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use crate::debug_span;
use chalk_derive::FallibleTypeFolder;
use chalk_ir::fold::{TypeFoldable, TypeFolder};
use chalk_ir::interner::{HasInterner, Interner};
use chalk_ir::visit::{TypeVisitable, TypeVisitor};
use chalk_ir::*;
use std::ops::ControlFlow;
use super::InferenceTable;
impl<I: Interner> InferenceTable<I> {
pub fn u_canonicalize<T>(interner: I, value0: &Canonical<T>) -> UCanonicalized<T>
where
T: Clone + HasInterner<Interner = I> + TypeFoldable<I> + TypeVisitable<I>,
T: HasInterner<Interner = I>,
{
debug_span!("u_canonicalize", "{:#?}", value0);
// First, find all the universes that appear in `value`.
let mut universes = UniverseMap::new();
for universe in value0.binders.iter(interner) {
universes.add(*universe.skip_kind());
}
value0.value.visit_with(
&mut UCollector {
universes: &mut universes,
interner,
},
DebruijnIndex::INNERMOST,
);
// Now re-map the universes found in value. We have to do this
// in a second pass because it is only then that we know the
// full set of universes found in the original value.
let value1 = value0
.value
.clone()
.try_fold_with(
&mut UMapToCanonical {
universes: &universes,
interner,
},
DebruijnIndex::INNERMOST,
)
.unwrap();
let binders = CanonicalVarKinds::from_iter(
interner,
value0
.binders
.iter(interner)
.map(|pk| pk.map_ref(|&ui| universes.map_universe_to_canonical(ui).unwrap())),
);
UCanonicalized {
quantified: UCanonical {
universes: universes.num_canonical_universes(),
canonical: Canonical {
value: value1,
binders,
},
},
universes,
}
}
}
#[derive(Debug)]
pub struct UCanonicalized<T: HasInterner> {
/// The canonicalized result.
pub quantified: UCanonical<T>,
/// A map between the universes in `quantified` and the original universes
pub universes: UniverseMap,
}
pub trait UniverseMapExt {
fn add(&mut self, universe: UniverseIndex);
fn map_universe_to_canonical(&self, universe: UniverseIndex) -> Option<UniverseIndex>;
fn map_universe_from_canonical(&self, universe: UniverseIndex) -> UniverseIndex;
fn map_from_canonical<T, I>(&self, interner: I, canonical_value: &Canonical<T>) -> Canonical<T>
where
T: Clone + TypeFoldable<I> + HasInterner<Interner = I>,
T: HasInterner<Interner = I>,
I: Interner;
}
impl UniverseMapExt for UniverseMap {
fn add(&mut self, universe: UniverseIndex) {
if let Err(i) = self.universes.binary_search(&universe) {
self.universes.insert(i, universe);
}
}
/// Given a universe U that appeared in our original value, return
/// the universe to use in the u-canonical value. This is done by
/// looking for the index I of U in `self.universes`. We will
/// return the universe with "counter" I. This effectively
/// "compresses" the range of universes to things from
/// `0..self.universes.len()`. If the universe is not present in the map,
/// we return `None`.
fn map_universe_to_canonical(&self, universe: UniverseIndex) -> Option<UniverseIndex> {
self.universes
.binary_search(&universe)
.ok()
.map(|index| UniverseIndex { counter: index })
}
/// Given a "canonical universe" -- one found in the
/// `u_canonicalize` result -- returns the original universe that
/// it corresponded to.
fn map_universe_from_canonical(&self, universe: UniverseIndex) -> UniverseIndex {
if universe.counter < self.universes.len() {
self.universes[universe.counter]
} else {
// If this universe is out of bounds, we assume an
// implicit `forall` binder, effectively, and map to a
// "big enough" universe in the original space. See
// comments on `map_from_canonical` for a detailed
// explanation.
let difference = universe.counter - self.universes.len();
let max_counter = self.universes.last().unwrap().counter;
let new_counter = max_counter + difference + 1;
UniverseIndex {
counter: new_counter,
}
}
}
/// Returns a mapped version of `value` where the universes have
/// been translated from canonical universes into the original
/// universes.
///
/// In some cases, `value` may contain fresh universes that are
/// not described in the original map. This occurs when we return
/// region constraints -- for example, if we were to process a
/// constraint like `for<'a> 'a == 'b`, where `'b` is an inference
/// variable, that would generate a region constraint that `!2 ==
/// ?0`. (This constraint is typically not, as it happens,
/// satisfiable, but it may be, depending on the bounds on `!2`.)
/// In effect, there is a "for all" binder around the constraint,
/// but it is not represented explicitly -- only implicitly, by
/// the presence of a U2 variable.
///
/// If we encounter universes like this, which are "out of bounds"
/// from our original set of universes, we map them to a distinct
/// universe in the original space that is greater than all the
/// other universes in the map. That is, if we encounter a
/// canonical universe `Ux` where our canonical vector is (say)
/// `[U0, U3]`, we would compute the difference `d = x - 2` and
/// then return the universe `3 + d + 1`.
///
/// The important thing is that we preserve (a) the relative order
/// of universes, since that determines visibility, and (b) that
/// the universe we produce does not correspond to any of the
/// other original universes.
fn map_from_canonical<T, I>(&self, interner: I, canonical_value: &Canonical<T>) -> Canonical<T>
where
T: Clone + TypeFoldable<I> + HasInterner<Interner = I>,
T: HasInterner<Interner = I>,
I: Interner,
{
debug_span!("map_from_canonical", ?canonical_value, universes = ?self.universes);
let binders = canonical_value
.binders
.iter(interner)
.map(|cvk| cvk.map_ref(|&universe| self.map_universe_from_canonical(universe)));
let value = canonical_value
.value
.clone()
.try_fold_with(
&mut UMapFromCanonical {
interner,
universes: self,
},
DebruijnIndex::INNERMOST,
)
.unwrap();
Canonical {
binders: CanonicalVarKinds::from_iter(interner, binders),
value,
}
}
}
/// The `UCollector` is a "no-op" in terms of the value, but along the
/// way it collects all universes that were found into a vector.
struct UCollector<'q, I> {
universes: &'q mut UniverseMap,
interner: I,
}
impl<I: Interner> TypeVisitor<I> for UCollector<'_, I> {
type BreakTy = ();
fn as_dyn(&mut self) -> &mut dyn TypeVisitor<I, BreakTy = Self::BreakTy> {
self
}
fn visit_free_placeholder(
&mut self,
universe: PlaceholderIndex,
_outer_binder: DebruijnIndex,
) -> ControlFlow<()> {
self.universes.add(universe.ui);
ControlFlow::Continue(())
}
fn forbid_inference_vars(&self) -> bool {
true
}
fn interner(&self) -> I {
self.interner
}
}
#[derive(FallibleTypeFolder)]
struct UMapToCanonical<'q, I: Interner> {
interner: I,
universes: &'q UniverseMap,
}
impl<'i, I: Interner> TypeFolder<I> for UMapToCanonical<'i, I> {
fn as_dyn(&mut self) -> &mut dyn TypeFolder<I> {
self
}
fn forbid_inference_vars(&self) -> bool {
true
}
fn fold_free_placeholder_ty(
&mut self,
universe0: PlaceholderIndex,
_outer_binder: DebruijnIndex,
) -> Ty<I> {
let ui = self
.universes
.map_universe_to_canonical(universe0.ui)
.expect("Expected UCollector to encounter this universe");
PlaceholderIndex {
ui,
idx: universe0.idx,
}
.to_ty(TypeFolder::interner(self))
}
fn fold_free_placeholder_lifetime(
&mut self,
universe0: PlaceholderIndex,
_outer_binder: DebruijnIndex,
) -> Lifetime<I> {
let universe = self
.universes
.map_universe_to_canonical(universe0.ui)
.expect("Expected UCollector to encounter this universe");
PlaceholderIndex {
ui: universe,
idx: universe0.idx,
}
.to_lifetime(TypeFolder::interner(self))
}
fn fold_free_placeholder_const(
&mut self,
ty: Ty<I>,
universe0: PlaceholderIndex,
_outer_binder: DebruijnIndex,
) -> Const<I> {
let universe = self
.universes
.map_universe_to_canonical(universe0.ui)
.expect("Expected UCollector to encounter this universe");
PlaceholderIndex {
ui: universe,
idx: universe0.idx,
}
.to_const(TypeFolder::interner(self), ty)
}
fn interner(&self) -> I {
self.interner
}
}
#[derive(FallibleTypeFolder)]
struct UMapFromCanonical<'q, I: Interner> {
interner: I,
universes: &'q UniverseMap,
}
impl<'i, I: Interner> TypeFolder<I> for UMapFromCanonical<'i, I> {
fn as_dyn(&mut self) -> &mut dyn TypeFolder<I> {
self
}
fn fold_free_placeholder_ty(
&mut self,
universe0: PlaceholderIndex,
_outer_binder: DebruijnIndex,
) -> Ty<I> {
let ui = self.universes.map_universe_from_canonical(universe0.ui);
PlaceholderIndex {
ui,
idx: universe0.idx,
}
.to_ty(TypeFolder::interner(self))
}
fn fold_free_placeholder_lifetime(
&mut self,
universe0: PlaceholderIndex,
_outer_binder: DebruijnIndex,
) -> Lifetime<I> {
let universe = self.universes.map_universe_from_canonical(universe0.ui);
PlaceholderIndex {
ui: universe,
idx: universe0.idx,
}
.to_lifetime(TypeFolder::interner(self))
}
fn forbid_inference_vars(&self) -> bool {
true
}
fn interner(&self) -> I {
self.interner
}
}