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Merged
merged 1 commit into from
Dec 19, 2019
Merged

Suggest associated type when the specified one cannot be found #67406

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103 changes: 72 additions & 31 deletions src/librustc_typeck/astconv.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1145,11 +1145,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
} else {
// Otherwise, we have to walk through the supertraits to find
// those that do.
let candidates = traits::supertraits(tcx, trait_ref).filter(|r| {
self.trait_defines_associated_type_named(r.def_id(), binding.item_name)
});
self.one_bound_for_assoc_type(
candidates,
|| traits::supertraits(tcx, trait_ref),
&trait_ref.print_only_trait_path().to_string(),
binding.item_name,
binding.span
Expand Down Expand Up @@ -1531,50 +1528,48 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {

debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);

let bounds = predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());

// Check that there is exactly one way to find an associated type with the
// correct name.
let suitable_bounds = traits::transitive_bounds(tcx, bounds)
.filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));

let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
let param_name = tcx.hir().ty_param_name(param_hir_id);
self.one_bound_for_assoc_type(suitable_bounds,
&param_name.as_str(),
assoc_name,
span)
self.one_bound_for_assoc_type(
|| traits::transitive_bounds(tcx, predicates
.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref())),
&param_name.as_str(),
assoc_name,
span,
)
}

// Checks that `bounds` contains exactly one element and reports appropriate
// errors otherwise.
fn one_bound_for_assoc_type<I>(&self,
mut bounds: I,
all_candidates: impl Fn() -> I,
ty_param_name: &str,
assoc_name: ast::Ident,
span: Span)
-> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
where I: Iterator<Item = ty::PolyTraitRef<'tcx>>
{
let bound = match bounds.next() {
let mut matching_candidates = all_candidates().filter(|r| {
self.trait_defines_associated_type_named(r.def_id(), assoc_name)
});

let bound = match matching_candidates.next() {
Some(bound) => bound,
None => {
struct_span_err!(self.tcx().sess, span, E0220,
"associated type `{}` not found for `{}`",
assoc_name,
ty_param_name)
.span_label(span, format!("associated type `{}` not found", assoc_name))
.emit();
self.complain_about_assoc_type_not_found(
all_candidates,
ty_param_name,
assoc_name,
span
);
return Err(ErrorReported);
}
};

debug!("one_bound_for_assoc_type: bound = {:?}", bound);

if let Some(bound2) = bounds.next() {
if let Some(bound2) = matching_candidates.next() {
debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);

let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
let mut err = struct_span_err!(
self.tcx().sess, span, E0221,
"ambiguous associated type `{}` in bounds of `{}`",
Expand Down Expand Up @@ -1606,6 +1601,50 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
return Ok(bound);
}

fn complain_about_assoc_type_not_found<I>(&self,
all_candidates: impl Fn() -> I,
ty_param_name: &str,
assoc_name: ast::Ident,
span: Span)
where I: Iterator<Item = ty::PolyTraitRef<'tcx>> {
let mut err = struct_span_err!(self.tcx().sess, span, E0220,
"associated type `{}` not found for `{}`",
assoc_name,
ty_param_name);

let all_candidate_names: Vec<_> = all_candidates()
.map(|r| self.tcx().associated_items(r.def_id()))
.flatten()
.filter_map(|item|
if item.kind == ty::AssocKind::Type {
Some(item.ident.name)
} else {
None
}
)
.collect();

if let Some(suggested_name) = find_best_match_for_name(
all_candidate_names.iter(),
&assoc_name.as_str(),
None,
) {
err.span_suggestion(
span,
"there is an associated type with a similar name",
suggested_name.to_string(),
Applicability::MaybeIncorrect,
);
} else {
err.span_label(
span,
format!("associated type `{}` not found", assoc_name)
);
}

err.emit();
}

// Create a type from a path to an associated type.
// For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
// and item_segment is the path segment for `D`. We return a type and a def for
Expand Down Expand Up @@ -1660,10 +1699,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
}
};

let candidates = traits::supertraits(tcx, ty::Binder::bind(trait_ref))
.filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_ident));

self.one_bound_for_assoc_type(candidates, "Self", assoc_ident, span)?
self.one_bound_for_assoc_type(
|| traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
"Self",
assoc_ident,
span
)?
}
(&ty::Param(_), Res::SelfTy(Some(param_did), None)) |
(&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
Expand Down
2 changes: 1 addition & 1 deletion src/test/ui/span/type-binding.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@ error[E0220]: associated type `Trget` not found for `std::ops::Deref`
--> $DIR/type-binding.rs:6:20
|
LL | fn homura<T: Deref<Trget = i32>>(_: T) {}
| ^^^^^^^^^^^ associated type `Trget` not found
| ^^^^^^^^^^^ help: there is an associated type with a similar name: `Target`

error: aborting due to previous error

Expand Down