ERB monkypatch creates incompatibilities

In 2.3.6, ERB is monkeypatched rather than subclassed to use ActiveSupport::SafeBuffer. This breaks any libraries that are using ERB and expecting it to work with a plain string. One such use is Haml's :erb filter, which integrates the ERB-compiled Ruby into the Haml-compiled Ruby, and breaks when ERB tries to call #safe_concat on a plain string.

Why is ERB being monkeypatched in the first place? I was under the impression that Erubis was used for XSS-safety. This monkeypatch doesn't exist in the master branch. I suggest removing it entirely. If removal isn't an option, subclass before you change the behavior of a class.