falcon

Rules / Correctness / valid-regexps

valid-regexps

lint/correctness/valid-regexps
recommended
Same as valid_regexps · Dart lints

Disallow RegExp patterns that are structurally invalid.

Flags a RegExp constructed from a string literal whose pattern is unmistakably broken — unbalanced (/) groups, an unterminated [...] character class, or a trailing backslash. Such a pattern throws a FormatException the moment the RegExp is built, so catching it statically turns a runtime crash into a lint. The check is deliberately conservative: it inspects only literal, non-interpolated patterns and applies a structural test rather than a full regex parse, so it never false-positives on the JavaScript-flavored constructs (lookahead, backreferences, named groups) that Dart's RegExp accepts. Interpolated patterns, and non-raw literals containing backslash escapes, are skipped.

Invalid

example.dartdart
// Bad: literal patterns that are structurally invalid regular expressions.
void examples() {
  final a = RegExp('(');
  final b = RegExp(')');
  final c = RegExp('[a-z');
  final d = RegExp('(abc');
  final e = RegExp('a(b(c)');
  final f = new RegExp('foo)');
  print([a, b, c, d, e, f]);
}
Invalid regular expression: unbalanced groups or character class.
2void examples() {
3 final a = RegExp('(');
Invalid regular expression: unbalanced groups or character class.
3 final a = RegExp('(');
4 final b = RegExp(')');
Invalid regular expression: unbalanced groups or character class.
4 final b = RegExp(')');
5 final c = RegExp('[a-z');
Invalid regular expression: unbalanced groups or character class.
5 final c = RegExp('[a-z');
6 final d = RegExp('(abc');
Invalid regular expression: unbalanced groups or character class.
6 final d = RegExp('(abc');
7 final e = RegExp('a(b(c)');
Invalid regular expression: unbalanced groups or character class.
7 final e = RegExp('a(b(c)');
8 final f = new RegExp('foo)');

Valid

example.dartdart
// Good: valid patterns, or patterns that are not statically checkable literals.
void examples(String dynamicPattern) {
  final a = RegExp('abc');
  final b = RegExp('[a-z]+');
  final c = RegExp('(foo|bar)');
  final d = RegExp('a(b(c)d)e'); // balanced nested groups
  final e = RegExp(r'\d{3}-\d{4}'); // raw string, balanced
  final f = RegExp('\\d+'); // non-raw with escapes — pattern not resolved, skipped
  final g = RegExp(dynamicPattern); // not a literal, skipped
  final h = RegExp('prefix-${dynamicPattern}'); // interpolated, skipped
  print([a, b, c, d, e, f, g, h]);
}

How to configure

Set the severity of valid-regexps in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "correctness": {
        "valid-regexps": "error"
      }
    }
  }
}

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