Make git-cherry handle root trees

This patch on top of 'next' makes built-in git-cherry handle root
commits.

It moves the static function log-tree.c::diff_root_tree() to
tree-diff.c and makes it more similar to diff_tree_sha1() by
shuffling around arguments and factoring out the call to
log_tree_diff_flush().  Consequently the name is changed to
diff_root_tree_sha1().  It is a version of diff_tree_sha1() that
compares the empty tree (= root tree) against a single 'real' tree.

This function is then used in get_patch_id() to compute patch IDs
for initial commits instead of SEGFAULTing, as the current code
does if confronted with parentless commits.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/diff.h b/diff.h
index ce3058e437..ac7b21c46b 100644
--- a/diff.h
+++ b/diff.h
@@ -102,6 +102,8 @@ extern int diff_tree(struct tree_desc *t1, struct tree_desc *t2,
 		     const char *base, struct diff_options *opt);
 extern int diff_tree_sha1(const unsigned char *old, const unsigned char *new,
 			  const char *base, struct diff_options *opt);
+extern int diff_root_tree_sha1(const unsigned char *new, const char *base,
+                               struct diff_options *opt);
 
 struct combine_diff_path {
 	struct combine_diff_path *next;