diff options
| -rw-r--r-- | src/librustc/ty/wf.rs | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/src/librustc/ty/wf.rs b/src/librustc/ty/wf.rs index 84bcec6bd19..9f8e62a0614 100644 --- a/src/librustc/ty/wf.rs +++ b/src/librustc/ty/wf.rs @@ -179,6 +179,47 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { let item_span = item.map(|i| tcx.sess.source_map().def_span(i.span)); match pred { ty::Predicate::Projection(proj) => { + // The obligation comes not from the current `impl` nor the `trait` being + // implemented, but rather from a "second order" obligation, like in + // `src/test/ui/associated-types/point-at-type-on-obligation-failure.rs`: + // + // error[E0271]: type mismatch resolving `<Foo2 as Bar2>::Ok == ()` + // --> $DIR/point-at-type-on-obligation-failure.rs:13:5 + // | + // LL | type Ok; + // | -- associated type defined here + // ... + // LL | impl Bar for Foo { + // | ---------------- in this `impl` item + // LL | type Ok = (); + // | ^^^^^^^^^^^^^ expected u32, found () + // | + // = note: expected type `u32` + // found type `()` + // + // FIXME: we would want to point a span to all places that contributed to this + // obligation. In the case above, it should be closer to: + // + // error[E0271]: type mismatch resolving `<Foo2 as Bar2>::Ok == ()` + // --> $DIR/point-at-type-on-obligation-failure.rs:13:5 + // | + // LL | type Ok; + // | -- associated type defined here + // LL | type Sibling: Bar2<Ok=Self::Ok>; + // | -------------------------------- obligation set here + // ... + // LL | impl Bar for Foo { + // | ---------------- in this `impl` item + // LL | type Ok = (); + // | ^^^^^^^^^^^^^ expected u32, found () + // ... + // LL | impl Bar2 for Foo2 { + // | ---------------- in this `impl` item + // LL | type Ok = u32; + // | -------------- obligation set here + // | + // = note: expected type `u32` + // found type `()` if let Some(hir::ItemKind::Impl(.., impl_items)) = item.map(|i| &i.kind) { let trait_assoc_item = tcx.associated_item(proj.projection_def_id()); if let Some(impl_item) = impl_items.iter().filter(|item| { @@ -193,6 +234,38 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { } } ty::Predicate::Trait(proj) => { + // An associated item obligation born out of the `trait` failed to be met. + // Point at the `impl` that failed the obligation, the associated item that + // needed to meet the obligation, and the definition of that associated item, + // which should hold the obligation in most cases. An example can be seen in + // `src/test/ui/associated-types/point-at-type-on-obligation-failure-2.rs`: + // + // error[E0277]: the trait bound `bool: Bar` is not satisfied + // --> $DIR/point-at-type-on-obligation-failure-2.rs:8:5 + // | + // LL | type Assoc: Bar; + // | ----- associated type defined here + // ... + // LL | impl Foo for () { + // | --------------- in this `impl` item + // LL | type Assoc = bool; + // | ^^^^^^^^^^^^^^^^^^ the trait `Bar` is not implemented for `bool` + // + // FIXME: if the obligation comes from the where clause in the `trait`, we + // should point at it: + // + // error[E0277]: the trait bound `bool: Bar` is not satisfied + // --> $DIR/point-at-type-on-obligation-failure-2.rs:8:5 + // | + // | trait Foo where <Self as Foo>>::Assoc: Bar { + // | -------------------------- obligation set here + // LL | type Assoc; + // | ----- associated type defined here + // ... + // LL | impl Foo for () { + // | --------------- in this `impl` item + // LL | type Assoc = bool; + // | ^^^^^^^^^^^^^^^^^^ the trait `Bar` is not implemented for `bool` if let ( ty::Projection(ty::ProjectionTy { item_def_id, .. }), Some(hir::ItemKind::Impl(.., impl_items)), |