[Mono] NuGet version too old on Linux

[grendello]

Hi,

I use omnisharp-roslyn with Emacs on Linux and because Mono bundled with omnisharp doesn't have any other .NET SDKs than 4.5 (and I mostly work with 4.7.2 these days),
I tend to modify the run script to start omnisharp with my locally built Mono from the master branch. Until recently it's been working fine, but with the latest update to MSBuild
16.8, it broke with:

[16:27:28] ERROR: OmniSharp.MSBuild.ProjectLoader, The "ResolvePackageAssets" task failed unexpectedly.
System.MissingMethodException: Method not found: NuGet.ProjectModel.LockFileTarget NuGet.ProjectModel.LockFile.GetTarget(string,string)
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets+CacheReader.CreateReaderFromDisk (Microsoft.NET.Build.Tasks.ResolvePackageAssets task, System.Byte[] settingsHash) [0x0003a] in <1362f3759017415f99456b8adb293671>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets+CacheReader..ctor (Microsoft.NET.Build.Tasks.ResolvePackageAssets task) [0x00015] in <1362f3759017415f99456b8adb293671>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ReadItemGroups () [0x00000] in <1362f3759017415f99456b8adb293671>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ExecuteCore () [0x00018] in <1362f3759017415f99456b8adb293671>:0 
  at Microsoft.NET.Build.Tasks.TaskBase.Execute () [0x0002e] in <1362f3759017415f99456b8adb293671>:0 
  at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute () [0x00029] in <f7274894ce154696afba1f0ffcd06434>:0 
  at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask (Microsoft.Build.BackEnd.ITaskExecutionHost taskExecutionHost, Microsoft.Build.BackEnd.Logging.TaskLoggingContext taskLoggingContext, Microsoft.Build.BackEnd.TaskHost taskHost, Microsoft.Build.BackEnd.ItemBucket bucket, Microsoft.Build.BackEnd.TaskExecutionMode howToExecuteTask) [0x002fc] in <f7274894ce154696afba1f0ffcd06434>:0

It appears that NuGet 5.2.0 which is used by omnisharp is too old. I fixed it by updating nuget to 5.8.0 (the latest) and rebuilding omnisharp. Everything works perfectly now :)
I tested it only on Linux but I suppose the same might be true on macOS.

Could you please update NuGet to the above-mentioned version? I'm happy to open a PR if needed. Thanks :)

[RealityAnomaly]

Same issue here.

[JordanAnthonyKing]

I seem to be having a similar issue? Also on Emacs using omnisharp-roslyn via lsp-mode. Mine is a .NET Core 3.1 project:

OmniSharp.MSBuild.ProjectLoader: The "ResolvePackageAssets" task failed unexpectedly.
NuGet.Packaging.Core.PackagingException: Unable to find fallback package folder 'C:\Program Files\dotnet\sdk\NuGetFallbackFolder'.
  at NuGet.Packaging.FallbackPackagePathResolver..ctor (System.String userPackageFolder, System.Collections.Generic.IEnumerable`1[T] fallbackPackageFolders) [0x00064] in <665a1c83623344819944d40680140855>:0 
  at Microsoft.NET.Build.Tasks.NuGetPackageResolver..ctor (System.String userPackageFolder, System.Collections.Generic.IEnumerable`1[T] fallbackPackageFolders) [0x00006] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.NuGetPackageResolver.CreateResolver (System.Collections.Generic.IEnumerable`1[T] packageFolders) [0x00018] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.NuGetPackageResolver.CreateResolver (NuGet.ProjectModel.LockFile lockFile) [0x0002a] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets+CacheWriter..ctor (Microsoft.NET.Build.Tasks.ResolvePackageAssets task) [0x00030] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets+CacheReader.CreateReaderFromDisk (Microsoft.NET.Build.Tasks.ResolvePackageAssets task, System.Byte[] settingsHash) [0x0003a] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets+CacheReader..ctor (Microsoft.NET.Build.Tasks.ResolvePackageAssets task) [0x00015] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ReadItemGroups () [0x00000] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ExecuteCore () [0x00018] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.TaskBase.Execute () [0x0002e] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute () [0x00029] in <ea47b2df30ad4051b6681ba57ba83dc9>:0 
  at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask (Microsoft.Build.BackEnd.ITaskExecutionHost taskExecutionHost, Microsoft.Build.BackEnd.Logging.TaskLoggingContext taskLoggingContext, Microsoft.Build.BackEnd.TaskHost taskHost, Microsoft.Build.BackEnd.ItemBucket bucket, Microsoft.Build.BackEnd.TaskExecutionMode howToExecuteTask) [0x002fc] in <ea47b2df30ad4051b6681ba57ba83dc9>:0  | 
OmniSharp.MSBuild.ProjectLoader: The "ResolvePackageAssets" task failed unexpectedly.
NuGet.Packaging.Core.PackagingException: Unable to find fallback package folder 'C:\Program Files\dotnet\sdk\NuGetFallbackFolder'.
  at NuGet.Packaging.FallbackPackagePathResolver..ctor (System.String userPackageFolder, System.Collections.Generic.IEnumerable`1[T] fallbackPackageFolders) [0x00064] in <665a1c83623344819944d40680140855>:0 
  at Microsoft.NET.Build.Tasks.NuGetPackageResolver..ctor (System.String userPackageFolder, System.Collections.Generic.IEnumerable`1[T] fallbackPackageFolders) [0x00006] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.NuGetPackageResolver.CreateResolver (System.Collections.Generic.IEnumerable`1[T] packageFolders) [0x00018] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.NuGetPackageResolver.CreateResolver (NuGet.ProjectModel.LockFile lockFile) [0x0002a] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets+CacheWriter..ctor (Microsoft.NET.Build.Tasks.ResolvePackageAssets task) [0x00030] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets+CacheReader.CreateReaderFromDisk (Microsoft.NET.Build.Tasks.ResolvePackageAssets task, System.Byte[] settingsHash) [0x0003a] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets+CacheReader..ctor (Microsoft.NET.Build.Tasks.ResolvePackageAssets task) [0x00015] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ReadItemGroups () [0x00000] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ExecuteCore () [0x00018] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.NET.Build.Tasks.TaskBase.Execute () [0x0002e] in <c1a29c5daf134e4ba6d73cbbae7974d1>:0 
  at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute () [0x00029] in <ea47b2df30ad4051b6681ba57ba83dc9>:0 
  at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask (Microsoft.Build.BackEnd.ITaskExecutionHost taskExecutionHost, Microsoft.Build.BackEnd.Logging.TaskLoggingContext taskLoggingContext, Microsoft.Build.BackEnd.TaskHost taskHost, Microsoft.Build.BackEnd.ItemBucket bucket, Microsoft.Build.BackEnd.TaskExecutionMode howToExecuteTask) [0x002fc] in <ea47b2df30ad4051b6681ba57ba83dc9>:0  | 

Is this related?

[JoeRobich]

@JordanAnthonyKing It doesn't seem to be the same issue. Can you confirm that the folder 'C:\Program Files\dotnet\sdk\NuGetFallbackFolder' exists?

[JordanAnthonyKing]

@JoeRobich Hi, I eventually figured this out as a misnomer for an incorrectly configured project.

Thanks