From e6bc540ce0714a02a5e7d1677622e3308b6252c5 Mon Sep 17 00:00:00 2001
From: r-vdp <ramses@well-founded.dev>
Date: Tue, 28 Jan 2025 11:40:38 +0100
Subject: [PATCH] nixos/activation: pass the action as an argument to the
 pre-switch-checks

This allows for instance to reject switching into a configuration, while
still allowing to reboot into that same configuration.

This can be useful for instance to reject switching to a configuration
with a new systemd major version, but setting that same configuration as
the new boot default with `switch-to-configuration boot` is fine.
---
 nixos/modules/system/activation/switch-to-configuration.pl | 2 +-
 nixos/tests/switch-test.nix                                | 6 ++++--
 pkgs/by-name/sw/switch-to-configuration-ng/src/src/main.rs | 5 +++--
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/nixos/modules/system/activation/switch-to-configuration.pl b/nixos/modules/system/activation/switch-to-configuration.pl
index 3553c5fce4ce..672291541d03 100755
--- a/nixos/modules/system/activation/switch-to-configuration.pl
+++ b/nixos/modules/system/activation/switch-to-configuration.pl
@@ -103,7 +103,7 @@ if (($ENV{"NIXOS_NO_CHECK"} // "") ne "1") {
     chomp(my $pre_switch_checks = <<'EOFCHECKS');
 @preSwitchCheck@
 EOFCHECKS
-    system("$pre_switch_checks $out") == 0 or exit 1;
+    system("$pre_switch_checks $out $action") == 0 or exit 1;
     if ($action eq "check") {
         exit 0;
     }
diff --git a/nixos/tests/switch-test.nix b/nixos/tests/switch-test.nix
index 37a808c3c471..4ad08b726bf5 100644
--- a/nixos/tests/switch-test.nix
+++ b/nixos/tests/switch-test.nix
@@ -612,8 +612,10 @@ in {
       system.switch.enable = true;
       users.mutableUsers = true;
       system.preSwitchChecks.succeeds = ''
-        echo this will succeed
-        true
+        config="$1"
+        action="$2"
+        echo "this should succeed (config: $config, action: $action)"
+        [ "$action" == "check" ] || [ "$action" == "test" ]
       '';
       specialisation.failingCheck.configuration.system.preSwitchChecks.failEveryTime = ''
         echo this will fail
diff --git a/pkgs/by-name/sw/switch-to-configuration-ng/src/src/main.rs b/pkgs/by-name/sw/switch-to-configuration-ng/src/src/main.rs
index 93da7aff7406..ecd6a6a71390 100644
--- a/pkgs/by-name/sw/switch-to-configuration-ng/src/src/main.rs
+++ b/pkgs/by-name/sw/switch-to-configuration-ng/src/src/main.rs
@@ -139,7 +139,7 @@ fn parse_os_release() -> Result<HashMap<String, String>> {
         }))
 }
 
-fn do_pre_switch_check(command: &str, toplevel: &Path) -> Result<()> {
+fn do_pre_switch_check(command: &str, toplevel: &Path, action: &Action) -> Result<()> {
     let mut cmd_split = command.split_whitespace();
     let Some(argv0) = cmd_split.next() else {
         bail!("missing first argument in install bootloader commands");
@@ -148,6 +148,7 @@ fn do_pre_switch_check(command: &str, toplevel: &Path) -> Result<()> {
     match std::process::Command::new(argv0)
         .args(cmd_split.collect::<Vec<&str>>())
         .arg(toplevel)
+        .arg::<&str>(action.into())
         .spawn()
         .map(|mut child| child.wait())
     {
@@ -1053,7 +1054,7 @@ fn do_system_switch(action: Action) -> anyhow::Result<()> {
         .unwrap_or_default()
         != "1"
     {
-        do_pre_switch_check(&pre_switch_check, &toplevel)?;
+        do_pre_switch_check(&pre_switch_check, &toplevel, action)?;
     }
 
     if *action == Action::Check {