fix to dup default values to make it safe if plugins modify provided values

lib/fluent/config/section.rb

@@ -88,7 +88,7 @@ def self.generate(proxy, conf, logger, plugin_class, stack = [])
 
         proxy.defaults.each_pair do |name, defval|
           varname = name.to_sym
-          section_params[varname] = defval
+          section_params[varname] = (defval.dup rescue defval)
         end
 
         if proxy.argument

test/config/test_configurable.rb

@@ -158,6 +158,12 @@ class Example5
       config_param :secret_param2, :string, secret: true
     end
   end
+
+  class Example6
+    include Fluent::Configurable
+    config_param :obj1, :hash, default: {}
+    config_param :obj2, :array, default: []
+  end
 end
 
 module Fluent::Config
@@ -251,6 +257,37 @@ def e(attrs)
           assert_raise(Fluent::ConfigError) { b2.configure(default.merge({"opt2" => "fooooooo"})) }
           assert_raise(Fluent::ConfigError) { b2.configure(default.merge({"opt3" => "c"})) }
         end
+
+        sub_test_case 'default values should be duplicated before touched in plugin code' do
+          test 'default object should be dupped for cases configured twice' do
+            x6a = ConfigurableSpec::Example6.new
+            assert_nothing_raised { x6a.configure(e({})) }
+            assert_equal({}, x6a.obj1)
+            assert_equal([], x6a.obj2)
+
+            x6b = ConfigurableSpec::Example6.new
+            assert_nothing_raised { x6b.configure(e({})) }
+            assert_equal({}, x6b.obj1)
+            assert_equal([], x6b.obj2)
+
+            assert { x6a.obj1.object_id != x6b.obj1.object_id }
+            assert { x6a.obj2.object_id != x6b.obj2.object_id }
+
+            x6c = ConfigurableSpec::Example6.new
+            assert_nothing_raised { x6c.configure(e({})) }
+            assert_equal({}, x6c.obj1)
+            assert_equal([], x6c.obj2)
+
+            x6c.obj1['k'] = 'v'
+            x6c.obj2 << 'v'
+
+            assert_equal({'k' => 'v'}, x6c.obj1)
+            assert_equal(['v'], x6c.obj2)
+
+            assert_equal({}, x6a.obj1)
+            assert_equal([], x6a.obj2)
+          end
+        end
       end
     end
 

test/config/test_types.rb

@@ -128,6 +128,12 @@ class TestConfigTypes < ::Test::Unit::TestCase
 
     test 'array' do
       assert_equal(["1","2",1], Config::ARRAY_TYPE.call('["1","2",1]', {}))
+
+      array_options = {
+        default: [],
+      }
+      assert_equal(["1","2"], Config::ARRAY_TYPE.call('["1","2"]', array_options))
+      assert_equal(["3"], Config::ARRAY_TYPE.call('["3"]', array_options))
     end
   end
 end