Answer by EKW for Could not find a part of the path ... bin\roslyn\csc.exe

I ran into this issue with the publishing pipeline (which produces a _PublishedWebsites directory), and used this as a Target in the project:

<Target Name="CopyRoslynCompilerFilesToPublishedWebsitesDirectory" AfterTargets="AfterBuild" Condition="Exists('$(OutDir)\_PublishedWebsites\$(TargetName)')"><Copy SourceFiles="@(RoslyCompilerFiles)" DestinationFolder="$(OutDir)\_PublishedWebsites\$(TargetName)\bin\roslyn" ContinueOnError="true" SkipUnchangedFiles="true" /></Target>

The downside is that there will be two copies of the Roslyn files in the output.