Running tasks compiled for netcore throws ReflectionTypeLoadException

When I simply run my task as part of MSBuild, it works as expected. AFAIR, I was able to run/debug it specifically StructuredLogViewer, but yesterday it failed on me.

Unhandled Exception: System.Reflection.ReflectionTypeLoadException: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.
   at System.Reflection.RuntimeModule.GetTypes(RuntimeModule module)
   at System.Reflection.RuntimeModule.GetTypes()
   at System.Reflection.Assembly.GetTypes()
   at TaskRunner.Executor.Execute(Task task) in C:\MSBuildStructuredLog\src\TaskRunner\Executor.cs:line 32
   at TaskRunner.Program.Run(String binlog, Int32 index, String taskName) in C:\MSBuildStructuredLog\src\TaskRunner\Program.cs:line 114
   at TaskRunner.Program.Main(String[] args) in C:\MSBuildStructuredLog\src\TaskRunner\Program.cs:line 61

One of the assemblies is System.Runtime:

=== Pre-bind state information ===
LOG: DisplayName = System.Runtime, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 (Fully-specified)
LOG: Appbase = file:///C:/Users/matthias.koch/AppData/Local/MSBuildStructuredLogViewer/app-2.1.208/
LOG: Initial PrivatePath = NULL
Calling assembly : CustomTasks, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null.
===
LOG: This bind starts in LoadFrom load context.
WRN: Native image will not be probed in LoadFrom context. Native image will only be probed in default load context, like with Assembly.Load().
LOG: Using application configuration file: C:\Users\matthias.koch\AppData\Local\MSBuildStructuredLogViewer\app-2.1.208\TaskRunner.exe.Config
LOG: Using host configuration file: 
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Post-policy reference: System.Runtime, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
LOG: Attempting download of new URL file:///C:/Users/matthias.koch/AppData/Local/MSBuildStructuredLogViewer/app-2.1.208/System.Runtime.DLL.
LOG: Attempting download of new URL file:///C:/Users/matthias.koch/AppData/Local/MSBuildStructuredLogViewer/app-2.1.208/System.Runtime/System.Runtime.DLL.
LOG: Attempting download of new URL file:///C:/Users/matthias.koch/AppData/Local/MSBuildStructuredLogViewer/app-2.1.208/System.Runtime.EXE.
LOG: Attempting download of new URL file:///C:/Users/matthias.koch/AppData/Local/MSBuildStructuredLogViewer/app-2.1.208/System.Runtime/System.Runtime.EXE.
LOG: Attempting download of new URL file:///C:/code/custom-msbuild-task/src/CustomTasks/bin/Debug/netcoreapp2.1/publish/System.Runtime.DLL.
LOG: Attempting download of new URL file:///C:/code/custom-msbuild-task/src/CustomTasks/bin/Debug/netcoreapp2.1/publish/System.Runtime/System.Runtime.DLL.
LOG: Attempting download of new URL file:///C:/code/custom-msbuild-task/src/CustomTasks/bin/Debug/netcoreapp2.1/publish/System.Runtime.EXE.
LOG: Attempting download of new URL file:///C:/code/custom-msbuild-task/src/CustomTasks/bin/Debug/netcoreapp2.1/publish/System.Runtime/System.Runtime.EXE.

Anything else I can provide to give more insight?

[matkoch]

@KirillOsenkov arg! I actually thought about this but must have forgotten to update one of the references. Can confirm that it’s working with net472 just fine. Thanks for your quick response! ❤️

[KirillOsenkov]

Quick repro steps to get the binlog:

1. git clone https://github.com/matkoch/custom-msbuild-task
2. edit kirill.bat to make sure this path exists: C:/Program Files/dotnet/sdk/3.1.401/MSBuild.dll and change to whatever you have installed
3. run kirill.bat, it will produce C:\custom-msbuild-task\src\TestProject\msbuild.binlog
4. open msbuild.binlog in the viewer, find $task CustomTask, right-click and Run or Debug

Expected: should work

Actual: ReflectionTypeLoadException because trying to load a task assembly targeting .NET Core on a .NET Framework process.