Fix tracking of junctions used in project.conf.

Stream._load() now returns early without resolving build pipeline when
only tracking. Resolving track pipelines does not require to fully
load project configurations when when elements to track are only
junctions.

However build pipelines require to fully load project
configurations. This might not be possible in the case a project
configuration includes a file from a junction that yet needs to be
tracked.

Fixes #565.

1 files changed, 15 insertions, 2 deletions

diff --git a/buildstream/_stream.py b/buildstream/_stream.py
index 37636b353..cceb3d3a5 100644
--- a/buildstream/_stream.py
+++ b/buildstream/_stream.py
@@ -267,8 +267,11 @@ class Stream():
               except_targets=None,
               cross_junctions=False):
 
+        # We pass no target to build. Only to track. Passing build targets
+        # would fully load project configuration which might not be
+        # possible before tracking is done.
         _, elements = \
-            self._load(targets, targets,
+            self._load([], targets,
                        selection=selection, track_selection=selection,
                        except_targets=except_targets,
                        track_except_targets=except_targets,
@@ -824,6 +827,12 @@ class Stream():
     #
     # A convenience method for loading element lists
     #
+    # If `targets` is not empty used project configuration will be
+    # fully loaded. If `targets` is empty, tracking will still be
+    # resolved for elements in `track_targets`, but no build pipeline
+    # will be resolved. This is behavior is import for track() to
+    # not trigger full loading of project configuration.
+    #
     # Args:
     #    targets (list of str): Main targets to load
     #    track_targets (list of str): Tracking targets
@@ -871,7 +880,7 @@ class Stream():
         #
         # This can happen with `bst build --track`
         #
-        if not self._pipeline.targets_include(elements, track_elements):
+        if targets and not self._pipeline.targets_include(elements, track_elements):
             raise StreamError("Specified tracking targets that are not "
                               "within the scope of primary targets")
 
@@ -907,6 +916,10 @@ class Stream():
         for element in track_selected:
             element._schedule_tracking()
 
+        if not targets:
+            self._pipeline.resolve_elements(track_selected)
+            return [], track_selected
+
         # ArtifactCache.setup_remotes expects all projects to be fully loaded
         for project in self._context.get_projects():
             project.ensure_fully_loaded()