Re: [PATCH 4/4] tag: "git tag" refuses to use HEAD as a tagname

["Rubén Justo" <rjusto@gmail.com>]

On Mon, Dec 02, 2024 at 04:07:14PM +0900, Junio C Hamano wrote:
> Even though the plumbing level allows you to create refs/tags/HEAD
> and refs/heads/HEAD, doing so makes it confusing within the context
> of the UI Git Porcelain commands provides.  Just like we prevent a
> branch from getting called "HEAD" at the Porcelain layer (i.e. "git
> branch" command), teach "git tag" to refuse to create a tag "HEAD".

This sounds like a good step in the right direction for me.

From the subject in this patch, I was worried that we were also
preventing deletion.  However, I have confirmed that we still allow
the intuitive deletion of a tag named 'HEAD' with "git tag -d HEAD";
for example, in repositories where such a tag already exists.

Perhaps tangential, but a silly change like this hasn't broken any
tests:

diff --git a/builtin/tag.c b/builtin/tag.c
index 670e564178..b65f56e5b4 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -88,6 +88,8 @@ static int for_each_tag_name(const char **argv, each_tag_name_fn fn,
 
        for (p = argv; *p; p++) {
                strbuf_reset(&ref);
+               if (!strcmp(*p, "HEAD"))
+                     die("Hi!");
                strbuf_addf(&ref, "refs/tags/%s", *p);
                if (refs_read_ref(get_main_ref_store(the_repository), ref.buf, &oid)) {
                        error(_("tag '%s' not found."), *p);

Therefore, if the previous seems reasonable, perhaps we should add a
test like:

--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -97,6 +97,11 @@ test_expect_success 'HEAD is forbidden as a tagname' '
 	test_must_fail git tag -a -m "useless" HEAD
 '
 
+test_expect_success 'allow deleting a tag named HEAD' '
+	git update-ref refs/tags/HEAD HEAD &&
+	git tag -d HEAD
+'
+
 test_expect_success 'creating a tag with --create-reflog should create reflog' '
 	git log -1 \
 		--format="format:tag: tagging %h (%s, %cd)%n" \

> 
> Helped-by: Jeff King <peff@peff.net>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>  refs.c         | 2 +-
>  t/t7004-tag.sh | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/refs.c b/refs.c
> index a24bfe3845..01ef2a3093 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -735,7 +735,7 @@ int check_branch_ref(struct strbuf *sb, const char *name)
>  
>  int check_tag_ref(struct strbuf *sb, const char *name)
>  {
> -	if (name[0] == '-')
> +	if (name[0] == '-' || !strcmp(name, "HEAD"))
>  		return -1;
>  
>  	strbuf_reset(sb);
> diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
> index b1316e62f4..2082ce63f7 100755
> --- a/t/t7004-tag.sh
> +++ b/t/t7004-tag.sh
> @@ -91,6 +91,12 @@ test_expect_success 'creating a tag using default HEAD should succeed' '
>  	test_must_fail git reflog exists refs/tags/mytag
>  '
>  
> +test_expect_success 'HEAD is forbidden as a tagname' '
> +	test_when_finished "git tag -d HEAD || :" &&

I'm not considering this as a test for it :-)

> +	test_must_fail git tag HEAD &&
> +	test_must_fail git tag -a -m "useless" HEAD
> +'
> +
>  test_expect_success 'creating a tag with --create-reflog should create reflog' '
>  	git log -1 \
>  		--format="format:tag: tagging %h (%s, %cd)%n" \
> -- 
> 2.47.1-514-g9b43e7ecc4
>