merge-recursive: don't segfault while handling rename clashes

When a branch moves A to B while the other branch created B (or moved C to
B), the code tried to rename one of them to B~something to preserve both
versions, and failed to register temporary resolution for the original
path B at stage#0 during virtual ancestor computation.  This left the
index in unmerged state and caused a segfault.

A better solution is to merge these two versions of B's in place and use
the (potentially conflicting) result as the intermediate merge result in
the virtual ancestor.

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

1 files changed, 25 insertions, 3 deletions

diff --git a/merge-recursive.c b/merge-recursive.c
index b97026bd5c..54d23b214c 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -947,9 +947,31 @@ static int process_renames(struct merge_options *o,
 				       "%s added in %s",
 				       ren1_src, ren1_dst, branch1,
 				       ren1_dst, branch2);
-				new_path = unique_path(o, ren1_dst, branch2);
-				output(o, 1, "Adding as %s instead", new_path);
-				update_file(o, 0, dst_other.sha1, dst_other.mode, new_path);
+				if (o->call_depth) {
+					struct merge_file_info mfi;
+					struct diff_filespec one, a, b;
+
+					one.path = a.path = b.path =
+						(char *)ren1_dst;
+					hashcpy(one.sha1, null_sha1);
+					one.mode = 0;
+					hashcpy(a.sha1, ren1->pair->two->sha1);
+					a.mode = ren1->pair->two->mode;
+					hashcpy(b.sha1, dst_other.sha1);
+					b.mode = dst_other.mode;
+					mfi = merge_file(o, &one, &a, &b,
+							 branch1,
+							 branch2);
+					output(o, 1, "Adding merged %s", ren1_dst);
+					update_file(o, 0,
+						    mfi.sha,
+						    mfi.mode,
+						    ren1_dst);
+				} else {
+					new_path = unique_path(o, ren1_dst, branch2);
+					output(o, 1, "Adding as %s instead", new_path);
+					update_file(o, 0, dst_other.sha1, dst_other.mode, new_path);
+				}
 			} else if ((item = string_list_lookup(ren1_dst, renames2Dst))) {
 				ren2 = item->util;
 				clean_merge = 0;