anchor.diff:  [<NoComparison>]
   type private SlowStageData =
       { Snapshot: ITextSnapshot 
  -      UnusedSpans: Map<WordSpan, CategorizedColumnSpan> }
  +      UnusedSpans: Map<WordSpan, CategorizedColumnSpan>
  +      IsUpdating: bool }
   
   [<NoComparison>]
   type private SlowStage =
  -    | NoData
  +    | NoData of isUpdating: bool
       | Data of SlowStageData
   
   type SyntaxConstructClassifier
  
positive.code:     }
  
      let updateSyntaxConstructClassifiers force =
          let cancelToken = new CancellationTokenSource() 
          cancellationToken.Swap (fun _ -> Some (cancelToken))
          |> Option.iter (fun oldToken -> 
              oldToken.Cancel()
              oldToken.Dispose())
  
          let snapshot = getCurrentSnapshot()
          let needUpdate =
              match snapshot, force, fastState.Value with
  
negative.code: [<NoComparison>]
  type private FastStageData =
      { Snapshot: ITextSnapshot
        Spans: CategorizedColumnSpan[]
        SymbolUses: SymbolUse[]
        SingleSymbolsProjects: CheckingProject list }
  