Remote stays conflicted after jj git fetch

[samhza]

Description

If a remote's URL is removed and re-added after a force-push ocurred remotely but before the force pushed was fetched on the local repo, a subsequent jj git fetch will result in an unresolvable conflict for the remote branch.

Steps to Reproduce the Problem

#!/bin/sh
set -o xtrace

# dummy "remote"
git init --bare /tmp/jjbug.git
jj git clone /tmp/jjbug.git /tmp/jjbug-jj
git clone /tmp/jjbug.git /tmp/jjbug-git

cd /tmp/jjbug-git
git commit -m 'some commit' --allow-empty
git push
# the remote is now at commit 'some commit'

cd /tmp/jjbug-jj
jj git fetch
# jj's clone is now at commit 'some commit'

cd /tmp/jjbug-git
git commit --amend --allow-empty -m 'now a different commit'
git push --force
# the remote now has been force pushed such that 'some commit' no longer exists
# and master is at 'now a different commit'

cd /tmp/jjbug-jj
jj git remote remove origin
jj git remote add origin /tmp/jjbug.git
jj git fetch
jj st

Expected Behavior

There is no conflict

Actual Behavior

There is a conflict

Specifications

• Platform: NixOS x86_64
• Version: 6d500ed

[martinvonz]

Thanks for the report and for making it so easy to reproduce. I think the issue is that jj git remote remove origin doesn't clean up its record of existing git refs, so we think that there's still a refs/remotes/origin/main pointing to "some commit". So I think the fix is to make sure we delete the branch in the git repo (https://github.com/rust-lang/git2-rs/blob/c93d29bebf9097da50505ff9d84a5c98b1a2e813/src/repo.rs#L672-L675 doesn't seem to be correct), and we also need remove the ref from our record.

[elasticdog]

For what it's worth, I think I'm hitting this regularly with a repository that's using the Bors-NG merge bot, where there are permanent trying and staging branches that are force-pushed to by the bot on a regular basis. I can try to pay a bit closer attention, but I think it has manifested conflicts whether I'm using a colocated repository or not.

[samhza]

I believe this has been fixed, it no longer reproduces.