Why does this tiny program give "Common Language Runtime detected an invalid program"?

user_500976 0
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I have a very minimal .NET 6 program:

using System.Numerics;

var transform = new Transform2(default);

public readonly record struct Transform2(Vector2 Position, float Rotation)
{
    public Transform2(Vector2 position) : this()
    {
        Position = position;
    }
}

When I run it, I get an exception:

 System.InvalidProgramException: Common Language Runtime detected an invalid program.
   at Transform2..ctor(Vector2 position)

Reproducible dotnetfiddle

Why does this happen? Is it a bug in the C# compiler?

.net-6.0 exception c#
2 Answers

Looking into this with SharpLab, you will find this = default(Transform2); in the constructor which is weird and seem to be a bug as mentioned by Matthew Watson in the comments. Any way, I don't see any reason not to change the constructor to public Transform2(Vector2 position) : this(position, default) which does not seem to cause this problem.

user_97482600

Based on Sohaiub Jundi's answer, I used SharpLab to dig some more (that site is awesome!), turns out the latest Roslyn build flags this as a compiler error:

error CS8982: A constructor declared in a 'record struct' with parameter list must have a 'this' initializer that calls the primary constructor or an explicitly declared constructor.

So apparently it is a bug in the currently latest .NET 6 version, and will be fixed in an upcoming release.

A workaround for now is to explicitly call the full constructor with all arguments:

using System.Numerics;

var transform = new Transform2(default);

public readonly record struct Transform2(Vector2 Position, float Rotation)
{
    public Transform2(Vector2 position) : this(position, default)
    {
        Position = position;
    }
}
user_5009760
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