getModificationTimeImpl
  :: Bool
  -> NormalizedFilePath
  -> Action (Maybe BS.ByteString, ([FileDiagnostic], Maybe FileVersion))
getModificationTimeImpl missingFileDiags file = do
    let file' = fromNormalizedFilePath file
    let wrap time = (Just $ LBS.toStrict $ B.encode $ toRational time, ([], Just $ ModificationTime time))
    mbVf <- getVirtualFile file
    case mbVf of
        Just (virtualFileVersion -> ver) -> do
            alwaysRerun
            pure (Just $ LBS.toStrict $ B.encode ver, ([], Just $ VFSVersion ver))
        Nothing -> do
            isWF <- use_ AddWatchedFile file
            if isWF
                then -- the file is watched so we can rely on FileWatched notifications,
                        -- but also need a dependency on IsFileOfInterest to reinstall
                        -- alwaysRerun when the file becomes VFS
                    void (use_ IsFileOfInterest file)
                else if isInterface file
                    then -- interface files are tracked specially using the closed world assumption
                        pure ()
                    else -- in all other cases we will need to freshly check the file system
                        alwaysRerun
                        
           ...