I have never been asked such a thing, in the US or elsewhere. It would be on the customer to inform the staff of any allergies.

Five years ago it was a rarity (in fact the first place I can clearly recall being asked was a Five Guys, when I said I didn't want a bun - no gluten problems, thanks, just don't need the extra calories). Nowadays I'd say it's more common than not at full-service restaurants.

Southern US; I live in a modest-size metro of about 400k and spend plenty of time in bigger cities.

> Pretty common expectation in many countries.

I've been to 40+ countries and not once have I been asked about allergies at a restaurant or food shop (i.e., ice cream, etc.)

I'd say I am asked this question at about half of the restaurants I eat at in the US (in the northeast.)

I don't have experience in many countries, but e.g. in Germany, while everything is labeled according to law, I have never heard anyone asking. I think the persons with allergies know this well themselves.

Not sure, but there's a funny saga about sesame in bread cause of lawsuits here