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improve normalization of Pointee::Metadata #120354

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Merged
merged 4 commits into from
Feb 9, 2024
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Merged

improve normalization of Pointee::Metadata #120354

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77fb540
extend docs for `predicate_must_hold_considering_regions`
Feb 5, 2024
0c1f401
old solver: improve normalization of `Pointee::Metadata`
Feb 5, 2024
42cc1d2
new solver: improve normalization of `Pointee::Metadata`
Feb 5, 2024
15ffe83
add fixme
Feb 6, 2024
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5 changes: 4 additions & 1 deletion compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -410,7 +410,10 @@ impl<'tcx> assembly::GoalKind<'tcx> for NormalizesTo<'tcx> {
}

ty::Alias(_, _) | ty::Param(_) | ty::Placeholder(..) => {
// FIXME(ptr_metadata): It would also be possible to return a `Ok(Ambig)` with no constraints.
// This is the "fallback impl" for type parameters, unnormalizable projections
// and opaque types: If the `self_ty` is `Sized`, then the metadata is `()`.
// FIXME(ptr_metadata): This impl overlaps with the other impls and shouldn't
// exist. Instead, `Pointee<Metadata = ()>` should be a supertrait of `Sized`.
let sized_predicate = ty::TraitRef::from_lang_item(
tcx,
LangItem::Sized,
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7 changes: 4 additions & 3 deletions compiler/rustc_trait_selection/src/traits/project.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2302,9 +2302,10 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
};
let metadata_ty = self_ty.ptr_metadata_ty_or_tail(tcx, normalize).unwrap_or_else(|tail| {
if tail == self_ty {
// This is the fallback case for type parameters, unnormalizable projections
// and opaque types.
// If the `self_ty` is `Sized`, then the metadata is `()`.
// This is the "fallback impl" for type parameters, unnormalizable projections
// and opaque types: If the `self_ty` is `Sized`, then the metadata is `()`.
// FIXME(ptr_metadata): This impl overlaps with the other impls and shouldn't
// exist. Instead, `Pointee<Metadata = ()>` should be a supertrait of `Sized`.
let sized_predicate = ty::TraitRef::from_lang_item(
tcx,
LangItem::Sized,
Expand Down