@NotNull
  private static String getPrefix(int offset, @NotNull final PsiFile file) {
    if (offset > 0) {
      offset--;
    }
    final String text = file.getText();
    final StringBuilder prefixBuilder = new StringBuilder();
    while (offset > 0 && Character.isLetterOrDigit(text.charAt(offset))) {
      prefixBuilder.insert(0, text.charAt(offset));
      offset--;
    }
    return prefixBuilder.toString();
  }
@NotNull
  private static String getPrefix(int offset, @NotNull final PsiFile file)