NuGet.Protocol disappears from bin in version 3.0.4 or greater

[joelverhagen]

Repro steps

1. Open Visual Studio (I have 16.5.3)
2. Create a new Azure Function project.
3. Install the latest version of NuGet.Protocol (I have 5.5.1)
4. Update the Microsoft.NET.Sdk.Functions package to 3.0.4 (My template had 3.0.3)
5. Add a bit of code to reference the package.
6. Start the function locally (Ctrl+ F5)

This is the code I used.

using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using NuGet.Protocol;
using NuGet.Protocol.Core.Types;

namespace WhyNoNuGet
{
    public static class Function1
    {
        [FunctionName("Function1")]
        public static async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = null)] HttpRequest req)
        {
            var repository = Repository.Factory.GetCoreV3("https://api.nuget.org/v3/index.json");
            await repository.GetResourceAsync<FindPackageByIdResource>();
            return new OkObjectResult("Done.");
        }
    }
}

Excepted

App should start, and find NuGet.Protocol.

This is what I see when I am using Microsoft.NET.Sdk.Functions 3.0.3:

NuGet.Protocol should be in the bin directory.

Actual

The app shows error on start-up with 3.0.4, 3.0.5, and 3.0.6 (I tried them all)

[4/18/2020 8:51:43 AM] The 'Function1' function is in error: Unable to load one or more of the requested types.
[4/18/2020 8:51:43 AM] Could not load file or assembly 'NuGet.Protocol, Version=5.5.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. The system cannot find the file specified.
[4/18/2020 8:51:43 AM] Microsoft.Azure.WebJobs.Host: Error indexing method 'Function1'. System.Private.CoreLib: Could not load file or assembly 'NuGet.Protocol, Version=5.5.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. The system cannot find the file specified.

Note that the bin directory is much more empty with 3.0.4 and on (note there is no NuGet.Protocol)

[simonness]

@joelverhagen I bumped into a very similar issue, see Azure/azure-functions-host#5894 for a temporary workaround.

[ghost]

I had the exact same problem with Microsoft.NET.Sdk.Functions 3.0.9 and NuGet.Protocol 5.8.0.
The workaround suggested in Azure/azure-functions-host#5894 did help:

<PropertyGroup>
    <_FunctionsSkipCleanOutput>true</_FunctionsSkipCleanOutput>
  </PropertyGroup>

Thanks a lot @simonness 👍