function getLineIndentText(line) {
      const lineText = sourceCode.getLines()[line - 1]
      const charIndex = lineText.search(/\S/)
      // already checked
      // if (charIndex < 0) {
      //   return lineText
      // }
      return lineText.slice(0, charIndex)
    }
Get the actual indentation of the given line.
@param {number} line The number of line. Begins with 1.
@returns {string} The actual indentation text