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pub use self::def_id_forest::DefIdForest;
use crate::ty;
use crate::ty::context::TyCtxt;
use crate::ty::{AdtDef, FieldDef, Ty, VariantDef};
use crate::ty::{AdtKind, Visibility};
use crate::ty::{DefId, SubstsRef};
use rustc_type_ir::sty::TyKind::*;
mod def_id_forest;
// The methods in this module calculate `DefIdForest`s of modules in which an
// `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<'tcx> TyCtxt<'tcx> {
/// Checks whether a type is visibly uninhabited from a particular module.
///
/// # Example
/// ```
/// #![feature(never_type)]
/// # fn main() {}
/// enum Void {}
/// mod a {
/// pub mod b {
/// pub struct SecretlyUninhabited {
/// _priv: !,
/// }
/// }
/// }
///
/// mod c {
/// use super::Void;
/// 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
/// ```ignore (illustrative)
/// 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>,
param_env: ty::ParamEnv<'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()
// ```
ty.uninhabited_from(self, param_env).contains(self, module)
}
}
impl<'tcx> AdtDef<'tcx> {
/// Calculates the forest of `DefId`s from which this ADT is visibly uninhabited.
fn uninhabited_from(
self,
tcx: TyCtxt<'tcx>,
substs: SubstsRef<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> DefIdForest<'tcx> {
// 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(), param_env)),
)
}
}
}
impl<'tcx> VariantDef {
/// Calculates the forest of `DefId`s from which this variant is visibly uninhabited.
pub fn uninhabited_from(
&self,
tcx: TyCtxt<'tcx>,
substs: SubstsRef<'tcx>,
adt_kind: AdtKind,
param_env: ty::ParamEnv<'tcx>,
) -> DefIdForest<'tcx> {
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, param_env)),
)
}
}
}
impl<'tcx> FieldDef {
/// Calculates the forest of `DefId`s from which this field is visibly uninhabited.
fn uninhabited_from(
&self,
tcx: TyCtxt<'tcx>,
substs: SubstsRef<'tcx>,
is_enum: bool,
param_env: ty::ParamEnv<'tcx>,
) -> DefIdForest<'tcx> {
let data_uninhabitedness = move || self.ty(tcx, substs).uninhabited_from(tcx, param_env);
if is_enum {
data_uninhabitedness()
} else {
match self.vis {
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<'tcx> Ty<'tcx> {
/// Calculates the forest of `DefId`s from which this type is visibly uninhabited.
fn uninhabited_from(
self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> DefIdForest<'tcx> {
tcx.type_uninhabited_from(param_env.and(self))
}
}
// Query provider for `type_uninhabited_from`.
pub(crate) fn type_uninhabited_from<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
) -> DefIdForest<'tcx> {
let ty = key.value;
let param_env = key.param_env;
match *ty.kind() {
Adt(def, substs) => def.uninhabited_from(tcx, substs, param_env),
Never => DefIdForest::full(),
Tuple(ref tys) => {
DefIdForest::union(tcx, tys.iter().map(|ty| ty.uninhabited_from(tcx, param_env)))
}
Array(ty, len) => match len.try_eval_usize(tcx, param_env) {
Some(0) | None => DefIdForest::empty(),
// If the array is definitely non-empty, it's uninhabited if
// the type of its elements is uninhabited.
Some(1..) => ty.uninhabited_from(tcx, param_env),
},
// References to uninitialised memory are 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(),
}
}
|
