Error code E0565

A literal was used in a built-in attribute that doesn't support literals.

Erroneous code example:

#[repr("C")] // error: meta item in `repr` must be an identifier
struct Repr {}

fn main() {}

Literals in attributes are new and largely unsupported in built-in attributes. Work to support literals where appropriate is ongoing. Try using an unquoted name instead:

#[repr(C)] // ok!
struct Repr {}

fn main() {}