error[E0658]: use of unstable library feature 'trace_macros': `trace_macros` is not stable enough for use and is subject to change --> $DIR/feature-gate-trace_macros.rs:2:5 | LL | trace_macros!(true); | ^^^^^^^^^^^^ | = note: see issue #29598 for more information = help: add `#![feature(trace_macros)]` to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.