warning: trait objects without an explicit `dyn` are deprecated
  --> $DIR/avoid-ice-on-warning-2.rs:4:13
   |
LL | fn id<F>(f: Copy) -> usize {
   |             ^^^^
   |
   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
   = note: `#[warn(bare_trait_objects)]` on by default
help: if this is an object-safe trait, use `dyn`
   |
LL | fn id<F>(f: dyn Copy) -> usize {
   |             +++

warning: trait objects without an explicit `dyn` are deprecated
  --> $DIR/avoid-ice-on-warning-2.rs:4:13
   |
LL | fn id<F>(f: Copy) -> usize {
   |             ^^^^
   |
   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
help: if this is an object-safe trait, use `dyn`
   |
LL | fn id<F>(f: dyn Copy) -> usize {
   |             +++

error[E0038]: the trait `Copy` cannot be made into an object
  --> $DIR/avoid-ice-on-warning-2.rs:4:13
   |
LL | fn id<F>(f: Copy) -> usize {
   |             ^^^^ `Copy` cannot be made into an object
   |
   = note: the trait cannot be made into an object because it requires `Self: Sized`
   = note: for a trait to be "object safe" 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>

error[E0618]: expected function, found `(dyn Copy + 'static)`
  --> $DIR/avoid-ice-on-warning-2.rs:11:5
   |
LL | fn id<F>(f: Copy) -> usize {
   |          - `f` has type `(dyn Copy + 'static)`
...
LL |     f()
   |     ^--
   |     |
   |     call expression requires function

error[E0277]: the size for values of type `(dyn Copy + 'static)` cannot be known at compilation time
  --> $DIR/avoid-ice-on-warning-2.rs:4:10
   |
LL | fn id<F>(f: Copy) -> usize {
   |          ^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `(dyn Copy + 'static)`
   = help: unsized fn params are gated as an unstable feature
help: you can use `impl Trait` as the argument type
   |
LL | fn id<F>(f: impl Copy) -> usize {
   |             ++++
help: function arguments must have a statically known size, borrowed types always have a known size
   |
LL | fn id<F>(f: &dyn Copy) -> usize {
   |             ++++

error: aborting due to 3 previous errors; 2 warnings emitted

Some errors have detailed explanations: E0038, E0277, E0618.
For more information about an error, try `rustc --explain E0038`.