error[E0277]: the trait bound `T: Default` is not satisfied
  --> $DIR/issue-52843.rs:8:5
   |
LL |     t
   |     ^ the trait `Default` is not implemented for `T`
   |
note: required by a bound in an opaque type
  --> $DIR/issue-52843.rs:3:20
   |
LL | type Foo<T> = impl Default;
   |                    ^^^^^^^
note: this definition site has more where clauses than the opaque type
  --> $DIR/issue-52843.rs:7:1
   |
LL | fn foo<T: Default>(t: T) -> Foo<T> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider restricting type parameter `T` with trait `Default`
   |
LL | type Foo<T: std::default::Default> = impl Default;
   |           +++++++++++++++++++++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.