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

[Johannes Schindelin <Johannes.Schindelin@xxxxxx>]

Hi Rodrigo,

On Thu, 9 Jun 2022, Rodrigo Silva Mendoza wrote:

> On Thu, Jun 9, 2022 at 1:02 AM Johannes Schindelin
> <Johannes.Schindelin@xxxxxx> wrote:
> >
> > The reason is that `set-head` expects options to come before arguments,
> > like so:
> >
> >         git remote set-head -a origin
>
> Hmm, that doesn't seem to work for me either - I get the same type of
> error as before.
> Here's a minimal repro:
>     $ git clone git@xxxxxxxxxx:git/gitscm-old.git --mirror

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`.

>     $ cd gitscm-old.git
>     $ git remote set-head -a origin
>       error: Not a valid ref: refs/remotes/origin/master

... yet that's exactly what `set-head` assumes. The following patch fixes
it for me:

-- snip --
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");
+		}
+	}

 	if (!opt_a && !opt_d && argc == 2) {
 		head_name = xstrdup(argv[1]);
@@ -1383,7 +1391,10 @@ static int set_head(int argc, const char **argv)
 		usage_with_options(builtin_remote_sethead_usage, options);

 	if (head_name) {
-		strbuf_addf(&buf2, "refs/remotes/%s/%s", argv[0], head_name);
+		if (is_mirror)
+			strbuf_addf(&buf2, "refs/heads/%s", head_name);
+		else
+			strbuf_addf(&buf2, "refs/remotes/%s/%s", argv[0], head_name);
 		/* make sure it's valid */
 		if (!ref_exists(buf2.buf))
 			result |= error(_("Not a valid ref: %s"), buf2.buf);

-- snap --

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

Ciao,
Johannes