error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
  --> $DIR/associated-types-unconstrained.rs:14:20
   |
LL |     fn bar() -> isize;
   |     ------------------ `Foo::bar` defined here
...
LL |     let x: isize = Foo::bar();
   |                    ^^^^^^^^ cannot call associated function of trait
   |
help: use the fully-qualified path to the only available implementation
   |
LL |     let x: isize = <isize as Foo>::bar();
   |                    +++++++++    +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0790`.