clo4
commented
11 months ago This is a quick recap of this issue for people without much experience with Nix internals (like me!), people that don't want to read the thread, or people that just want a solid solution.
What's the problem?
The script nixos-env-preinit.fish is executed on shell startup. You can find this at /etc/fish/nixos-env-preinit.fish on your system. This file executes another script that sets up environment variables, including the $PATH. The path is set up correctly here!
However, this happens before fish runs its own config scripts. Only when Fish is set as your login shell, it reads from /etc/paths and /etc/paths.d/*, sets that as the path, and then appends the pre-existing $PATH. Here's the code that does this. This is normally what you want, but in this case, it ends up putting your Nix directories at the end.
What paths exactly need to be moved?
Before Fish clobbers the path variable, the important directories in it are the /bin subdirectories of the values of environment.profiles.
This is set, by default, by:
... but anything can add to this value. Using hardcoded paths is probably fine but isn't completely "correct" in the programmer-y ideology kind of way.
What's the fix?
The paths in environment.profiles need to be moved to the front of $PATH but behind $fish_user_paths, which is a magic fish variable that's always prepended to your path. (When you use the fish_add_path command, it prepends to $fish_user_paths universally by default. Universal means it modifies ~/.config/fish/fish_variables)
This module works correctly -- you can copy/paste it or save it as a file and add it to imports. I'm pretty new to Nix so this might not be super idiomatic, but this is about as correct as it can be I think.
{ lib, config, ... }:
{
programs.fish.loginShellInit =
let
# This naive quoting is good enough in this case. There shouldn't be any
# double quotes in the input string, and it needs to be double quoted in case
# it contains a space (which is unlikely!)
dquote = str: "\"" + str + "\"";
makeBinPathList = map (path: path + "/bin");
in ''
fish_add_path --move --prepend --path ${lib.concatMapStringsSep " " dquote (makeBinPathList config.environment.profiles)}
set fish_user_paths $fish_user_paths
'';
}You can probably get away without double quoting at all, it just makes me a little uncomfortable to think that a stray space could blow up my shell init 😅
The set fish_user_paths $fish_user_paths line is done for the side-effect of reordering $PATH, putting the user paths in the front.
(There are lots of valid ways of doing this -- another is to use string split " " $NIX_PROFILES)[-1..1]/bin, but this will always happen at runtime)
This is valid either in your home-manager config or nix-darwin config, both define programs.fish.loginShellInit, but as @yoav-lavi noted, you need to change config to osConfig when using it as a home-manager module.
A note about Fish's weird source order
Fish is kinda weird about what order to source things in. Currently, as of fish 3.6, fish sources user config **first** (~/.config/fish/conf.d/*), then system config (/etc/fish/conf.d/*), then vendor config, then user config.fish, and only *then* the system config.fish. This means using `programs.fish.loginShellInit` will execute **last**. Everything that gets executed before that will have the wrong path, but your interactive shell will be correct. This will be fixed in the future by sourcing config snippets (conf.d/*.fish) in order of name, regardless of the directory. So the *most* correct thing to do would be using something like ```nix environment.etc."fish/conf.d/00-nix.fish".text = let # ... in '' if status is-login # config snippet... end ''; ``` But again, this doesn't really matter that much right now, because files under `/etc/fish` will always be executed *after* your user config. --- There's also the issue that fish doesn't technically source /etc/fish/..., it looks in `$__fish_sysconf_dir` which is set at compile time to a location in the nix store. The only reason `/etc/fish/config.fish` is executed is [because of a shim](https://github.com/NixOS/nixpkgs/blob/7cf96f8ebb562afa7bf2f40f0d5d06cb7fe096dd/pkgs/shells/fish/default.nix#L88-L89)). But nothing knows about `/etc/fish/conf.d`, so it's not used. To fix this, maybe it's worth changing nixpkgs' fish preinit to add `/etc/fish` to `__extra_confdir`? I'm not sure what the ramifications would be for this ...
yoav-lavi
khaneliman
britter
lilyball
jjant
zhou13
I updated nix-darwin today and had to rollback to a version from October because my
$PATHwas broken (using fish shell).Before (correct):
After (broken):
The important part being that
/run/currenty-system/sw/bincomes too late and the Nix provided binaries are not picked up correctly, resolving to/usr/bin/gitfor example. I'm also not sure where all this duplication is coming from …I tried to get to the source of this error but was not able to figure it out exactly. What worked was to switch to an older generation and then to the newest generation again: in this case, the
$PATHwas set correctly. But when I exit fish shell and enter it again, the$PATHis broken.It could be that this problem was introduced in https://github.com/LnL7/nix-darwin/commit/676ef103771aa3fc4b150290294b8ad5610d2750#diff-02a3bd02a5cdf5583b2e516a0e92d58a because the version of nix-darwin that worked for me was from 2018-10-17 and this is the major change that happened to the environment a few days later. But then maybe not because no one else has this problem?