Nullable warning isn't emitted when passing default to a struct parameter

Repro:

using System;
#nullable enable

public class Person
{
    public string Name { get; }
    
    public Person(string name) =>
        Name = name ?? throw new ArgumentNullException(nameof(name));
}

public struct MyStruct
{
    public Person person;
}

public static class Program
{
    public static void Foo(MyStruct s)
    {
        Console.WriteLine(s.person.Name);
    }
    
    public static void Main() => Foo(default); // Expected warning here. Because MyStruct contains a non-nullable reference type.
}

The previous example throws NullReferenceException.

I think any struct containing a non-nullable reference type should have a warning when it takes the value “default”.

[sharwell]

https://github.com/dotnet/csharplang/issues/99#issuecomment-601792573

[Youssef1313]

The current behavior is “By Design”.

I wouldn’t classify this as “blocked” because generally I associate that with bug fixes or design decisions. Essentially I internalize “blocked” as “yes this is a bug but we can’t make progress due to a related work item or decision from LDM”.

In this particular case though the language is operating as designed. The use of default with struct is a known hole in the C# nullable analysis, similar to null in array elements. The referenced csharplang issue isn’t a proposal to change this design. Rather it’s a proposal to add a new feature which users could then take advantage of to potentially work around this hole.

That’s clear enough. Let me close.