Re: Best way to update `HEAD` in mirrored repos

[Rodrigo Silva Mendoza <rodrigosilvamendoza3@gmail.com>]

Hello,

Apologies for the delay, I'd never built Git from source so I put it
off until I had a chunk of time, assuming it might take me a bit -
thankfully it was painless.

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
> Here, you set this up as a fetch mirror. That is something I've missed
> before. It is also important because it means that there is no
> `refs/remotes/origin/HEAD`.

Ahhh, the reason it wasn't working before clicked for me now, thanks
for the explanation.

> diff --git a/builtin/remote.c b/builtin/remote.c
> index eddd40c8f87..fead15adb97 100644
> --- a/builtin/remote.c
> +++ b/builtin/remote.c
> @@ -1344,7 +1344,7 @@ static int show(int argc, const char **argv)
>
>  static int set_head(int argc, const char **argv)
>  {
> -     int i, opt_a = 0, opt_d = 0, result = 0;
> +     int i, opt_a = 0, opt_d = 0, result = 0, is_mirror = 0;
>       struct strbuf buf = STRBUF_INIT, buf2 = STRBUF_INIT;
>       char *head_name = NULL;
>
> @@ -1357,8 +1357,16 @@ static int set_head(int argc, const char **argv)
>       };
>       argc = parse_options(argc, argv, NULL, options, builtin_remote_sethead_usage,
>                            0);
> -     if (argc)
> -             strbuf_addf(&buf, "refs/remotes/%s/HEAD", argv[0]);
> +     if (argc) {
> +             struct remote *remote = remote_get(argv[0]);
> +
> +             if (!remote || !remote->mirror)
> +                     strbuf_addf(&buf, "refs/remotes/%s/HEAD", argv[0]);
> +             else {
> +                     is_mirror = 1;
> +                     strbuf_addstr(&buf, "HEAD");
> +             }
> +     }

> Would you have a chance to build Git with this patch and verify that it
> works for you, too?

Good news Johannes, your patch worked for me as well! Here's a run
with the patched code.

    $ git --version
    git version 2.37.0.rc0.dirty
    $ git clone git@github.com:xvandish/livegrep-fragment.git --mirror
    $ cd livegrep-fragment
    $ git symbolic-ref HEAD
    refs/heads/good_main_5
    $ // I changed the github default branch name at this moment
    $ git ls-remote --symref origin HEAD
    ref: refs/heads/good_main_5     HEAD
    0666a519f94b8500ab6f14bdf7c9c2e5ca7d5821        HEAD
    $ git fetch -p
    From github.com:xvandish/livegrep-fragment
    - [deleted]         (none)     -> good_main_4
    * [new branch]      good_main_5 -> good_main_5
    $ git remote set-head -a origin
    origin/HEAD set to good_main_5
    $ git symbolic-ref HEAD
    refs/heads/good_main_5


On Fri, Jun 10, 2022 at 2:53 PM Junio C Hamano <gitster@pobox.com> wrote:
> Good.
>
> Regardless of the "mirror" issue, it makes tons of sense to ask the
> remote API how the remote-tracking refs for the given remote is set
> up, instead of assuming that it must be "refs/remotes/<remote>"
> blindly like in the original code.
>
> That way, we could even handle a case like so:
>
>         [remote "frotz"]
>                 fetch = +refs/heads/*:refs/remotes/nitfol/*
>
> Their HEAD should be mapped to refs/remotes/nitfol/HEAD on our end,
> so set-head should be able to notice that, too, if we go further
> with your "do not assume, instead ask remote API" approach.
>
> Thanks.

This makes sense to me as well, as a continuation of the "ask remote " style.
I only have a very vague idea of how I'd implement this from a look at
the codebase, so I'd be of more
help testing things out. If this idea carries forward let me know if I
can be of help testing, or if you'd like me to
like me to try to put a patch up let me know.


Thanks to both of you for your time.