Fix a bug not to use plugin root directory for buffer path even if configured correctly

lib/fluent/plugin/out_file.rb

@@ -93,14 +93,15 @@ def configure(conf)
 
       configured_time_slice_format = conf['time_slice_format']
 
-      # v0.14 file buffer handles path as directory if '*' is missing
-      # 'dummy_path' is not to raise configuration error for 'path' in file buffer plugin,
-      # but raise it in this plugin.
       if conf.elements(name: 'buffer').empty?
         conf.add_element('buffer', 'time')
       end
       buffer_conf = conf.elements(name: 'buffer').first
-      unless buffer_conf.has_key?('path')
+      # Fluent::PluginId#configure is not called yet, so we can't use #plugin_root_dir here.
+      if !buffer_conf.has_key?('path') && !(conf['@id'] && system_config.root_dir)
+        # v0.14 file buffer handles path as directory if '*' is missing
+        # 'dummy_path' is not to raise configuration error for 'path' in file buffer plugin,
+        # but raise it in this plugin.
         buffer_conf['path'] = conf['path'] || '/tmp/dummy_path'
       end
 

test/plugin/test_out_file.rb

@@ -22,8 +22,8 @@ def setup
     utc
   ]
 
-  def create_driver(conf = CONFIG)
-    Fluent::Test::Driver::Output.new(Fluent::Plugin::FileOutput).configure(conf)
+  def create_driver(conf = CONFIG, opts = {})
+    Fluent::Test::Driver::Output.new(Fluent::Plugin::FileOutput, opts: opts).configure(conf)
   end
 
   sub_test_case 'configuration' do
@@ -37,7 +37,29 @@ def create_driver(conf = CONFIG)
       assert_equal :gzip, d.instance.instance_eval{ @compress_method }
     end
 
+    test 'using root_dir for buffer path' do
+      system_conf_opts = {'root_dir' => File.join(TMP_DIR, 'testrootdir')}
+      buf_conf = config_element('buffer', '', {'flush_interval' => '1s'})
+      conf = config_element('match', '**', {'@id' => 'myout', 'path' => 'test_path', 'append' => 'true'}, [buf_conf])
+      d = create_driver(conf, system_conf_opts)
+
+      assert_equal 'test_path', d.instance.path
+      assert d.instance.append
+
+      assert d.instance.buffer.respond_to?(:path) # file buffer
+      assert_equal 1, d.instance.buffer_config.flush_interval
+
+      assert_equal File.join(TMP_DIR, 'testrootdir', 'worker0', 'myout'), d.instance.plugin_root_dir
+
+      buffer_path_under_root_dir = File.join(TMP_DIR, 'testrootdir', 'worker0', 'myout', 'buffer', 'buffer.*.log')
+      assert_equal buffer_path_under_root_dir, d.instance.buffer.path
+    end
+
     test 'path should be writable' do
+      assert_raise(Fluent::ConfigError.new("'path' parameter is required")) do
+        create_driver ""
+      end
+
       assert_nothing_raised do
         create_driver %[path #{TMP_DIR}/test_path]
       end