I don't like that third parties who are developing things like Phabricator applications and arc extensions need to maintain a list of un-disables on these rules. There's no way for them to keep this list in sync with the "correct" list in the upstream.

One possibility that I was considering was to introduce an xhpast.standard which can be phutil or psr-2 (see D13512 for another use case).

Alternatively, we could do something like this:

public function getLintSeverity() {
  if ($this->isPhutilLibrary()) {
      return ArcanistLintSeverity::SEVERITY_ADVICE;
  }

  return ArcanistLintSeverity::SEVERITY_DISABLED;
}

I think I like the "standard" approach. The other one feels maybe a little too magical to me.