error[E0308]: method not compatible with trait
  --> $DIR/issue-37884.rs:6:5
   |
LL | /     fn next(&'a mut self) -> Option<Self::Item>
LL | |
LL | |
LL | |     {
LL | |         Some(&mut self.0)
LL | |     }
   | |_____^ lifetime mismatch
   |
   = note: expected type `fn(&mut RepeatMut<'a, T>) -> std::option::Option<&mut T>`
              found type `fn(&'a mut RepeatMut<'a, T>) -> std::option::Option<&mut T>`
note: the anonymous lifetime #1 defined on the method body at 6:5...
  --> $DIR/issue-37884.rs:6:5
   |
LL | /     fn next(&'a mut self) -> Option<Self::Item>
LL | |
LL | |
LL | |     {
LL | |         Some(&mut self.0)
LL | |     }
   | |_____^
note: ...does not necessarily outlive the lifetime 'a as defined on the impl at 3:6
  --> $DIR/issue-37884.rs:3:6
   |
LL | impl<'a, T: 'a> Iterator for RepeatMut<'a, T> {
   |      ^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.