code: func (fd *IndexFileDeleter) deleteNewFiles(files []string) {
  	// assert locked
  	for _, filename := range files {
  		// NOTE: it's very unusual yet possible for the
  		// refCount to be present and 0: it can happen if you
  		// open IW on a crashed index, and it removes a bunch
  		// of unref'd files, and then you add new docs / do
  		// merging, and it reuses that segment name.
  		// TestCrash.testCrashAfterReopen can hit this:
  		if rf, ok := fd.refCounts[filename]; !ok || rf.count == 0 {
  			if fd.infoStream.IsEnabled("IFD") {
  				fd.infoStream.Message("IFD", "delete new file '%v'", filename)
  			}
  			fd.deleteFile(filename)
  		}
  	}
  }
docs: /*
  Deletes the specified files, but only if they are new (have not yet
  been incref'd).
  */