Compiler error when combines throw expression together with generic types and null-coalescing operator

[sgjsakura]

Version Used:
Visual Studio 2017
Steps to Reproduce:
The following code can reproduce the error:

public void Test<T>(T value)
{
  var x = value ?? throw new ArgumentNullException(nameof(value));
}

Expected Behavior:
The above code should be compiled correctly.
Actual Behavior:
CS0019: The '??' operator cannot be apply between type T and <throw expression>

[0xd4d]

Try public void Test<T>(T value) where T : class

[gafter]

The interaction with the throw expression is a red herring. This also fails, as it should:

        var y = value ?? default(T);

The problem is that value isn't a nullable type or a reference type. Try the suggestion made by @0xd4d .

[sgjsakura]

While the C# language sepcification says comparison between an unrestricted genertic value and null is accepable, and it will returns true/false if the actual type is non-nullable. actually, the following code can pass the compilation check:

var x = (value != null) ? value : default(T);

So does it possible to enhance the compiler to accept nul-coalescing for unrestricted genertic value?

Thanks~

[gafter]

@sgjsakura Yes, the language specification can be changed to make the compiler support that. Language feature requests are taken at https://github.com/dotnet/csharplang