error[E0308]: mismatched types
  --> $DIR/issue-79187.rs:5:5
   |
LL |     thing(f);
   |     ^^^^^^^^ one type is more general than the other
   |
   = note: expected trait `for<'a> FnOnce(&'a u32)`
              found trait `FnOnce(&u32)`
note: this closure does not fulfill the lifetime requirements
  --> $DIR/issue-79187.rs:4:13
   |
LL |     let f = |_| ();
   |             ^^^
note: the lifetime requirement is introduced here
  --> $DIR/issue-79187.rs:1:18
   |
LL | fn thing(x: impl FnOnce(&u32)) {}
   |                  ^^^^^^^^^^^^
help: consider specifying the type of the closure parameters
   |
LL |     let f = |_: &_| ();
   |             ~~~~~~~

error: implementation of `FnOnce` is not general enough
  --> $DIR/issue-79187.rs:5:5
   |
LL |     thing(f);
   |     ^^^^^^^^ implementation of `FnOnce` is not general enough
   |
   = note: closure with signature `fn(&'2 u32)` must implement `FnOnce<(&'1 u32,)>`, for any lifetime `'1`...
   = note: ...but it actually implements `FnOnce<(&'2 u32,)>`, for some specific lifetime `'2`

error: aborting due to 2 previous errors

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