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Auto merge of rust-lang#101989 - fee1-dead-contrib:const_trait_impl-a…
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…ssoc-caller-bounds, r=oli-obk

make projection bounds with const bounds satisfy const

Fixes rust-lang#101982.
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bors committed Sep 20, 2022
2 parents 4136b59 + ee96ae0 commit cd8cc91
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Showing 5 changed files with 33 additions and 15 deletions.
5 changes: 3 additions & 2 deletions compiler/rustc_middle/src/traits/select.rs
Original file line number Diff line number Diff line change
Expand Up @@ -119,8 +119,9 @@ pub enum SelectionCandidate<'tcx> {

/// This is a trait matching with a projected type as `Self`, and we found
/// an applicable bound in the trait definition. The `usize` is an index
/// into the list returned by `tcx.item_bounds`.
ProjectionCandidate(usize),
/// into the list returned by `tcx.item_bounds`. The constness is the
/// constness of the bound in the trait.
ProjectionCandidate(usize, ty::BoundConstness),

/// Implementation of a `Fn`-family trait by one of the anonymous types
/// generated for an `||` expression.
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Original file line number Diff line number Diff line change
Expand Up @@ -362,7 +362,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
.infcx
.probe(|_| self.match_projection_obligation_against_definition_bounds(obligation));

candidates.vec.extend(result.into_iter().map(ProjectionCandidate));
candidates
.vec
.extend(result.into_iter().map(|(idx, constness)| ProjectionCandidate(idx, constness)));
}

/// Given an obligation like `<SomeTrait for T>`, searches the obligations that the caller
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Original file line number Diff line number Diff line change
Expand Up @@ -68,10 +68,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
ImplSource::AutoImpl(data)
}

ProjectionCandidate(idx) => {
ProjectionCandidate(idx, constness) => {
let obligations = self.confirm_projection_candidate(obligation, idx)?;
// FIXME(jschievink): constness
ImplSource::Param(obligations, ty::BoundConstness::NotConst)
ImplSource::Param(obligations, constness)
}

ObjectCandidate(idx) => {
Expand Down
20 changes: 11 additions & 9 deletions compiler/rustc_trait_selection/src/traits/select/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1192,6 +1192,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
ImplCandidate(def_id) if tcx.constness(def_id) == hir::Constness::Const => {}
// const param
ParamCandidate(trait_pred) if trait_pred.is_const_if_const() => {}
// const projection
ProjectionCandidate(_, ty::BoundConstness::ConstIfConst) => {}
// auto trait impl
AutoImplCandidate(..) => {}
// generator, this will raise error in other places
Expand Down Expand Up @@ -1399,7 +1401,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn match_projection_obligation_against_definition_bounds(
&mut self,
obligation: &TraitObligation<'tcx>,
) -> smallvec::SmallVec<[usize; 2]> {
) -> smallvec::SmallVec<[(usize, ty::BoundConstness); 2]> {
let poly_trait_predicate = self.infcx().resolve_vars_if_possible(obligation.predicate);
let placeholder_trait_predicate =
self.infcx().replace_bound_vars_with_placeholders(poly_trait_predicate);
Expand Down Expand Up @@ -1447,7 +1449,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
_ => false,
}
}) {
return Some(idx);
return Some((idx, pred.constness));
}
}
None
Expand Down Expand Up @@ -1683,9 +1685,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| BuiltinCandidate { .. }
| TraitAliasCandidate(..)
| ObjectCandidate(_)
| ProjectionCandidate(_),
| ProjectionCandidate(..),
) => !is_global(cand),
(ObjectCandidate(_) | ProjectionCandidate(_), ParamCandidate(ref cand)) => {
(ObjectCandidate(_) | ProjectionCandidate(..), ParamCandidate(ref cand)) => {
// Prefer these to a global where-clause bound
// (see issue #50825).
is_global(cand)
Expand All @@ -1707,20 +1709,20 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
is_global(cand) && other.evaluation.must_apply_modulo_regions()
}

(ProjectionCandidate(i), ProjectionCandidate(j))
(ProjectionCandidate(i, _), ProjectionCandidate(j, _))
| (ObjectCandidate(i), ObjectCandidate(j)) => {
// Arbitrarily pick the lower numbered candidate for backwards
// compatibility reasons. Don't let this affect inference.
i < j && !needs_infer
}
(ObjectCandidate(_), ProjectionCandidate(_))
| (ProjectionCandidate(_), ObjectCandidate(_)) => {
(ObjectCandidate(_), ProjectionCandidate(..))
| (ProjectionCandidate(..), ObjectCandidate(_)) => {
bug!("Have both object and projection candidate")
}

// Arbitrarily give projection and object candidates priority.
(
ObjectCandidate(_) | ProjectionCandidate(_),
ObjectCandidate(_) | ProjectionCandidate(..),
ImplCandidate(..)
| ClosureCandidate
| GeneratorCandidate
Expand All @@ -1742,7 +1744,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| TraitUpcastingUnsizeCandidate(_)
| BuiltinCandidate { .. }
| TraitAliasCandidate(..),
ObjectCandidate(_) | ProjectionCandidate(_),
ObjectCandidate(_) | ProjectionCandidate(..),
) => false,

(&ImplCandidate(other_def), &ImplCandidate(victim_def)) => {
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Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
// check-pass
#![feature(const_trait_impl)]

#[const_trait]
trait Foo {
type Assoc: ~const Foo;
fn foo() {}
}

const fn foo<T: ~const Foo>() {
<T as Foo>::Assoc::foo();
}

fn main() {}

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