Is this a recent change? I've with 100% been bitten by this before, repeatedly, and the go compiler did nothing to warn about it.

Maybe for a side-effecting function which would only return an error?

edit: nope, fails with "err evaluated but not used".

I'm genuinely stumped. If they've fixed this, that's fantastic because I have absolutely shipped code with this bug to a production environment.

I've been working with Go for 4 years and I've not encountered it. Perhaps there was an edge case where it was allowed, but I don't recall it.