error[E0038]: the trait `Bar` is not dyn compatible
  --> $DIR/issue-18959.rs:11:12
   |
LL | fn foo(b: &dyn Bar) {
   |            ^^^^^^^ `Bar` is not dyn compatible
   |
note: for a trait to be dyn compatible it needs to allow building a vtable
      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
  --> $DIR/issue-18959.rs:1:20
   |
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 is not dyn compatible...
   = help: consider moving `foo` to another trait

error[E0038]: the trait `Bar` is not dyn compatible
  --> $DIR/issue-18959.rs:18:20
   |
LL |     let test: &dyn Bar = &mut thing;
   |                    ^^^ `Bar` is not dyn compatible
   |
note: for a trait to be dyn compatible it needs to allow building a vtable
      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
  --> $DIR/issue-18959.rs:1:20
   |
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 is not dyn compatible...
   = help: consider moving `foo` to another trait

error[E0038]: the trait `Bar` is not dyn compatible
  --> $DIR/issue-18959.rs:20:9
   |
LL |     foo(test);
   |         ^^^^ `Bar` is not dyn compatible
   |
note: for a trait to be dyn compatible it needs to allow building a vtable
      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
  --> $DIR/issue-18959.rs:1:20
   |
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 is not dyn compatible...
   = help: consider moving `foo` to another trait

error: aborting due to 3 previous errors

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