error[E0658]: yield syntax is experimental
  --> $DIR/feature-gate-yield-expr.rs:5:5
   |
LL |     yield ();
   |     ^^^^^^^^
   |
   = note: see issue #43122 <https://github.com/rust-lang/rust/issues/43122> for more information
   = help: add `#![feature(yield_expr)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0658]: yield syntax is experimental
  --> $DIR/feature-gate-yield-expr.rs:5:5
   |
LL |     yield ();
   |     ^^^^^^^^
   |
   = note: see issue #43122 <https://github.com/rust-lang/rust/issues/43122> for more information
   = help: add `#![feature(yield_expr)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error: `yield` can only be used in `#[coroutine]` closures, or `gen` blocks
  --> $DIR/feature-gate-yield-expr.rs:5:5
   |
LL |     yield ();
   |     ^^^^^^^^
   |
help: use `#[coroutine]` to make this closure a coroutine
   |
LL | #[coroutine] fn main() {
   | ++++++++++++

error[E0627]: yield expression outside of coroutine literal
  --> $DIR/feature-gate-yield-expr.rs:5:5
   |
LL |     yield ();
   |     ^^^^^^^^

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0627, E0658.
For more information about an error, try `rustc --explain E0627`.