Skip to content

Commit

Permalink
Add comments
Browse files Browse the repository at this point in the history
  • Loading branch information
@estebank
estebank committed Oct 23, 2019
1 parent 580a93e commit 3a4cacd
Showing 1 changed file with 73 additions and 0 deletions.
73 changes: 73 additions & 0 deletions src/librustc/ty/wf.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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| {
Expand All @@ -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)),
Expand Down

0 comments on commit 3a4cacd

Please sign in to comment.