Should we unify the behaviours of depexts installations regarding system database upgrades?

[kit-ty-kate]

Currently the behaviours of opam-depext regarding system database upgrades (e.g. apt update on Debian) is completely different accross platforms:

• On Debian, Alpine, NetBSD, Archlinux, Macports: the installation command does not fetch the packages database
• On Gentoo: same, but it matters less as Gentoo is a source package manager and stores all the package tree locally
• On Homebrew, RedHat variants (Fedora, CentOS, …), OpenSUSE: the installation command fetches the package database automatically everytime the package manager decides it's been too long.
• On FreeBSD and DragonflyBSD(?): the packages database is downloaded every time.
• On OpenBSD: untested

It could be interesting to unify all these different behaviours in one way or another.
I have no specific opinions about that personally but I'd like to get the discussion going. Here is some pro and cons about unifying in one way or the other:

Make everything download the database every time

• Pros: No more Download failed, error 404 on m4.1.4.18-5.tar.gz type failures.
• Cons: Slows everything down 😢 (some distributions can be really slow to sync)

Make everything download the database only when it's been too long

• Pros: Best of both worlds
• Cons: Cons of both world 😄 .. on top of being more complicated to maintain

Make everything not download the database

• Pros: Fast and predicable
• Cons: More annoying for users of some fast-moving distributions, they have to remember to call opam update --depexts first.

After writing everything down I feel more inclined to the latest with maybe a new opam install -u/--update-depexts for a more streamline way of updating the local database.

[dra27]

Another option would be to maintain the current state (some do, some don’t), but expose it as a global option. I would expect that if a user wishes to install with --update-depexts once, they probably want to use it every time (so a setting would be preferable)