Watched word regular expression crash (2025)

Bug
, ,
1

Similar to this one

Repro

  • watched words regular expressions enabled
  • watched words tag action
  • regular expression *abc

Result

It is impossible to create topics or posts

RegexpError (target of repeat operator is not specified: /(*abc)/i)
app/services/word_watcher.rb:239:in `initialize'
app/services/word_watcher.rb:239:in `new'
app/services/word_watcher.rb:239:in `word_matches?'
lib/topic_creator.rb:214:in `block in setup_tags'
lib/topic_creator.rb:213:in `each'
lib/topic_creator.rb:213:in `setup_tags'
lib/topic_creator.rb:48:in `create'
lib/post_creator.rb:493:in `create_topic'

Cause

  • * means “repeat the previous token zero or more times”
  • there is no previous token
2 Likes
2

So really the regex should be validated before allowing it to be added? And there should be a rescue so an invalid regex can’t crash the whole world?

1 Like
3

What obviously happened here is that the watched words were regular watched words and * was the wildcard, and then watched words regular expressions enabled was enabled.

So this

1 Like
4

Well, now it’s obvious when you say it like that. :rofl:

5

Valildating regex in on save seems like a very sane thing to do.

putting a pr-welcome on this, but team will triage and decide if it makes sense to do this in the upcoming weeks to save us future support.

1 Like
6

That won’t prevent people entering “normal” wildcard expressions, and then turning on watched words regular expressions enabled, which is what happened here.

I think it just needs an exception handler around the regexp call

  def word_matches?(word, case_sensitive: false)
    options = case_sensitive ? nil : Regexp::IGNORECASE
    Regexp.new(WordWatcher.word_to_regexp(word), options).match?(@raw)
  end
2 Likes