error[E0369]: binary operation `*` cannot be applied to type `Thing`
  --> $DIR/issue-3820.rs:14:15
   |
LL |     let w = u * 3;
   |             - ^ - {integer}
   |             |
   |             Thing
   |
   = note: an implementation of `std::ops::Mul` might be missing for `Thing`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0369`.