error[E0658]: The attribute `rustfmt::bar` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
  --> $DIR/tool-attributes-disabled-1.rs:14:1
   |
LL | #[rustfmt::bar] //~ ERROR The attribute `rustfmt::bar` is currently unknown to the compiler
   | ^^^^^^^^^^^^^^^
   |
   = help: add #![feature(custom_attribute)] to the crate attributes to enable

error: aborting due to previous error

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