Fix Jbuilder#merge! inside block

lib/jbuilder.rb

@@ -255,18 +255,25 @@ def _extract_method_values(object, *attributes)
   def _merge_block(key, &block)
     current_value = _blank? ? BLANK : @attributes.fetch(_key(key), BLANK)
     raise NullError.build(key) if current_value.nil?
+    new_value = _scope{ yield self }
+    _merge_values(current_value, new_value)
+  end
 
-    value = _scope{ yield self }
-
-    if _blank?(value)
+  def _merge_values(current_value, updates)
+    if _blank?(updates)
       current_value
-    elsif _blank?(current_value) || value.nil?
-      value
+    elsif _blank?(current_value) || updates.nil?
+      updates
+    elsif ::Array === updates
+      current_value = ::Array === current_value ? current_value.dup : []
+      current_value.concat updates
     else
-      _merge_values(current_value, value)
+      current_value = current_value.dup
+      current_value.update updates
     end
   end
 
+
   def _write(key, value)
     @attributes = {} if _blank?
     @attributes[_key(key)] = value
@@ -302,19 +309,6 @@ def _mapable_arguments?(value, *args)
     value.respond_to?(:map)
   end
 
-  def _merge_values(attributes, hash_or_array)
-    attributes = attributes.dup
-
-    if ::Array === hash_or_array
-      attributes = [] unless ::Array === attributes
-      attributes.concat hash_or_array
-    else
-      attributes.update hash_or_array
-    end
-
-    attributes
-  end
-
   def _blank?(value=@attributes)
     BLANK == value
   end

test/jbuilder_test.rb

@@ -157,6 +157,24 @@ class JbuilderTest < ActiveSupport::TestCase
     assert_equal 32, result['author']['age']
   end
 
+  test 'support merge! method' do
+    result = jbuild do |json|
+      json.merge! 'foo' => 'bar'
+    end
+
+    assert_equal 'bar', result['foo']
+  end
+
+  test 'support merge! method in a block' do
+    result = jbuild do |json|
+      json.author do
+        json.merge! 'name' => 'Pavel'
+      end
+    end
+
+    assert_equal 'Pavel', result['author']['name']
+  end
+
   test 'blocks are additive via extract syntax' do
     person = Person.new('Pavel', 27)