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Nix Hackers

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For people hacking on the Nix package manager itself187 Servers

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11 Oct 2025
@Ericson2314:matrix.orgJohn Ericson Sergei Zimmerman (xokdvium): oh no c97b050a6c212d0b748303080b5604309b7abdce is this the thing that does the closure that I guess is no good 00:27:50
@Ericson2314:matrix.orgJohn Ericsonnevermind maybe not the same bug00:27:54
@Ericson2314:matrix.orgJohn Ericsonor at least that one is also a problem00:27:59
@fzakaria:one.ems.hostfzakaria any good issues to try and tackle?
Sergei Zimmerman (xokdvium) i guess you figured out that weird postgres one
02:26:09
@fzakaria:one.ems.hostfzakariai'm not sure how you narrowed it down to path length; i missed that part of the RCA02:26:20
@perra23:mozilla.orgperra23 joined the room.04:38:38
@lovesegfault:matrix.orglovesegfaultHot off the press: https://github.com/NixOS/nix/pull/1421818:43:30
@lovesegfault:matrix.orglovesegfaultHot off the press: https://github.com/NixOS/nix/pull/1421919:11:00
@Ericson2314:matrix.orgJohn Ericsonnevermind, that is just a fairly innocuous boolean field20:07:03
@Ericson2314:matrix.orgJohn Ericsonso it won't cause "that bad" of UB20:07:09
@Ericson2314:matrix.orgJohn Ericsonand we just saw the issue from the first commit20:07:15
@Ericson2314:matrix.orgJohn Ericsonso I am back to my "one bug, two symptoms" theory 20:07:31
@midischwarz12:libg.somidischwarz12 joined the room.20:27:33
@tavinator:matrix.orgtavinator

nix, or nixpkgs, does not really have a concept of multiple extant versions of a package. i see this worked around in cases of overwhelming importance with e.g. python312, python313 etc.

but in general if you need an older version of package XYZ you are dealing with a git history search and pinning to a commit

there is no fundamental reason why nixpkgs HEAD could not contain the logic for multiple versions of package XYZ

so - to start from the beginning - is there something in nix itself that keeps me from e.g. writing opentofu-1.6.3 or opentofu==1.6.3 or whatever as the package i want to install?

background: i want to introduce nix devshells in a company where this kind of situation happens all the time (i.e. some project has to be checked out from github and worked on using a list of software versions that is both brittle and not recent)

22:35:31
12 Oct 2025
@lovesegfault:matrix.orglovesegfault John Ericson, Sergei Zimmerman (xokdvium) why do we run functional tests against an old version of Nix? It's causing my new multiple-outputs cycle detection functional tests to fail under nix-daemon-compat-tests 00:05:50
@lovesegfault:matrix.orglovesegfaultShould I make the test agnostic to the old version or just not have it run when in compat tests?00:06:10
@midischwarz12:libg.somidischwarz12 removed their profile picture.02:45:01
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@lovesegfault:matrix.orglovesegfault(i made the test agnostic)02:46:01
@midischwarz12:libg.somidischwarz12 Yea, you're not technically wrong that packages on the same version of nixpkgs could have different versions. But you'd have to have a package for every version of its dependencies as well. At which point, it is usually easier to dig through git or just override the package with a different version of source. That said, you'd have to do the same for its dependencies as well. But it's much easier to push this unto the user than force all of the nixpkgs maintainers to keep every package up to date. That said, I do agree that there should be an easier CLI interface to dig through nixpkgs and find necessary package versions or versions within requirements such as version ranges 03:26:54
@midischwarz12:libg.somidischwarz12So for some packages, yes, we do support multiple versions b/c we need to in the current version of nixpkgs (clang, python, gcc, glibc, etc). But for most packages, that is very unnecessary to maintain the current round of packages in nixpkgs03:28:01
@tavinator:matrix.orgtavinator

Thanks midischwarz12 I guess I am just looking for a framework to approach the problem. I would not have minded contributing the code to nixpkgs for packaging specific old versions of this or that. But it was pointed out to me that it would have an infeasible impact on Hydra -- a piece of the puzzle I wasn't seeing until now.

override the package with a different version of source.

Sounds like what I am looking for... this means using "overlays" then?

09:22:08
@0x9t:matrix.org0x9t joined the room.09:55:46
@Ericson2314:matrix.orgJohn Ericson @lovesegfault:matrix.org: we make tests require a new enough daemon version all the time 14:04:52
@Ericson2314:matrix.orgJohn EricsonIf you grep for DaemonVersion I think you'll see it14:05:28
@justinrestivo:matrix.orgjustinrestivo Hello! Any chance there's a spec about the different Fields provided for each ActivityType in the nix logger? Right now to answer this question I'm grepping the nix codebase for each ActivityType and looking at the arguments to the Activity::Activity constructor to infer the field types and number (if any exist). I'm wondering if there's an easier/more canonical way to do this. 15:30:35
@midischwarz12:libg.somidischwarz12You overlay when you want to stitch multiple overrides together or want the package that's available across your entire package set such as nixpkgs. What you're really desiring is just a single override and probably not overriding every package that consumes this package as a dependency. So an overlay would be unnecessary 16:39:36
@midischwarz12:libg.somidischwarz12* You overlay when you want to stitch multiple overrides together or want the override available across your entire package set such as nixpkgs. What you're really desiring is just a single override and probably not overriding every package that consumes this package as a dependency. So an overlay would be unnecessary 16:40:03
@midischwarz12:libg.somidischwarz12* You overlay when you want to stitch multiple overrides together or want the override available across your entire package set such as nixpkgs when used as a dependency. What you're really desiring is just a single override and probably not overriding every package that consumes this package as a dependency. So an overlay would be unnecessary 16:40:25
@midischwarz12:libg.somidischwarz12 I think overlays are often reached for a bit too early and people should take note more often that this ruins a lot of the reproducible nature of nix. Your nixpkgs will no longer be the same as everyone else's when you use an overlay 16:41:25

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