text: /**
   * @fileoverview Rule to flag the use of empty character classes in regular expressions
   * @author Ian Christian Myers
   */
  
  "use strict";
  
  //------------------------------------------------------------------------------
  // Helpers
  //------------------------------------------------------------------------------
  
  /*
  plain-English description of the following regexp:
  0. `^` fix the match at the beginning of the string
  1. `\/`: the `/` that begins the regexp
  2. `([^\\[]|\\.|\[([^\\\]]|\\.)+\])*`: regexp contents; 0 or more of the following
    2.0. `[^\\[]`: any character that's not a `\` or a `[` (anything but escape sequences and character classes)
    2.1. `\\.`: an escape sequence
    2.2. `\[([^\\\]]|\\.)+\]`: a character class that isn't empty
  3. `\/` the `/` that ends the regexp
  4. `[gimuy]*`: optional regexp flags
  5. `$`: fix the match at the end of the string
  */
  const regex = /^\/([^\\[]|\\.|\[([^\\\]]|\\.)+])*\/[gimuy]*$/;
  
  //------------------------------------------------------------------------------
  // Rule Definition
  //------------------------------------------------------------------------------
  
  module.exports = {
      meta: {
          docs: {
              description: "disallow empty character classes in regular expressions",
              category: "Possible Errors",
              recommended: true
          },
  
          schema: []
      },
  
      create(context) {
          const sourceCode = context.getSourceCode();
  
          return {
  
              Literal(node) {
                  const token = sourceCode.getFirstToken(node);
  
                  if (token.type === "RegularExpression" && !regex.test(token.value)) {
                      context.report({ node, message: "Empty class." });
                  }
              }
  
          };
  
      }
  };
  