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Rollup merge of #67747 - estebank:bare-assoc-const, r=Centril

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Explain that associated types and consts can't be accessed directly on the trait's path

Partially address #44539.
This commit is contained in:
Mazdak Farrokhzad 2020-01-09 00:22:07 +01:00 • committed by GitHub
commit 1a0b2a5aaa
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4 changed files with 50 additions and 5 deletions
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31
src/librustc/traits/error_reporting.rs
View file

@ -2075,7 +2075,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
}
let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0283);
err.note(&format!("cannot resolve `{}`", predicate));
if let (Ok(ref snippet), ObligationCauseCode::BindingObligation(ref def_id, _)) =
if let ObligationCauseCode::ItemObligation(def_id) = obligation.cause.code {
self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
} else if let (
Ok(ref snippet),
ObligationCauseCode::BindingObligation(ref def_id, _),
) =
(self.tcx.sess.source_map().span_to_snippet(span), &obligation.cause.code)
{
let generics = self.tcx.generics_of(*def_id);
@ -2173,6 +2178,30 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
err.emit();
}
fn suggest_fully_qualified_path(
&self,
err: &mut DiagnosticBuilder<'_>,
def_id: DefId,
span: Span,
trait_ref: DefId,
) {
if let Some(assoc_item) = self.tcx.opt_associated_item(def_id) {
if let ty::AssocKind::Const | ty::AssocKind::Type = assoc_item.kind {
err.note(&format!(
"{}s cannot be accessed directly on a `trait`, they can only be \
accessed through a specific `impl`",
assoc_item.kind.suggestion_descr(),
));
err.span_suggestion(
span,
"use the fully qualified path to an implementation",
format!("<Type as {}>::{}", self.tcx.def_path_str(trait_ref), assoc_item.ident),
Applicability::HasPlaceholders,
);
}
}
}
/// Returns `true` if the trait predicate may apply for *some* assignment
/// to the type parameters.
fn predicate_can_apply(

12
src/test/ui/associated-const/issue-63496.stderr
View file

@ -5,9 +5,13 @@ LL | const C: usize;
| --------------- required by `A::C`
LL |
LL | fn f() -> ([u8; A::C], [u8; A::C]);
| ^^^^ cannot infer type
| ^^^^
| |
| cannot infer type
| help: use the fully qualified path to an implementation: `<Type as A>::C`
|
= note: cannot resolve `_: A`
= note: associated constants cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
error[E0283]: type annotations needed
--> $DIR/issue-63496.rs:4:33
@ -16,9 +20,13 @@ LL | const C: usize;
| --------------- required by `A::C`
LL |
LL | fn f() -> ([u8; A::C], [u8; A::C]);
| ^^^^ cannot infer type
| ^^^^
| |
| cannot infer type
| help: use the fully qualified path to an implementation: `<Type as A>::C`
|
= note: cannot resolve `_: A`
= note: associated constants cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
error: aborting due to 2 previous errors

6
src/test/ui/associated-item/issue-48027.stderr
View file

@ -13,9 +13,13 @@ error[E0283]: type annotations needed
LL | const X: usize;
| --------------- required by `Bar::X`
LL | fn return_n(&self) -> [u8; Bar::X];
| ^^^^^^ cannot infer type
| ^^^^^^
| |
| cannot infer type
| help: use the fully qualified path to an implementation: `<Type as Bar>::X`
|
= note: cannot resolve `_: Bar`
= note: associated constants cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
error: aborting due to 2 previous errors

6
src/test/ui/issues/issue-58022.stderr
View file

@ -11,9 +11,13 @@ LL | const SIZE: usize;
| ------------------ required by `Foo::SIZE`
LL |
LL | fn new(slice: &[u8; Foo::SIZE]) -> Self;
| ^^^^^^^^^ cannot infer type
| ^^^^^^^^^
| |
| cannot infer type
| help: use the fully qualified path to an implementation: `<Type as Foo>::SIZE`
|
= note: cannot resolve `_: Foo`
= note: associated constants cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
error: aborting due to 2 previous errors