From 444219bb175602264dd7e74760cee629f60ee654 Mon Sep 17 00:00:00 2001
From: Havoc Pennington <hp@pobox.com>
Date: Tue, 29 Nov 2011 10:02:26 -0500
Subject: [PATCH] Optimize no-op object merges by throwing away the new HashMap
 and using the old one

One side effect of this is that if an object merge does nothing, the ConfigOrigin
for the fallback is discarded instead of merged in, but I think that's OK.
---
 .../config/impl/AbstractConfigObject.java     | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/config/src/main/java/com/typesafe/config/impl/AbstractConfigObject.java b/config/src/main/java/com/typesafe/config/impl/AbstractConfigObject.java
index 3f7cc0ed..7a5868da 100644
--- a/config/src/main/java/com/typesafe/config/impl/AbstractConfigObject.java
+++ b/config/src/main/java/com/typesafe/config/impl/AbstractConfigObject.java
@@ -135,6 +135,7 @@ abstract class AbstractConfigObject extends AbstractConfigValue implements
         if (ignoresFallbacks())
             throw new ConfigException.BugOrBroken("should not be reached");
 
+        boolean changed = false;
         boolean allResolved = true;
         Map<String, AbstractConfigValue> merged = new HashMap<String, AbstractConfigValue>();
         Set<String> allKeys = new HashSet<String>();
@@ -150,12 +151,26 @@ abstract class AbstractConfigObject extends AbstractConfigValue implements
                 kept = first;
             else
                 kept = first.withFallback(second);
+
             merged.put(key, kept);
+
+            if (first != kept)
+                changed = true;
+
             if (kept.resolveStatus() == ResolveStatus.UNRESOLVED)
                 allResolved = false;
         }
-        return new SimpleConfigObject(mergeOrigins(this, fallback), merged,
-                ResolveStatus.fromBoolean(allResolved), fallback.ignoresFallbacks());
+
+        ResolveStatus newResolveStatus = ResolveStatus.fromBoolean(allResolved);
+        boolean newIgnoresFallbacks = fallback.ignoresFallbacks();
+
+        if (changed)
+            return new SimpleConfigObject(mergeOrigins(this, fallback), merged, newResolveStatus,
+                    newIgnoresFallbacks);
+        else if (newResolveStatus != resolveStatus() || newIgnoresFallbacks != ignoresFallbacks())
+            return newCopy(newResolveStatus, newIgnoresFallbacks);
+        else
+            return this;
     }
 
     @Override