anchor.diff:              match getSourcesAndFlags() with
               | Some(_, flags) -> flags
               | _ -> [||]
  +
  +        let getActiveConfigProperty (tag: string) =
  +            let prop = try project.ConfigurationManager.ActiveConfiguration.Properties.[tag] with _ -> null
  +            match prop with
  +            | null -> null
  +            | _ -> try prop.Value.ToString() with _ -> null
   
           let targetFramework() =
               match getProperty "TargetFrameworkMoniker" with
  
positive.code:     abstract TargetFramework: FSharpTargetFramework
      abstract CompilerOptions: string []
      abstract SourceFiles: string []
      abstract GetReferencedProjects: unit -> IProjectProvider list
      abstract GetAllReferencedProjectFileNames: unit -> string list
      abstract GetProjectCheckerOptions: LanguageService -> Async<ProjectOptions>
  
negative.code:                        else Some(Path.GetFileNameSafe file))
  
              member x.GetProjectCheckerOptions languageService =
                  async {
                      let x = x :> IProjectProvider
                      let! opts = languageService.GetProjectCheckerOptions (x.ProjectFileName, x.SourceFiles, x.CompilerOptions)
                      let refs = x.GetReferencedProjects()
                      return { opts with ReferencedProjects = 
                                             [| for refp in refs do
                                                  yield refp.ProjectFileName, 
                                                        refp.GetProjectCheckerOptions(languageService) 
                                                        |> Async.RunSynchronously |]
                                         ProjectOptions = 
                                             [| yield! opts.ProjectOptions 
                                                yield! refs |> List.map (fun p -> sprintf "-r:%s" p.OutputPath) |] }
                          
                  }
              
      type private VirtualProjectProvider (filePath: string) = 
          do Debug.Assert (filePath <> null, "FilePath should not be null.")
  