core: complain if Before= dep on .device is declared

[Unit]
Before=foobar.device

[Service]
ExecStart=/bin/true
Type=oneshot

$ systemd-analyze verify before-device.service
before-device.service: Dependency Before=foobar.device ignored (.device units cannot be delayed)

1 files changed, 5 insertions, 0 deletions

diff --git a/src/core/unit.c b/src/core/unit.c
index 5d284a359d..693f75c928 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -2225,6 +2225,11 @@ int unit_add_dependency(Unit *u, UnitDependency d, Unit *other, bool add_referen
                 return 0;
         }
 
+        if (d == UNIT_BEFORE && other->type == UNIT_DEVICE) {
+                log_unit_warning(u, "Dependency Before=%s ignored (.device units cannot be delayed)", other->id);
+                return 0;
+        }
+
         r = set_ensure_allocated(&u->dependencies[d], NULL);
         if (r < 0)
                 return r;