Optimized merging algorithm

1 files changed, 9 insertions, 3 deletions

diff --git a/sphinx/versioning.py b/sphinx/versioning.py
index 753629042..5f3254554 100644
--- a/sphinx/versioning.py
+++ b/sphinx/versioning.py
@@ -45,11 +45,17 @@ def merge_doctrees(old, new, condition):
     old_nodes = old.traverse(condition)
     new_nodes = new.traverse(condition)
     ratios = defaultdict(list)
+    seen = set()
     for old_node, new_node in product(old_nodes, new_nodes):
-        ratios[old_node, new_node] = get_ratio(old_node.rawsource,
-                                               new_node.rawsource)
+        if new_node in seen:
+            continue
+        ratio = get_ratio(old_node.rawsource, new_node.rawsource)
+        if ratio == 0:
+            new_node.uid = old_node.uid
+            seen.add(new_node)
+        else:
+            ratios[old_node, new_node] = ratio
     ratios = sorted(ratios.iteritems(), key=itemgetter(1))
-    seen = set()
     for (old_node, new_node), ratio in ratios:
         if new_node in seen:
             continue