Re: [PATCH v2] git-tag: Allow --points-at syntax to create a tag pointing to specified commit

[John Keeping <john@keeping.me.uk>]

On Thu, Mar 14, 2013 at 01:34:54PM +0100, Michal Novotny wrote:
> This patch adds the option to specify SHA-1 commit hash using --points-at
> option of git tag to create a tag pointing to a historical commit.

What does this do that "git tag <name> <commit>" doesn't?

> This was pretty easy in the past for the lightweight tags that are just simple
> pointers (by creating .git/refs/tags/$tagname with SHA-1 hash) but it was not
> possible for signed and annotated commits.
> 
> It's been tested for all of the tag types mentioned - lightweight tags, signed
> tags and also annotated tags and everything is working fine in all scenarios
> mentioned above.
> 
> Differences between v1 and v2 (this one):
>  - The bogus sha1-lookup.h hunk has been removed as it's not required and
>    I accidentally forgot to remove it before posting v1
> 
> Michal
> 
> Signed-off-by: Michal Novotny <minovotn@redhat.com>
> ---
>  builtin/tag.c | 32 ++++++++++++++++++++++++++------
>  1 file changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/builtin/tag.c b/builtin/tag.c
> index f826688..f642acd 100644
> --- a/builtin/tag.c
> +++ b/builtin/tag.c
> @@ -437,7 +437,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
>  	struct create_tag_options opt;
>  	char *cleanup_arg = NULL;
>  	int annotate = 0, force = 0, lines = -1, list = 0,
> -		delete = 0, verify = 0;
> +		delete = 0, verify = 0, points_at_commit = 0;
>  	const char *msgfile = NULL, *keyid = NULL;
>  	struct msg_arg msg = { 0, STRBUF_INIT };
>  	struct commit_list *with_commit = NULL;
> @@ -521,8 +521,24 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
>  		die(_("-n option is only allowed with -l."));
>  	if (with_commit)
>  		die(_("--contains option is only allowed with -l."));
> -	if (points_at.nr)
> -		die(_("--points-at option is only allowed with -l."));
> +	if (points_at.nr) {
> +		if (points_at.nr > 1)
> +			die(_("--points-at option is only allowed with -l or a single "
> +				"SHA-1 hash is allowed to create a tag to commit."));
> +		else {
> +			unsigned char *ref = points_at.sha1[0];
> +
> +			struct object *obj = parse_object(ref);
> +			if ((obj != NULL) && (obj->type == OBJ_COMMIT)) {
> +				memcpy(object, ref, 20);
> +				points_at_commit = 1;
> +			}
> +			else
> +				die(_("--points-at option points to an invalid commit"));
> +
> +			free(ref);
> +		}
> +	}
>  	if (delete)
>  		return for_each_tag_name(argv, delete_tag);
>  	if (verify)
> @@ -548,12 +564,16 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
>  
>  	tag = argv[0];
>  
> -	object_ref = argc == 2 ? argv[1] : "HEAD";
>  	if (argc > 2)
>  		die(_("too many params"));
>  
> -	if (get_sha1(object_ref, object))
> -		die(_("Failed to resolve '%s' as a valid ref."), object_ref);
> +	/* Option --points-at option is setting this already */
> +	if (!points_at_commit) {
> +		object_ref = argc == 2 ? argv[1] : "HEAD";
> +
> +		if (get_sha1(object_ref, object))
> +			die(_("Failed to resolve '%s' as a valid ref."), object_ref);
> +	}
>  
>  	if (strbuf_check_tag_ref(&ref, tag))
>  		die(_("'%s' is not a valid tag name."), tag);
> -- 
> 1.7.11.7