Change 238439 had a related patch set uploaded (by Catrope):
Ignore exceptions from document.querySelector()

https://gerrit.wikimedia.org/r/238439

Change 238439 merged by jenkins-bot:
Ignore exceptions from document.querySelector()

https://gerrit.wikimedia.org/r/238439

This is currently listed in MW-1.26-release as a possible release blocker. Did Roan's patch fix this bug, or just sweep it under the carpet for now?

I don't think this needs to be a blocker, it was just tagged automatically by the bot since Roan's exception ignoring patch will make it in.

The Safari issue is fixed in the next Safari release. https://bugs.webkit.org/show_bug.cgi?id=149160
Greetings to the person who in x years from now is wondering why that try catch is needed and if it can be removed :)

For what it's worth, I don't think removing this try-catch is something we can do even if all supported browsers implement querySelector such that it accepts all selectors that they also accept in CSS.

The reason being that querySelector is required, by spec, to throw for selectors that the browser knows are not valid. This means, this particular bug aside, there will likely always be selectors somewhere in a stylesheet aimed at a different browser that a current browser might consider invalid. Plus, given user-generated contents, there can indeed also be selectors that aren't valid in any browser. Seems like that try-catch is here to stay!