error[E0308]: mismatched types
  --> $DIR/issue-51154.rs:2:30
   |
LL | fn foo<F: FnMut()>() {
   |        - this type parameter
LL |     let _: Box<F> = Box::new(|| ());
   |                     -------- ^^^^^ expected type parameter `F`, found closure
   |                     |
   |                     arguments to this function are incorrect
   |
   = note: expected type parameter `F`
                     found closure `[closure@$DIR/issue-51154.rs:2:30: 2:32]`
   = help: every closure has a distinct type and so could not always match the caller-chosen type of parameter `F`
note: associated function defined here
  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
   |
LL |     pub fn new(x: T) -> Self {
   |            ^^^

error: aborting due to previous error

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