Critical issue: changing branches while pushing to a new branch can mix-up merge configuration

[peppy]

Describe the bug

If you change branch while pushing a branch, it is possible that the old and new branch are now linked to the same branch on the remote.

I've hit this four times so far, sometimes with severe unexpected implications (pushing commits publicly that I never intended to).

To Reproduce
Steps to reproduce the behavior:

1. Create a new branch from a branch that already has an upstream set
2. Push the new branch
3. While the push operation is in progress, switch back to the previous branch
4. Observe broken configuration

Screenshots

kitty.2025-01-24.at.09.09.21.mp4

Version info:

❯ lazygit --version
commit=, build date=, build source=homebrew, version=HEAD-40d6800, os=darwin, arch=arm64, git version=2.48.1

❯ git --version
git version 2.48.1

[jesseduffield]

Sorry that this led to erroneously pushing commits.

I don't believe we're doing anything fancy when it comes to pushing or checking out, so I suspect that this would also happen if performing the actions in the CLI (in separate terminal tabs concurrently).

If that's true, then we should pester the guys on the git mailing list, and potentially disallow checking out while pushing. It would also be good to know if this only happens in certain situations e.g. I use:

[push]
	default = current

And have not observed this problem.

[jesseduffield]

Actually something that just came to mind, we do have a mutex on sync operations, so I can imagine a situation where a background fetch is happening when you trigger the push so the push only actually happens after the checkout completes. @peppy is this an intermittent issue for you?

[stefanhaller]

The problem was introduced with #3630, which changed the command line we use for pushing a branch for the first time to git push --set-upstream origin HEAD:branchname. When checking out a branch while the push is still running, it will then set the upstream of the branch which is then the HEAD. The same happens on the command line, of course. Yes, you might consider this a bug in git; you would expect it to parse the HEAD ref at the beginning of the operation and then use the result at the end, and I might bring this up on the mailing list when I find the time.

But we can easily work around it by supplying the actual branch name instead of HEAD. Here's a PR: #4214

we do have a mutex on sync operations

We no longer do, I removed this quite a while ago (see be3b4bd). But I also believe that fetching concurrently is not an issue here.

[jesseduffield]

We no longer do, I removed this quite a while ago (see be3b4bd). But I also believe that fetching concurrently is not an issue here.

Ah yep, my bad.