threads / discuss / 1185

tag referring to a commit but not directly?

Subject: tag referring to a commit but not directly?

## tl;dr

3 messages between Jul 9, 2005 and Jul 11, 2005.

replies: 2people: 2as markdown or json

Junio C Hamano· Jul 9, 2005, 10:00 UTC · lore

I was playing with a tag that refers to another tag which refers to a commit, and found out that some things did not work as I expected.

Is it a PEBCAK on my part to expect tag-to-tag-to-commit to behave the same way as a bare commit (or a tag to commit), or is this just a bug? I think the following two would fix what I found, but I am not sure if I am using the "struct object" and friends the way they are expected to be used. I am uncertain about what the expected behaviour should be either for that matter; I admit that tags are new to me.

---

*** To find whom to ask about the thing I am butchering, I *** used the following pickaxe:

git-rev-list linus |
git-diff-tree --stdin -v -s \
-S'	if (obj->type == tag_type)
		obj = ((struct tag *)obj)->tagged;'

git-rev-list linus |
git-diff-tree --stdin -v -s \
-S'	/*
	 * Tag object? Look what it points to..
	 */
	if (object->type == tag_type) {'

------------ cd /opt/packrat/playpen/public/in-place/git/git.junio/ jit-diff 0:5 # - master: format-patch: fix skipping of blank-lines (take 2) # + 5: tag deref until we get non tag

diff --git a/commit.c b/commit.c
--- a/commit.c
+++ b/commit.c
@@ -52,8 +52,9 @@ struct commit *lookup_commit_reference(c
 
 	if (!obj)
 		return NULL;
-	if (obj->type == tag_type)
-		obj = ((struct tag *)obj)->tagged;
+	while (obj->type == tag_type)
+		obj = parse_object(((struct tag *)obj)->tagged->sha1);
+
 	return check_commit(obj, sha1);
 }
 
diff --git a/rev-list.c b/rev-list.c
--- a/rev-list.c
+++ b/rev-list.c
@@ -354,12 +354,12 @@ static struct commit *get_commit_referen
 	/*
 	 * Tag object? Look what it points to..
 	 */
-	if (object->type == tag_type) {
+	while (object->type == tag_type) {
 		struct tag *tag = (struct tag *) object;
 		object->flags |= flags;
 		if (tag_objects && !(object->flags & UNINTERESTING))
 			add_pending_object(object, tag->tag);
-		object = tag->tagged;
+		object = parse_object(tag->tagged->sha1);
 	}
 
 	/*

Compilation finished at Sat Jul  9 02:37:16

Junio C Hamano· Jul 11, 2005, 06:55 UTC · re: Junio C Hamano · lore

[PATCH] Dereference tag repeatedly until we get a non-tag.

When we allow a tag object in place of a commit object, we only dereferenced the given tag once, which causes a tag that points at a tag that points at a commit to be rejected. Instead, dereference tag repeatedly until we get a non-tag.

This patch makes change to two functions:

 - commit.c::lookup_commit_reference() is used by merge-base,
   rev-tree and rev-parse to convert user supplied SHA1 to that of
   a commit.
 - rev-list uses its own get_commit_reference() to do the same.

Dereferencing tags this way helps both of these uses.

Signed-off-by: Junio C Hamano <junkio@cox.net>
---

*** Whether having a tag pointing at another tag is a separate *** issue, but I do not see a reason to forbid it. Maybe it *** is used to represent a chain of trust.

 commit.c   |    5 +++--
 rev-list.c |    4 ++--
 2 files changed, 5 insertions(+), 4 deletions(-)

0dc9377363ee73c5e3f3711d6f82e49886ce8c6a

diff --git a/commit.c b/commit.c
--- a/commit.c
+++ b/commit.c
@@ -52,8 +52,9 @@ struct commit *lookup_commit_reference(c
 
 	if (!obj)
 		return NULL;
-	if (obj->type == tag_type)
-		obj = ((struct tag *)obj)->tagged;
+	while (obj->type == tag_type)
+		obj = parse_object(((struct tag *)obj)->tagged->sha1);
+
 	return check_commit(obj, sha1);
 }
 
diff --git a/rev-list.c b/rev-list.c
--- a/rev-list.c
+++ b/rev-list.c
@@ -367,12 +367,12 @@ static struct commit *get_commit_referen
 	/*
 	 * Tag object? Look what it points to..
 	 */
-	if (object->type == tag_type) {
+	while (object->type == tag_type) {
 		struct tag *tag = (struct tag *) object;
 		object->flags |= flags;
 		if (tag_objects && !(object->flags & UNINTERESTING))
 			add_pending_object(object, tag->tag);
-		object = tag->tagged;
+		object = parse_object(tag->tagged->sha1);
 	}
 
 	/*

Jon Seymour· Jul 11, 2005, 15:14 UTC · re: Junio C Hamano · lore

Re: [PATCH] Dereference tag repeatedly until we get a non-tag.

This seems reasonable to me. I have thought this would be useful on several occasions and haven't yet conceived of a counterexample where it would break something.

On 7/11/05, Junio C Hamano <junkio@cox.net> wrote:

Show 65 quoted lines

> When we allow a tag object in place of a commit object, we only
> dereferenced the given tag once, which causes a tag that points
> at a tag that points at a commit to be rejected.  Instead,
> dereference tag repeatedly until we get a non-tag.
> 
> This patch makes change to two functions:
> 
>  - commit.c::lookup_commit_reference() is used by merge-base,
>    rev-tree and rev-parse to convert user supplied SHA1 to that of
>    a commit.
>  - rev-list uses its own get_commit_reference() to do the same.
> 
> Dereferencing tags this way helps both of these uses.
> 
> Signed-off-by: Junio C Hamano <junkio@cox.net>
> ---
> 
> *** Whether having a tag pointing at another tag is a separate
> *** issue, but I do not see a reason to forbid it.  Maybe it
> *** is used to represent a chain of trust.
> 
>  commit.c   |    5 +++--
>  rev-list.c |    4 ++--
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> 0dc9377363ee73c5e3f3711d6f82e49886ce8c6a
> diff --git a/commit.c b/commit.c
> --- a/commit.c
> +++ b/commit.c
> @@ -52,8 +52,9 @@ struct commit *lookup_commit_reference(c
> 
>         if (!obj)
>                 return NULL;
> -       if (obj->type == tag_type)
> -               obj = ((struct tag *)obj)->tagged;
> +       while (obj->type == tag_type)
> +               obj = parse_object(((struct tag *)obj)->tagged->sha1);
> +
>         return check_commit(obj, sha1);
>  }
> 
> diff --git a/rev-list.c b/rev-list.c
> --- a/rev-list.c
> +++ b/rev-list.c
> @@ -367,12 +367,12 @@ static struct commit *get_commit_referen
>         /*
>          * Tag object? Look what it points to..
>          */
> -       if (object->type == tag_type) {
> +       while (object->type == tag_type) {
>                 struct tag *tag = (struct tag *) object;
>                 object->flags |= flags;
>                 if (tag_objects && !(object->flags & UNINTERESTING))
>                         add_pending_object(object, tag->tag);
> -               object = tag->tagged;
> +               object = parse_object(tag->tagged->sha1);
>         }
> 
>         /*
> 
> -
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-- 
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