error[E0283]: type annotations needed
  --> $DIR/issue-85735.rs:7:8
   |
LL |     T: FnMut(&'a ()),
   |        ^^^^^^^^^^^^^ cannot infer type for type parameter `T`
   |
   = note: cannot satisfy `T: FnMut<(&'a (),)>`
note: required by a bound in `FnMut`
  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
   |
LL | / pub trait FnMut<Args>: FnOnce<Args> {
LL | |     /// Performs the call operation.
LL | |     #[unstable(feature = "fn_traits", issue = "29625")]
LL | |     extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output;
LL | | }
   | |_^ required by this bound in `FnMut`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.