Fix comment_location for merged ClassModule (#1531)

Fix #1530

Author: tompng

lib/rdoc/code_object/class_module.rb

@@ -477,7 +477,12 @@ def merge(class_module)
       document = document.merge other_document
 
       @comment = RDoc::Comment.from_document(document)
-      @comment_location = document
+
+      @comment_location = if document.parts.first.is_a?(RDoc::Markup::Document)
+                            document.parts.map { |doc| [doc, doc.file] }
+                          else
+                            [[document, document.file]]
+                          end
     end
 
     cm = class_module

test/rdoc/code_object/class_module_test.rb

@@ -655,8 +655,10 @@ def test_merge
     tl = @store.add_file 'one.rb'
     p1  = tl.add_class RDoc::NormalClass, 'Parent'
     c1  = p1.add_class RDoc::NormalClass, 'Klass'
+    c1.add_comment 'comment1', tl
 
     c2 = RDoc::NormalClass.new 'Klass'
+    c2.add_comment 'comment2', tl
 
     c2.merge c1
 
@@ -665,6 +667,10 @@ def test_merge
 
     assert c1.current_section, 'original current_section'
     assert c2.current_section, 'merged current_section'
+
+    comment, location = c2.comment_location.first
+    assert_kind_of RDoc::Markup::Document, comment
+    assert_equal tl.relative_name, location
   end
 
   def test_merge_attributes