swiftlint custom rules for explicit non-final classes

gistfile1.txt

custom_rules:
  explicit_non_final_class:
    included: ".*\\.swift"
    excluded: ".*Tests\\.swift"
    name: "Implicitly non-final class"
    regex: "^\\s*(class) (?!func|var)"
    capture_group: 0
    match_kinds:
      - keyword
    message: "Classes should be `final` by default, use explicit `internal` or `public` for non-final classes."
    severity: error