Subject: Re: [PATCH] contrib/subtree bugfix: Can't `add` annotated tag

From: Junio C Hamano <[email-masked]>
Date: Thu, 08 May 2014 10:38:32 -0700

James Denholm <[email-masked]> writes:

> cmd_add_commit() is passed FETCH_HEAD by cmd_add_repository, which is
> then rev-parsed into an object ID. However, if the user is fetching a
> tag rather than a branch HEAD, such as by executing:
>
> $ git subtree add -P oldGit https://github.com/git/git.git tags/v1.8.0
>
> The object ID is a tag and is never peeled, and the git commit-tree call
> (line 561) slaps us in the face because it doesn't handle tag IDs.

The "rev" (not "revs") seems to be used by more things than the
final commit-tree state.  Are we losing some useful information by
peeling it too early like this patch does?  The reason why we
stopped peeling when writing FETCH_HEAD was because we wanted to
record the fact that we merged a tag (and use the GPG signature if
found in it) when constructing the log message for the merge, and
peeling the tag too early and recording the commit in FETCH_HEAD
would make it impossible to do, and I am wondering if this change is
making the same kind of mistake here.

I see that add_msg does not use anything useful from latest_new, so
with the current state of the code, it does not make that much
difference (except that it says "from commit '$latest_new'", and by
peeling, the fact that the user wanted to use a tag is lost from the
result).

> On a side note, if merging a tag without --squash, git merge recognises
> that it's a tag and adds a note to the merge commit body. It may be
> worth mimicking this when using "subtree merge --squash" or
> "subtree add".

Yes, and this change makes such a change harder to implement on top,
I suspect.

Would it be sufficient to do

	git commit-tree $tree $headp -p "$rev^0"

in that "not squashing" codepath instead?

>  contrib/subtree/git-subtree.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
> index dc59a91..9453dae 100755
> --- a/contrib/subtree/git-subtree.sh
> +++ b/contrib/subtree/git-subtree.sh
> @@ -538,7 +538,7 @@ cmd_add_commit()
>  {
>  	revs=$(git rev-parse $default --revs-only "$@") || exit $?
>  	set -- $revs
> -	rev="$1"
> +	rev=$(peel_committish "$1")
>  	
>  	debug "Adding $dir as '$rev'..."
>  	git read-tree --prefix="$dir" $rev || exit $?