element.py: Calculate strict key from cached artifact if available

This code path was previously storing its results in the obsolete
__cache_key member, leaving __strict_cache_key unset. This was broken
as code relies on __strict_cache_key being set once there is a strict
cache key available.

1 files changed, 8 insertions, 0 deletions

diff --git a/buildstream/element.py b/buildstream/element.py
index abbea929e..f8b388a22 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -1409,6 +1409,14 @@ class Element(Plugin):
             ]
             self.__strict_cache_key = self.__calculate_cache_key(dependencies)
 
+            if self.__strict_cache_key is None and self._cached():
+                # Strict cache key could not be calculated yet, but we can load
+                # it from the artifact. (This happens after we pull using the
+                # weak key).
+                metadir = os.path.join(self.__artifacts.extract(self), 'meta')
+                meta = _yaml.load(os.path.join(metadir, 'artifact.yaml'))
+                self.__strict_cache_key = meta['keys']['strong']
+
             if self.__strict_cache_key is None:
                 # Strict cache key could not be calculated yet
                 return