Add method RDoc::ClassModule#super_classes

The purpose is to list all class ancestors in a new theme (see PR ruby#1182).

lib/rdoc/code_object/class_module.rb

@@ -710,6 +710,20 @@ def superclass=(superclass)
     @superclass = superclass
   end
 
+  ##
+  # Get all super classes of this class in an array. The last element might be
+  # a string if the name is unknown.
+
+  def super_classes
+    result = []
+    parent = self
+    while parent = parent.superclass
+      result << parent
+      return result if parent.is_a?(String)
+    end
+    result
+  end
+
   def to_s # :nodoc:
     if is_alias_for then
       "#{self.class.name} #{self.full_name} -> #{is_alias_for}"

test/rdoc/test_rdoc_class_module.rb

@@ -1279,6 +1279,12 @@ def test_superclass
     assert_equal @c3_h1, @c3_h2.superclass
   end
 
+  def test_super_classes
+    rdoc_c3_h1 = @xref_data.find_module_named('C3::H1')
+    rdoc_object = @xref_data.find_module_named('Object')
+    assert_equal [rdoc_c3_h1, rdoc_object, "BasicObject"], @c3_h2.super_classes
+  end
+
   def test_update_aliases_class
     n1 = @xref_data.add_module RDoc::NormalClass, 'N1'
     n1_k2 = n1.add_module RDoc::NormalClass, 'N2'