Below is a test case which shows a way that the git-annex branch can become corrupted and lose data, including location log records and uuid.log lines.
At the end, a commit on the git-annex branch removes one of the 2 lines from the uuid.log; which should never happen.
The actual problem occurs earlier, at the "push point". Here a repo is cloned from the main one, initialized (adding the last uuid.log line), and then pushed back to the main one. That push is a fast-forward, so is allowed to directly update the git-annex branch in the main repo:
b884fe5..c497739 git-annex -> git-annex
Now the git-annex branch has a change that is not reflected in
.git/annex/index
, so the next time a change is made, it's committed
using the out of date index, which causes a reversion of the changes
that were pushed to the branch.
Thoughts
This is essentially the same reason why git blocks pushes to the checked-out branch of a non-bare repository.
This problem only affects workflows that involve pushing. Pulling workflows do not directly update the local git-annex branch, so avoid the problem.
And while bare repos are pushed to, they rarely have changes made directly to their git-annex branches, so while I think the same problem could happen with pushing to a bare repo, it's unlikely.
None of which is to say this is not a bad bug that needs to be comprehensively fixed.
Probably git-annex needs to record which ref of the git-annex branch corresponds to its index, and if the branch is at a different ref, merge it into the index.
And now that's done. I managed to do it with very little slowdown.
A side benefit is that users can now safely check out the git-annex branch and commit changes to it, and git-annex will notice them. Before, it was documented to ignore such changes. --Joey
Workaround
Users who want to prevent this bug from occuring when pushing to their
non-bare repositories can install this script as .git/hooks/update
#!/bin/sh if [ "$1" = refs/heads/git-annex ]; then exit 1 fi
--Joey
Test Case
#!/bin/sh mkdir annextest cd annextest git init dir1 cd dir1 git annex init touch foo echo hi > bar git annex add git commit -m add cd .. git clone dir1 dir2 cd dir2 git annex init otherdir git annex get # push point git push cd .. cd dir1 echo "before" git show git-annex:uuid.log git annex drop foo --force echo "after" git show git-annex:uuid.log