Re: [PATCH] branch: Forbid to create local branches with confusing names

>   git branch remotes/origin/master
>   git branch refs/remotes/origin/master
>   git branch heads/master
>   git branch tags/v3.4
> All of these local branch names lead to severe confusion,
> not only for a user but also for git itself.
>
> This patch forbids to create local branches, with names which start
> with any of
>
>   refs/
>   heads/
>   remotes/
>   tags/
>
> With this patch, you might still create these kind of local branches,
> but now you have to additionally specify the '-f' option.
>
> Signed-off-by: Ingo Rohloff <ingo.rohloff@lauterbach.com>
> ---
>  branch.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
>  This patch refers way back to the discussion from 2014:
>    From: Josef Wolf
>    To: git@vger.kernel.org
>    Subject: error: src refspec refs/heads/master matches more than one.
>    Date: Fri, 14 Feb 2014 12:31:36 +0100
>  See for example here:
>    https://public-inbox.org/git/20140214113136.GA17817@raven.inka.de/
>
>  The origin of the problem is, that git has (almost) no constraints
>  what kind of names are allowed for local branches.
>  There nowadays is a constraint that you are NOT allowed to create
>  a branch which is called HEAD. See commit 16169285f1e6 ("Merge
>  branch 'jc/branch-name-sanity'", 2017-11-28).
>
>  In the old mail thread a lot of potential constraints for local
>  branch names were discussed; in particular a lot of strategies
>  were discussed what kind of local branch names might be a problem
>  (the gist is: avoid ambiguities, by finding out which names
>  lead to ambiguities NOW).
>
>  I personally think it makes more sense to forbid a much
>  bigger class of confusing branch names.
>  In particular I think all local branch names starting with
>    refs/
>    heads/
>    remotes/
>    tags/
>  should be forbidden (per default, can still be forced).
>  This also avoids trouble for an unforseeable future.
>  Example:
>    git branch remotes/blub/master
>  This might not be a problem now, because you have no
>  remote called "blub" right now.
>  But if you later use
>    git remote add blub <URL>
>    git fetch blub
>  you very likely run into trouble.
>
>  The above approach still allows you to create local branches
>  with a name of the form
>     <remote name>/<something ...>
>  but I cannot see how this might be avoided; remotes might
>  be added later so what would you do in the case that a local
>  branch already existed named like the remote or a remote
>  tracking branch.
>
>  With the proposed constraints you are at least are able to use
>     heads/<remote name>/<something ...>
>     remotes/<remote name>/<something ...>
>  to differentiate between the two.
>
>  This really is an issue; people seem to stumble over it
>  and I guess this is particularly true if you control git
>  via scripts. See for example (two years later):
>    From: Duy Nguyen
>    To: Junio C Hamano
>    Cc: Git Mailing List <git@vger.kernel.org>,
>    Subject: Re: error: src refspec refs/heads/master matches more than one.
>    Date: Wed, 23 Mar 2016 18:17:05 +0700
>
>  So with this patch I want to pick up this old discussion yet again.
>
>  This code can probably be done a lot better I guess, but I wanted to
>  send in something, to start the discussion.

>
> diff --git a/branch.c b/branch.c
> index 579494738a..e74872dac5 100644
> --- a/branch.c
> +++ b/branch.c
> @@ -256,6 +256,16 @@ void create_branch(struct repository *r,
>  	int dont_change_ref = 0;
>  	int explicit_tracking = 0;
>
> +	if (!force && (
> +		starts_with(name, "refs/") ||
> +		starts_with(name, "heads/") ||
> +		starts_with(name, "remotes/") ||
> +		starts_with(name, "tags/")

> +	)) {
> +		die(_("A local branch name should not start with "
> +		      "\"refs/\", \"heads/\", \"remotes/\" or \"tags/\""));
> +	}
> +
>  	if (track == BRANCH_TRACK_EXPLICIT || track == BRANCH_TRACK_OVERRIDE)
>  		explicit_tracking = 1;
>
> --
> 2.24.0.1.g6c2c19214d.dirty
>
>