Need annotation for nullable property with non-nullable setter

[jcouv]

Let's bring this up with LDM.

        public ITaskItem[]? Sources
        {
            set
            {
                if (UsedCommandLineTool)
                {
                    NormalizePaths(value!); // PROTOTYPE(NullableDogfood): value set should be non-null
                }

                _store[nameof(Sources)] = value;
            }
            get { return (ITaskItem[])_store[nameof(Sources)]; }
        }

[sharwell]

💭 In most cases where I hit this so far, the property was able to be rewritten in this form. It doesn't work for everything but likely covers many.

public SomeType Property
{
  get => _value ?? throw new InvalidOperationException("The object is not yet initialized");
  set => _value = value;
}

[jcouv]

This was resolved by the new attribute design. We can restrict or relax inbound values with [Disallow/AllowNull] and restrict/relax outbound values with [Not/MaybeNull].

See https://github.com/dotnet/csharplang/blob/master/meetings/2019/LDM-2019-05-15.md