Is it possible to get a warning if return value is not used?

Question

I have an extension method which returns a value. In this case, it should set a specific bit in a byte:

public static byte SetBit(this byte b, int bitNumber, bool value)
{
    if (value)
    {
        return (byte)(b | (1 << bitNumber));
    }
    return (byte)(b & ~(1 << bitNumber));
}

The returned value needs to be assigned to a variable again, because I cannot combine this and ref:

byte myByte = 3;
myByte = myByte.SetBit(1, false);

It is easy to forget the assignment by accident. Someone might think that the method changes the value directly.

For a String.Replace, ReSharper/Visual Studio^(?) is warning me that the Return value of pure method is not used:

Is this also possible for my method in some way?

Answer 1

Update:

Now there is a PureAttribute in the System.Diagnostics.Contracts namespace.

[Pure]
public byte Foo()
{
    //...
}

---

Pre .NET Standard 2.0 Answer:

There seems to be a Nuget Package for ReSharper Annotations.

This includes a MustUseReturnValueAttribute:

[MustUseReturnValue("Use the return value to...")]
public byte Foo()
{    
}

As @Kirk Woll pointed out in the comments, it is also possible to write a custom Roslyn Analyzer.