artifactcache: improve _create_tree()

* Rename it to _commit_directory() because… it is what it does; and
  also for symmetry with _fetch_directory().
* Rename digest to dir_digest to make it clear this is a digest for a
  directory. A following commit will also reuse the same variable name
* Document method.

1 files changed, 19 insertions, 4 deletions

diff --git a/buildstream/_artifactcache/cascache.py b/buildstream/_artifactcache/cascache.py
index d673c224d..105f57c5d 100644
--- a/buildstream/_artifactcache/cascache.py
+++ b/buildstream/_artifactcache/cascache.py
@@ -117,7 +117,7 @@ class CASCache(ArtifactCache):
     def commit(self, element, content, keys):
         refs = [self.get_artifact_fullname(element, key) for key in keys]
 
-        tree = self._create_tree(content)
+        tree = self._commit_directory(content)
 
         for ref in refs:
             self.set_ref(ref, tree)
@@ -665,7 +665,21 @@ class CASCache(ArtifactCache):
     def _refpath(self, ref):
         return os.path.join(self.casdir, 'refs', 'heads', ref)
 
-    def _create_tree(self, path, *, digest=None):
+    # _commit_directory():
+    #
+    # Adds local directory to content addressable store.
+    #
+    # Adds files, symbolic links and recursively other directories in
+    # a local directory to the content addressable store.
+    #
+    # Args:
+    #     path (str): Path to the directory to add.
+    #     dir_digest (Digest): An optional Digest object to use.
+    #
+    # Returns:
+    #     (Digest): Digest object for the directory added.
+    #
+    def _commit_directory(self, path, *, dir_digest=None):
         directory = remote_execution_pb2.Directory()
 
         for name in sorted(os.listdir(path)):
@@ -674,7 +688,7 @@ class CASCache(ArtifactCache):
             if stat.S_ISDIR(mode):
                 dirnode = directory.directories.add()
                 dirnode.name = name
-                self._create_tree(full_path, digest=dirnode.digest)
+                self._commit_directory(full_path, dir_digest=dirnode.digest)
             elif stat.S_ISREG(mode):
                 filenode = directory.files.add()
                 filenode.name = name
@@ -690,7 +704,8 @@ class CASCache(ArtifactCache):
             else:
                 raise ArtifactError("Unsupported file type for {}".format(full_path))
 
-        return self.add_object(digest=digest, buffer=directory.SerializeToString())
+        return self.add_object(digest=dir_digest,
+                               buffer=directory.SerializeToString())
 
     def _get_subdir(self, tree, subdir):
         head, name = os.path.split(subdir)