error[E0599]: no method named `is_subset` found for reference `&HashSet<T>` in the current scope
  --> $DIR/issue-35677.rs:4:10
   |
LL |     this.is_subset(other)
   |          ^^^^^^^^^ method not found in `&HashSet<T>`
   |
   = note: the method `is_subset` exists but the following trait bounds were not satisfied:
           `T: Eq`
           `T: Hash`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0599`.