NuGet config file name inconsistent when accessing via WSL UNC paths

[paulmedynski]

NuGet Product Used

dotnet.exe, NuGet.exe

Product Version

9.0.101

Worked before?

Unknown

Impact

It bothers me. A fix would be nice

Repro Steps & Context

Describe the bug

On WSL Linux and Windows, with the project on the local filesystem, dotnet nuget config paths will consider a file named nuget.config, NuGet.config, or NuGet.Config at the solution/project root.

On Windows, accessing the project via WSL UNC paths or mapped drives, dotnet nuget config paths will only consider a file named NuGet.Config.

The CLI tools should be consistent regarding which NuGet config filenames are considered regardless of paths or filesystems.

To Reproduce

In WSL, create a new project

$ mkdir NugetIssue
$ cd NugetIssue
$ dotnet new console

Create a Nuget config file named nuget.config with the following content:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
  </packageSources>
</configuration>

In WSL, check that the NuGet config file will be considered:

$ dotnet nuget config paths
/home/paul/dev/NugetIssue/nuget.config
/home/paul/.nuget/NuGet/NuGet.Config

In a Windows CMD or PowerShell prompt, navigate to the WSL directory:

PS C:\Users\paulmedynski> D:
PS D:\> cd \home\paul\dev\NugetIssue

In this case, I have mapped the root filesystem of my WSL distro to D: in Windows, since CMD doesn't support UNC paths. Using the full UNC path in PowerShell exhibits the same behaviour.

Check what config files NuGet will consider:

PS D:\home\paul\dev\NugetIssue> dotnet nuget config paths
C:\Users\paulmedynski\AppData\Roaming\NuGet\NuGet.Config

Rename the config file to "NuGet.Config":

PS D:\home\paul\dev\NugetIssue> move nuget.config NuGet.config
PS D:\home\paul\dev\NugetIssue> dotnet nuget config paths
D:\home\paul\dev\NugetIssue\NuGet.Config
C:\Users\paulmedynski\AppData\Roaming\NuGet\NuGet.Config

Additionally, the public documentation regarding NuGet configs uses a mix of NuGet.Config and nuget.config, making it unclear exactly which config filenames are supported by default:

https://learn.microsoft.com/en-us/nuget/consume-packages/configuring-nuget-behavior

Verbose Logs

WSL Linux:

$ dotnet --info
.NET SDK:
 Version:           9.0.101
 Commit:            eedb237549
 Workload version:  9.0.100-manifests.3068a692
 MSBuild version:   17.12.12+1cce77968

Runtime Environment:
 OS Name:     debian
 OS Version:  12
 OS Platform: Linux
 RID:         linux-x64
 Base Path:   /usr/share/dotnet/sdk/9.0.101/

.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.

Host:
  Version:      9.0.0
  Architecture: x64
  Commit:       9d5a6a9aa4

.NET SDKs installed:
  9.0.101 [/usr/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 9.0.0 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 9.0.0 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
  None

Environment variables:
  Not set

global.json file:
  /home/paul/dev/sandbox/ctaip/global.json

Learn more:
  https://aka.ms/dotnet/info

Download .NET:
  https://aka.ms/dotnet/download

Windows 11:

dotnet --info
.NET SDK:
 Version:           9.0.101
 Commit:            eedb237549
 Workload version:  9.0.100-manifests.3068a692
 MSBuild version:   17.12.12+1cce77968

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.26100
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\9.0.101\

.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.

Host:
  Version:      9.0.0
  Architecture: x64
  Commit:       9d5a6a9aa4

.NET SDKs installed:
  9.0.101 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  None

Environment variables:
  Not set

global.json file:
  C:\Users\paulmedynski\dev\ctaip\global.json

Learn more:
  https://aka.ms/dotnet/info

Download .NET:
  https://aka.ms/dotnet/download

[paulmedynski]

I originally submitted this issue to the .NET SDK project:

dotnet/sdk#45357