Empty NuGet.config file causing restore failures with 5.0.202

[marcpopMSFT]

Description:
I was told this might be the right repo for filing this issue. Also sent email to a few contacts at GH.

We're seeing customer reports of customers using GitHub Actions with 5.0.202 and failing to restore any files from Nuget.org. This appears to be because the machine has an empty nuget.config file picked up by the build process which causes NuGet to ignore nuget.org.

Example customer reports along with workaround
dotnet/installer#10171

NuGet change that affected this
NuGet/NuGet.Client#3907

Task version:
Unknown

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Repro steps:
name: .NET
on:
push:
branches: [ master ]
pull_request:
branches: [ master ]
jobs:
build:
runs-on: windows-latest
steps:

• uses: actions/checkout@v2
• name: Setup .NET
  uses: actions/setup-dotnet@v1
  with:
  dotnet-version: 5.0.x
• name: Restore dependencies
  run: dotnet restore
• name: Build
  run: dotnet build --no-restore
• name: Test
  run: dotnet test --no-build --verbosity normal

Expected behavior:
Build succeeds restoring files from NuGet.org.
https://github.com/pownas/asp-net-yaml-yml-build-tester/runs/2283517744?check_suite_focus=true

Actual behavior:
error NU1101: Unable to find package Microsoft.AspNetCore.Identity.UI. No packages exist with this id in source(s): Microsoft Visual Studio Offline Packages
https://github.com/pownas/asp-net-yaml-yml-build-tester/runs/2283517744?check_suite_focus=true

[marcpopMSFT]

Sample repro from Andy. Looks like Maxim is engaged in email now.
https://github.com/zivkan/ci-nugetconfig-check/runs/2292176156?check_suite_focus=true

[maxim-lobanov]

Related issue: actions/runner-images#3038

[samsmithnz]

I'm hitting this too. Short term workaround seems to be to use .NET 5.0.201:

    - uses: actions/setup-dotnet@v1
      with:
        dotnet-version: 5.0.201

[vsafonkin]

PR with fix for Windows runner was merged: actions/runner-images#3144

[vsafonkin]

Related issue in choco repository: chocolatey/choco#2233

[vsafonkin]

Hi @marcpopMSFT, do you still have this issue?

[marcpopMSFT]

From internal emails, I believe this has been resolved in GH actions at this point.