[PATCH 0/3] object-name: don't allow @ as a branch name

From: Kristoffer Haugsbakk <code@khaugsbakk.name>
Date: Oct 7, 2024, 20:15 UTC
Message-ID: <cover.1728331771.git.code@khaugsbakk.name>

I use `@` a lot for Git commands in the terminal. I accidentally did something that made me create a branch named `@`. This puzzled me since `HEAD` is not allowed.

Note that the bare/one-level `@` ref name is already banned. So this is just about not allowing `refs/heads/@`.

§ Research

This has come up before. There even is a test which guards the current behavior (allow `@` as a branch name) with the comment:[1]

``` # The thing we are testing here is that "@" is the real branch refs/heads/@, # and not refs/heads/HEAD. These tests should not imply that refs/heads/@ is a # sane thing, but it _is_ technically allowed for now. If we disallow it, these # can be switched to test_must_fail. ```

There was no reply to this change in neither the first[2] nor second version.

That series points back to a bug report thread[3] which is about expanding `@` to a branch named `HEAD`.

Peff found a way for the branch name `HEAD` to be created While figuring out a solution:[4]

> Checking "HEAD" afterwards means you can't actually have a branch
> named "HEAD". Doing so is probably insane, but we probably really _do_
> want to just disallow the @-conversion here.

So that was tangential to the bug fix (`HEAD` as a branch name was not disallowed in the patch series that resulted from this bug).

🔗 1: https://lore.kernel.org/git/20170302082306.n6kfc5uqz2kdxtpm@sigill.intra.peff.net/ 🔗 2: https://public-inbox.org/git/20170228121514.qajydm5bjdbzsucg@sigill.intra.peff.net/ 🔗 3: https://public-inbox.org/git/20170228120633.zkwfqms57fk7dkl5@sigill.intra.peff.net/ 🔗 4: https://public-inbox.org/git/20170227090233.uk7dfruggytgmuw2@sigill.intra.peff.net/

  §2 Disallow `HEAD` as a branch name

This was done later in 2017:

https://lore.kernel.org/git/20171114114259.8937-1-kaartic.sivaraam@gmail.com/

  §2 `refs/heads/@` is apparently disallowed by git-refs(1)

See `t/t1508-at-combinations.sh`:

``` error: refs/heads/@: badRefName: invalid refname format ```

Kristoffer Haugsbakk (3):
  object-name: fix whitespace
  object-name: don't allow @ as a branch name
  t1402: exercise disallowed branch names

 object-name.c                         | 5 ++---
 t/t1402-check-ref-format.sh           | 4 ++++
 t/t3204-branch-name-interpretation.sh | 9 ++-------
 3 files changed, 8 insertions(+), 10 deletions(-)

-- 
2.46.1.641.g54e7913fcb6