error[E0539]: malformed `inline` attribute input
  --> $DIR/E0539.rs:1:1
   |
LL | #[inline(unknown)]
   | ^^^^^^^^^-------^^
   |          |
   |          valid arguments are `always` or `never`
   |
   = note: for more information, visit <https://doc.rust-lang.org/reference/attributes/codegen.html#the-inline-attribute>
help: try changing it to one of the following valid forms of the attribute
   |
LL - #[inline(unknown)]
LL + #[inline(always)]
   |
LL - #[inline(unknown)]
LL + #[inline(never)]
   |
LL - #[inline(unknown)]
LL + #[inline]
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0539`.