Irrelevant nuget.config on parent directory makes build failure on project directory

[huypn12]

Describe the bug

Irrelevant nuget.config on parent directory makes build failure on project directory.

To Reproduce

Create a solution directory

$ mkdir $HOME/Projects/some-project

Initialize a solution with a console project inside the solution directory

$ cd $HOME/Projects/some-project
$ dotnet new sln --name SomeProject \
        && dotnet new console --name SomeProject \
        && dotnet sln add SomeProject

Test build success

$ dotnet build
  Determining projects to restore...
  All projects are up-to-date for restore.
  SomeProject -> /home/huypn12/Projects/some-project/SomeProject/bin/Debug/net8.0/SomeProject.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:03.35

Now create an invalid nuget config on the parent directory:

$ touch $HOME/Projects/nuget.config
$ tee $HOME/Projects/nuget.config <<EOF
<packageSources>
    <add key="some-invalid-source" value="https://some-invalid-source/v3/index.json" protocolVersion="3" />
</packageSources>
EOF

Test build: failed

$ cd $HOME/Projects/some-project
$ dotnet build
  Determining projects to restore...
/usr/share/dotnet/sdk/8.0.404/NuGet.targets(745,5): error : NuGet.Config does not contain the expected root element: 'configuration'. Path: '/home/huypn12/Projects/nuget.config'. [/home/huypn12/Projects/some-project/SomeProject/SomeProject.csproj]

Build FAILED.

/usr/share/dotnet/sdk/8.0.404/NuGet.targets(745,5): error : NuGet.Config does not contain the expected root element: 'configuration'. Path: '/home/huypn12/Projects/nuget.config'. [/home/huypn12/Projects/some-project/SomeProject/SomeProject.csproj]
    0 Warning(s)
    1 Error(s)

Discussion

Why is such behaviour? Is it because of some recursive nuget.config checking?
Perhaps it makes more sense to have dotnet build command to check the nuget.config file of the current project directory?
Which part of the dotnet sdk is responsible for the behaviour?

Further technical details

.NET SDK:
 Version:           8.0.404
 Commit:            7b190310f2
 Workload version:  8.0.400-manifests.4d7d414a
 MSBuild version:   17.11.9+a69bbaaf5

Runtime Environment:
 OS Name:     debian
 OS Version:  12
 OS Platform: Linux
 RID:         linux-x64
 Base Path:   /usr/share/dotnet/sdk/8.0.404/

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

Host:
  Version:      8.0.11
  Architecture: x64
  Commit:       9cb3b725e3

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

.NET runtimes installed:
  Microsoft.AspNetCore.App 8.0.11 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 8.0.11 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
  None

Environment variables:
  Not set

global.json file:
  Not found

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

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

[KalleOlaviNiemitalo]

https://learn.microsoft.com/en-us/nuget/consume-packages/configuring-nuget-behavior seems to say this is by design.

[marcpopMSFT]

@nkolev92 @aortiz-msft to confirm this is expected behavior and we can close.

[aortiz-msft]

@KalleOlaviNiemitalo already linked to the relevant documentation. We should close this issue.