error[E0594]: cannot assign to `t.v`, which is behind a `&` reference
  --> $DIR/suggest-mut-method-for-loop-closure.rs:15:13
   |
LL |         for mut t in buzz.values() {
   |                      -------------
   |                      |    |
   |                      |    help: use mutable method: `values_mut()`
   |                      this iterator yields `&` references
...
LL |             t.v += 1;
   |             ^^^^^^^^ `t` is a `&` reference, so the data it refers to cannot be written

error: aborting due to previous error

For more information about this error, try `rustc --explain E0594`.