Only display other method receiver candidates if they actually apply

Previously, we would suggest `Box<Self>` as a valid receiver, even if
method resolution only succeeded due to an autoderef (e.g. to `&self`)

src/librustc_typeck/check/expr.rs

@@ -913,10 +913,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  rcvr,
  probe::ProbeScope::AllTraits,
  ) {
- err.span_label(
- pick.item.ident.span,
- &format!("the method is available for `{}` here", new_rcvr_t),
- );
+ debug!("try_alt_rcvr: pick candidate {:?}", pick);
+ // Make sure the method is defined for the *actual* receiver:
+ // we don't want to treat `Box<Self>` as a receiver if
+ // it only works because of an autoderef to `&self`
+ if pick.autoderefs == 0 {
+ err.span_label(
+ pick.item.ident.span,
+ &format!("the method is available for `{}` here", new_rcvr_t),
+ );
+ }
  }
  }
  };

src/test/ui/impl-trait/no-method-suggested-traits.stderr

@@ -49,14 +49,6 @@ LL | use foo::Bar;
 error[E0599]: no method named `method` found for struct `std::rc::Rc<&mut std::boxed::Box<&char>>` in the current scope
  --> $DIR/no-method-suggested-traits.rs:32:43
  |
-LL | fn method(&self) {}
- | ------
- | |
- | the method is available for `std::boxed::Box<std::rc::Rc<&mut std::boxed::Box<&char>>>` here
- | the method is available for `std::pin::Pin<std::rc::Rc<&mut std::boxed::Box<&char>>>` here
- | the method is available for `std::sync::Arc<std::rc::Rc<&mut std::boxed::Box<&char>>>` here
- | the method is available for `std::rc::Rc<std::rc::Rc<&mut std::boxed::Box<&char>>>` here
-...
 LL | std::rc::Rc::new(&mut Box::new(&'a')).method();
  | ^^^^^^ method not found in `std::rc::Rc<&mut std::boxed::Box<&char>>`
  |
@@ -83,16 +75,6 @@ error[E0599]: no method named `method` found for struct `std::rc::Rc<&mut std::b
  |
 LL | std::rc::Rc::new(&mut Box::new(&1i32)).method();
  | ^^^^^^ method not found in `std::rc::Rc<&mut std::boxed::Box<&i32>>`
- | 
- ::: $DIR/auxiliary/no_method_suggested_traits.rs:8:12
- |
-LL | fn method(&self) {}
- | ------
- | |
- | the method is available for `std::boxed::Box<std::rc::Rc<&mut std::boxed::Box<&i32>>>` here
- | the method is available for `std::pin::Pin<std::rc::Rc<&mut std::boxed::Box<&i32>>>` here
- | the method is available for `std::sync::Arc<std::rc::Rc<&mut std::boxed::Box<&i32>>>` here
- | the method is available for `std::rc::Rc<std::rc::Rc<&mut std::boxed::Box<&i32>>>` here
  |
  = help: items from traits can only be used if the trait is in scope
 help: the following trait is implemented but not in scope; perhaps add a `use` for it:

src/test/ui/traits/trait-item-privacy.stderr

@@ -20,13 +20,6 @@ error[E0599]: no method named `b` found for struct `S` in the current scope
 LL | struct S;
  | --------- method `b` not found for this
 ...
-LL | fn b(&self) { }
- | -
- | |
- | the method is available for `std::boxed::Box<S>` here
- | the method is available for `std::sync::Arc<S>` here
- | the method is available for `std::rc::Rc<S>` here
-...
 LL | S.b();
  | ^ method not found in `S`
  |