For those who are using the new command-line interface of Nix, you've most likely went through to pain of searching packages through `nix search`.
For reference, here's what the experience looks like searching for a package from nixpkgs except it always like that every time you run the command. footnote:[Not necessarily, just every few hours as you'll see why.]
[#video:nix-search-demo]
.A part of the `nix search nixpkgs` experience which took 8 minutes in total to complete the whole search
It's painful to use to the point where people tend to recommend https://search.nixos.org/packages[search.nixos.org] or https://mynixos.com/[MyNixOS] for searching packages. footnote:[They also include searching for NixOS options so that may be another reason these tools are always recommended.]
Ideally, searching packages for your system shouldn't rely on online services.
Luckily for us, there are ways how to mitigate against that.
[chat, Ezran]
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I'm just going to say it.
That package search result looks ugly.
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[chat, foodogsquared, role=reversed]
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That might be another reason why `nix search` is not much used.
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[WARNING]
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We're using Nix v2.18 for this post.
Everything that is featured here is considered to be experimental: from flakes, the command-line interface, and even the referenced manual may change over time.
In order to enable them in the first place, you'll have to add `experimental-features = nix-command flake` into the Nix configuration (see https://nixos.org/manual/nix/stable/command-ref/conf-file[`nix.conf` options] for more details).
But first, let's take a closer inspection as to why `nix search` is behaving like that.
Let's look at the following command which is https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-search[one of the examples from the manual].
[source, shell]
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nix search nixpkgs blender
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At first glance, most people expect `nix search nixpkgs blender` searches for package `blender` from their nixpkgs instance.
It does work as intended which is searching through packages from nixpkgs containing the word `blender`.
Just not our own nixpkgs instance.
It just doesn't behave to how most people expect as they overlook one thing about flakes: the registry.
Per https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-registry[the manual]:
[#quote:flake-registry-intro]
[quote, Nix manual]
____
Flake registries are a convenience feature that allows you to refer to flakes using symbolic identifiers such as `nixpkgs`, rather than full URLs such as `git://github.com/NixOS/nixpkgs`.
You can use these identifiers on the command line (e.g. when you do `nix run nixpkgs#hello`) or in flake input specifications in `flake.nix` files.
The latter are automatically resolved to full URLs and recorded in the flake’s `flake.lock` file.
____
In short, `nixpkgs` from `nix search nixpkgs blender` points to a flake from the registry.
We can view what `nixpkgs` points to by running `nix registry list`.
[#lst:cmd-nix-registry-list]
.Results from `nix registry list | grep flake:nixpkgs`
[source]
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global flake:nixpkgs github:NixOS/nixpkgs/nixpkgs-unstable
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As stated from https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-registry-list[the manual], the format from the `nix registry list` output comes in the form of `<type> <from> <to>` where...
* `type` denotes which registry it came from (which we'll discuss shortly later in this post).
This seems fine except the flake reference isn't pointing to a fixed point like a specific commit, it points to a branch of a remote Git repo which can change over time.
This is why it downloads and evaluates a new nixpkgs instance every time it runs (or between every few hours, which is the pace for nixpkgs-unstable updates).
Not exactly a good experience for a system package search compared to other operating systems like Arch Linux, Fedora, or OpenSUSE.
[chat, Ezran]
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Seem like flake registry is not a convenience feature at all.
More like a hindrance, really.
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[chat, foodogsquared, role=reversed]
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It is a CONVENIENCE FEATURE!
I use it to quickly test and run packages from my nixpkgs instance as well as other projects with flake.
It's just that most NixOS systems are not properly configured with it by default.
You'll see what I mean.
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[#pinning-nixpkgs-to-the-registry]
== Pinning nixpkgs to the registry
Most would expect to search packages in their nixpkgs instance of their NixOS system.
As hinted from the previous section, we can make use of multiple registries.
As stated right after the <<quote:flake-registry-intro, previous excerpt from the manual>>:
[#quote:manual-multiple-flake-registries]
[quote, Nix manual]
____
There are multiple registries.
These are, in order from lowest to highest precedence:
* The global registry, which is a file downloaded from the URL specified by the setting `flake-registry`.
It is cached locally and updated automatically when it's older than `tarball-ttl` seconds.
The default global registry is kept in https://github.com/NixOS/flake-registry[a GitHub repository].
* The system registry, which is shared by all users.
The default location is `/etc/nix/registry.json`.
On NixOS, the system registry can be specified using the NixOS option `nix.registry`.
* The user registry `~/.config/nix/registry.json`.
This registry can be modified by commands such as `nix registry pin`.
* Overrides specified on the command line using the option `--override-flake`.
____
A quick way to show this would be pinning `nixpkgs` from the global registry to the user registry with `nix registry pin nixpkgs`.
.Results from `nix registry list | grep 'flake:nixpkgs'` after pinning
[source, shell]
----
user flake:nixpkgs github:NixOS/nixpkgs/ec750fd01963ab6b20ee1f0cb488754e8036d89d
global flake:nixpkgs github:NixOS/nixpkgs/nixpkgs-unstable
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[NOTE]
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Since we're going to show configuring the system registry with NixOS, don't forget to remove the entry from the user registry with `nix registry remove nixpkgs`.
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Both the global and system registry can be configured in the NixOS system.
In this case, we'll be focusing on adding our flake inputs of our NixOS system into the system registry.
system flake:nixpkgs path:/nix/store/kcmipm57ph9bpzz8bs80iiijiwbyzwy3-source?lastModified=1699099776&narHash=sha256-X09iKJ27mGsGambGfkKzqvw5esP1L/Rf8H3u3fCqIiU%3D&rev=85f1ba3e51676fa8cc604a3d863d729026a6b8eb
system flake:nixpkgs-stable path:/nix/store/3s69yxbbl116zwga3i6cy7prplywq0bn-source?lastModified=1699291058&narHash=sha256-5ggduoaAMPHUy4riL%2BOrlAZE14Kh7JWX4oLEs22ZqfU%3D&rev=41de143fda10e33be0f47eab2bfe08a50f234267
system flake:nixpkgs-unstable path:/nix/store/mj0hy52z22q5gpsf33akndxiclxd8ray-source?lastModified=1699343069&narHash=sha256-s7BBhyLA6MI6FuJgs4F/SgpntHBzz40/qV0xLPW6A1Q%3D&rev=ec750fd01963ab6b20ee1f0cb488754e8036d89d
system flake:self path:/nix/store/v68idbapq3m8sz0fds66vzgg7agg10g9-source?lastModified=1699449415&narHash=sha256-Whc5OQzHTJtyBbnFsDAzdjICWK2BnCDCBP6s%2Bk/oLGQ%3D&rev=e1a0efea49b2e22055d2454e76f3d01ae42fde07&revCount=3
Setting flake inputs to the system registry <<lst:nixos-set-system-registry, that way>> is convenient.
But <<lst:nix-registry-with-system-registry, as shown from the results>>, there is a slight oversight with the flake input `self` which is a special named flake input for the current flake.
Depending on your case, this can be convenient or not.
At most, it is just left there... existing.
If you want, you can remove it like in the following snippet.
Otherwise, you'll have to give the `self` flake input from the registry a different name if you want to use it in your other flakes like in the following snippet.
If we run `nix search nixpkgs blender` once again, it should still evaluate but it should be done only once since:
* We have `nixpkgs` pinned to our nixpkgs instance.
* We're fully taking advantage of https://www.tweag.io/blog/2020-06-25-eval-cache/[flake evaluation caching] meaning subsequent package searches should be (almost) instantaneous.
By configuring our registry through NixOS, we're only evaluating nixpkgs once until we update our flake inputs with `nix flake update`.
[chat, Ezran, role=full]
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So instead of suffering every time you run the command like in the <<video:nix-search-demo, video at the beginning>>, you suffer at least once every update.
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As another bonus, we can now take advantage of other `nix` subcommands such as `nix build`, `nix shell`, or `nix develop`.
[source, shell]
----
# These commands should now use our nixpkgs instance. Hoorah!
nix run nixpkgs#neofetch
nix develop nixpkgs#gcc
nix build nixpkgs#vale
nix search nixpkgs asciidoctor
# From the previous example, we can quickly run packages from other nixpkgs
