error[E0599]: the method `is_subset` exists for reference `&HashSet<T>`, but its trait bounds were not satisfied
  --> $DIR/issue-35677.rs:7:10
   |
LL |     this.is_subset(other)
   |          ^^^^^^^^^ method cannot be called on `&HashSet<T>` due to unsatisfied trait bounds
   |
   = note: the following trait bounds were not satisfied:
           `T: Eq`
           `T: PartialEq`
           which is required by `T: Eq`
           `T: Hash`
help: consider restricting the type parameters to satisfy the trait bounds
   |
LL | fn is_subset<T>(this: &HashSet<T>, other: &HashSet<T>) -> bool where T: Eq, T: Hash {
   |                                                                ++++++++++++++++++++

error: aborting due to 1 previous error

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