Overload resolution ambiguity introduced by SDK 8.0.300-preview.24203.14

[danielcweber]

The SDK 8 preview that comes with the latest VS2022 preview introduces an overload resolution ambiguity that is not in the stable SDK.

Version Used:

8.0.300-preview.24203.14

Steps to Reproduce:

See this repo for a reproduction and this or this workflow run to watch a build fail.

The issue is also in the latest SDK 9 preview. It's not reproducible on dotnetfiddle/sharplab, the latest SDK bits there are seemingly not recent enough.

Everything is fine on 8.0.204.

This might be related to collection expression conversions since the method overload in question has a params [] parameter.

Note: I also opened an issue in the sdk repo but this might be the more appropriate place.

Update
AzDO issues:

• https://dev.azure.com/devdiv/DevDiv/_workitems/edit/2065691

[cston]

Overload resolution is not preferring the overload with the more specific params array type in this case (in BetterFunctionMember).

cc @AlekseyTs

[AlekseyTs]

The code from the repo:

using System;

namespace OverloadResolutionRepro
{
    public class Foo
    {
        public void Method<S>(params Func<Bar, S>[] projections) => throw new NotImplementedException();
        public void Method<S>(params Func<Bar, Wrapper<S>>[] projections) => throw new NotImplementedException();
    }

    public class Bar
    {
        public Wrapper<int> WrappedValue { get; set; } = new Wrapper<int>();
    }

    public struct Wrapper<TValue>
    {
    }

    public class EntryPoint
    {
        static void Main()
        {
            new Foo().Method(x => x.WrappedValue);
        }
    }
}

[danielcweber]

The error code is CS0121 (if you came here by searching issues for this code) and apparently the bug made it's way into SDK 8.0.300.