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() {}