maintainer-feedback requested: [Bug 256342] devel/msbuild: default targets are unusable with lang/mono5.20 and lang/mono6.8

Bugzilla Automation <bugzilla@FreeBSD.org> has asked freebsd-mono (Nobody)
<mono@FreeBSD.org> for maintainer-feedback:
Bug 256342: devel/msbuild: default targets are unusable with lang/mono5.20 and
lang/mono6.8
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=256342



--- Description ---
$ pkg install -A msbuild
$ pkg delete -f mono
$ pkg install -A mono6.8
$ pkg set -n mono6.8:mono
$ pkg set -o lang/mono6.8:lang/mono

$ cat hello.cs
namespace HelloWorld
{
    class Hello {	  
	static void Main(string[] args)
	{
	    System.Console.WriteLine("Hello World!");
	}
    }
}

$ cat hello.csproj
<Project>
  <ItemGroup>
    <Compile Include="hello.cs" />
  </ItemGroup>
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
</Project>

$ msbuild hello.csproj
Microsoft (R) Build Engine version 42.42.42.42 ( Fri May 14 04:36:25 UTC 2021)
for Mono
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 6/1/2021 3:42:43 PM.
Project "/tmp/hello.csproj" on node 1 (default targets).
/usr/local/lib/mono/msbuild/15.0/bin/Microsoft.CSharp.CurrentVersion.targets(33
1,5):
error MSB4019: The imported project
"/usr/local/lib/mono/msbuild/15.0/bin/Roslyn/Microsoft.CSharp.Core.targets" was
not found. Confirm that the path in the <Import> declaration is correct, and
that the file exists on disk. [/tmp/hello.csproj]
Done Building Project "/tmp/hello.csproj" (default targets) -- FAILED.

Build FAILED.

"/tmp/hello.csproj" (default target) (1) ->
 
/usr/local/lib/mono/msbuild/15.0/bin/Microsoft.CSharp.CurrentVersion.targets(33
1,5):
error MSB4019: The imported project
"/usr/local/lib/mono/msbuild/15.0/bin/Roslyn/Microsoft.CSharp.Core.targets" was
not found. Confirm that the path in the <Import> declaration is correct, and
that the file exists on disk. [/tmp/hello.csproj]

    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.27