error[E0308]: mismatched types
  --> $DIR/constraint-assoc-type-suggestion.rs:10:23
   |
LL |     let b: Vec<i32> = a;
   |            --------   ^ expected `Vec<i32>`, found associated type
   |            |
   |            expected due to this
   |
   = note:       expected struct `Vec<i32>`
           found associated type `<T as X>::Y<i32>`
help: consider constraining the associated type `<T as X>::Y<i32>` to `Vec<i32>`
   |
LL | fn f<T: X<Y<i32> = Vec<i32>>>(a: T::Y<i32>) {
   |          +++++++++++++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.