message: ParametersSpec minor code cleanup
diff: @@ -136,12 +136,12 @@ impl<V> ParametersSpecBuilder<V> {
  let i = self.kinds.len();
  self.kinds.push(val);
  let old = self.names.insert(name, i);
  + assert!(old.is_none(), "Repeated parameter `{}`", name);
  if self.args.is_none() && !self.no_args {
  // If you've already seen `args` or `no_args`, you can't enter these
  // positionally
  self.positional = i + 1;
  }
  - assert!(old.is_none());
  }
  /// Add a required parameter. Will be an error if the caller doesn't supply
  