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adjust obligation spans for super projections

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This commit is contained in:
Lukas Markeffsky 2024-02-08 16:56:47 +01:00
parent 6fa58be8f4
commit 189e7843e8
6 changed files with 84 additions and 52 deletions
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92
compiler/rustc_trait_selection/src/traits/wf.rs
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@ -223,60 +223,84 @@ enum Elaborate {
None,
}
/// Points the cause span of a super predicate at the relevant associated type.
///
/// Given a trait impl item:
///
/// ```ignore (incomplete)
/// impl TargetTrait for TargetType {
/// type Assoc = SomeType;
/// }
/// ```
///
/// And a super predicate of `TargetTrait` that has any of the following forms:
///
/// 1. `<OtherType as OtherTrait>::Assoc = <TargetType as TargetTrait>::Assoc`
/// 2. `<<TargetType as TargetTrait>::Assoc as OtherTrait>::Assoc = OtherType`
/// 3. `<TargetType as TargetTrait>::Assoc: OtherTrait`
///
/// Replace the span of the cause with the span of the associated item:
///
/// ```ignore (incomplete)
/// impl TargetTrait for TargetType {
/// type Assoc = SomeType;
/// // ^^^^^^^^ this span
/// }
/// ```
///
/// Note that bounds that can be expressed as associated item bounds are **not**
/// super predicates. This means that form 2 and 3 from above are only relevant if
/// the [`GenericArgsRef`] of the projection type are not its identity arguments.
fn extend_cause_with_original_assoc_item_obligation<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::TraitRef<'tcx>,
item: Option<&hir::Item<'tcx>>,
cause: &mut traits::ObligationCause<'tcx>,
pred: ty::Predicate<'tcx>,
) {
debug!(
"extended_cause_with_original_assoc_item_obligation {:?} {:?} {:?} {:?}",
trait_ref, item, cause, pred
);
debug!(?item, ?cause, ?pred, "extended_cause_with_original_assoc_item_obligation");
let (items, impl_def_id) = match item {
Some(hir::Item { kind: hir::ItemKind::Impl(impl_), owner_id, .. }) => {
(impl_.items, *owner_id)
}
_ => return,
};
let fix_span =
|impl_item_ref: &hir::ImplItemRef| match tcx.hir().impl_item(impl_item_ref.id).kind {
hir::ImplItemKind::Const(ty, _) | hir::ImplItemKind::Type(ty) => ty.span,
_ => impl_item_ref.span,
};
let ty_to_impl_span = |ty: Ty<'_>| {
if let ty::Alias(ty::Projection, projection_ty) = ty.kind()
&& let Some(&impl_item_id) =
tcx.impl_item_implementor_ids(impl_def_id).get(&projection_ty.def_id)
&& let Some(impl_item) =
items.iter().find(|item| item.id.owner_id.to_def_id() == impl_item_id)
{
Some(tcx.hir().impl_item(impl_item.id).expect_type().span)
} else {
None
}
};
// It is fine to skip the binder as we don't care about regions here.
match pred.kind().skip_binder() {
ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj)) => {
// The obligation comes not from the current `impl` nor the `trait` being implemented,
// but rather from a "second order" obligation, where an associated type has a
// projection coming from another associated type. See
// `tests/ui/associated-types/point-at-type-on-obligation-failure.rs` and
// `traits-assoc-type-in-supertrait-bad.rs`.
if let Some(ty::Alias(ty::Projection, projection_ty)) =
proj.term.ty().map(|ty| ty.kind())
&& let Some(&impl_item_id) =
tcx.impl_item_implementor_ids(impl_def_id).get(&projection_ty.def_id)
&& let Some(impl_item_span) = items
.iter()
.find(|item| item.id.owner_id.to_def_id() == impl_item_id)
.map(fix_span)
// Form 1: The obligation comes not from the current `impl` nor the `trait` being
// implemented, but rather from a "second order" obligation, where an associated
// type has a projection coming from another associated type.
// See `tests/ui/traits/assoc-type-in-superbad.rs` for an example.
if let Some(term_ty) = proj.term.ty()
&& let Some(impl_item_span) = ty_to_impl_span(term_ty)
{
cause.span = impl_item_span;
}
// Form 2: A projection obligation for an associated item failed to be met.
if let Some(impl_item_span) = ty_to_impl_span(proj.self_ty()) {
cause.span = impl_item_span;
}
}
ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
// An associated item obligation born out of the `trait` failed to be met. An example
// can be seen in `ui/associated-types/point-at-type-on-obligation-failure-2.rs`.
// Form 3: A trait obligation for an associated item failed to be met.
debug!("extended_cause_with_original_assoc_item_obligation trait proj {:?}", pred);
if let ty::Alias(ty::Projection, ty::AliasTy { def_id, .. }) = *pred.self_ty().kind()
&& let Some(&impl_item_id) = tcx.impl_item_implementor_ids(impl_def_id).get(&def_id)
&& let Some(impl_item_span) = items
.iter()
.find(|item| item.id.owner_id.to_def_id() == impl_item_id)
.map(fix_span)
{
if let Some(impl_item_span) = ty_to_impl_span(pred.self_ty()) {
cause.span = impl_item_span;
}
}
@ -355,9 +379,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
traits::ObligationCauseCode::DerivedObligation,
);
}
extend_cause_with_original_assoc_item_obligation(
tcx, trait_ref, item, &mut cause, predicate,
);
extend_cause_with_original_assoc_item_obligation(tcx, item, &mut cause, predicate);
traits::Obligation::with_depth(tcx, cause, depth, param_env, predicate)
};