Enforce Required, Named Parameters

[felangel]

As a developer, when I define a class with a required, named parameter I would like all subclasses to have errors (or at least a warning) if the required parameter was not passed to the superclass.

class A {
  const A(this.x);

  final int x;
}

class B extends A {}

The above snippet currently won't compile (expected):

If I refactor class A to make x a required, named parameter, however, the code compiles just fine without any error/warning (not expected).

import 'package:meta/meta.dart';

class A {
  const A({@required this.x});

  final int x;
}

class B extends A {}

This will definitely not be an issue once NNBD lands in stable but for now it's seems there isn't a good way to safely support required, named parameters.

Additional Info

This tracker is for issues related to:

• Analyzer
• Dart core libraries ("meta")

Dart Version

Dart VM version: 2.8.4 (stable) (Wed Jun 3 12:26:04 2020 +0200) on "macos_x64"

OS

MacOSX

[lrhn]

The analyzer does indeed fail to recognize that the implicit super() of the default constructors (or a user-written generative constructor with an omitted super-call) is not passing a @required parameter.

Compiling should work because Dart compilers mostly ignore metadata like @required. Only the Dart analyzer understand the meaning of @required, but it too fails to give a warning here, (dartanalyzer version 2.9.0-18.0.dev).

[srawlins]

This works now with the null-safety feature, required. No further work will be done to support the @required annotation.