error[E0308]: mismatched types
  --> $DIR/issue-2951.rs:13:10
   |
LL |     xx = y;
   |          ^ expected type parameter, found a different type parameter
   |
   = note: expected type `T`
              found type `U`

error: aborting due to previous error

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