warning: method `add_points` is never used
  --> $DIR/issue-3563-3.rs:115:8
   |
LL | trait Canvas {
   |       ------ method in this trait
...
LL |     fn add_points(&mut self, shapes: &[Point]) {
   |        ^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: 1 warning emitted