error[E0495]: cannot infer an appropriate lifetime for lifetime parameter '_ in generic type due to conflicting requirements
  --> $DIR/resolve-re-error-ice.rs:12:5
   |
LL |     fn key_set(&self) -> Subject<'a, Keys<K, V>, (), R> {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime defined here...
  --> $DIR/resolve-re-error-ice.rs:5:16
   |
LL |     fn key_set(&self) -> Subject<Keys<K, V>, (), R>;
   |                ^^^^^
note: ...so that the method type is compatible with trait
  --> $DIR/resolve-re-error-ice.rs:12:5
   |
LL |     fn key_set(&self) -> Subject<'a, Keys<K, V>, (), R> {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: expected `fn(&Subject<'_, _, _, _>) -> Subject<'_, std::collections::hash_map::Keys<'_, _, _>, _, _>`
              found `fn(&Subject<'_, _, _, _>) -> Subject<'a, std::collections::hash_map::Keys<'_, _, _>, _, _>`
note: but, the lifetime must be valid for the lifetime `'a` as defined here...
  --> $DIR/resolve-re-error-ice.rs:10:6
   |
LL | impl<'a, K, V, R> MapAssertion<'a, K, V, R> for Subject<'a, HashMap<K, V>, (), R>
   |      ^^
note: ...so that the type `std::collections::hash_map::Keys<'_, K, V>` will meet its required lifetime bounds...
  --> $DIR/resolve-re-error-ice.rs:12:5
   |
LL |     fn key_set(&self) -> Subject<'a, Keys<K, V>, (), R> {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...that is required by this bound
  --> $DIR/resolve-re-error-ice.rs:8:29
   |
LL | struct Subject<'a, T, V, R>(PhantomData<(&'a T, V, R)>);
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0495`.