Add NotNullWhen attribute to IsInstanceValid argument

[Joy-less]

The code for Node.IsInstanceValid in C# is as follows, according to the reflector:

public static bool IsInstanceValid(GodotObject? instance)
{
    if (instance != null)
    {
        return instance.NativeInstance != IntPtr.Zero;
    }
    return false;
}

One common use case of IsInstanceValid is to check whether an instance is not null and not disposed.
However, if you use it this way:

Node? MyNode = new();
public override void _Ready() {
    if (!IsInstanceValid(MyNode)) {
        return;
    }
    GD.Print(MyNode.Name); // Dereference of a possibly null reference.
}

This can be resolved by adding a NotNullWhenAttribute to the instance argument.
This tells the C# compiler that if the method returns true, the instance cannot be null.

public static bool IsInstanceValid([NotNullWhen(true)] GodotObject? instance)
{
    if (instance != null)
    {
        return instance.NativeInstance != IntPtr.Zero;
    }
    return false;
}

[raulsntos]

Sounds good. Feel free to open a pull request to add the attribute 🙂.

[Joy-less]

Opened: godotengine/godot#95431