fix: C variables should never show up in Ancestors tree

lib/rdoc/rdoc.rb

@@ -415,6 +415,8 @@ def parse_files files
       parse_file filename
     end.compact
 
+    @store.resolve_c_superclasses
+
     @stats.done_adding
     @options = original_options
 

lib/rdoc/store.rb

@@ -197,6 +197,18 @@ def add_file absolute_name, relative_name: absolute_name, parser: nil
     top_level
   end
 
+  ##
+  # Make sure any references to C variable names are resolved to the corresponding class.
+  #
+
+  def resolve_c_superclasses
+    @classes_hash.each_value do |klass|
+      if klass.superclass.is_a?(String) && (candidate = find_c_enclosure(klass.superclass))
+        klass.superclass = candidate
+      end
+    end
+  end
+
   ##
   # Sets the parser of +absolute_name+, unless it from a source code file.
 

test/rdoc/test_rdoc_store.rb

@@ -281,6 +281,26 @@ def test_find_c_enclosure_from_cache_legacy
     assert_nil @s.find_c_enclosure('cObject')
   end
 
+  def test_resolve_c_superclasses
+    # first parse a child that references an unknown parent
+    c_file1 = @s.add_file 'ext1.c'
+    c_file1.add_class RDoc::NormalClass, 'Child', 'cExternParent'
+
+    # then parse the parent and register the C variable name as a C enclosure
+    c_file2 = @s.add_file 'ext2.c'
+    parent = c_file2.add_class RDoc::NormalClass, 'Parent', 'rb_cObject'
+
+    @s.add_c_enclosure('cExternParent', parent)
+
+    # at this point, the child's superclass is still the name of the C variable
+    assert_equal("cExternParent", @s.classes_hash['Child'].superclass)
+
+    @s.resolve_c_superclasses
+
+    # now the ancestor tree correctly references the NormalClass objects
+    assert_equal(parent, @s.classes_hash['Child'].superclass)
+  end
+
   def test_find_class_named
     assert_equal @c1, @store.find_class_named('C1')