Compatibility layers for v0.12 plugins (#912)

* Add Base#inspect to show this object in simple/short way

* add fluent/compat/filter and make Fluent::Filter with it

* add fluent/compat/input and make Fluent::Input with it

* add comments about time handling

* fix to extend chunk to add method for event iteration

* fix test with added (missing) error definition

* remove fileutils

* add optimization

* take care about NaN & Inf

* add buffer path pattern only for suffix

* initialize minimal internal things as early as possible for tests

* Add compatibility layers for output plugin
* change internal APIs to emit events to plugins/routers with newer one
* remove all output chains from cores

* fix tests for core modules/classes with newer API

* fix to use test driver for buffered output

* re-implement symlink_path feature on v0.14 buffer APIs

* add break condition to wait checks to run

* update comments for correctness

* add deprecation warning for "type" in secondary section

* fix to use more explicit name

* fix tests for exponential_backoff

* for readability

* remove/merge dup code

lib/fluent/agent.rb

@@ -160,7 +160,7 @@ def initialize(log)
         @count = 0
       end
 
-      def emit(tag, es, chain)
+      def emit_events(tag, es)
         # TODO use time instead of num of records
         c = (@count += 1)
         if c < 512

lib/fluent/compat/filter.rb

@@ -0,0 +1,26 @@
+#
+# Fluentd
+#
+#    Licensed under the Apache License, Version 2.0 (the "License");
+#    you may not use this file except in compliance with the License.
+#    You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS,
+#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#    See the License for the specific language governing permissions and
+#    limitations under the License.
+#
+
+require 'fluent/plugin'
+require 'fluent/plugin/filter'
+
+module Fluent
+  module Compat
+    class Filter < Fluent::Plugin::Filter
+      # TODO: warn when deprecated
+    end
+  end
+end

lib/fluent/compat/input.rb

@@ -0,0 +1,26 @@
+#
+# Fluentd
+#
+#    Licensed under the Apache License, Version 2.0 (the "License");
+#    you may not use this file except in compliance with the License.
+#    You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS,
+#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#    See the License for the specific language governing permissions and
+#    limitations under the License.
+#
+
+require 'fluent/plugin'
+require 'fluent/plugin/input'
+
+module Fluent
+  module Compat
+    class Input < Fluent::Plugin::Input
+      # TODO: warn when deprecated
+    end
+  end
+end