Warn if a class with const constructor can actually never be const constructed

[goderbauer]

My understanding from flutter/flutter#102460 (comment) and dart-lang/language#1296 is that the following class can actually never be const constructed.

@immutable
class Foo {
  const Foo(this.list) : assert(list.length > 2);
  final List<int> list;
}

To make this clear, the const should be removed from the constructor. Would it be possible to have a lint for that reminds people to not mark it as const?

[eernstg]

dart-lang/language#1296 would actually make list.length in the assertion a compile-time error, so this issue could be considered to be a request for a lint in the case where dart-archive/linter#1296 is rejected.

Also note that dart-lang/language#2219 would introduce support for that expression, so it would just work.