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Avoid trait_ref when lowering ExistentialProjections

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This commit is contained in:
Matthew Jasper 2021-02-12 22:32:46 +00:00
parent 0bf1d73d22
commit 9526c0c6e8
2 changed files with 44 additions and 36 deletions
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23
compiler/rustc_middle/src/ty/sty.rs
View file

@ -1477,12 +1477,11 @@ impl<'tcx> ExistentialProjection<'tcx> {
/// For example, if this is a projection of `exists T. <T as Iterator>::Item == X`,
/// then this function would return a `exists T. T: Iterator` existential trait
/// reference.
pub fn trait_ref(&self, tcx: TyCtxt<'_>) -> ty::ExistentialTraitRef<'tcx> {
// FIXME(generic_associated_types): substs is the substs of the
// associated type, which should be truncated to get the correct substs
// for the trait.
pub fn trait_ref(&self, tcx: TyCtxt<'tcx>) -> ty::ExistentialTraitRef<'tcx> {
let def_id = tcx.associated_item(self.item_def_id).container.id();
ty::ExistentialTraitRef { def_id, substs: self.substs }
let subst_count = tcx.generics_of(def_id).count() - 1;
let substs = tcx.intern_substs(&self.substs[..subst_count]);
ty::ExistentialTraitRef { def_id, substs }
}
pub fn with_self_ty(
@ -1501,6 +1500,20 @@ impl<'tcx> ExistentialProjection<'tcx> {
ty: self.ty,
}
}
pub fn erase_self_ty(
tcx: TyCtxt<'tcx>,
projection_predicate: ty::ProjectionPredicate<'tcx>,
) -> Self {
// Assert there is a Self.
projection_predicate.projection_ty.substs.type_at(0);
Self {
item_def_id: projection_predicate.projection_ty.item_def_id,
substs: tcx.intern_substs(&projection_predicate.projection_ty.substs[1..]),
ty: projection_predicate.ty,
}
}
}
impl<'tcx> PolyExistentialProjection<'tcx> {

57
compiler/rustc_typeck/src/astconv/mod.rs
View file

@ -985,10 +985,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
//
// We want to produce `<B as SuperTrait<i32>>::T == foo`.
debug!(
"add_predicates_for_ast_type_binding(hir_ref_id {:?}, trait_ref {:?}, binding {:?}, bounds {:?}",
hir_ref_id, trait_ref, binding, bounds
);
debug!(?hir_ref_id, ?trait_ref, ?binding, ?bounds, "add_predicates_for_ast_type_binding",);
let tcx = self.tcx();
let candidate =
@ -1326,37 +1323,35 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
debug!("regular_traits: {:?}", regular_traits);
debug!("auto_traits: {:?}", auto_traits);
// Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
// removing the dummy `Self` type (`trait_object_dummy_self`).
let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
if trait_ref.self_ty() != dummy_self {
// FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
// which picks up non-supertraits where clauses - but also, the object safety
// completely ignores trait aliases, which could be object safety hazards. We
// `delay_span_bug` here to avoid an ICE in stable even when the feature is
// disabled. (#66420)
tcx.sess.delay_span_bug(
DUMMY_SP,
&format!(
"trait_ref_to_existential called on {:?} with non-dummy Self",
trait_ref,
),
);
}
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
};
// Erase the `dummy_self` (`trait_object_dummy_self`) used above.
let existential_trait_refs =
regular_traits.iter().map(|i| i.trait_ref().map_bound(trait_ref_to_existential));
let existential_trait_refs = regular_traits.iter().map(|i| {
i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
if trait_ref.self_ty() != dummy_self {
// FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
// which picks up non-supertraits where clauses - but also, the object safety
// completely ignores trait aliases, which could be object safety hazards. We
// `delay_span_bug` here to avoid an ICE in stable even when the feature is
// disabled. (#66420)
tcx.sess.delay_span_bug(
DUMMY_SP,
&format!(
"trait_ref_to_existential called on {:?} with non-dummy Self",
trait_ref,
),
);
}
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
})
});
let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
bound.map_bound(|b| {
let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
ty::ExistentialProjection {
ty: b.ty,
item_def_id: b.projection_ty.item_def_id,
substs: trait_ref.substs,
if b.projection_ty.self_ty() != dummy_self {
tcx.sess.delay_span_bug(
DUMMY_SP,
&format!("trait_ref_to_existential called on {:?} with non-dummy Self", b),
);
}
ty::ExistentialProjection::erase_self_ty(tcx, b)
})
});