[oranlooney]

Yes and no. If you push an update and sysadmins all over the world dutifully upgrade and immediately notice programs breaking, their first thought is not going to be "oh, those programs must have had latent bugs." No, they're going to blame you. Besides, having stuff work correctly is always more fun than assigning blame, and validating flags is an easy way to avoid these scenarios.

[sillysaurus3]

Hm, fair enough. To be clear, I wasn't arguing against validating flags. I was commenting about "This kernel function only gets 32 possible bitflags, but since they never validated their flags, they can no longer add any additional flags, ever, because it might break other programs which may or may not even exist."

That sort of mentality seems like it would push designers in the direction of poor design decisions. If a bitflag is the best design for a new feature, but they're prevented from using it out of a sense of "Let's not ever break anything ever," then the result may be a bad design that people are stuck with for the next 50+ years, which seems objectively worse.

But my reaction is based on theory and not backed by experience, so it's probably unfounded.