error[E0599]: no method named `drain` found for type `&mut std::collections::HashMap<K, V>` in the current scope
  --> $DIR/issue-35677.rs:3:10
   |
LL |     this.drain()
   |          ^^^^^
   |
   = note: the method `drain` exists but the following trait bounds were not satisfied:
           `K : std::cmp::Eq`
           `K : std::hash::Hash`

error: aborting due to previous error

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