merge revision(s) 72d1a790cfe0e4a457db98c587f1acaa5e39f001: [Backport #19833]

	[Bug #19833] Fix index underflow at superclasses of `BasicObject`

	---
	 object.c                | 4 ++++
	 test/ruby/test_class.rb | 7 +++++++
	 2 files changed, 11 insertions(+)

3 files changed, 12 insertions, 1 deletions

diff --git a/object.c b/object.c
index 04e2af96e7..48dd1e7e6e 100644
--- a/object.c
+++ b/object.c
@@ -2079,6 +2079,10 @@ rb_class_superclass(VALUE klass)
         if (klass == rb_cBasicObject) return Qnil;
         rb_raise(rb_eTypeError, "uninitialized class");
     }
+
+    if (!RCLASS_SUPERCLASS_DEPTH(klass)) {
+        return Qnil;
+    }
     else {
         super = RCLASS_SUPERCLASSES(klass)[RCLASS_SUPERCLASS_DEPTH(klass) - 1];
         RUBY_ASSERT(RB_TYPE_P(klass, T_CLASS));
diff --git a/test/ruby/test_class.rb b/test/ruby/test_class.rb
index 5086e60398..300ab950ac 100644
--- a/test/ruby/test_class.rb
+++ b/test/ruby/test_class.rb
@@ -96,6 +96,13 @@ class TestClass < Test::Unit::TestCase
 
   def test_superclass_of_basicobject
     assert_equal(nil, BasicObject.superclass)
+
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      module Mod end
+      BasicObject.include(Mod)
+      assert_equal(nil, BasicObject.superclass)
+    end;
   end
 
   def test_module_function
diff --git a/version.h b/version.h
index b0a66d5b0a..ff4e47e0c6 100644
--- a/version.h
+++ b/version.h
@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 2
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 109
+#define RUBY_PATCHLEVEL 110
 
 #include "ruby/version.h"
 #include "ruby/internal/abi.h"