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|
//! Type inhabitedness logic.
use std::ops::ControlFlow::{self, Break, Continue};
use chalk_ir::{
visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor},
DebruijnIndex,
};
use hir_def::{
adt::VariantData, attr::Attrs, type_ref::ConstScalar, visibility::Visibility, AdtId,
EnumVariantId, HasModule, Lookup, ModuleId, VariantId,
};
use crate::{
db::HirDatabase, Binders, ConcreteConst, Const, ConstValue, Interner, Substitution, Ty, TyKind,
};
/// Checks whether a type is visibly uninhabited from a particular module.
pub(crate) fn is_ty_uninhabited_from(ty: &Ty, target_mod: ModuleId, db: &dyn HirDatabase) -> bool {
let mut uninhabited_from = UninhabitedFrom { target_mod, db };
let inhabitedness = ty.visit_with(&mut uninhabited_from, DebruijnIndex::INNERMOST);
inhabitedness == BREAK_VISIBLY_UNINHABITED
}
/// Checks whether a variant is visibly uninhabited from a particular module.
pub(crate) fn is_enum_variant_uninhabited_from(
variant: EnumVariantId,
subst: &Substitution,
target_mod: ModuleId,
db: &dyn HirDatabase,
) -> bool {
let enum_data = db.enum_data(variant.parent);
let vars_attrs = db.variants_attrs(variant.parent);
let is_local = variant.parent.lookup(db.upcast()).container.krate() == target_mod.krate();
let mut uninhabited_from = UninhabitedFrom { target_mod, db };
let inhabitedness = uninhabited_from.visit_variant(
variant.into(),
&enum_data.variants[variant.local_id].variant_data,
subst,
&vars_attrs[variant.local_id],
is_local,
);
inhabitedness == BREAK_VISIBLY_UNINHABITED
}
struct UninhabitedFrom<'a> {
target_mod: ModuleId,
db: &'a dyn HirDatabase,
}
const CONTINUE_OPAQUELY_INHABITED: ControlFlow<VisiblyUninhabited> = Continue(());
const BREAK_VISIBLY_UNINHABITED: ControlFlow<VisiblyUninhabited> = Break(VisiblyUninhabited);
#[derive(PartialEq, Eq)]
struct VisiblyUninhabited;
impl TypeVisitor<Interner> for UninhabitedFrom<'_> {
type BreakTy = VisiblyUninhabited;
fn as_dyn(&mut self) -> &mut dyn TypeVisitor<Interner, BreakTy = VisiblyUninhabited> {
self
}
fn visit_ty(
&mut self,
ty: &Ty,
outer_binder: DebruijnIndex,
) -> ControlFlow<VisiblyUninhabited> {
match ty.kind(Interner) {
TyKind::Adt(adt, subst) => self.visit_adt(adt.0, subst),
TyKind::Never => BREAK_VISIBLY_UNINHABITED,
TyKind::Tuple(..) => ty.super_visit_with(self, outer_binder),
TyKind::Array(item_ty, len) => match try_usize_const(len) {
Some(0) | None => CONTINUE_OPAQUELY_INHABITED,
Some(1..) => item_ty.super_visit_with(self, outer_binder),
},
TyKind::Ref(..) | _ => CONTINUE_OPAQUELY_INHABITED,
}
}
fn interner(&self) -> Interner {
Interner
}
}
impl UninhabitedFrom<'_> {
fn visit_adt(&mut self, adt: AdtId, subst: &Substitution) -> ControlFlow<VisiblyUninhabited> {
let attrs = self.db.attrs(adt.into());
let adt_non_exhaustive = attrs.by_key("non_exhaustive").exists();
let is_local = adt.module(self.db.upcast()).krate() == self.target_mod.krate();
if adt_non_exhaustive && !is_local {
return CONTINUE_OPAQUELY_INHABITED;
}
// An ADT is uninhabited iff all its variants uninhabited.
match adt {
// rustc: For now, `union`s are never considered uninhabited.
AdtId::UnionId(_) => CONTINUE_OPAQUELY_INHABITED,
AdtId::StructId(s) => {
let struct_data = self.db.struct_data(s);
self.visit_variant(s.into(), &struct_data.variant_data, subst, &attrs, is_local)
}
AdtId::EnumId(e) => {
let vars_attrs = self.db.variants_attrs(e);
let enum_data = self.db.enum_data(e);
for (local_id, enum_var) in enum_data.variants.iter() {
let variant_inhabitedness = self.visit_variant(
EnumVariantId { parent: e, local_id }.into(),
&enum_var.variant_data,
subst,
&vars_attrs[local_id],
is_local,
);
match variant_inhabitedness {
Break(VisiblyUninhabited) => continue,
Continue(()) => return CONTINUE_OPAQUELY_INHABITED,
}
}
BREAK_VISIBLY_UNINHABITED
}
}
}
fn visit_variant(
&mut self,
variant: VariantId,
variant_data: &VariantData,
subst: &Substitution,
attrs: &Attrs,
is_local: bool,
) -> ControlFlow<VisiblyUninhabited> {
let non_exhaustive_field_list = attrs.by_key("non_exhaustive").exists();
if non_exhaustive_field_list && !is_local {
return CONTINUE_OPAQUELY_INHABITED;
}
let is_enum = matches!(variant, VariantId::EnumVariantId(..));
let field_tys = self.db.field_types(variant);
let field_vis = self.db.field_visibilities(variant);
for (fid, _) in variant_data.fields().iter() {
self.visit_field(field_vis[fid], &field_tys[fid], subst, is_enum)?;
}
CONTINUE_OPAQUELY_INHABITED
}
fn visit_field(
&mut self,
vis: Visibility,
ty: &Binders<Ty>,
subst: &Substitution,
is_enum: bool,
) -> ControlFlow<VisiblyUninhabited> {
if is_enum || vis.is_visible_from(self.db.upcast(), self.target_mod) {
let ty = ty.clone().substitute(Interner, subst);
ty.visit_with(self, DebruijnIndex::INNERMOST)
} else {
CONTINUE_OPAQUELY_INHABITED
}
}
}
fn try_usize_const(c: &Const) -> Option<u128> {
let data = &c.data(Interner);
if data.ty.kind(Interner) != &TyKind::Scalar(chalk_ir::Scalar::Uint(chalk_ir::UintTy::Usize)) {
return None;
}
match data.value {
ConstValue::Concrete(ConcreteConst { interned: ConstScalar::UInt(value) }) => Some(value),
_ => None,
}
}
|
