commit: add for_each_mergetag()

In the same way as there is for_each_ref() to iterate on refs,
for_each_mergetag() allows the caller to iterate on the mergetags of
a given commit.  Use it to rewrite show_mergetag() used in "git log".

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/commit.c b/commit.c
index 4ff8077dbf..94b1af9392 100644
--- a/commit.c
+++ b/commit.c
@@ -1316,6 +1316,19 @@ struct commit_extra_header *read_commit_extra_headers(struct commit *commit,
 	return extra;
 }
 
+void for_each_mergetag(each_mergetag_fn fn, struct commit *commit, void *data)
+{
+	struct commit_extra_header *extra, *to_free;
+
+	to_free = read_commit_extra_headers(commit, NULL);
+	for (extra = to_free; extra; extra = extra->next) {
+		if (strcmp(extra->key, "mergetag"))
+			continue; /* not a merge tag */
+		fn(commit, extra, data);
+	}
+	free_commit_extra_headers(to_free);
+}
+
 static inline int standard_header_field(const char *field, size_t len)
 {
 	return ((len == 4 && !memcmp(field, "tree ", 5)) ||