element.py: Return all refs in _track()

TrackQueue must call _set_ref() for all sources, otherwise the source
will never get out of the inconsistent state. This fixes --track when
using local sources.

Fixes: 03412a9e ("Use explicit source state updates")

1 files changed, 3 insertions, 4 deletions

diff --git a/buildstream/element.py b/buildstream/element.py
index c7b13232e..15a4f043b 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -967,13 +967,12 @@ class Element(Plugin):
     #    (list): A list of Source object ids and their new references
     #
     def _track(self):
-        changed = []
+        refs = []
         for source in self.__sources:
             new_ref = source._track()
-            if new_ref is not None:
-                changed.append((source._get_unique_id(), new_ref))
+            refs.append((source._get_unique_id(), new_ref))
 
-        return changed
+        return refs
 
     # _assemble():
     #