.is_field_list_non_exhaustive() && !self.def_id.is_local() {
161 self.fields.iter().map(|f| f.uninhabited_from(tcx, substs, is_enum, param_env)),
167 impl<'tcx> FieldDef {
168 /// Calculates the forest of `DefId`s from which this field is visibly uninhabited.
172 substs: SubstsRef<'tcx>,
174 param_env: ty::ParamEnv<'tcx>,
176 let data_uninhabitedness = move || self.ty(tcx, substs).uninhabited_from(tcx, param_env);
177 // FIXME(canndrew): Currently enum fields are (incorrectly) stored with
178 // `Visibility::Invisible` so we need to override `self.vis` if we're
179 // dealing with an enum.
181 data_uninhabitedness()
184 Visibility::Invisible => DefIdForest::empty(),
185 Visibility::Restricted(from) => {
186 let forest = DefIdForest::from_id(from);
187 let iter = Some(forest).into_iter().chain(Some(data_uninhabitedness()));
188 DefIdForest::intersection(tcx, iter)
190 Visibility::Public => data_uninhabitedness(),
196 impl<'tcx> TyS<'tcx> {
197 /// Calculates the forest of `DefId`s from which this type is visibly uninhabited.
198 fn uninhabited_from(&self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> DefIdForest {
200 Adt(def, substs) => {
201 ensure_sufficient_stack(|| def.uninhabited_from(tcx, substs, param_env))
204 Never => DefIdForest::full(tcx),
206 Tuple(ref tys) => DefIdForest::union(
208 tys.iter().map(|ty| ty.expect_ty().uninhabited_from(tcx, param_env)),
211 Array(ty, len) => match len.try_eval_usize(tcx, param_env) {
212 // If the array is definitely non-empty, it's uninhabited if
213 // the type of its elements is uninhabited.
214 Some(n) if n != 0 => ty.uninhabited_from(tcx, param_env),
215 _ => DefIdForest::empty(),
218 // References to uninitialised memory is valid for any type, including
219 // uninhabited types, in unsafe code, so we treat all references as
221 // The precise semantics of inhabitedness with respect to references is currently
223 Ref(..) => DefIdForest::empty(),
225 _ => DefIdForest::empty(),