element.py: Discard __artifact/__strict_artifact in update_state()

When we determine that current cache keys are to be discarded, we
should also discard the associated members for correctness. This
should act as a safeguard against accessing Artifact instances that
have discarded cache keys.

A side effect of this is the querying of element buildtree state
from cli methods on elements that don't have a cached artifact
would lead to the artifact member methods not being reachable.
Ensuring the element is cached before trying to call said accessor
methods resolves this.

1 files changed, 2 insertions, 9 deletions

diff --git a/buildstream/_artifact.py b/buildstream/_artifact.py
index 41dc14367..4d9e4bf08 100644
--- a/buildstream/_artifact.py
+++ b/buildstream/_artifact.py
@@ -195,17 +195,13 @@ class Artifact():
     #
     # Returns:
     #     (bool): True if artifact cached with buildtree, False if
-    #             element not cached or missing expected buildtree.
-    #             Note this only confirms if a buildtree is present,
-    #             not its contents.
+    #             missing expected buildtree. Note this only confirms
+    #             if a buildtree is present, not its contents.
     #
     def cached_buildtree(self):
 
         element = self._element
 
-        if not element._cached():
-            return False
-
         key = self.get_extract_key()
         if not self._artifacts.contains_subdir_artifact(element, key, 'buildtree'):
             return False
@@ -222,9 +218,6 @@ class Artifact():
     #
     def buildtree_exists(self):
 
-        if not self._element._cached():
-            return False
-
         artifact_vdir, _ = self._get_directory()
         return artifact_vdir._exists('buildtree')