`[ArgumentsSource]` does not support ref struct

[timcassell]

This works:

[Arguments(new int[] { 1, 2, 3 })]
public void Benchmark(Span<int> args) { }

But this errors:

[ArgumentsSource(nameof(GetArgs))]
public void Benchmark(Span<int> args) { }

public IEnumerable<object[]> GetArgs()
{
    yield return new object[] { new int[] { 1, 2, 3 } };
}

Ambiguous user defined conversions 'Span.implicit operator Span(ArraySegment)' and 'Span.implicit operator Span(int[]?)' when converting from 'object' to 'Span'

Looking at the generated code, it's because of this:

__argField0 = (System.Span<System.Int32>)BenchmarkDotNet.Parameters.ParameterExtractor.GetParameter(GetArgs(), 0);;

So the code generator should take into account the actual type of the element if the argument is a ref struct so that both attributes work the same (which it seems it already does partially, because the field type is correct, only the cast is incorrect).

[dmitrenko-v]

Hi! Can I work on this one?

[timcassell]

@dmitrenko-v Yes, it's marked up-for-grabs.