commit: copy merged signed tags to headers of merge commit

Now MERGE_HEAD records the tag objects without peeling, we could record
the result of manual conflict resolution via "git commit" without losing
the tag information. Introduce a new "mergetag" multi-line header field to
the commit object, and use it to store the entire contents of each signed
tag merged.

A commit header that has a multi-line payload begins with the header tag
(e.g. "mergetag" in this case), SP, the first line of payload, LF, and all
the remaining lines have a SP inserted at the beginning.

In hindsight, it would have been better to make "merge --continue" as the
way to continue from such an interrupted merge, not "commit", but this is
a backward compatibility baggage we would need to carry around for now.

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

1 files changed, 19 insertions, 2 deletions

diff --git a/commit.h b/commit.h
index 5b57eab578..c1a723ecdb 100644
--- a/commit.h
+++ b/commit.h
@@ -181,9 +181,26 @@ static inline int single_parent(struct commit *commit)
 
 struct commit_list *reduce_heads(struct commit_list *heads);
 
+struct commit_extra_header {
+	struct commit_extra_header *next;
+	char *key;
+	char *value;
+	size_t len;
+};
+
+extern void append_merge_tag_headers(struct commit_list *parents,
+				     struct commit_extra_header ***tail);
+
 extern int commit_tree(const char *msg, unsigned char *tree,
-		struct commit_list *parents, unsigned char *ret,
-		const char *author);
+		       struct commit_list *parents, unsigned char *ret,
+		       const char *author);
+
+extern int commit_tree_extended(const char *msg, unsigned char *tree,
+				struct commit_list *parents, unsigned char *ret,
+				const char *author,
+				struct commit_extra_header *);
+
+extern void free_commit_extra_headers(struct commit_extra_header *extra);
 
 struct merge_remote_desc {
 	struct object *obj; /* the named object, could be a tag */