MissingMethodException UnconfiguredProject.get_Services() in VS2019 when referencing ProjectSystem.15

[MBulli]

Visual Studio Version: VS2019 Preview 3

Summary:
Our extension fails to build in VS2019. We reference Microsoft.VisualStudio.ProjectSystem, Microsoft.VisualStudio.ProjectSystem.Managed and Microsoft.VisualStudio.ProjectSystem.VS all with version 15 because we still want to support VS2017. But we can't build the extension because ProjectSystem depends on Microsoft.Build assemblies which are targeting .Net framework 4.7. I don't know whether we do something wrong or it's a problem with VS2019.

Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem.Managed, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem.VS, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Utilities.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem.VS, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Framework, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem.VS, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Framework, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem.VS, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem.Managed, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Utilities.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Utilities.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem.Managed, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem.Managed, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build.Framework, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".
Warning		The primary reference "Microsoft.VisualStudio.ProjectSystem, Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Build, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which was built against the ".NETFramework,Version=v4.7.2" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.6".			

Steps to Reproduce:
Happens as soon as we try to build our extension in VS2019.

Expected Behavior:
Shouldn't visual studio assembly references be backwards compatible? I expected that VS2019 redirects the references to v16 assemblies which should work silently.

Actual Behavior:
Build fails because our extension targets .Net framework 4.6 but Microsoft.Build assemblies target 4.7.

User Impact:
We would need to build one assembly targeting VS2017 and one for VS2019 but sharing the same code.

[jmarolf]

@MBulli Microsoft.MSBuild from nuget is built against .NET Framework 4.6 so it's unclear how this is happening unless you are building your project against whatever MSBuild happens to be installed on the machine. Is that the case?

[MBulli]

Yes you're right, we weren't using the Nuget version. That fixed the warning. Thanks, silly mistake!

[MBulli]

Okay after fixing the wrong MSBuild references our extension still won't work.
We're still targeting ProjectSystem v15.
When we try to obtain the command args of the current project this code fails with the following exception:

IVsBrowseObjectContext context = project as IVsBrowseObjectContext;
var launchSettingsProvider = context.UnconfiguredProject.Services.ExportProvider.GetExportedValue<ILaunchSettingsProvider>();

Method not found: 'Microsoft.VisualStudio.ProjectSystem.IUnconfiguredProjectServices Microsoft.VisualStudio.ProjectSystem.UnconfiguredProject.get_Services()'.

This only happens in VS2019 and if I update the Nuget reference to ProjectSystem.16.0.374-pre it works again. Is this expected behavior or am I'm missing something obvious again?

[jmarolf]

This was an intentional breaking change by the VS team. Microsoft.VisualStudio.ProjectSystem.UnconfiguredProject.Services now returns the class UnconfiguredProjectServices instread of the interface IUnconfiguredProjectServices. To have your extension work in both VS 2017 and VS 2019 you will likely need to use reflection.

[MBulli]

Again, thank you for the quick help :)