feat: implement X-StopOnRemoval=false in service activation

Author: jfroche

crates/system-manager-engine/src/activate/services.rs

@@ -73,7 +73,8 @@ pub fn activate(
         .into_iter()
         .partition(|(_, cfg)| cfg.masked);
 
-    let services_to_stop = old_services.clone().relative_complement(active.clone());
+    let services_to_stop =
+        get_services_to_stop(old_services.clone().relative_complement(active.clone()));
     let services_to_reload = get_services_to_reload(active.clone(), old_services.clone());
 
     let service_manager = systemd::ServiceManager::new_session()
@@ -156,6 +157,21 @@ fn get_services_to_reload(services: Services, old_services: Services) -> Service
     services_to_reload
 }
 
+fn get_services_to_stop(services_to_stop: Services) -> Services {
+    let mut services_to_stop = services_to_stop;
+    services_to_stop.retain(|name, service| {
+        if let Some(ref path) = service.store_path {
+            let unit_data = parse_unit(Path::new(&path.store_path)).ok();
+            if !parse_systemd_bool(unit_data.as_ref(), "Unit", "X-StopOnRemoval", true) {
+                log::info!("Skipping stop of {name}: X-StopOnRemoval=false");
+                return false;
+            }
+        }
+        true
+    });
+    services_to_stop
+}
+
 fn systemd_system_dir(ephemeral: bool) -> PathBuf {
     if ephemeral {
         Path::new(path::MAIN_SEPARATOR_STR)

testFlake/container-tests/stop-on-removal.nix

@@ -0,0 +1,60 @@
+{
+  forEachDistro,
+  system-manager,
+  system,
+  ...
+}:
+
+let
+  configV2 = system-manager.lib.makeSystemConfig {
+    modules = [
+      {
+        nixpkgs.hostPlatform = system;
+      }
+    ];
+  };
+in
+
+forEachDistro "stop-on-removal" {
+  modules = [
+    {
+      systemd.services.long-running-task = {
+        description = "Long Running Task";
+        wantedBy = [ "system-manager.target" ];
+        unitConfig.X-StopOnRemoval = false;
+        serviceConfig.Type = "simple";
+        script = ''
+          sleep infinity
+        '';
+      };
+    }
+  ];
+  extraPathsToRegister = [ configV2 ];
+  testScriptFunction =
+    { toplevel, hostPkgs, ... }:
+    ''
+      start_all()
+
+      machine.wait_for_unit("multi-user.target")
+
+      with subtest("activate configV1 and verify service is running"):
+          machine.activate()
+          machine.wait_for_unit("system-manager.target")
+          result = machine.succeed("systemctl is-active long-running-task.service").strip()
+          assert result == "active", f"Expected active, got {result}"
+
+      with subtest("record initial PID"):
+          pid_before = machine.succeed("systemctl show -p MainPID --value long-running-task.service").strip()
+          assert pid_before != "0", "Service should have a non-zero PID"
+
+      with subtest("activate configV2 with X-StopOnRemoval=false (service removed from config)"):
+          activation_logs = machine.activate("${configV2}")
+
+      with subtest("service was not stopped (process still alive)"):
+          machine.succeed(f"test -d /proc/{pid_before}")
+
+      with subtest("activation logs show skip message"):
+          assert "Skipping stop" in activation_logs and "long-running-task" in activation_logs, \
+              f"Expected skip message in logs, got: {activation_logs}"
+    '';
+}