Do not pull/fetch/build elements that are not required

For `bst build --deps plan`, do not process elements in pull/fetch/build
queues until they are requested by a reverse dependency.

3 files changed, 15 insertions, 0 deletions

diff --git a/buildstream/_scheduler/buildqueue.py b/buildstream/_scheduler/buildqueue.py
index 46ce72ca7..24a124b32 100644
--- a/buildstream/_scheduler/buildqueue.py
+++ b/buildstream/_scheduler/buildqueue.py
@@ -38,6 +38,11 @@ class BuildQueue(Queue):
         # state of dependencies may have changed, recalculate element state
         element._update_state()
 
+        if not element._is_required():
+            # Artifact is not currently required but it may be requested later.
+            # Keep it in the queue.
+            return QueueStatus.WAIT
+
         if element._cached():
             return QueueStatus.SKIP
 
diff --git a/buildstream/_scheduler/fetchqueue.py b/buildstream/_scheduler/fetchqueue.py
index c2bceb270..61055725d 100644
--- a/buildstream/_scheduler/fetchqueue.py
+++ b/buildstream/_scheduler/fetchqueue.py
@@ -47,6 +47,11 @@ class FetchQueue(Queue):
         # state of dependencies may have changed, recalculate element state
         element._update_state()
 
+        if not element._is_required():
+            # Artifact is not currently required but it may be requested later.
+            # Keep it in the queue.
+            return QueueStatus.WAIT
+
         # Optionally skip elements that are already in the artifact cache
         if self._skip_cached:
             if not element._can_query_cache():
diff --git a/buildstream/_scheduler/pullqueue.py b/buildstream/_scheduler/pullqueue.py
index 0d6b5dbfb..f9928a342 100644
--- a/buildstream/_scheduler/pullqueue.py
+++ b/buildstream/_scheduler/pullqueue.py
@@ -39,6 +39,11 @@ class PullQueue(Queue):
         # state of dependencies may have changed, recalculate element state
         element._update_state()
 
+        if not element._is_required():
+            # Artifact is not currently required but it may be requested later.
+            # Keep it in the queue.
+            return QueueStatus.WAIT
+
         if not element._can_query_cache():
             return QueueStatus.WAIT