diff -r 8157c6b82f40 -r 0707bbec682d contrib/check-code.py
--- a/contrib/check-code.py	Sun Feb 07 22:18:24 2016 -0800
+++ b/contrib/check-code.py	Mon Feb 08 18:29:17 2016 +0900
@@ -176,6 +176,8 @@
      'write "file:/*/$TESTTMP" + (glob) to match on windows too'),
     (r'^  (cat|find): .*: No such file or directory',
      'use test -f to test for file existence'),
+    (r'^  diff -[^ -]*p',
+     "don't use (external) diff with -p for portability"),
   ],
   # warnings
   [