现货？ 正则表达式字符串中的字符文字

Question

I'm building a developer tool, and in one input field my users can input regular expressions.

If they enter an expression that tries to match a literal ? character anywhere then they've probably made a mistake, as I know that ? specifically is guaranteed to never appear in the string to match (and if they're trying to spot one, then there's a different action they should take instead). I would like to show a warning in that case.

How can I quickly check from a string containing a regular expression whether it contains a literal ? character? Eg I want to warn about regular expression strings like hello\\? , but not https? .

Detecting \\? is probably a good start, but I imagine there's other cases too.

I'm building this in JavaScript. Solutions based on simple string processing are preferable to fully parsing the regular expression, if possible.

Answer 1

Consider using an existing Regular Expression parser which outputs an AST .

For example for JavaScript:
https://www.npmjs.com/package/regjsparser
https://github.com/jviereck/regjsparser

The demo page here allows you to see the generated AST:
http://www.julianviereck.de/regjsparser/

Then you could look through the "codePoint" (63) in the AST:

{
      "type": "value",
      "kind": "identifier",
      "codePoint": 63,
      "range": [
        15,
        17
      ],
      "raw": "\\?"
    }

Also note that "characterClassRange" types might also include your "?" character in it's range, the following includes a range of characters including "?" (63): http://www.julianviereck.de/regjsparser/#%2F%5B%5Cu003e-%5Cu0040%5D%2Fiu

You could check the "codePoint" range between min and max for your character.

{
      "type": "characterClassRange",
      "min": {
        "type": "value",
        "kind": "unicodeEscape",
        "codePoint": 62,
        "range": [
          1,
          7
        ],
        "raw": "\\u003e"
      },
      "max": {
        "type": "value",
        "kind": "unicodeEscape",
        "codePoint": 64,
        "range": [
          8,
          14
        ],
        "raw": "\\u0040"
      },
      "range": [
        1,
        14
      ],
      "raw": "\\u003e-\\u0040"
    }

Obviously check other test cases for other "types" that might include your character, but generally using an AST to perform these checks will improve how you "catch" them ("Gotta Catch 'Em All").

Also note there is a JS library to generate regular expressions from the AST:
https://www.npmjs.com/package/regjsgen
https://github.com/bnjmnt4n/regjsgen