From: shejialuo <shejialuo@gmail.com>
Date: Tue, 08 Oct 2024 13:19:51 GMT
Subject: Re: [PATCH 0/3] object-name: don't allow @ as a branch name
Message-ID: <ZwUxdz_HobRGF9yq@ArchLinux>
In-Reply-To: <cover.1728331771.git.code@khaugsbakk.name>

On Mon, Oct 07, 2024 at 10:15:16PM +0200, Kristoffer Haugsbakk wrote:

[snip]

>   §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
> ```
> 

It's true that using "git refs verify" will report "refs/heads/@" is a
bad refname.

From the man page of the "git-check-ref-format(1)", it is clear that

    9. They cannot be the single character @.

Because I am interesting in this patch which is highly relevant with my
recent work, so I try somethings here and find some interesting results
as below shows.

    $ git check-ref-format refs/heads/@
    $ echo $? # will be 0
    # git check-ref-format --allow-onelevel @
    # echo $? # will be 1

The reason why "git refs verify" will report this error is that in the
code implementation, I have to iterate every file in the filesystem. So
it's convenient for me to do the following:

    if (check_refname_format(iter->basename, REFNAME_ALLOW_ONELEVEL)) {
        ret = fsck_report(...);
    }

Because I specify "REFNAME_ALLOW_ONELEVEL" here, so it will follow the
"git check-ref-format --allow-onelevel" command thus reporting an error
to the user.

I am curious why "git check-ref-format refs/heads/@" will succeed, so I
try to use "git symbolic-ref" and "git update-ref" to verify to test the
behavior.

    $ git symbolic-ref refs/heads/@ refs/heads/master
    error: cannot lock ref 'refs/heads/@': unable to resolve reference 'refs/heads/@': reference broken
    $ git update-ref refs/heads/@ refs/heads/master
    fatal: update_ref failed for ref 'refs/heads/@': cannot lock ref 'refs/heads/@': unable to resolve reference 'refs/heads/@': reference broken

So, we are not consistent here. I guess the reason why "git
check-ref-format refs/heads/@" will succeed is that we allow user create
this kind of branch.

If we decide to not allow user to create such refs. We should also
change the behavior of the "check_refname_format" function. (I am not
familiar with the internal implementation, this is my guess)

Thanks,
Jialuo