1 files changed, 10 insertions, 4 deletions
diff --git a/activesupport/lib/active_support/core_ext/hash/deep_merge.rb b/activesupport/lib/active_support/core_ext/hash/deep_merge.rb
index 023bf68a87..22acedcf81 100644
--- a/activesupport/lib/active_support/core_ext/hash/deep_merge.rb
+++ b/activesupport/lib/active_support/core_ext/hash/deep_merge.rb
@@ -6,15 +6,21 @@ class Hash
   #
   #   h1.deep_merge(h2) #=> {:x => {:y => [7, 8, 9]}, :z => "xyz"}
   #   h2.deep_merge(h1) #=> {:x => {:y => [4, 5, 6]}, :z => [7, 8, 9]}
-  def deep_merge(other_hash)
-    dup.deep_merge!(other_hash)
+  #   h1.deep_merge(h2) { |key, old, new| Array.wrap(old) + Array.wrap(new) }
+  #   #=> {:x => {:y => [4, 5, 6, 7, 8, 9]}, :z => [7, 8, 9, "xyz"]}
+  def deep_merge(other_hash, &block)
+    dup.deep_merge!(other_hash, &block)
   end
 
   # Same as +deep_merge+, but modifies +self+.
-  def deep_merge!(other_hash)
+  def deep_merge!(other_hash, &block)
     other_hash.each_pair do |k,v|
       tv = self[k]
-      self[k] = tv.is_a?(Hash) && v.is_a?(Hash) ? tv.deep_merge(v) : v
+      if tv.is_a?(Hash) && v.is_a?(Hash)
+        self[k] = tv.deep_merge(v, &block)
+      else
+        self[k] = block && tv ? block.call(k, tv, v) : v
+      end
     end
     self
   end