False positive CS8618 null reference type warning when using required members and [SetsRequiredMembers] in derived class

[SapiensAnatis]

Version Used:

Compiler version: '4.10.0-3.24314.14 (259e82e9)'. Language version: 12.0., but also reproduces on main (11 Jun 2024) on Sharplab.

Steps to Reproduce:

1. Compile the following code (sharplab):

using System.Diagnostics.CodeAnalysis;

public abstract class Base
{
    [SetsRequiredMembers]
    public Base(string @string)
    {
        this.String = @string;
    }
    
    public required abstract string String { get; init; }
}

public class Derived : Base
{
    [SetsRequiredMembers]
    public Derived(string @string) : base(@string)
    {
    }

    public override required string String { get; init; }
}

Diagnostic Id:

CS8618: Non-nullable property 'String' must contain a non-null value when exiting constructor. Consider declaring the property as nullable.

Expected Behavior:

No diagnostics, because the base class sets the value.

Actual Behavior:

A diagnotic on the constructor of Derived.

Additional Information

If I remove the : Base from Derived and make it an independent class, I get the same warning. This leads me to suspect this is a case of the nullable reference type analysis not being sophisticated enough to determine I have set String in the base constructor. I am aware that NRT analysis doesn't support every pattern under the sun and there are many ways you can 'trick' it. If this is one of those cases, I apologize - but I thought it was worth mentioning all the same.

[jaredpar]

@333fred for comment as I'm unsure what the correct behavior is here.

[333fred]

I told them to open this bug. It doesn't seem like we're correctly handling the virtual property here.