Install instruction for nixos in package search recommend nix-env

[symphorien]

Introduce your stance

nix-env is awkward to use, nix-env -u is fully broken so on nixos at least, it is better to advise people to use /etc/nixos/configuration.nix to install things.

Describe the issue

When one selects a package in the package search, two installations methods are provided:

1. nix-env -iA nixos.foo for nixos
2. nix-env -iA nixpkgs.foo for non nixos

The nixos tab should be something along the lines of "add environment.systemPackages = [ pkgs.foo ] to /etc/nixos/configuration.nix"
It may or may not mention using nix-env, but only as a second possibilty.

Page links

https://search.nixos.org/packages?channel=20.09&show=hello&from=0&size=50&sort=relevance&query=hello

Additional context
cc @flokli @Ekleog

• I already created a Pull Request

[edolstra]

No, nix-env is much easier to use than the declarative approach (where we can't even provide exact instructions, since "add environment.systemPackages = [ pkg.foo ]; to confguration.nix" is error-prone and not exact).

What is broken about nix-env -u?

[symphorien]

What makes nix-env broken in my opinion:

nix-env -u is broken

Steps to reproduce

1. install jdk8

#  nix-env -f "<nixpkgs>" -iA jdk8
installing 'openjdk-8u272-b10'
building '/nix/store/vwd7xj1jlwygr5fwdixsszwjdy8qwci8-user-environment.drv'...
created 102 symlinks in user environment

2. update !

#  nix-env -u
upgrading 'openjdk-8u272-b10' to 'openjdk-15.0.1-ga-jre'

3. jdk8 is gone 😱 Now I have jdk15 instead !

nix-env inherits the strangeness of channels

Ever since I have a user-wide <home-manager> channel, neither nix-env -iA nixos.jdk8 nor nix-env -iA nixpkgs.jdk8 works on my system. I must use nix-env -f "<nixpkgs>" -iA jdk8. I hear it is due to the legacy "defexpr", but I don't know for sure.

[edolstra]

jdk8 is gone 😱 Now I have jdk15 instead !

Isn't that what you would expect to happen? 15.0.1 is a higher version than 8u272...

[flokli]

The problem here is that the "versioned" part in the attribute name is resolved once during nix-env, and is lost afterwards. If I install jdk8, I'd expect to only get jdk8 minor version updates.

Using jdk8 in the NixOS configuration preserves this.

[fricklerhandwerk]

@symphorien @garbas fixed by NixOS/nixos-search#514

[symphorien]

nice !