Analyzer treats required named parameters in superclasses as non-optional from legacy libraries

[munificent]

Given this legacy library:

// @dart=2.8
import 'null_safe.dart';

class Legacy extends NullSafe {}

main() {
  Legacy();
}

// And this null-safe one:

class NullSafe {
  NullSafe({required String s});
}

I would expect this code to be OK. The implicit super() call in Legacy to call NullSafe() should be allowed because NullSafe's required named parameter should be treated as optional from the context of a legacy library.

Instead, I get:

Analyzing /Users/rnystrom/Documents/legacy.dart...
  error • The superclass 'NullSafe' doesn't have a zero argument constructor. • /Users/rnystrom/Documents/legacy.dart:4:7 • no_default_super_constructor
1 error found.

[nshahan]

And a reference to required parameters being optional in the definition of LEGACY_SUBTYPE(S, T) https://github.com/dart-lang/language/blob/master/accepted/future-releases/nnbd/feature-specification.md#subtyping.

[leafpetersen]

@munificent we evidently don't have a test for this, any chance you could add one?

[munificent]

How did I know you were going to say that? :) @scheglov, would you like me to write a test for this or will you in the process of fixing it? I won't get to it until Monday, but I'm happy to then.

[scheglov]

This should fix the issue in the analyzer.

https://dart-review.googlesource.com/c/sdk/+/162584

[munificent]

Language test: https://dart-review.googlesource.com/c/sdk/+/163740