Ditch your version manager

Link to the thread for other people: https://nitter.net/dmitriid/status/1439957729909559298#m

Ju (@Arkham) proposed a solution:

1- Finding the commit hash of of nixpkgs which contains a specific version of a dependency (e.g. ruby 2.6.3) and use that to bring in the dependency

2- If a specific version does not exist in any of the hashes, we should patch the `.nix` file and build the dependency ourselves. This causes all other transitive dependencies to be rebuilt.

Arguments against 1:

Why should we rely on an external thrid-party webservice to find the hashes of a specific package? This should be integrated to the `nix` tooling. Hope the community incorporates history search into the tooling :)

Arguments against 2:

@dimitriid says the solution is cumbersome.

Arguments for 2:

- What if rvm or nvm don't have a specific version or deprecate that version from their repos? At least there is a solution via Nix.

- What are you going to do for other languages which don't have a package/VM manager like Java, C/C++, etc? At least the Nix solution is universal and you don't have to learn the tooling of every technology.

I think @technomancy over at Lobste.rs has a wise take on this issue: https://lobste.rs/s/emyfhx/ditch_your_version_manager#c_5acg...

> I feel like Nix/Guix vs Docker is like … do you want the right idea with not-enough-polish-applied, or do you want the wrong idea with way-too-much-polish-applied?

> Arguments for 2:

> - What if rvm or nvm don't have a specific version

Let's get back to reality for a second. For most development needs this is a hypothetical situation.

Right now, in reality, ruby-lang hosts versions dating to 2002.

Also, right now, in reality nix limits the number of available versions. Quote: "in NixPkgs we choose to restrict the number of maintained versions", https://github.com/NixOS/nixpkgs/issues/93327#issuecomment-6... So it's already worse than the hypothetical "what if rvm don't have a specific version".

Also, right now, in reality there's no easy way to pin a version of a tool in nix. Except going to a third-party website (lazamar's site), hope that your specific version is listed there (he only maintains a snapshot of a few years), and dig through nixpckg commit hashes. And this has been a known issue for as long as nix has been around. 18 years, at least. And we're still hoping that someone somewhere will incorporate this into standard tooling. You yourself linked to an issue on this.

I'd like to link to a reply in that issue: https://github.com/NixOS/nixpkgs/issues/93327#issuecomment-6...

And to this reply: https://github.com/NixOS/nixpkgs/issues/93327#issuecomment-7...

> What are you going to do for other languages which don't have a package/VM manager like Java, C/C++, etc?

That varies between languages, of course. I have several Java versions installed side-by-side. C/C++ is worse because they are mostly stuck in 1960s, tooling-wise (though on windows you can have multiple msvcrt versions installed side-by-side).

This still can be (and is) handled. And nix doesn't offer great advantages, except providing a complex, complicated, poorly documented tool.

>Right now, in reality, ruby-lang hosts versions dating to 2002.

OK, so you want to pin ruby 1.3.4 in your project and use a ruby gem that is dependent on a specific glibc (or maybe some standard ruby library itself is dependent on a low-level C dependency.). With python these stuff happens all the time. What would you do?

Craft a dockerfile inheriting from an old Debian and hope ruby 1.3.4 installed with rvm would play nicely with this specific version of Debian? How do you find what version of say, Ubuntu, has fixed security updates of the low-level dependencies of your project? And what happens if the apt-managed JRE v.1.6.x in that instance would break other parts of the project that was dependent on JRE v1.6.y?

>That varies between languages, of course.

Well, that's the point. For each technology, you have to handle their specific "VM manager" and put up with their quirks + random state-changes imposed by apt. With Nix, the solution would not vary between languages, setups and teams. I mean, at least theoretically, the Nix/Guix way makes much more sense than shipping the whole state of the computer (with docker).

Sorry if I may have come up as a Nix professional/proponent. I'm actually a nix beginner and as can be seen in this thread, I've asked the author similar question to yours. Using Ubuntu, I have been bitten by glibc and other dependency mismatch in my projects and I'm looking for something more elegant than docker/VBox.

I've read posts from both sides of this discussion.

> Oh. Wait. There's literally no such way.

I think there is? Check to see if the nixpkgs history have that version (+), if not, patch the derivation (could be as simple as bumping the version and recalculating the hash, or, doing so could cause a breakage in one of the transitive dependencies, at which point, you have to fix that also (meaning a version increment of decrement for the dependency or more. Essentially you have to build the specific ruby version down to all its dependencies)

(+) How can we see what versions are available in nixpkgs history?

It seems we have to use third-party webservices! I agree with you here that this should have been implemented in the nix tooling itself. I know of two such services:

https://4shells.com/nixdb/pkg/ruby/2.6.6

https://lazamar.co.uk/nix-versions/?channel=nixpkgs-unstable...

I think this also answers that quote from the github issue.

> What was this solution again?

From what I understood, in the project `.nix` file, we inherent from a forked nixpkgs repo which has our patched `default.nix` in the ruby folder, for building ruby. (Nix pros, correct me if I'm wrong here). Now we have to build all deps locally since a matching hash would not be present on Nix cache servers.

Now, with nvm, how could you guarantee that a particular version would not conflict with one the host OSs low-level libraries (Like glibC)? The difficulty and complexity of patching the Nix derivation has to do with this part. In Ubuntu/Debian, you can't simply mess with system level low level libraries.

That's the point: without using Nix, you'd have to do LD_LIBRARY_PATH hacking to have two programs use two different versions of glibc. When people say "oh nix looks so complicated I can do this using bash scripts" I reply "well show me these beautifully expressive and simple bash scripts then".