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

From: Kristoffer Haugsbakk <[email-masked]>
Date: Mon, 7 Oct 2024 22:15:16 +0200

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/[email-masked]/
🔗 2: https://public-inbox.org/git/[email-masked]/
🔗 3: https://public-inbox.org/git/[email-masked]/
🔗 4: https://public-inbox.org/git/[email-masked]/

  §2 Disallow `HEAD` as a branch name

This was done later in 2017:

https://lore.kernel.org/git/[email-masked]/

  §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