--expect-no-changes                     Return an error if any changes occur during this update

is somewhat ambiguous

I believe it’s supposed to stop processing if changes are detected. I just tested this and it does not seem to be the case.

It's only really useful on

pulumi preview

it simply adds a check at the end of the engine operations to see if any changes we're done (or proposed for preview)

Ok, interesting

Yeh I think we should either improve the wording of this option, or change it to actually error out before any change. Changing it sounds better but there might be things depending on this current behaviour.

yeah, obviously my opinion doesn't count for much here, but I'd vote to deprecate it and then promote something using your new plans feature with a log message 🤷‍♂️