[ RFC ] Adding an optional allow list to hhast-lint.json

[Lexidor Digital]

The following describes a suggestion. This issue is not meant to be implemented right away. This might not be a direction hhast wants to go in.

---

I would like to propose an allow_list for HHAST_FIXME comments, analogous to the hhconfig setting allowed_fixme_codes_strict introduced in hhvm 4.62. If a FIXME is found for a linter that is not in the allow list, an error like the following would be emitted. You may not use a comment to suppress a {{LintErrorName}} error. See lintFixmeAllowList in hhast-lint.json. The default value (unspecified) should be equivalent to "allow all fixmes" rather than "allow none".

Some linters should always be adhered to and adding a FIXME for them is always a bad idea. Other linters have valid uses for a FIXME. This use of await-in-a-loop is critical to the functionality.

function wait_until_service_is_ready_async(string $url, Deadline $deadline): Awaitable<bool> {
  while($deadline->hasTimeLeft()) {
    // HHAST_IGNORE_ERROR[DontAwaitInALoop]
    $status = await get_http_status_async($url);
    switch ($status) {
      case 200:
        return true;
      case 404:
        throw new RuntimeException(Str\format('Service %s does not exist', $url);
      case 0:
      case 503:
        $sleep = $deadline->microsLeftOr(25000) - 5000;
        if ($sleep <= 0) {
          return false;
        }
        //HHAST_IGNORE_ERROR[DontAwaitInALoop]
        await Asio\usleep($sleep);
      default:
        // etc...
    }
  }
  return false;
}

A configuration file for this project could look like:

{
  "roots": ["src/"],
  "lintFixmeAllowList": [
    "Facebook\\HHAST\\DontAwaitInALoopLinter",
  ],
  "overrides": [
    {
      "patterns": ["src/codegen/**"],
      "lintFixmeAllowList": [
        "YourCorp\\SomeLinter"
      ]
    }
  ]
}

[Yang, Bo]

Sounds reasonable to me, except for the property name lintFixmeAllowList. I would name it lintMarkerAllowList to cover other markers.