warning: trait objects without an explicit `dyn` are deprecated
  --> $DIR/not-on-bare-trait.rs:7:12
   |
LL | fn foo(_x: Foo + Send) {
   |            ^^^^^^^^^^
   |
   = 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 a dyn-compatible trait, use `dyn`
   |
LL | fn foo(_x: dyn Foo + Send) {
   |            +++

error[E0277]: the size for values of type `(dyn Foo + Send + 'static)` cannot be known at compilation time
  --> $DIR/not-on-bare-trait.rs:7:12
   |
LL | fn foo(_x: Foo + Send) {
   |            ^^^^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `(dyn Foo + Send + 'static)`
   = help: unsized fn params are gated as an unstable feature
help: you can use `impl Trait` as the argument type
   |
LL | fn foo(_x: impl Foo + Send) {
   |            ++++
help: function arguments must have a statically known size, borrowed types always have a known size
   |
LL | fn foo(_x: &(dyn Foo + Send)) {
   |            +++++           +

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

error: aborting due to 2 previous errors; 1 warning emitted

For more information about this error, try `rustc --explain E0277`.