More diff rename tests; better split swap handling

This adds a couple more tests of different rename scenarios.

Also, this fixes a problem with the case where you have two
"split" deltas and the left half of one matches the right half of
the other.  That case was already being handled, but in the wrong
order in a way that could result in bad output.  Also, if the swap
also happened to put the other two halves into the correct place
(i.e. two files exchanged places with each other), then the second
delta was left with the SPLIT flag set when it really should be
cleared.

2 files changed, 26 insertions, 9 deletions

diff --git a/src/diff.h b/src/diff.h
index a9a543ecd..ac8ab2aed 100644
--- a/src/diff.h
+++ b/src/diff.h
@@ -44,6 +44,8 @@ enum {
 
 #define GIT_DIFF_FLAG__CLEAR_INTERNAL(F) (F) = ((F) & 0x00FFFF)
 
+#define GIT_DIFF__VERBOSE  (1 << 30)
+
 struct git_diff_list {
 	git_refcount     rc;
 	git_repository   *repo;
diff --git a/src/diff_tform.c b/src/diff_tform.c
index b481e64ce..0f4ecc7b5 100644
--- a/src/diff_tform.c
+++ b/src/diff_tform.c
@@ -828,22 +828,37 @@ int git_diff_find_similar(
 				if (similarity < (int)opts.rename_from_rewrite_threshold)
 					continue;
 
-				memcpy(&swap, &from->new_file, sizeof(swap));
+				memcpy(&swap, &to->new_file, sizeof(swap));
 
-				from->status = GIT_DELTA_RENAMED;
-				from->similarity = (uint32_t)similarity;
-				memcpy(&from->new_file, &to->new_file, sizeof(from->new_file));
-				if ((from->flags & GIT_DIFF_FLAG__TO_SPLIT) != 0) {
-					from->flags &= ~GIT_DIFF_FLAG__TO_SPLIT;
+				to->status = GIT_DELTA_RENAMED;
+				to->similarity = (uint32_t)similarity;
+				memcpy(&to->new_file, &from->new_file, sizeof(to->new_file));
+				if ((to->flags & GIT_DIFF_FLAG__TO_SPLIT) != 0) {
+					to->flags &= ~GIT_DIFF_FLAG__TO_SPLIT;
 					num_rewrites--;
 				}
 
-				memcpy(&to->new_file, &swap, sizeof(to->new_file));
-				if ((to->flags & GIT_DIFF_FLAG__TO_SPLIT) == 0) {
-					to->flags |= GIT_DIFF_FLAG__TO_SPLIT;
+				memcpy(&from->new_file, &swap, sizeof(from->new_file));
+				if ((from->flags & GIT_DIFF_FLAG__TO_SPLIT) == 0) {
+					from->flags |= GIT_DIFF_FLAG__TO_SPLIT;
 					num_rewrites++;
 				}
 
+				/* in the off chance that we've just swapped the new
+				 * element into the correct place, clear the SPLIT flag
+				 */
+				if (matches[matches[i].idx].idx == i &&
+					matches[matches[i].idx].similarity >
+					opts.rename_from_rewrite_threshold) {
+
+					from->status = GIT_DELTA_RENAMED;
+					from->similarity =
+						(uint32_t)matches[matches[i].idx].similarity;
+					matches[matches[i].idx].similarity = 0;
+					from->flags &= ~GIT_DIFF_FLAG__TO_SPLIT;
+					num_rewrites--;
+				}
+
 				num_updates++;
 			}
 		}