error[E0658]: `builtin #` syntax is unstable --> $DIR/feature-gate-builtin_syntax.rs:6:15 | LL | builtin # offset_of(Foo, v); | ^^^^^^^^^ | = note: see issue #110680 for more information = help: add `#![feature(builtin_syntax)]` to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.