git-merge-file: refuse to merge binary files

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-merge-file.c

@@ -36,9 +36,13 @@ int cmd_merge_file(int argc, char **argv, char **envp)
 	for (; i < 3; i++)
 		names[i] = argv[i + 1];
 
-	for (i = 0; i < 3; i++)
+	for (i = 0; i < 3; i++) {
 		if (read_mmfile(mmfs + i, argv[i + 1]))
 			return -1;
+		if (buffer_is_binary(mmfs[i].ptr, mmfs[i].size))
+			return error("Cannot merge binary files: %s\n",
+					argv[i + 1]);
+	}
 
 	ret = xdl_merge(mmfs + 1, mmfs + 0, names[0], mmfs + 2, names[2],
 			&xpp, XDL_MERGE_ZEALOUS, &result);

t/t6023-merge-file.sh

@@ -134,5 +134,10 @@ EOF
 
 test_expect_success "expected conflict markers" "git diff expect out"
 
+test_expect_success 'binary files cannot be merged' '
+	! git merge-file -p orig.txt ../test4012.png new1.txt 2> merge.err &&
+	grep "Cannot merge binary files" merge.err
+'
+
 test_done