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Rollup merge of #70892 - lcnr:interators_are_nice, r=nikomatsakis
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wf: refactor `compute_trait_ref`

moves `extend_cause_with_original_assoc_item_obligation` out of `compute_trait_ref` and
changes `trait_assoc_items` to an iterator. This saves us from building an unnecessary `Vec<_>`

r? @eddyb i guess
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@Dylan-DPC
Dylan-DPC authored Apr 8, 2020
2 parents 6696666 + ab4178b commit e3346e5
Showing 1 changed file with 151 additions and 155 deletions.
306 changes: 151 additions & 155 deletions src/librustc_trait_selection/traits/wf.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -134,6 +134,152 @@ enum Elaborate {
None,
}

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<'_>,
mut trait_assoc_items: impl Iterator<Item = ty::AssocItem>,
) {
let trait_item =
tcx.hir().as_local_hir_id(trait_ref.def_id).and_then(|trait_id| tcx.hir().find(trait_id));
let (trait_name, trait_generics) = match trait_item {
Some(hir::Node::Item(hir::Item {
ident,
kind: hir::ItemKind::Trait(.., generics, _, _),
..
}))
| Some(hir::Node::Item(hir::Item {
ident,
kind: hir::ItemKind::TraitAlias(generics, _),
..
})) => (Some(ident), Some(generics)),
_ => (None, None),
};

let item_span = item.map(|i| tcx.sess.source_map().guess_head_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 { items, .. }) = item.map(|i| &i.kind) {
let trait_assoc_item = tcx.associated_item(proj.projection_def_id());
if let Some(impl_item) =
items.iter().find(|item| item.ident == trait_assoc_item.ident)
{
cause.span = impl_item.span;
cause.code = traits::AssocTypeBound(Box::new(AssocTypeBoundData {
impl_span: item_span,
original: trait_assoc_item.ident.span,
bounds: vec![],
}));
}
}
}
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`
//
// If the obligation comes from the where clause in the `trait`, we 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 {
// | -------------------------- restricted in this bound
// 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 { items, .. }),
) = (&proj.skip_binder().self_ty().kind, item.map(|i| &i.kind))
{
if let Some((impl_item, trait_assoc_item)) = trait_assoc_items
.find(|i| i.def_id == *item_def_id)
.and_then(|trait_assoc_item| {
items
.iter()
.find(|i| i.ident == trait_assoc_item.ident)
.map(|impl_item| (impl_item, trait_assoc_item))
})
{
let bounds = trait_generics
.map(|generics| {
get_generic_bound_spans(&generics, trait_name, trait_assoc_item.ident)
})
.unwrap_or_else(Vec::new);
cause.span = impl_item.span;
cause.code = traits::AssocTypeBound(Box::new(AssocTypeBoundData {
impl_span: item_span,
original: trait_assoc_item.ident.span,
bounds,
}));
}
}
}
_ => {}
}
}

impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
fn cause(&mut self, code: traits::ObligationCauseCode<'tcx>) -> traits::ObligationCause<'tcx> {
traits::ObligationCause::new(self.span, self.body_id, code)
Expand Down Expand Up @@ -163,170 +309,20 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
let cause = self.cause(traits::MiscObligation);
let param_env = self.param_env;

let item = &self.item;
let extend_cause_with_original_assoc_item_obligation =
|cause: &mut traits::ObligationCause<'_>,
pred: &ty::Predicate<'_>,
trait_assoc_items: &[ty::AssocItem]| {
let trait_item = tcx
.hir()
.as_local_hir_id(trait_ref.def_id)
.and_then(|trait_id| tcx.hir().find(trait_id));
let (trait_name, trait_generics) = match trait_item {
Some(hir::Node::Item(hir::Item {
ident,
kind: hir::ItemKind::Trait(.., generics, _, _),
..
}))
| Some(hir::Node::Item(hir::Item {
ident,
kind: hir::ItemKind::TraitAlias(generics, _),
..
})) => (Some(ident), Some(generics)),
_ => (None, None),
};

let item_span = item.map(|i| tcx.sess.source_map().guess_head_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 { items, .. }) = item.map(|i| &i.kind) {
let trait_assoc_item = tcx.associated_item(proj.projection_def_id());
if let Some(impl_item) =
items.iter().find(|item| item.ident == trait_assoc_item.ident)
{
cause.span = impl_item.span;
cause.code = traits::AssocTypeBound(Box::new(AssocTypeBoundData {
impl_span: item_span,
original: trait_assoc_item.ident.span,
bounds: vec![],
}));
}
}
}
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`
//
// If the obligation comes from the where clause in the `trait`, we 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 {
// | -------------------------- restricted in this bound
// 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 { items, .. }),
) = (&proj.skip_binder().self_ty().kind, item.map(|i| &i.kind))
{
if let Some((impl_item, trait_assoc_item)) = trait_assoc_items
.iter()
.find(|i| i.def_id == *item_def_id)
.and_then(|trait_assoc_item| {
items
.iter()
.find(|i| i.ident == trait_assoc_item.ident)
.map(|impl_item| (impl_item, trait_assoc_item))
})
{
let bounds = trait_generics
.map(|generics| {
get_generic_bound_spans(
&generics,
trait_name,
trait_assoc_item.ident,
)
})
.unwrap_or_else(Vec::new);
cause.span = impl_item.span;
cause.code = traits::AssocTypeBound(Box::new(AssocTypeBoundData {
impl_span: item_span,
original: trait_assoc_item.ident.span,
bounds,
}));
}
}
}
_ => {}
}
};
let item = self.item;

if let Elaborate::All = elaborate {
// FIXME: Make `extend_cause_with_original_assoc_item_obligation` take an iterator
// instead of a slice.
let trait_assoc_items: Vec<_> =
tcx.associated_items(trait_ref.def_id).in_definition_order().copied().collect();

let predicates = obligations.iter().map(|obligation| obligation.predicate).collect();
let implied_obligations = traits::elaborate_predicates(tcx, predicates);
let implied_obligations = implied_obligations.map(|pred| {
let mut cause = cause.clone();
extend_cause_with_original_assoc_item_obligation(
tcx,
trait_ref,
item,
&mut cause,
&pred,
&*trait_assoc_items,
tcx.associated_items(trait_ref.def_id).in_definition_order().copied(),
);
traits::Obligation::new(cause, param_env, pred)
});
Expand Down

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