error[E0658]: use of unstable library feature 'concat_bytes' --> $DIR/feature-gate-concat_bytes.rs:2:13 | LL | let a = concat_bytes!(b'A', b"BC"); | ^^^^^^^^^^^^ | = note: see issue #87555 for more information = help: add `#![feature(concat_bytes)]` to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.