error[E0283]: type annotations needed
  --> $DIR/unstable_impl_method_selection.rs:11:12
   |
LL |     vec![].foo();
   |            ^^^ cannot infer type for struct `Vec<_>`
   |
   = note: multiple `impl`s satisfying `Vec<_>: Trait` found in the `unstable_impl_method_selection_aux` crate:
           - impl Trait for Vec<u32>;
           - impl Trait for Vec<u64>
             where feature(bar) is enabled;

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0283`.