error[E0038]: the trait `issue_3907::Foo` cannot be made into an object
  --> $DIR/issue-3907-2.rs:11:12
   |
LL | fn bar(_x: Foo) {}
   |            ^^^ `issue_3907::Foo` cannot be made into an object
   |
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> $DIR/auxiliary/issue-3907.rs:2:8
   |
LL |     fn bar();
   |        ^^^ the trait cannot be made into an object because associated function `bar` has no `self` parameter

error[E0277]: the size for values of type `(dyn issue_3907::Foo + 'static)` cannot be known at compilation time
  --> $DIR/issue-3907-2.rs:11:12
   |
LL | fn bar(_x: Foo) {}
   |            ^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `(dyn issue_3907::Foo + 'static)`
   = help: unsized fn params are gated as an unstable feature
help: function arguments must have a statically known size, borrowed types always have a known size
   |
LL | fn bar(_x: &Foo) {}
   |            +

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0038, E0277.
For more information about an error, try `rustc --explain E0038`.