System.Exception: Did not find MSBuild for runtime Mono - macos

Question

I'm compiling the sources in Visual Studio Community 2017 for Mac and I've got the following error:
Building: ServiceLayer.API (Debug)
Error: Build failed. See the build log for details. (ServiceLayer.API)
---------------------- Done ----------------------
Build failed.
Build: 1 error, 0 warnings
In Ide.log log file, I've the following entry:
ERROR [2017-10-08 20:20:45Z]: Inspector does not support this project type
ERROR [2017-10-08 20:20:45Z]: Build failed.
System.Exception: Did not find MSBuild for runtime Mono 4.0.2 (c99aa0c)
at MonoDevelop.Projects.MSBuild.MSBuildProjectService.GetNewestInstalledToolsVersion (MonoDevelop.Core.Assemblies.TargetRuntime runtime, System.Boolean requiresMicrosoftBuild, System.String& binDir) [0x0006e] in /Users/builder/data/lanes/5144/cab57de4/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.MSBuild/MSBuildProjectService.cs:1087
at MonoDevelop.Projects.MSBuild.MSBuildProjectService+<GetProjectBuilder>d__100.MoveNext () [0x00133] in /Users/builder/data/lanes/5144/cab57de4/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.MSBuild/MSBuildProjectService.cs:1116
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:151
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00037] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:357
at MonoDevelop.Projects.Project+<GetProjectBuilder>d__157.MoveNext () [0x001bb] in /Users/builder/data/lanes/5144/cab57de4/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs:1418
...
ERROR [2017-10-08 20:21:16Z]: An unhandled exception has occured. Terminating Visual Studio? False
Notes: In total like 381 lines on each attempt to build. 'End of stack trace' line is repeated 52 times.
This pointed me to this line in MonoDevelop (see: MSBuildProjectService.cs):
throw new Exception ("Did not find MSBuild for runtime " + runtime.Id);
I've checked and msbuild command exist in the command-line:
$ which msbuild
/Library/Frameworks/Mono.framework/Versions/Current/Commands/msbuild
$ msbuild --version
Microsoft (R) Build Engine version 15.4.0.0 (master/f296e67b Thu Sep 21 19:38:16 EDT 2017) for Mono
$ stat /Library/Frameworks/Mono.framework/Versions/Current
File: /Library/Frameworks/Mono.framework/Versions/Current -> /Library/Frameworks/Mono.framework/Versions/5.4.0
What I've tried so far:
I've tested both channels (Stable and Beta) in Visual Studio Update without success.
I've tried to Clean All and Rebuild All.
I've tried to remove the cache files in ~/Library/Caches/VisualStudio.
Reinstalling VisualStudio.
I've checked in Visual Studio, Preference..., Projects, .NET Runtimes and I've the latest Mono set as Default (to 5.4.x):
However when debugging, it's trying to open msbuild for 4.0.2 instead, e.g.:
$ sudo fs_usage -f pathname VisualStudio | grep -i msbuild
12:34:38 stat64 /Library/Frameworks/Mono.framework/Versions/4.0.2/lib/mono/msbuild>>>>>>>>>>>>>>>>>>>>>> 0.000007 VisualStudio
12:34:38 lstat64 /Library/Frameworks/Mono.framework/Versions/4.0.2/lib/mono/msbuild>>>>>>>>>>>>>>>>>>>>>> 0.000002 VisualStudio
12:34:38 access /Library/Frameworks/Mono.framework/Versions/4.0.2/lib/mono/msbuild>>>>>>>>>>>>>>>>>>>>>> 0.000002 VisualStudio
which doesn't exist.
How should I add a missing MSBuild to my Solution (project) (as per mentioned error)?

Answer 1

Mono 4.0.2 did not have msbuild, it was included in 4.8.0+ . Check where does /Library/Frameworks/Mono.framework/Versions/Current (symlink) point to. It probably points to some mono 5.x.y . Try changing the .NET runtime that VSMac is set to use in Preferences -> Projects -> .NET Runtimes, to the latest one.
For some reason it is still looking it in 4.0.2. I would try to, at least temporarily, remove that 4.0.2 directory and then check. But otherwise I think your installation is broken and I would try to reinstall the whole thing (VSMac, Mono, ..).
Also, check in your Ide.log file for any references to 4.0.2, before that exception.
If you run into the same issue even with a fresh install, then please file a bug at bugzilla.xamarin.com and we can try to debug it there.