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Explain that associated types and consts can't be accessed directly o…

…n the trait's path
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estebank committed Dec 31, 2019
1 parent ed6468d commit ac3d4cccea3225468a3c8ff8ea18b60166c84fb8
@@ -2075,7 +2075,30 @@ 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 {
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.def_id()),
assoc_item.ident
),
Applicability::HasPlaceholders,
);
}
}
} 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);
@@ -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

@@ -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

@@ -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

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