error: Parent message
   |
error: Child message
  --> $DIR/sub-error-diag.rs:9:1
   |
LL | #[sub_error_diag::proc_emit_err]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this error originates in the attribute macro `sub_error_diag::proc_emit_err` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 1 previous error