error[E0658]: the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate which contains compiler-rt intrinsics and will never be stable --> $DIR/feature-gate-compiler-builtins.rs:1:1 | LL | #![compiler_builtins] | ^^^^^^^^^^^^^^^^^^^^^ | = help: add `#![feature(compiler_builtins)]` to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.