Gate on `update-generated`

[jeckersb]

Spun off from #1835 (comment)

We should ensure that just update-generated is a no-op. In other words, if the PR changes something that necessitates updating the generated content, then it should be included as part of the PR.

[jeckersb]

My first thought is just to inline this as part of the just validate flow, although that would entail building the xtask crate as part of that flow (I don't think it happens currently) so it might slow things a bit. It obviously could be split into its own target (validate-generated or whatever) as well.

[cgwalters]

Fine by me in having this in just validate.

One concern Chris raised is that right now we deploy the website from git main - which means if we require updating the man pages right away then the website will show unreleased changes.

In the medium term though...I think we need to do at least one of two things:

• Add explicit "Added in version " to each option (like systemd does it e.g.)
• Add versioning to the website (like Rust crates do it)

The latter I think could be done with a bit of CI work, there has to be some prior art for it too.

[cgwalters]

I was looking at things related to this and an issue right now is just validate runs xtask code in Rust, and so for consistency we do that as part of the main container build.

But there are things we want to validate (like the website) that aren't copied into that build intentionally.

Like in theory the scope of "validate" is everything stored in git. Maybe it's simplest to just require a host Rust toolchain and run the xtask stuff there, but in the general case it would require building the xtask code twice.

A different option I guess is that since validate conceptually has no "output" other than stdout/stderr (it doesn't result in binaries/containers) we could have it be done in a podman run using the devenv toolchain, though I think an annoying thing there is that --mount=type=cache isn't exposed to that, but we could probably hack it with a volume.