From d0f10e610f5a1e3d02ee14084062a932a4089d0e Mon Sep 17 00:00:00 2001
From: Emily <vcs@emily.moe>
Date: Tue, 11 Feb 2025 19:46:21 +0000
Subject: [PATCH] {activation-scripts,activate-system}: check `gcroots` before
 linking
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When `nix.enable` is off, we don’t necessarily have an active
Nix installation, so there won’t necessarily be an active
`/nix/var/nix/gcroots` directory to link things into. NixOS just skips
this unconditionally when `nix.enable` is off, but that doesn’t
work well with a context in which we usually expect `nix.enable`
to be coupled with an unmanaged system installation of Nix.

(cherry picked from commit 731910af010086c4dbe23eb6ae79d81bcec703aa)
---
 modules/services/activate-system/default.nix | 4 +++-
 modules/system/activation-scripts.nix        | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/modules/services/activate-system/default.nix b/modules/services/activate-system/default.nix
index 6a982fe83..58d2e2422 100644
--- a/modules/services/activate-system/default.nix
+++ b/modules/services/activate-system/default.nix
@@ -21,7 +21,9 @@
         ln -sfn $(cat ${config.system.profile}/systemConfig) /run/current-system
 
         # Prevent the current configuration from being garbage-collected.
-        ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+        if [[ -d /nix/var/nix/gcroots ]]; then
+          ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+        fi
 
         ${config.system.activationScripts.etcChecks.text}
         ${config.system.activationScripts.etc.text}
diff --git a/modules/system/activation-scripts.nix b/modules/system/activation-scripts.nix
index b051972b5..4f42d4112 100644
--- a/modules/system/activation-scripts.nix
+++ b/modules/system/activation-scripts.nix
@@ -109,7 +109,9 @@ in
       ln -sfn "$(readlink -f "$systemConfig")" /run/current-system
 
       # Prevent the current configuration from being garbage-collected.
-      ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+      if [[ -d /nix/var/nix/gcroots ]]; then
+        ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+      fi
 
       exit $_status
     '';