MSBuildWorkspace cannot compile project with <ProjectReference> to another project - msbuild

Question

Note I've also asked this question (with reproduction code) on Roslyn's GitHub
Create a new solution with 2 projects (CoreLibrary and DownstreamLibrary).
Add a project reference from DownstreamLibrary to CoreLibrary.
Run the following code and note that DownstreamLibrary no longer compiles.
Note that I've tried net461, netcoreapp2.1 and netstandard2.0 as target frameworks for the projects - same problem each time.
static async Task Main(string[] args)
{
MSBuildLocator.RegisterDefaults();
using (var workspace = MSBuildWorkspace.Create())
{
workspace.WorkspaceFailed += (sender, workspaceFailedArgs) => WriteLine(workspaceFailedArgs.Diagnostic.Message);
var solution = await workspace.OpenSolutionAsync(#"c:\source\ForRoslynTest\ForRoslynTest.sln");
WriteLine($"Loaded solution {solution.FilePath}");
var projectTree = workspace.CurrentSolution.GetProjectDependencyGraph();
foreach (var projectId in projectTree.GetTopologicallySortedProjects())
{
await CompileProject(workspace.CurrentSolution.GetProject(projectId));
}
}
}
private static async Task CompileProject(Project project)
{
WriteLine($"Compiling {project.Name}. It has {project.MetadataReferences.Count} metadata references.");
var compilation = await project.GetCompilationAsync();
var errors = compilation.GetDiagnostics().Where(diagnostic => diagnostic.Severity == DiagnosticSeverity.Error);
if (errors.Any())
{
WriteLine($"COMPILATION ERROR: {compilation.AssemblyName}: {errors.Count()} compilation errors: \n\t{string.Join("\n\t", errors.Where(e => false).Select(e => e.ToString()))}");
}
else
{
WriteLine($"Project {project.Name} compiled with no errors");
}
}
You will receive the following output:
Msbuild failed when processing the file 'c:\source\ForRoslynTest\DownstreamLibrary\DownstreamLibrary.csproj' with message: C:\Program Files\dotnet\sdk\2.1.602\Microsoft.Common.CurrentVersion.targets: (1548, 5): The "Microsoft.Build.Tasks.ResolveNonMSBuildProjectOutput" task could not be loaded from the assembly Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a. Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.
Found project reference without a matching metadata reference: c:\source\ForRoslynTest\CoreLibrary\CoreLibrary.csproj
Loaded solution c:\source\ForRoslynTest\ForRoslynTest.sln
Compiling CoreLibrary. It has 113 metadata references.
Project CoreLibrary compiled with no errors
Compiling DownstreamLibrary. It has 0 metadata references.
COMPILATION ERROR: DownstreamLibrary: 3 compilation errors:
c:\source\ForRoslynTest\DownstreamLibrary\Class1.cs(1,7): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
c:\source\ForRoslynTest\DownstreamLibrary\Class1.cs(5,18): error CS0518: Predefined type 'System.Object' is not defined or imported
c:\source\ForRoslynTest\DownstreamLibrary\Class1.cs(5,18): error CS1729: 'object' does not contain a constructor that takes 0 arguments
So my question is how do I fix the above errors and get DownstreamLibrary to compile?
EDIT
I'm 99% sure the underlying cause is this error
The "Microsoft.Build.Tasks.ResolveNonMSBuildProjectOutput" task could not be loaded from the assembly Microsoft.Build.Tasks.Core, Version=15.1.0.0
I've confirmed with procmon that it's loading the following DLL (C:\Program Files\dotnet\sdk\2.1.602\Microsoft.Build.Tasks.Core.dll) which I've confirmed with ILSpy DOESN'T have the ResolveNonMSBuildProjectOutput task in it. Older versions of this DLL did have this task.

Answer 1

I found a manual workaround to this WorkspaceFailed error:
[Failure] Msbuild failed when processing the with message: The "Microsoft.Build.Tasks.ResolveNonMSBuildProjectOutput" task could not be loaded from the assembly Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a. Confirm that the declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.
There were a few resolution steps:
following https://github.com/microsoft/msbuild/issues/4770 I updated VS 2019 from 16.2 to 16.5.3... This didn't fix my bug, but it's worth documenting I did this.
I upgraded my Microsoft.Build.* and Microsoft.CodeAnalysis dependencies to latest, THIS DIDN'T FIX THINGS YET, same bug.
I navigated to C:\Program Files\dotnet\sdk which previously had a few directories:
1.0.0/ 1.0.0-rc4-004771/ 2.0.3/ 2.1.505/
1.0.0-preview1-002702/ 1.0.3/ 2.1.202/ 3.1.100/
1.0.0-preview2-003121/ 1.0.4/ 2.1.4/ 3.1.201/
1.0.0-preview4-004233/ 1.1.0/ 2.1.502/ NuGetFallbackFolder/
I renamed this to sdk_o and created a new folder C:\Program Files\dotnet\sdk, copying in only 3.1.201/
Success! This error was gone, but running my roslyn app then resulted in some error like (paths stripped)
[Failure] Msbuild failed when processing the file with message The "ProcessFrameworkReferences" task failed unexpectedly. System.IO.FileNotFoundException: Could not load file or assembly 'NuGet.Frameworks, Version=5.5.0.4, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. The system cannot find the file specified. File name: 'NuGet.Frameworks, Version=5.5.0.4, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
Solved this one by adding NuGet.ProjectModel 5.5.1 to my project, the csproj now has the following package references:
<ItemGroup>
<PackageReference Include="Microsoft.Build" Version="16.5.0" ExcludeAssets="runtime" />
<PackageReference Include="Microsoft.Build.Framework" Version="16.5.0" ExcludeAssets="runtime" />
<PackageReference Include="Microsoft.Build.Locator" Version="1.2.6" />
<PackageReference Include="Microsoft.Build.Tasks.Core" Version="16.5.0" ExcludeAssets="runtime" />
<PackageReference Include="Microsoft.CodeAnalysis" Version="3.5.0" />
<PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="3.5.0" />
<PackageReference Include="Microsoft.CodeAnalysis.Workspaces.MSBuild" Version="3.5.0" />
<PackageReference Include="NuGet.ProjectModel" Version="5.5.1" />
</ItemGroup>
No more WorkspaceFailed events for this code:
Microsoft.Build.Locator.MSBuildLocator.RegisterDefaults();
var workspace = MSBuildWorkspace.Create();
workspace.WorkspaceFailed += (s, e) => { Console.WriteLine(e.Diagnostic); };
var project = await workspace.OpenProjectAsync(#"C:/path/to.csproj");
The csproj I'm loading with Roslyn looks as follows:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>netcoreapp3.1</TargetFramework>
<UseWindowsForms>true</UseWindowsForms>
<OutputType>Library</OutputType>
<ApplicationIcon />
<StartupObject />
</PropertyGroup>
<ItemGroup>
<ProjectReference Include="..\..\dependencies\some.csproj" />
</ItemGroup>
</Project>