|  | error[E0658]: use of an internal attribute | 
|  | --> $DIR/feature-gate-pattern-complexity-limit.rs:3:1 | 
|  | | | 
|  | LL | #![pattern_complexity_limit = "42"] | 
|  | | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | 
|  | | | 
|  | = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable | 
|  | = note: the `#[pattern_complexity_limit]` attribute is an internal implementation detail that will never be stable | 
|  | = note: the `#[pattern_complexity_limit]` attribute is used for rustc unit tests | 
|  |  | 
|  | error: aborting due to 1 previous error | 
|  |  | 
|  | For more information about this error, try `rustc --explain E0658`. |