error[E0038]: the trait `Bar` cannot be made into an object
  --> $DIR/issue-18959.rs:11:11
   |
LL | pub trait Foo { fn foo<T>(&self, ext_thing: &T); }
   |                    --- ...because method `foo` has generic type parameters
LL | pub trait Bar: Foo { }
   |           --- this trait cannot be made into an object...
...
LL | fn foo(b: &dyn Bar) {
   |           ^^^^^^^^ the trait `Bar` cannot be made into an object
   |
   = help: consider moving `foo` to another trait

error: aborting due to previous error

For more information about this error, try `rustc --explain E0038`.