log --show-signature: reword the common two-head merge case

While identifying the commit merged to our history as "parent #2" is
technically correct, we will never say "parent #1" (as that is the tip of
our history before the merge is made), and we rarely would say "parent #3"
(which would mean the merge is an octopus), especially when responding to
a request to pull a signed tag.

Treat the most common case to merge a single commit specially, and just
say "merged tag '<tagname>'" instead.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/log-tree.c b/log-tree.c
index 61a12a7cb01cbc36e8ed1d1a8997a8ca9bba3b05..3cf569ce7eccc07cd69cf659df0814724647c5a2 100644 (file)
--- a/log-tree.c
+++ b/log-tree.c
@@ -456,6 +456,13 @@ static int which_parent(const unsigned char *sha1, const struct commit *commit)
        return -1;
 }
 
+static int is_common_merge(const struct commit *commit)
+{
+       return (commit->parents
+               && commit->parents->next
+               && !commit->parents->next->next);
+}
+
 static void show_one_mergetag(struct rev_info *opt,
                              struct commit_extra_header *extra,
                              struct commit *commit)
@@ -474,6 +481,11 @@ static void show_one_mergetag(struct rev_info *opt,
        strbuf_init(&verify_message, 256);
        if (parse_tag_buffer(tag, extra->value, extra->len))
                strbuf_addstr(&verify_message, "malformed mergetag\n");
+       else if (is_common_merge(commit) &&
+                !hashcmp(tag->tagged->sha1,
+                         commit->parents->next->item->object.sha1))
+               strbuf_addf(&verify_message,
+                           "merged tag '%s'\n", tag->tag);
        else if ((nth = which_parent(tag->tagged->sha1, commit)) < 0)
                strbuf_addf(&verify_message, "tag %s names a non-parent %s\n",
                                    tag->tag, tag->tagged->sha1);