element.py: Fix buildable check in non-strict modejuerg/non-strict-buildable

Ensure that the strong cache key of each build dependency is available
before an element is built. Otherwise the strong cache key of the
element cannot be calculated and caching the artifact produces an
AssertionError.

In non-strict mode an element's strong cache key may not be available
yet even though an artifact is available in the local cache. This can
happen if the pull job is still pending as the remote cache may have an
artifact that matches the strict cache key, which is preferred over a
locally cached artifact with a weak cache key match.

Fixes #383.

1 files changed, 6 insertions, 1 deletions

diff --git a/buildstream/element.py b/buildstream/element.py
index 3c532c716..b49a75692 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -958,7 +958,12 @@ class Element(Plugin):
             return False
 
         for dependency in self.dependencies(Scope.BUILD):
-            if not dependency._cached():
+            # In non-strict mode an element's strong cache key may not be available yet
+            # even though an artifact is available in the local cache. This can happen
+            # if the pull job is still pending as the remote cache may have an artifact
+            # that matches the strict cache key, which is preferred over a locally
+            # cached artifact with a weak cache key match.
+            if not dependency._cached() or not dependency._get_cache_key(strength=_KeyStrength.STRONG):
                 return False
 
         if not self.__assemble_scheduled: