Reload the service manager's units before restarting a service whose files changed, and start the guard before the network as the controller declares it (hq ADR 0100)

internal/apply/apply.go

@@ -688,11 +688,27 @@ func reflected(r *declaration.Service, changed map[string]bool) []string {
 	return restartedBy(r.RestartOn, changed)
 }
 
+// unitReloader is a service manager that caches unit files and must be told to read them again.
+type unitReloader interface {
+	ReloadUnits(ctx context.Context, run system.Runner) error
+}
+
 func applyService(ctx context.Context, sys system.System, r *declaration.Service, run Runner,
 	changed map[string]bool) (Outcome, error) {
 	out := begin(r)
 	var changes []string
 
+	// A file the service reflects changed, and it may be the unit's own file or a drop-in: the
+	// service manager reads those again only when told to, and a restart without it runs the unit
+	// it had already loaded.
+	if reflects(r, changed) {
+		if u, ok := sys.(unitReloader); ok {
+			if err := u.ReloadUnits(ctx, run); err != nil {
+				return out, fmt.Errorf("reloading the service manager's units for %s: %w", r.Unit, err)
+			}
+		}
+	}
+
 	// Boot first. A unit asked to be running and enabled should survive this apply failing
 	// half way in the more useful direction: enabled-and-stopped comes back at the next boot,
 	// where running-and-disabled does not.

internal/apply/apply_test.go

@@ -1114,6 +1114,18 @@ func TestAServiceIsRestartedWhenWhatItReflectsChanges(t *testing.T) {
 		if !stopped || !started {
 			t.Errorf("the file changed and the service was not restarted; commands were %v", commands)
 		}
+		reloaded, stop := -1, -1
+		for i, c := range commands {
+			if strings.Contains(c, "daemon-reload") && reloaded < 0 {
+				reloaded = i
+			}
+			if strings.Contains(c, "stop thing.service") && stop < 0 {
+				stop = i
+			}
+		}
+		if reloaded < 0 || reloaded > stop {
+			t.Errorf("the service was restarted without the unit files being read again first; commands were %v", commands)
+		}
 	}
 }