error: Does not hold :
         feature = "unknown"
 --> ../../../rust/test/diagnostics/inc/cta_true_fail.rs:5:3
  |
5 |   cta_true!( feature = "unknown" );
  |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: this error originates in the macro `cta_true` (in Nightly builds, run with -Z macro-backtrace for more info)