nixos: Disable nix-channel by roberth · Pull Request #242098 · NixOS/nixpkgs

roberth · 2023-07-07T17:05:12Z

Motivation

This fixes a warning that's been bothering me.

warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring

Description of changes

Allow users to remove nix-channel and its accompanying files. Opt-in.

configuration.nix:
```
 nix.channel.enable = false;
```
Extends the installer test case to make sure users can switch from a traditional config to a flake.

Things done

For those who wish to get rid of nix-channel.

roberth · 2023-07-07T19:32:51Z

@ofborg test installer.simple
@ofborg test installer.switchToFlake

…abled

SuperSandro2000

I like the idea, then I no longer need to hack around removing channels

SuperSandro2000 · 2023-07-07T22:15:06Z

nixos/modules/config/nix-channel.nix

+        default =
+          if cfg.channel.enable
+          then [
+            "nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos"
+            "nixos-config=/etc/nixos/configuration.nix"
+            "/nix/var/nix/profiles/per-user/root/channels"
+          ]
+          else [];


Suggested change

default =

if cfg.channel.enable

then [

"nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos"

"nixos-config=/etc/nixos/configuration.nix"

"/nix/var/nix/profiles/per-user/root/channels"

]

else [];

default = lib.optionals cfg.channel.enable [

"nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos"

"nixos-config=/etc/nixos/configuration.nix"

"/nix/var/nix/profiles/per-user/root/channels"

];

This is not exactly equal to the documented default. Let's keep them in sync, and see other comment.

What's the difference?

SuperSandro2000 · 2023-07-07T22:15:29Z

nixos/modules/config/nix-channel.nix

+          if nix.channel.enable
+          then [
+            "nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos"
+            "nixos-config=/etc/nixos/configuration.nix"
+            "/nix/var/nix/profiles/per-user/root/channels"
+          ]
+          else [];


Suggested change

if nix.channel.enable

then [

"nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos"

"nixos-config=/etc/nixos/configuration.nix"

"/nix/var/nix/profiles/per-user/root/channels"

]

else [];

lib.optionals cfg.channel.enable [

"nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos"

"nixos-config=/etc/nixos/configuration.nix"

"/nix/var/nix/profiles/per-user/root/channels"

];

This is harder to understand for someone who doesn't contribute to nixpkgs or other expressions regularly. optionals is idiosyncratic to Nixpkgs lib, whereas everyone understand if then else.

we had multiple treewide replacement for this already, so I don't think we should add new candidates for this

This documentation should not require someone to know the optionals function.

nixos/modules/config/nix-channel.nix

nixos/tests/installer.nix

Ericson2314

Very nice!

Co-authored-by: Sandro <[email protected]>

github-actions · 2023-07-19T14:03:00Z

Successfully created backport PR for release-23.05:

[Backport release-23.05] nixos: Disable nix-channel #244354

SuperSandro2000 · 2023-07-20T19:40:16Z

nixos/modules/config/nix-channel.nix


-    system.activationScripts.nix-channel = stringAfter [ "etc" "users" ]
-      ''
+    nix.settings.nix-path = mkIf (! cfg.channel.enable) (mkDefault "");


I don't think we want to set this to empty string here because that clears the default nix-path setting of nix which breaks many programs like nix-tree or comma which rely on it to find some nixpkgs which in my case points to a flake.

I don't think so. The point of this is one really doesn't want to use a populated NIX_PATH. If other programs can't cope with that, they should be fixed.

One can always set nix.settings.nix-path elsewhere than this module instead.

By default nix-path is left empty which means it default to NIX_PATH env. When we explicitly set it to empty, that is no longer the case and things completely break for many tools which makes this option rather useless.

➜ nix show-config | rg nix-path nix-path = nixpkgs=/nix/store/x6ly3m0dylzsbrgz0sx937xxcyswr2yp-source nixos=/nix/store/x6ly3m0dylzsbrgz0sx937xxcyswr2yp-source nixos-config=/etc/nixos/configuration.nix ➜ (unset NIX_PATH; nix show-config | rg nix-path) nix-path = ➜ (unset NIX_PATH; nix --option nix-path "" show-config | rg nix-path) nix-path = ➜ nix --option nix-path "" show-config | rg nix-path nix-path =

That seems like the behaviour that someone ripping out a formerly-mandatory system component to avoid non-flakes things would want, given that properly flakes-aware tools like nixos-rebuild(8) won't look at the Nix path when used correctly.

hmmm, yeah, that sounds about right. Maybe I misunderstood the feature a bit.

I don't think so. The point of this is one really doesn't want to use a populated NIX_PATH

Kind of debatable, IMO. Feels like you're assuming that disabling channels automatically implies that:

The person is using flakes

The person wants to use a PURE flake workflow everywhere.

The reality is that:

nixpkgs is kind of special

You can use --impure with flakes

Some people may want a more "it just works" sort of thing with certain types of commands/ and /or the ability to build their system against a flake and then have all other commands use the same version of nixpkgs that their system was built against, or maybe still allow the NIX_PATH variable to take effect.

That seems like the behaviour that someone ripping out a formerly-mandatory system component to avoid non-flakes things would want, given that properly flakes-aware tools like nixos-rebuild(8) won't look at the Nix path when used correctly.

This is a weird position that doesn't make sense.

You can only use NIX_PATH at all, if you pass the --impure flag to these commands. If you dont, you'll get:

error: cannot look up '<nixpkgs>' in pure evaluation mode (use '--impure' to override)

If you're explicitly opting IN by passing the --impure flag, this behavior makes absolutely no sense.

Really, the problem is not setting nix-path to the empty string, the problem is NixOS/nix#8890 and NixOS/nix#8890

I'm also encountered the problem where I don't use channels but put aliases in NIX_PATH for commands. This setting disables NIX_PATH envvar entirely, which is not what I want. I'm kinda thinking we should revert this line.

colonelpanic8 · 2023-09-03T02:23:16Z

@roberth I find some of the details of this a little confusing:

In particular, this:

    environment.sessionVariables = {
      NIX_PATH = cfg.nixPath;
    };

    nix.settings.nix-path = mkIf (! cfg.channel.enable) (mkDefault "");

is very weird, because it makes it so that there are now two variables for setting the nix path:

nix.settings.nix-path and nix.nixPath

and nix.settings.nix-path is not defaulted to the value of nix.nixPath

it also seems to me that nix.settings.nix-path

should be defined in nix.nix, not in nix-channel.nix, but yeah I'm finding all of this pretty confusing.

This is especially an issue in light of NixOS/nix#8890 which is the same as NixOS/nix#8890

roberth · 2023-09-04T16:02:01Z

weird, because it makes it so that there are now two variables for setting the nix path:

nix.settings.nix-path and nix.nixPath

I have only preserved nix.nixPath, which was already somewhat redundant. It sets the environment instead of /etc/nix/nix.conf.
iirc I did have to affect both in order to achieve a Nix that doesn't have rudimentary channel behavior.

Main thing is that I wasn't aware of Nix's strange treatment of nix-path vs NIX_PATH.

My original intent with this PR had two layers

Make it possible to not have any channels, without Nix complaining about it. I didn't have any channels on a fresh install and it was bothering me.
Help find possible spurious usages of channels and/or the default NIX_PATH, for both flakes and - perhaps - pure mode without flakes.

It was not my intent to break NIX_PATH entirely. If you have, say, a nix shell which sets it to what the repo has pinned, that should just work.

colonelpanic8 · 2023-09-04T16:05:25Z

I have only preserved nix.nixPath, which was already somewhat redundant. It sets the environment instead of /etc/nix/nix.conf

Yeah I guess its just kind of confusing. If someone sets the value of that variable to something but disables channels, it actually just has no effect. I wasn't aware of the distinction. Would it really be so bad to default the nix-path setting to whatever nixPath is in the event where channels are disabled?

Alternatively, maybe we should make it an error to set nixPath at all when channels are disabled.

Or maybe its just fine to have different settings for the environment variable and the nix.conf setting, as long as my nix PR is merged.

roberth · 2023-09-04T16:25:22Z

If someone sets the value of that variable to something but disables channels, it actually just has no effect.

Yeah. It shouldn't be like that. I almost started explaining that it does have an effect, but that's the entire point of the bug, which I consider it to be.

Though I think it is worth noting that in the case where the bug is fixed in nix, we'll probably still want the NixOS behavior that we currently have.

The difference between the nix.nixPath and nix.settings.nix-path will matter when you unset NIX_PATH in a shell, and I'm sure there's some scripts and shellHooks out there that do it, and possibly even by mistake.

To be honest, applying a fix to both projects seems a bit daunting as we'll have three scenarios to consider, while even a single scenario is already quite confusing. So I'd prefer to focus on making Nix treat its option more sensibly, and come back to this NixOS change later if needed.

oxalica · 2023-12-09T17:05:08Z

I created #273170 to revert the line setting an empty nix-path.

nixos-discourse · 2024-06-01T18:42:28Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/24-05-add-flake-to-nix-path/46310/11

roberth added 3 commits July 7, 2023 19:00

nixosTests.installer: Make sure we boot into the config we generated

218ef2f

nixosTests.installer: Fix driverInteractive

faa1b3b

nixos: Add nixos.channel.enable

d00e242

For those who wish to get rid of nix-channel.

github-actions bot added 6.topic: nixos Issues or PRs affecting NixOS modules, or package usability issues specific to NixOS 8.has: module (update) This PR changes an existing module in `nixos/` labels Jul 7, 2023

roberth mentioned this pull request Jul 7, 2023

Split nixos/nix-daemon.nix #241690

Merged

12 tasks

ofborg bot added 10.rebuild-darwin: 0 This PR does not cause any packages to rebuild on Darwin. 10.rebuild-linux: 1-10 This PR causes between 1 and 10 packages to rebuild on Linux. labels Jul 7, 2023

nixos/nix-channel: Take care of NIX_PATH's non-empty default when dis…

61afc4d

…abled

SuperSandro2000 reviewed Jul 7, 2023

View reviewed changes

Ericson2314 approved these changes Jul 7, 2023

View reviewed changes

nixos/nix-channel: Apply suggestions from code review

a1d0ee8

Co-authored-by: Sandro <[email protected]>

roberth merged commit 8ad59ed into NixOS:master Jul 18, 2023

roberth added the backport release-23.05 label Jul 19, 2023

github-actions bot mentioned this pull request Jul 19, 2023

[Backport release-23.05] nixos: Disable nix-channel #244354

Merged

1 task

SuperSandro2000 reviewed Jul 20, 2023

View reviewed changes

r-vdp mentioned this pull request Jul 23, 2023

nixos/nix-channel: only try to remove the nix-channel binary if it exists #245038

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12 tasks

NickCao mentioned this pull request Jul 27, 2023

os.environ["NIX_PATH"] = self.nixpkgs_path() silently get ignored when nix-path is set in nix.conf Mic92/nixpkgs-review#343

Closed

This was referenced Sep 3, 2023

Make the NIX_PATH environment variable take precedence over config files NixOS/nix#8902

Closed

nix-shell fails to parse NIX_PATH NixOS/nix#8890

Open

oxalica mentioned this pull request Dec 9, 2023

nix-channel: do not set empty nix-path when disabling channels #273170

Closed

13 tasks

jian-lin mentioned this pull request Jul 22, 2024

emacs updater: trivialBuild -> melpaBuild #329008

Merged

13 tasks

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colonelpanic8 commented Sep 3, 2023

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roberth commented Sep 4, 2023

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colonelpanic8 commented Sep 4, 2023

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roberth commented Sep 4, 2023

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oxalica commented Dec 9, 2023

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roberth commented Jul 7, 2023 •

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