Revert "Simplify queue management"

This reverts commit aa25f6fcf49f0015fae34dfd79b4626a816bf886.

2 files changed, 14 insertions, 3 deletions

diff --git a/src/buildstream/_scheduler/queues/queue.py b/src/buildstream/_scheduler/queues/queue.py
index 39b7af4ce..986ac6c0a 100644
--- a/src/buildstream/_scheduler/queues/queue.py
+++ b/src/buildstream/_scheduler/queues/queue.py
@@ -241,6 +241,13 @@ class Queue:
             for element in ready
         ]
 
+    # set_required_element_check()
+    #
+    # This ensures that, for the first non-track queue, we must check
+    # whether elements are required before enqueuing them
+    def set_required_element_check(self):
+        self._required_element_check = True
+
     # any_failed_elements()
     #
     # Returns whether any elements in this queue have failed their jobs
diff --git a/src/buildstream/_stream.py b/src/buildstream/_stream.py
index bba3831c3..dc91db6b7 100644
--- a/src/buildstream/_stream.py
+++ b/src/buildstream/_stream.py
@@ -371,8 +371,8 @@ class Stream:
 
         self._scheduler.clear_queues()
         track_queue = TrackQueue(self._scheduler)
-        self._add_queue(track_queue)
-        self._enqueue_plan(elements)
+        self._add_queue(track_queue, track=True)
+        self._enqueue_plan(elements, queue=track_queue)
         self._run()
 
     # pull()
@@ -1308,7 +1308,11 @@ class Stream:
     # Args:
     #    queue (Queue): Queue to add to the pipeline
     #
-    def _add_queue(self, queue):
+    def _add_queue(self, queue, *, track=False):
+        if not track and not self.queues:
+            # First non-track queue
+            queue.set_required_element_check()
+
         self.queues.append(queue)
 
     # _enqueue_plan()