untested
This won't be super slow, but it does need to diff two likely large
trees, and since the git-annex branch rarely sits still, it will most
likely be run at the beginning of every import.
A possible speed improvement would be to only run this when the database
did not contain a ContentIdentifier. But that would only speed up
imports when there is no new version of a file on the special remote,
at most renames of existing files being imported.
A better speed improvement would be to record something in the git-annex
branch that indicates when an import has been run, and only do the diff
if the git-annex branch has record of a newer import than we've seen
before. Then, it would only run when there is in fact new
ContentIdentifier information available from a remote. Certianly doable,
but didn't want to complicate things yet.
An empty list of [ContentIdenfier] serialized to the same thing
as a single ContentIdentifier "". Avoid this ambiguity by requiring the
list be non-empty.
