Invalid suggest for methods in auto trait

[chenyukang]

Given the following code

#![feature(auto_traits)]

auto trait Foo {
    fn g(&self);
}

trait Bar  {
    fn f(&self) {
        self.g();
    }
}

fn main() {}

The current output is:

error[E0380]: auto traits cannot have associated items
 --> src/main.rs:4:8
  |
3 | auto trait Foo {
  |            --- auto trait cannot have associated items
4 |     fn g(&self);
  |     ---^-------- help: remove these associated items

error[E0554]: `#![feature]` may not be used on the stable release channel
 --> src/main.rs:1:1
  |
1 | #![feature(auto_traits)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^

error[E0599]: the method `g` exists for reference `&Self`, but its trait bounds were not satisfied
 --> src/main.rs:9:14
  |
9 |         self.g();
  |              ^
  |
note: trait bound `&Self: Foo` was not satisfied
  = note: the following trait bounds were not satisfied:
          `Self: Foo`
          which is required by `&Self: Foo`
  = help: items from traits can only be used if the type parameter is bounded by the trait
help: the following trait defines an item `g`, perhaps you need to add a supertrait for it:
  |
7 | trait Bar: Foo  {
  |          +++++

Some errors have detailed explanations: E0380, E0554, E0599.
For more information about an error, try `rustc --explain E0380`.
error: could not compile `playground` due to 3 previous errors

The second error is not reasonable, since we don't allow associated items in auto trait.
Ideally the output should look like:

error[E0599]: no method named `g` found for reference `&Self` in the current scope
 --> ./p/e.rs:9:14
  |
9 |         self.g();
  |

[chenyukang]

@compiler-errors
I spent some time to investigate it, I tried to filter the candidates from auto trait.
But seems unsatisfied_predicates here have two predicates, and the message for the second error comes from the first TraitPredicate:

[
    (Binder(TraitPredicate(<Self as Foo>, polarity:Positive), []), Some(Binder(TraitPredicate(<&Self as Foo>, polarity:Positive), [])), Some(ObligationCause { span: ./p/e.rs:9:14: 9:15 (#0), body_id: HirId { owner: OwnerId { def_id: DefId(0:6 ~ e[8a4c]::Bar::f) }, local_id: 9 }, code: BuiltinDerivedObligation(DerivedObligationCause { parent_trait_pred: Binder(TraitPredicate(<_ as Foo>, polarity:Positive), []), parent_code: MiscObligation }) })),

    (Binder(TraitPredicate(<&Self as Foo>, polarity:Positive), []), None, Some(ObligationCause { span: ./p/e.rs:9:14: 9:15 (#0), body_id: HirId { owner: OwnerId { def_id: DefId(0:6 ~ e[8a4c]::Bar::f) }, local_id: 9 }, code: ImplDerivedObligation(ImplDerivedObligationCause { derived: DerivedObligationCause { parent_trait_pred: Binder(TraitPredicate(<_ as Foo>, polarity:Positive), []), parent_code: BuiltinDerivedObligation(DerivedObligationCause { parent_trait_pred: Binder(TraitPredicate(<_ as Foo>, polarity:Positive), []), parent_code: MiscObligation }) }, impl_def_id: DefId(0:3 ~ e[8a4c]::Foo), span: no-location (#0) }) }))
]

I'm still trying to understand the code.

[chenyukang]

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