private @NotNull List<TodoItem> computeOldTodoItems() {
      PsiFile beforePsiFile = ReadAction.compute(
        () -> PsiFileFactory.getInstance(myProject).createFileFromText("old" + myAfterFile.getName(),
                                                                       myAfterFile.getFileType(), myBeforeContent));
      return collectTodoItems(beforePsiFile, true);
    }
private @NotNull List<TodoItem> computeOldTodoItems()