cascache.py: Ensure path exists before trying to update the mtime

If an artifact is pulled from the cache without its buildtree,
CASCache.prune() will fail when it tries to update the mtimes
of the build tree's object files.

A new integration test has been added to tests/integration/artifact.py
which reflects this.

2 files changed, 48 insertions, 6 deletions

diff --git a/buildstream/_cas/cascache.py b/buildstream/_cas/cascache.py
index 802fc13fd..02030bb68 100644
--- a/buildstream/_cas/cascache.py
+++ b/buildstream/_cas/cascache.py
@@ -791,16 +791,20 @@ class CASCache():
     def _reachable_refs_dir(self, reachable, tree, update_mtime=False):
         if tree.hash in reachable:
             return
+        try:
+            if update_mtime:
+                os.utime(self.objpath(tree))
 
-        if update_mtime:
-            os.utime(self.objpath(tree))
+            reachable.add(tree.hash)
 
-        reachable.add(tree.hash)
+            directory = remote_execution_pb2.Directory()
 
-        directory = remote_execution_pb2.Directory()
+            with open(self.objpath(tree), 'rb') as f:
+                directory.ParseFromString(f.read())
 
-        with open(self.objpath(tree), 'rb') as f:
-            directory.ParseFromString(f.read())
+        except FileNotFoundError:
+            # Just exit early if the file doesn't exist
+            return
 
         for filenode in directory.files:
             if update_mtime:
diff --git a/tests/frontend/artifact.py b/tests/frontend/artifact.py
index 3c3203d8a..b6f8fb91d 100644
--- a/tests/frontend/artifact.py
+++ b/tests/frontend/artifact.py
@@ -166,3 +166,41 @@ def test_artifact_delete_unbuilt_artifact(cli, tmpdir, datafiles):
     artifact = os.path.join('test', os.path.splitext(element)[0], cache_key)
     expected_err = "WARNING Could not find ref '{}'".format(artifact)
     assert expected_err in result.stderr
+
+
+# Test that an artifact pulled from it's remote cache (without it's buildtree) will not
+# throw an Exception when trying to prune the cache.
+@pytest.mark.datafiles(DATA_DIR)
+def test_artifact_delete_pulled_artifact_without_buildtree(cli, tmpdir, datafiles):
+    project = os.path.join(datafiles.dirname, datafiles.basename)
+    element = 'target.bst'
+
+    # Set up remote and local shares
+    local_cache = os.path.join(str(tmpdir), 'artifacts')
+    with create_artifact_share(os.path.join(str(tmpdir), 'remote')) as remote:
+        cli.configure({
+            'artifacts': {'url': remote.repo, 'push': True},
+            'cachedir': local_cache,
+        })
+
+        # Build the element
+        result = cli.run(project=project, args=['build', element])
+        result.assert_success()
+
+        # Make sure it's in the share
+        cache_key = cli.get_element_key(project, element)
+        assert remote.has_artifact('test', element, cache_key)
+
+        # Delete and then pull the artifact (without its buildtree)
+        result = cli.run(project=project, args=['artifact', 'delete', element])
+        result.assert_success()
+        assert cli.get_element_state(project, element) != 'cached'
+        result = cli.run(project=project, args=['artifact', 'pull', element])
+        result.assert_success()
+        assert cli.get_element_state(project, element) == 'cached'
+
+        # Now delete it again (it should have been pulled without the buildtree, but
+        # a digest of the buildtree is pointed to in the artifact's metadata
+        result = cli.run(project=project, args=['artifact', 'delete', element])
+        result.assert_success()
+        assert cli.get_element_state(project, element) != 'cached'