Protecting nix-shell dependencies from garbage collection?

Ozone6418 · June 29, 2023, 5:42pm

I have been looking for a way to keep packages used in my shell.nix from being garbage collected. Most online sources (1 2 3) point to using something along the lines of the following command:

nix-instantiate shell.nix --indirect --add-root ./.nix-gc-roots/shell.drv

and having keep-outputs = true in shell.nix, however I have not been able to get it to work. What I step I am missing?

Nebucatnetzer · June 29, 2023, 9:05pm

Direnv is the easiest that I know of with the additional benefit of it getting activated.
However be aware that aliases and functions in shellhooks don’t work automatically:

github.com/nix-community/nix-direnv

`shellHook` is executed, but `alias` and functions are lost

opened 06:44PM - 17 Oct 22 UTC

closed 07:36AM - 18 Oct 22 UTC

koiuo

I use nix-direnv together with flakes (`use flake`) My `flake.nix` contains a… `devShell` output with a non-empty `shellHook`. Any aliases, exported variables or custom functions I may define in the `shellHook` won't be sourced to the current shell. `flake.nix` to reproduce ``` { inputs.nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable"; inputs.flake-utils.url = "github:numtide/flake-utils"; outputs = { nixpkgs, flake-utils, ... }: flake-utils.lib.eachDefaultSystem (system: let pkgs = import nixpkgs { inherit system; }; in rec { devShell = pkgs.mkShell { shellHook = '' echo "This is executed" export VAR_FOO="This is set" function f_foo { echo "This is lost" } alias a_foo="true" ''; }; } ); } ``` `use flake` in the `.envrc`, `direnv allow` to enable devShell. In the shell - observe the line `This is executed` - echo `$VAR_FOO`, observe `This is set` - try calling `f_foo` (should fail) - try calling `a_foo` (should fail) I'd expect aliases and functions to be propagated to the current shell to be consistent with exported variables and other side-effects

Ozone6418 · June 29, 2023, 10:09pm

I am rather new to Nix and have not dipped my toes into flakes yet. My research leads me to believe that they aren’t necessary to accomplishing my goals, has that changed?

Nebucatnetzer · June 30, 2023, 4:31am

Direnv and shellhooks aren’t related to Flakes.
You can use shellhooks in a shell.nix file as well.

Ozone6418 · June 30, 2023, 6:48pm

Thanks for the tip! For most of my packages, direnv seems to be working. However, the following packages are still being garbage collected:

/nix/store/3mzd4jjvixjjkldnz3mjk7dpbjvl52hg-perl5.36.0-Any-URI-Escape-0.01
/nix/store/byb33msjlx9yaz603irlwkbzyj214bd6-perl5.36.0-YAML-PP-0.026
/nix/store/ihsm38jgs74qxpli4j7q6v1yv83zljq1-gcc-9.5.0-lib
/nix/store/ik9rhgnkagg9x9fb0hhhd3j0pacrcf66-kf5gpgmepp-16.08.3
/nix/store/jnc7klg39rdcravhm9f3jwg1xnfv81c0-xerces-c-3.2.4
/nix/store/pa7ad0v5hs8amap6j09dh72cwc36l0sv-python3-3.11.3
/nix/store/zayrihc2i9a2kl0mcmhqd9yn4xhc97ff-xsd-4.0.0

This is my shell.nix

{ pkgs ? import <nixos> {} }: pkgs.mkShell {
	packages = with pkgs; [
		bison
		boost
		cmake
		curl
		cyrus_sasl
		docbook_xml_dtd_45
		docbook-xsl-ns
		flex
		gperf
		intltool
		libsForQt5.accounts-qt
		libsForQt5.kf5gpgmepp
		libsForQt5.phonon
		libsForQt5.qcoro
		libsForQt5.qgpgme
		libsForQt5.qtkeychain
		libsForQt5.signond
		libgcrypt
		libical
		perl
		perl536Packages.AnyURIEscape
		perl536Packages.IOSocketSSL
		perl536Packages.YAMLPP
		pkg-config
		polkit
		python311
		qrencode
		qt5.qtbase
		qt5.qtnetworkauth
		qt5.qttools
		qt5.qtquickcontrols2
		qt5.qtwayland
		qt5.qtwebengine
		qt5.qtxmlpatterns
		qt5.qtx11extras
		util-linux
		wayland
		wayland-protocols
		xapian
		xercesc
		xsd
		xorg.libXdmcp
		xz
	];
}

Is there any reason why it wouldn’t work for these?

Nebucatnetzer · July 1, 2023, 9:02am

I honestly don’t know and would’ve to test how it behaves on my machine but that would have to wait until after the weekend.