error[E0391]: cycle detected when computing type of `Foo::X`
  --> $DIR/cycle-trait-default-type-trait.rs:4:23
   |
LL | trait Foo<X = Box<dyn Foo>> {
   |                       ^^^
   |
   = note: ...which immediately requires computing type of `Foo::X` again
note: cycle used when collecting item types in top-level module
  --> $DIR/cycle-trait-default-type-trait.rs:4:1
   |
LL | / trait Foo<X = Box<dyn Foo>> {
LL | |
LL | |
LL | | }
LL | |
LL | | fn main() { }
   | |_____________^

error[E0391]: cycle detected when computing type of `Foo::X`
  --> $DIR/cycle-trait-default-type-trait.rs:4:23
   |
LL | trait Foo<X = Box<dyn Foo>> {
   |                       ^^^
   |
   = note: ...which immediately requires computing type of `Foo::X` again
note: cycle used when collecting item types in top-level module
  --> $DIR/cycle-trait-default-type-trait.rs:4:1
   |
LL | / trait Foo<X = Box<dyn Foo>> {
LL | |
LL | |
LL | | }
LL | |
LL | | fn main() { }
   | |_____________^

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0391`.