merge-recursive: fix rename/rename(1to2) for working tree with a binary

With a rename/rename(1to2) conflict, we attempt to do a three-way merge
of the file contents, so that the correct contents can be placed in the
working tree at both paths.  If the file is a binary, however, no
content merging is possible and we should just use the original version
of the file at each of the paths.

Reported-by: Chunlin Zhang <zhangchunlin@gmail.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-recursive.c

@@ -1750,6 +1750,18 @@ static int handle_rename_rename_1to2(struct merge_options *opt,
 			return -1;
 	}
 
+	if (!mfi.clean && mfi.blob.mode == a->mode &&
+	    oideq(&mfi.blob.oid, &a->oid)) {
+		/*
+		 * Getting here means we were attempting to merge a binary
+		 * blob.  Since we can't merge binaries, the merge algorithm
+		 * just takes one side.  But we don't want to copy the
+		 * contents of one side to both paths; we'd rather use the
+		 * original content at the given path for each path.
+		 */
+		oidcpy(&mfi.blob.oid, &b->oid);
+		mfi.blob.mode = b->mode;
+	}
 	add = &ci->ren2->dst_entry->stages[flip_stage(3)];
 	if (is_valid(add)) {
 		add->path = mfi.blob.path = b->path;

t/t6042-merge-rename-corner-cases.sh

@@ -1379,4 +1379,59 @@ test_expect_success 'check nested conflicts from rename/rename(2to1)' '
 	)
 '
 
+# Testcase rename/rename(1to2) of a binary file
+#   Commit O: orig
+#   Commit A: orig-A
+#   Commit B: orig-B
+#   Expected: CONFLICT(rename/rename) message, three unstaged entries in the
+#             index, and contents of orig-[AB] at path orig-[AB]
+test_setup_rename_rename_1_to_2_binary () {
+	test_create_repo rename_rename_1_to_2_binary &&
+	(
+		cd rename_rename_1_to_2_binary &&
+
+		echo '* binary' >.gitattributes &&
+		git add .gitattributes &&
+
+		test_seq 1 10 >orig &&
+		git add orig &&
+		git commit -m orig &&
+
+		git branch A &&
+		git branch B &&
+
+		git checkout A &&
+		git mv orig orig-A &&
+		test_seq 1 11 >orig-A &&
+		git add orig-A &&
+		git commit -m orig-A &&
+
+		git checkout B &&
+		git mv orig orig-B &&
+		test_seq 0 10 >orig-B &&
+		git add orig-B &&
+		git commit -m orig-B
+
+	)
+}
+
+test_expect_success 'rename/rename(1to2) with a binary file' '
+	test_setup_rename_rename_1_to_2_binary &&
+	(
+		cd rename_rename_1_to_2_binary &&
+
+		git checkout A^0 &&
+
+		test_must_fail git merge -s recursive B^0 &&
+
+		# Make sure the index has the right number of entries
+		git ls-files -s >actual &&
+		test_line_count = 4 actual &&
+
+		git rev-parse A:orig-A B:orig-B >expect &&
+		git hash-object orig-A orig-B >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done