Re: Corrupt repo with force push when using a reference repo

> On 2023-08-15 at 04:05:34, Grant Singleton wrote:
> > Thank you for filling out a Git bug report!
> > Please answer the following questions to help us understand your issue.
> > 
> > What did you do before the bug happened? (Steps to reproduce your issue)
> > 
> > With 3 clones of a repo, one on branch-a one a mirror,  another using the mirror as a reference repo on branch-b, do the following
> > 
> > # in the repo on branch-a, make a change, commit and push
> > cd bad-object-test
> > echo $(( RANDOM % 1000 + 1 )) > file.txt
> > git ci -am "change a file"
> > git push
> > 
> > # do a git fetch in the reference repo
> > cd ../bad-object-test.git/
> > git fetch
> > 
> > # do a git pull in the repo on branch-b
> > cd ../bad-object-test-with-reference-repo/
> > git pull
> > 
> > # All good so far
> > 
> > # in the repo on branch-a, discard HEAD and force push
> > cd ../bad-object-test
> > git reset --hard HEAD~1
> > git push --force
> > 
> > # do a git fetch in the reference repo and then prune loose objects
> > cd ../bad-object-test.git/
> > git fetch
> > git prune -v --expire=now
> 
> When you clone using --shared or --reference, you implicitly depend on
> the objects in the referenced repository existing without being pruned
> for the integrity of the repository.
> 
> The manual page for git clone says this:
> 
>   NOTE: this is a possibly dangerous operation; do not use it unless you
>   understand what it does. If you clone your repository using this
>   option and then delete branches (or use any other Git command that
>   makes any existing commit unreferenced) in the source repository, some
>   objects may become unreferenced (or dangling). These objects may be
>   removed by normal Git operations (such as git commit) which
>   automatically call git maintenance run --auto. (See
>   git‐maintenance(1).) If these objects are removed and were referenced
>   by the cloned repository, then the cloned repository will become
>   corrupt.
> 
> If you want to change the references in any non-fast-forward way or do
> any sort of GC or pruning in the reference repository, you need to run
> `git repack -a` in the non-reference repository to repack all of the
> objects in that repository and dissociate it from the reference
> repository.
> 
> In general, unless you are _very_ sure you know what you're doing, you
> usually want to use `--dissociate` with `--reference` such that you
> detach immediately.
> -- 
> brian m. carlson (he/him or they/them)
> Toronto, Ontario, CA