error[E0038]: the trait `Bar` cannot be made into an object
  --> $DIR/issue-18959.rs:11:1
   |
LL | pub trait Foo { fn foo<T>(&self, ext_thing: &T); }
   |                    --- method `foo` has generic type parameters
...
LL | fn foo(b: &dyn Bar) {
   | ^^^^^^^^^^^^^^^^^^^ the trait `Bar` cannot be made into an object

error: aborting due to previous error

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