code: function findLeadingComments(comments, index, beginIndex, first) {
      const leadComments = [];
      if (first && ignoreComment.test(comments[index].raw)) {
          return leadComments;
      }
      let backIndex = index - 1;
      while (backIndex >= beginIndex &&
          (comments[backIndex].loc.end.line + 1 === comments[backIndex + 1].loc.start.line
              || comments[backIndex].loc.end.line === comments[backIndex + 1].loc.start.line)) {
          if (first && ignoreComment.test(comments[backIndex].raw)) {
              break;
          }
          backIndex -= 1;
      }
      for (let ind = backIndex + 1; ind <= index; ind += 1) {
          leadComments.push(comments[ind]);
      }
      return leadComments;
  }
docs: return leading comment list
  @param {*list<comment>} comments
  @param {*} the last match leading comment of one import
  @param {*} beginIndex the potential begin of the comment index of the import
  @param {*} first whether first import