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.
