// option. This file may not be copied, modified, or distributed
// except according to those terms.
-//! This module contains TyKind and its major components
+//! This module contains `TyKind` and its major components.
+use hir;
use hir::def_id::DefId;
use infer::canonical::Canonical;
use mir::interpret::ConstValue;
use syntax::symbol::{keywords, InternedString};
use serialize;
-
-use hir;
-
use self::InferTy::*;
use self::TyKind::*;
}
}
-/// N.B., If you change this, you'll probably want to change the corresponding
+/// N.B., if you change this, you'll probably want to change the corresponding
/// AST structure in `libsyntax/ast.rs` as well.
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
pub enum TyKind<'tcx> {
#[derive(Debug, Copy, Clone, PartialEq, PartialOrd, Ord, Eq, Hash, RustcEncodable, RustcDecodable)]
pub enum ExistentialPredicate<'tcx> {
- /// e.g. Iterator
+ /// e.g., Iterator
Trait(ExistentialTraitRef<'tcx>),
- /// e.g. Iterator::Item = T
+ /// e.g., Iterator::Item = T
Projection(ExistentialProjection<'tcx>),
- /// e.g. Send
+ /// e.g., Send
AutoTrait(DefId),
}
/// Binder<TraitRef>`). Note that when we instantiate,
/// erase, or otherwise "discharge" these bound vars, we change the
/// type from `Binder<T>` to just `T` (see
-/// e.g. `liberate_late_bound_regions`).
+/// e.g., `liberate_late_bound_regions`).
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
pub struct Binder<T>(T);
/// with some concrete region before being used. There are 2 kind of
/// bound regions: early-bound, which are bound in an item's Generics,
/// and are substituted by a Substs, and late-bound, which are part of
-/// higher-ranked types (e.g. `for<'a> fn(&'a ())`) and are substituted by
+/// higher-ranked types (e.g., `for<'a> fn(&'a ())`) and are substituted by
/// the likes of `liberate_late_bound_regions`. The distinction exists
/// because higher-ranked lifetimes aren't supported in all places. See [1][2].
///
/// Unlike Param-s, bound regions are not supposed to exist "in the wild"
-/// outside their binder, e.g. in types passed to type inference, and
+/// outside their binder, e.g., in types passed to type inference, and
/// should first be substituted (by placeholder regions, free regions,
/// or region variables).
///
ReFree(FreeRegion),
/// A concrete region naming some statically determined scope
- /// (e.g. an expression or sequence of statements) within the
+ /// (e.g., an expression or sequence of statements) within the
/// current function.
ReScope(region::Scope),
impl DebruijnIndex {
/// Returns the resulting index when this value is moved into
- /// `amount` number of new binders. So e.g. if you had
+ /// `amount` number of new binders. So e.g., if you had
///
/// for<'a> fn(&'a x)
///
///
/// for<'a> fn(for<'b> fn(&'a x))
///
- /// you would need to shift the index for `'a` into 1 new binder.
+ /// you would need to shift the index for `'a` into a new binder.
#[must_use]
pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
DebruijnIndex::from_u32(self.as_u32() + amount)
}
}
+ /// Checks whether a type is definitely uninhabited. This is
+ /// conservative: for some types that are uninhabited we return `false`,
+ /// but we only return `true` for types that are definitely uninhabited.
+ /// `ty.conservative_is_uninhabited` implies that any value of type `ty`
+ /// will be `Abi::Uninhabited`. (Note that uninhabited types may have nonzero
+ /// size, to account for partial initialisation. See #49298 for details.)
+ pub fn conservative_is_uninhabited(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> bool {
+ // FIXME(varkor): we can make this less conversative by substituting concrete
+ // type arguments.
+ match self.sty {
+ ty::Never => true,
+ ty::Adt(def, _) if def.is_union() => {
+ // For now, `union`s are never considered uninhabited.
+ false
+ }
+ ty::Adt(def, _) => {
+ // Any ADT is uninhabited if either:
+ // (a) It has no variants (i.e. an empty `enum`);
+ // (b) Each of its variants (a single one in the case of a `struct`) has at least
+ // one uninhabited field.
+ def.variants.iter().all(|var| {
+ var.fields.iter().any(|field| {
+ tcx.type_of(field.did).conservative_is_uninhabited(tcx)
+ })
+ })
+ }
+ ty::Tuple(tys) => tys.iter().any(|ty| ty.conservative_is_uninhabited(tcx)),
+ ty::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.conservative_is_uninhabited(tcx),
+ _ => false
+ }
+ }
+ ty::Ref(..) => {
+ // References to uninitialised memory is valid for any type, including
+ // uninhabited types, in unsafe code, so we treat all references as
+ // inhabited.
+ false
+ }
+ _ => false,
+ }
+ }
+
pub fn is_primitive(&self) -> bool {
match self.sty {
Bool | Char | Int(_) | Uint(_) | Float(_) => true,
}
}
- /// Returns the type and mutability of *ty.
+ /// Returns the type and mutability of `*ty`.
///
/// The parameter `explicit` indicates if this is an *explicit* dereference.
- /// Some types---notably unsafe ptrs---can only be dereferenced explicitly.
+ /// Some types -- notably unsafe ptrs -- can only be dereferenced explicitly.
pub fn builtin_deref(&self, explicit: bool) -> Option<TypeAndMut<'tcx>> {
match self.sty {
Adt(def, _) if def.is_box() => {
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