Git patch to override RB_TEST to attempt to check class instead of specific values. Didn't work very well.

0001-Override-the-RB_TEST-macro-to-check-falsiness.patch

From ee8b5f5c1f4072affd1c3d68209e39889831c56e Mon Sep 17 00:00:00 2001
From: Aidan Coyle <packrat386@gmail.com>
Date: Sun, 10 Feb 2019 15:54:21 +0000
Subject: [PATCH] Override the RB_TEST macro to check falsiness

Rather than only accepting the exact values Qnil and Qfalse, instead
check the class of the VALUE passed to see if it is FalseClass.
---
 eval.c              | 16 ++++++++++++++++
 include/ruby/ruby.h | 12 ++++++------
 object.c            |  2 --
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/eval.c b/eval.c
index 4476390270..5843005104 100644
--- a/eval.c
+++ b/eval.c
@@ -1976,3 +1976,19 @@ Init_eval(void)
     id_signo = rb_intern_const("signo");
     id_status = rb_intern_const("status");
 }
+
+int do_rb_test(VALUE v)
+{
+    if (v == RUBY_Qfalse) {
+        return 0;
+    }
+    if (v == RUBY_Qnil) {
+        return 0;
+    }
+
+    if (rb_obj_is_kind_of(v, rb_cFalseClass) == RUBY_Qtrue) {
+        return 0;
+    }
+
+    return 1;
+}
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index d983114e0a..7a2028de7b 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -474,8 +474,8 @@ enum ruby_special_consts {
 #define FLONUM_FLAG RUBY_FLONUM_FLAG
 #endif
 #define SYMBOL_FLAG RUBY_SYMBOL_FLAG
-
-#define RB_TEST(v) !(((VALUE)(v) & (VALUE)~RUBY_Qnil) == 0)
+int do_rb_test(VALUE v);
+#define RB_TEST(v) do_rb_test(v)
 #define RB_NIL_P(v) !((VALUE)(v) != RUBY_Qnil)
 #define RTEST(v) RB_TEST(v)
 #define NIL_P(v) RB_NIL_P(v)
@@ -2061,10 +2061,10 @@ rb_class_of(VALUE obj)
 	if (obj == RUBY_Qtrue)  return rb_cTrueClass;
 	if (RB_STATIC_SYM_P(obj)) return rb_cSymbol;
     }
-    else if (!RB_TEST(obj)) {
-	if (obj == RUBY_Qnil)   return rb_cNilClass;
-	if (obj == RUBY_Qfalse) return rb_cFalseClass;
-    }
+
+    if (obj == RUBY_Qnil)   return rb_cNilClass;
+    if (obj == RUBY_Qfalse) return rb_cFalseClass;
+
     return RBASIC(obj)->klass;
 }

diff --git a/object.c b/object.c
index d37c923fa6..a9d7a79a0d 100644
--- a/object.c
+++ b/object.c
@@ -4283,8 +4283,6 @@ InitVM_Object(void)
     rb_define_method(rb_cFalseClass, "|", false_or, 1);
     rb_define_method(rb_cFalseClass, "^", false_xor, 1);
     rb_define_method(rb_cFalseClass, "===", rb_equal, 1);
-    rb_undef_alloc_func(rb_cFalseClass);
-    rb_undef_method(CLASS_OF(rb_cFalseClass), "new");
     /*
      * An obsolete alias of +false+
      */
--
2.17.1