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Restore should fail when a non-existent fallback folder is provided

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#7,012 opened on Jun 8, 2018

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Functionality:RestorePartner:CLI-SDKPriority:3Type:Bughelp wanted

Description

MSBuild 15.7.179.6572

MSBuild of an SDK-style project with PackageReference fails because the generated .csproj.nuget.g.props file contains this line:

<NuGetPackageFolders Condition=" '$(NuGetPackageFolders)' == '' ">C:\Users\kirillo\.nuget\packages\;C:\Program Files (x86)\Microsoft SDKs\NuGetPackagesFallback\</NuGetPackageFolders>

The NuGetPackagesFallback folder doesn't exist on my machine, causing NuGet to fail the build with the exception:

C:\Program Files\dotnet\sdk\2.1.201\Sdks\Microsoft.NET.Sdk\build\Microsoft.PackageDependencyResolution.targets(172,5): error MSB4018: The "ResolvePackageDependencies" task failed unexpectedly.
NuGet.Packaging.Core.PackagingException: Unable to find fallback package folder 'C:\Program Files (x86)\Microsoft SDKs\NuGetPackagesFallback\'.
   at NuGet.Packaging.FallbackPackagePathResolver..ctor(String userPackageFolder, IEnumerable`1 fallbackPackageFolders)
   at Microsoft.NET.Build.Tasks.NuGetPackageResolver.CreateResolver(LockFile lockFile, String projectPath)
   at Microsoft.NET.Build.Tasks.ResolvePackageDependencies.get_PackageResolver()
   at Microsoft.NET.Build.Tasks.ResolvePackageDependencies.ResolvePackagePath(LockFileLibrary package)
   at Microsoft.NET.Build.Tasks.ResolvePackageDependencies.GetPackageAndFileDefinitions()
   at Microsoft.NET.Build.Tasks.ResolvePackageDependencies.ExecuteCore()
   at Microsoft.NET.Build.Tasks.TaskBase.Execute()
   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
   at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext() [C:\monodevelop\main\external\RefactoringEssentials\RefactoringEssentials\RefactoringEssentials.csproj]

None of the nuget.config files on my machine contain anything related to the fallback folder.

I don't have any environment variables set that start with NuGet*.

My VS offline package cache is a similar folder, but without the fallback: image

Why does NuGet decide to generate that non-existing folder into my .g.props files?

Where does that value come from?

Contributor guide

Tech stack
csharp
Domain
backendtooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
basic knowledge of NuGetC# programming
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
Investigate how the fallback folder path is determined (likely from machine wide NuGet configuration or VS settings). Check the NuGet.Client source code, particularly the FallbackPackagePathResolver class, to see where the fallback folder is sourced. If the folder does not exist, the restore should either skip it or fail gracefully with a clear error message. Review issue comments for any maintainer guidance on the intended behavior.