rustc_middle/ty/visit.rs
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use std::ops::ControlFlow;
use rustc_data_structures::fx::FxIndexSet;
use rustc_type_ir::fold::TypeFoldable;
pub use rustc_type_ir::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};
use crate::ty::{self, Binder, Ty, TyCtxt, TypeFlags};
///////////////////////////////////////////////////////////////////////////
// Region folder
impl<'tcx> TyCtxt<'tcx> {
/// Invoke `callback` on every region appearing free in `value`.
pub fn for_each_free_region(
self,
value: &impl TypeVisitable<TyCtxt<'tcx>>,
mut callback: impl FnMut(ty::Region<'tcx>),
) {
self.any_free_region_meets(value, |r| {
callback(r);
false
});
}
/// Returns `true` if `callback` returns true for every region appearing free in `value`.
pub fn all_free_regions_meet(
self,
value: &impl TypeVisitable<TyCtxt<'tcx>>,
mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
) -> bool {
!self.any_free_region_meets(value, |r| !callback(r))
}
/// Returns `true` if `callback` returns true for some region appearing free in `value`.
pub fn any_free_region_meets(
self,
value: &impl TypeVisitable<TyCtxt<'tcx>>,
callback: impl FnMut(ty::Region<'tcx>) -> bool,
) -> bool {
struct RegionVisitor<F> {
/// The index of a binder *just outside* the things we have
/// traversed. If we encounter a bound region bound by this
/// binder or one outer to it, it appears free. Example:
///
/// ```ignore (illustrative)
/// for<'a> fn(for<'b> fn(), T)
/// // ^ ^ ^ ^
/// // | | | | here, would be shifted in 1
/// // | | | here, would be shifted in 2
/// // | | here, would be `INNERMOST` shifted in by 1
/// // | here, initially, binder would be `INNERMOST`
/// ```
///
/// You see that, initially, *any* bound value is free,
/// because we've not traversed any binders. As we pass
/// through a binder, we shift the `outer_index` by 1 to
/// account for the new binder that encloses us.
outer_index: ty::DebruijnIndex,
callback: F,
}
impl<'tcx, F> TypeVisitor<TyCtxt<'tcx>> for RegionVisitor<F>
where
F: FnMut(ty::Region<'tcx>) -> bool,
{
type Result = ControlFlow<()>;
fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(
&mut self,
t: &Binder<'tcx, T>,
) -> Self::Result {
self.outer_index.shift_in(1);
let result = t.super_visit_with(self);
self.outer_index.shift_out(1);
result
}
fn visit_region(&mut self, r: ty::Region<'tcx>) -> Self::Result {
match *r {
ty::ReBound(debruijn, _) if debruijn < self.outer_index => {
ControlFlow::Continue(())
}
_ => {
if (self.callback)(r) {
ControlFlow::Break(())
} else {
ControlFlow::Continue(())
}
}
}
}
fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
// We're only interested in types involving regions
if ty.flags().intersects(TypeFlags::HAS_FREE_REGIONS) {
ty.super_visit_with(self)
} else {
ControlFlow::Continue(())
}
}
}
value.visit_with(&mut RegionVisitor { outer_index: ty::INNERMOST, callback }).is_break()
}
/// Returns a set of all late-bound regions that are constrained
/// by `value`, meaning that if we instantiate those LBR with
/// variables and equate `value` with something else, those
/// variables will also be equated.
pub fn collect_constrained_late_bound_regions<T>(
self,
value: Binder<'tcx, T>,
) -> FxIndexSet<ty::BoundRegionKind>
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
self.collect_late_bound_regions(value, true)
}
/// Returns a set of all late-bound regions that appear in `value` anywhere.
pub fn collect_referenced_late_bound_regions<T>(
self,
value: Binder<'tcx, T>,
) -> FxIndexSet<ty::BoundRegionKind>
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
self.collect_late_bound_regions(value, false)
}
fn collect_late_bound_regions<T>(
self,
value: Binder<'tcx, T>,
just_constrained: bool,
) -> FxIndexSet<ty::BoundRegionKind>
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
let mut collector = LateBoundRegionsCollector::new(just_constrained);
let value = value.skip_binder();
let value = if just_constrained { self.expand_weak_alias_tys(value) } else { value };
value.visit_with(&mut collector);
collector.regions
}
}
/// Collects all the late-bound regions at the innermost binding level
/// into a hash set.
struct LateBoundRegionsCollector {
current_index: ty::DebruijnIndex,
regions: FxIndexSet<ty::BoundRegionKind>,
/// `true` if we only want regions that are known to be
/// "constrained" when you equate this type with another type. In
/// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
/// them constraints `'a == 'b`. But if you have `<&'a u32 as
/// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
/// types may mean that `'a` and `'b` don't appear in the results,
/// so they are not considered *constrained*.
just_constrained: bool,
}
impl LateBoundRegionsCollector {
fn new(just_constrained: bool) -> Self {
Self { current_index: ty::INNERMOST, regions: Default::default(), just_constrained }
}
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for LateBoundRegionsCollector {
fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(&mut self, t: &Binder<'tcx, T>) {
self.current_index.shift_in(1);
t.super_visit_with(self);
self.current_index.shift_out(1);
}
fn visit_ty(&mut self, t: Ty<'tcx>) {
if self.just_constrained {
match t.kind() {
// If we are only looking for "constrained" regions, we have to ignore the
// inputs to a projection as they may not appear in the normalized form.
ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, _) => {
return;
}
// All weak alias types should've been expanded beforehand.
ty::Alias(ty::Weak, _) => bug!("unexpected weak alias type"),
_ => {}
}
}
t.super_visit_with(self)
}
fn visit_const(&mut self, c: ty::Const<'tcx>) {
// if we are only looking for "constrained" region, we have to
// ignore the inputs of an unevaluated const, as they may not appear
// in the normalized form
if self.just_constrained {
if let ty::ConstKind::Unevaluated(..) = c.kind() {
return;
}
}
c.super_visit_with(self)
}
fn visit_region(&mut self, r: ty::Region<'tcx>) {
if let ty::ReBound(debruijn, br) = *r {
if debruijn == self.current_index {
self.regions.insert(br.kind);
}
}
}
}
/// Finds the max universe present
pub struct MaxUniverse {
max_universe: ty::UniverseIndex,
}
impl MaxUniverse {
pub fn new() -> Self {
MaxUniverse { max_universe: ty::UniverseIndex::ROOT }
}
pub fn max_universe(self) -> ty::UniverseIndex {
self.max_universe
}
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MaxUniverse {
fn visit_ty(&mut self, t: Ty<'tcx>) {
if let ty::Placeholder(placeholder) = t.kind() {
self.max_universe = ty::UniverseIndex::from_u32(
self.max_universe.as_u32().max(placeholder.universe.as_u32()),
);
}
t.super_visit_with(self)
}
fn visit_const(&mut self, c: ty::consts::Const<'tcx>) {
if let ty::ConstKind::Placeholder(placeholder) = c.kind() {
self.max_universe = ty::UniverseIndex::from_u32(
self.max_universe.as_u32().max(placeholder.universe.as_u32()),
);
}
c.super_visit_with(self)
}
fn visit_region(&mut self, r: ty::Region<'tcx>) {
if let ty::RePlaceholder(placeholder) = *r {
self.max_universe = ty::UniverseIndex::from_u32(
self.max_universe.as_u32().max(placeholder.universe.as_u32()),
);
}
}
}