Re: [HELP] Corrupted repository

Ramkumar Ramachandra [off-list ref] writes:

  $ ~/src/git
  error: object file
.git/objects/8e/6a6dda24b017915449897fcc1353a9b848fd2f is empty
  error: object file
.git/objects/8e/6a6dda24b017915449897fcc1353a9b848fd2f is empty
  fatal: loose object 8e6a6dda24b017915449897fcc1353a9b848fd2f (stored
in .git/objects/8e/6a6dda24b017915449897fcc1353a9b848fd2f) is corrupt

So fsync() and close() thought that the filesystem stored this loose
object safely, but it turns out that the data is not on disk.

  artagnon|remote-cruft*+:~/src/git$ rm
.git/objects/8e/6a6dda24b017915449897fcc1353a9b848fd2f

As you know it is empty, removing (as long as you do not forget what
the object name was, which may later become useful when untangling
the mess further) does not hurt very much.

  artagnon|remote-cruft*+:~/src/git$ git prune
  artagnon|remote-cruft*+:~/src/git$ git status
  fatal: bad object HEAD
  fatal: bad object HEAD

And the value in the HEAD was???

  artagnon|remote-cruft*+:~/src/git$ git symbolic-ref HEAD refs/heads/master
  artagnon|master*+=:~/src/git$ git status
  ## master
  MM Documentation/git-ls-remote.txt
  MM remote.c
  MM t/t5505-remote.sh
  MM t/t5510-fetch.sh
  MM t/t5515-fetch-merge-logic.sh
  MM t/t5516-fetch-push.sh
  ?? lib/
  ?? outgoing/

That status is completely bogus, by the way.

... which may suggest that your index file may have been corrupted
on the filesystem.

  artagnon|master*+=:~/src/git$ git reset --hard

... and using that known-to-be-corrupt index, the working tree state
is discarded.

  artagnon|master*+=:~/src/git$ git checkout remote-cruft
  fatal: reference is not a tree: remote-cruft
  artagnon|master=:~/src/git$ git reflog
  21ff915 HEAD@{10 minutes ago}: rebase -i (finish): returning to
refs/heads/remote-cruft

What happened to the rest of my reflog?!

On the filesystem known to not record the last consistent state of
the repository, the answer to that question may be rather obvious,
no?

  artagnon|master=:~/src/git$ git branch -D remote-cruft
  error: Couldn't look up commit object for 'refs/heads/remote-cruft'

The command would want to report what was at the tip, so it is
understandable it may want to look up that commit before removing
the ref.

  artagnon|master=:~/src/git$ rm .git/refs/heads/remote-cruft
  artagnon|master=:~/src/git$ git checkout -b remote-cruft
  Switched to a new branch 'remote-cruft'

Huh?  What happened to my upstream?

  artagnon|remote-cruft:~/src/git$ git branch -u ram/remote-cruft
  warning: ignoring broken ref refs/remotes/ram/remote-cruft.

So remotes/ram/remote-cruft is also broken.

Fine, let's fetch.

Why?

"fetch" walks the ancestry graph on both ends to minimize transfers.
It's not something you would expect to work when you know refs at
your end does not even record what you do have.  It _may_ appear to
work if your refs are intact but you are missing objects, as they
will not be transferred again from the good copy if you let your
repository's ref claim that you have _all_ objects behind it when
you actually don't.

What would have been a better starting point to untangle is to make
a separate clone, pretending as if this repository did not even
exist, and copy the resulting packfile into this repository.  That
would at least give you a known good copies of objects that you
already have pushed out.

And the next step would have been (without doing any of the above
"remove this branch, recreate this one anew") to compare the tips
of refs in this broken repository and the clone.  The same ones you
can trust, and different ones you dig further.

Was I being stupid, or is fixing corrupted repositories really this
non-trivial?  Comments appreciated.

I think "Let's fetch first" was the step that took you in a wrong
direction that requires unnecessary work.