Allow derived record members with covariant properties

[alrz]

Currently record properties of the base type must be of the exact same type:

abstract record R(object Prop);
sealed record R1(string Prop) : R(Prop);
// error CS8866: Record member 'R.Prop' must be a readable instance property or field of type 'string' to match positional parameter 'Prop'.

But the compiler could use covariant return types to allow this:

abstract class R
{
    public abstract object Prop { get; }
}
sealed class R1(string Prop) : R
{
    public override string Prop { get; } = Prop;
}

[CyrusNajmabadi]

I don't understand how this would work. What would the following compile down to: R r = new R1(); r with { Prop = 4 }?

[333fred]

You're missing inits on those properties @alrz.

[alrz]

This is a huge inconvenience when thinking about how you would workaround it, because you may not need the init accessor as it is the case for this scenario.