Re: bugreport: "git checkout -B" allows checking out one branch across multiple worktrees

[Eric Sunshine <sunshine@sunshineco.com>]

On Sun, Jan 15, 2023 at 7:23 PM Carlo Marcelo Arenas Belón
<carenas@gmail.com> wrote:
> On Sat, Jan 14, 2023 at 06:45:34PM +0900, Jinwook Jeong wrote:
> > 1. `cd` into any git repo that has at least one commit.
> > 2. Identify the current branch, say main
> > 3. $ git branch foo # a new branch
> > 4. $ git worktree add ../new_worktree foo
> > 5. $ cd ../new_worktree
> > 6. $ git checkout -B master HEAD
>
> Was your intention to get this worktree's content back to what is in
> master's HEAD?, then the command should had been
>
> $ git reset --hard master
>
> The documentation might be confusing, but you most likely do NOT want
> to use -B unless you want to force things, but the lowercase version `-b`
>
> > Anything else you want to add:
> >
> > https://www.git-scm.com/docs/git-checkout#Documentation/git-checkout.txt-emgitcheckoutem-b-Bltnew-branchgtltstart-pointgt
> >
> > According to the documentation, "git checkout -B BRANCH START" is the
> > transactionally equivalent of:
> >
> >   git branch -f BRANCH START
> >   git checkout BRANCH
> >
> > When I ran the first command in place of the step 6 of the above
> > reproducing procedure, git refused to carry on;
> > I suppose that this is the intended behavior for "git checkout -B".
>
> I think you are correct, and this is therefore a bug, but there is also
> a reason why `--force` allows doing dangerous things and I am not sure
> if it might apply here.

I'd say there's a bug in `git-switch/git-checkout -B` not performing
the same checks as `git branch -f`. As a result, it is possible to get
into a state in which the same branch is checked out in multiple
worktrees, which is probably undesirable. I looked briefly through the
code but don't have the time presently to dig into it.