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use core::panic;
use rustc_type_ir::data_structures::IndexMap;
use rustc_type_ir::inherent::*;
use rustc_type_ir::{
self as ty, InferCtxtLike, Interner, TypeFoldable, TypeFolder, TypeSuperFoldable,
TypeVisitableExt,
};
pub struct BoundVarReplacer<'a, Infcx, I = <Infcx as InferCtxtLike>::Interner>
where
Infcx: InferCtxtLike<Interner = I>,
I: Interner,
{
infcx: &'a Infcx,
// These three maps track the bound variable that were replaced by placeholders. It might be
// nice to remove these since we already have the `kind` in the placeholder; we really just need
// the `var` (but we *could* bring that into scope if we were to track them as we pass them).
mapped_regions: IndexMap<I::PlaceholderRegion, I::BoundRegion>,
mapped_types: IndexMap<I::PlaceholderTy, I::BoundTy>,
mapped_consts: IndexMap<I::PlaceholderConst, I::BoundConst>,
// The current depth relative to *this* folding, *not* the entire normalization. In other words,
// the depth of binders we've passed here.
current_index: ty::DebruijnIndex,
// The `UniverseIndex` of the binding levels above us. These are optional, since we are lazy:
// we don't actually create a universe until we see a bound var we have to replace.
universe_indices: &'a mut Vec<Option<ty::UniverseIndex>>,
}
impl<'a, Infcx, I> BoundVarReplacer<'a, Infcx, I>
where
Infcx: InferCtxtLike<Interner = I>,
I: Interner,
{
/// Returns `Some` if we *were* able to replace bound vars. If there are any bound vars that
/// use a binding level above `universe_indices.len()`, we fail.
pub fn replace_bound_vars<T: TypeFoldable<I>>(
infcx: &'a Infcx,
universe_indices: &'a mut Vec<Option<ty::UniverseIndex>>,
value: T,
) -> (
T,
IndexMap<I::PlaceholderRegion, I::BoundRegion>,
IndexMap<I::PlaceholderTy, I::BoundTy>,
IndexMap<I::PlaceholderConst, I::BoundConst>,
) {
let mut replacer = BoundVarReplacer {
infcx,
mapped_regions: Default::default(),
mapped_types: Default::default(),
mapped_consts: Default::default(),
current_index: ty::INNERMOST,
universe_indices,
};
let value = value.fold_with(&mut replacer);
(value, replacer.mapped_regions, replacer.mapped_types, replacer.mapped_consts)
}
fn universe_for(&mut self, debruijn: ty::DebruijnIndex) -> ty::UniverseIndex {
let infcx = self.infcx;
let index =
self.universe_indices.len() + self.current_index.as_usize() - debruijn.as_usize() - 1;
let universe = self.universe_indices[index].unwrap_or_else(|| {
for i in self.universe_indices.iter_mut().take(index + 1) {
*i = i.or_else(|| Some(infcx.create_next_universe()))
}
self.universe_indices[index].unwrap()
});
universe
}
}
impl<Infcx, I> TypeFolder<I> for BoundVarReplacer<'_, Infcx, I>
where
Infcx: InferCtxtLike<Interner = I>,
I: Interner,
{
fn cx(&self) -> I {
self.infcx.cx()
}
fn fold_binder<T: TypeFoldable<I>>(&mut self, t: ty::Binder<I, T>) -> ty::Binder<I, T> {
self.current_index.shift_in(1);
let t = t.super_fold_with(self);
self.current_index.shift_out(1);
t
}
fn fold_region(&mut self, r: I::Region) -> I::Region {
match r.kind() {
ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), _)
if debruijn.as_usize()
>= self.current_index.as_usize() + self.universe_indices.len() =>
{
panic!(
"Bound vars {r:#?} outside of `self.universe_indices`: {:#?}",
self.universe_indices
);
}
ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), br)
if debruijn >= self.current_index =>
{
let universe = self.universe_for(debruijn);
let p = PlaceholderLike::new(universe, br);
self.mapped_regions.insert(p, br);
Region::new_placeholder(self.cx(), p)
}
_ => r,
}
}
fn fold_ty(&mut self, t: I::Ty) -> I::Ty {
match t.kind() {
ty::Bound(ty::BoundVarIndexKind::Bound(debruijn), _)
if debruijn.as_usize() + 1
> self.current_index.as_usize() + self.universe_indices.len() =>
{
panic!(
"Bound vars {t:#?} outside of `self.universe_indices`: {:#?}",
self.universe_indices
);
}
ty::Bound(ty::BoundVarIndexKind::Bound(debruijn), bound_ty)
if debruijn >= self.current_index =>
{
let universe = self.universe_for(debruijn);
let p = PlaceholderLike::new(universe, bound_ty);
self.mapped_types.insert(p, bound_ty);
Ty::new_placeholder(self.cx(), p)
}
_ if t.has_vars_bound_at_or_above(self.current_index) => t.super_fold_with(self),
_ => t,
}
}
fn fold_const(&mut self, ct: I::Const) -> I::Const {
match ct.kind() {
ty::ConstKind::Bound(ty::BoundVarIndexKind::Bound(debruijn), _)
if debruijn.as_usize() + 1
> self.current_index.as_usize() + self.universe_indices.len() =>
{
panic!(
"Bound vars {ct:#?} outside of `self.universe_indices`: {:#?}",
self.universe_indices
);
}
ty::ConstKind::Bound(ty::BoundVarIndexKind::Bound(debruijn), bound_const)
if debruijn >= self.current_index =>
{
let universe = self.universe_for(debruijn);
let p = PlaceholderLike::new(universe, bound_const);
self.mapped_consts.insert(p, bound_const);
Const::new_placeholder(self.cx(), p)
}
_ => ct.super_fold_with(self),
}
}
fn fold_predicate(&mut self, p: I::Predicate) -> I::Predicate {
if p.has_vars_bound_at_or_above(self.current_index) { p.super_fold_with(self) } else { p }
}
}
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