Index: lib/redmine/unified_diff.rb
===================================================================
--- lib/redmine/unified_diff.rb	(revision 4232)
+++ lib/redmine/unified_diff.rb	(working copy)
@@ -38,9 +38,78 @@
         end
       end
       self << diff_table unless diff_table.empty?
+
+      each do |table|
+        lines = { 'left' => [], 'right' => [] }
+        table.keys.sort.each do |key|
+          v = table[key]
+          if v.same?
+            count = min(lines['left'].length, lines['right'].length)
+            0.upto(count - 1) do |idx|
+              l = lines['left'][idx]
+              r = lines['right'][idx]
+
+              table[l].line_left, table[r].line_right = highlight(table[l].line_left, table[r].line_right)
+            end
+
+            lines = { 'left' => [], 'right' => [] }
+            next
+          end
+
+          unless v.type_diff_left.empty?
+            lines['left'] << key
+          end
+          unless v.type_diff_right.empty?
+            lines['right'] << key
+          end
+        end
+
+        count = min(lines['left'].length, lines['right'].length)
+        0.upto(count - 1) do |idx|
+          l = lines['left'][idx]
+          r = lines['right'][idx]
+
+          table[l].line_left, table[r].line_right = highlight(table[l].line_left, table[r].line_right)
+        end
+      end
+
       self
     end

+    def max(a, b)
+      [a, b].max
+    end
+
+    def min(a, b)
+      [a, b].min
+    end
+
+    def highlight(src, dst)
+      def get_change_extent(src, dst)
+        start = 0
+        limit = min(src.length, dst.length)
+        while start < limit and src[start] == dst[start]
+          start += 1
+        end
+        stop = -1
+        limit = limit - start
+        while -stop <= limit and src[stop] == dst[stop]
+          stop -= 1
+        end
+        [start, stop + 1]
+      end
+
+      start, stop = get_change_extent(src, dst)
+      if start != 0 or stop != 0
+        last = stop + src.length
+        src = src[0, start] + '<del>' + src[start, last - start] + '</del>' + src[last, src.length]
+
+        last = stop + dst.length
+        dst = dst[0, start] + '<ins>' + dst[start, last - start] + '</ins>' + dst[last, dst.length]
+      end
+      [src, dst]
+    end
+
     def truncated?; @truncated; end
   end

@@ -186,5 +255,9 @@
       puts self.nb_line_right
       puts self.line_right
     end
+
+    def same?
+      @type_diff_left.empty? and @type_diff_right.empty?
+    end
   end
 end
Index: public/stylesheets/scm.css
===================================================================
--- public/stylesheets/scm.css	(revision 4232)
+++ public/stylesheets/scm.css	(working copy)
@@ -193,3 +193,13 @@
 .syntaxhl .del .del { color: #800; font-weight:bold }
 .syntaxhl .chg .chg { color: #66f; }
 .syntaxhl .head .head { color: #f4f; }
+
+.syntaxhl td ins, .syntaxhl td del { text-decoration: none; }
+.syntaxhl ins {
+ background: #9e9;
+ color: #000;
+}
+.syntaxhl del {
+ background: #e99;
+ color: #000;
+}
\ No newline at end of file