error[E0658]: attributes on expressions are experimental
  --> $DIR/feature-gate-stmt_expr_attributes.rs:1:16
   |
LL | const X: i32 = #[allow(dead_code)] 8;
   |                ^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
   = help: add `#![feature(stmt_expr_attributes)]` 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   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date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]: attributes on expressions are experimental
  --> $DIR/feature-gate-stmt_expr_attributes.rs:5:5
   |
LL |     /// foo
   |     ^^^^^^^
   |
   = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
   = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
   = help: `///` is used for outer documentation comments; for a plain comment, use `//`

error[E0658]: attributes on expressions are experimental
  --> $DIR/feature-gate-stmt_expr_attributes.rs:10:5
   |
LL |     //! foo
   |     ^^^^^^^
   |
   = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
   = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
   = help: `//!` is used for inner documentation comments; for a plain comment, use `//` by removing the `!` or inserting a space in between them: `// !`

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0658`.