Enable to set nil to parameters in config file

Example setting:

  username: "#{ENV['USERNAME'] || raise(SetNil)}"

Signed-off-by: Takuro Ashie <ashie@clear-code.com>

lib/fluent/config/error.rb

@@ -23,4 +23,7 @@ class ConfigParseError < ConfigError
 
   class ObsoletedParameterError < ConfigError
   end
+
+  class SetNil < ConfigError
+  end
 end

lib/fluent/config/literal_parser.rb

@@ -81,7 +81,11 @@ def scan_double_quoted_string
         string = []
         while true
           if skip(/\"/)
-            return string.join
+            if string.include?(nil)
+              return nil
+            else
+              return string.join
+            end
           elsif check(/[^"]#{LINE_END_WITHOUT_SPACING_AND_COMMENT}/)
             if s = check(/[^\\]#{LINE_END_WITHOUT_SPACING_AND_COMMENT}/)
               string << s
@@ -168,7 +172,11 @@ def eval_embedded_code(code)
 hostname = Socket.gethostname
 worker_id = ENV['SERVERENGINE_WORKER_ID'] || ''
 EOM
-        @eval_context.instance_eval(code)
+        begin
+          @eval_context.instance_eval(code)
+        rescue SetNil => e
+          nil
+        end
       end
 
       def eval_escape_char(c)

lib/fluent/config/types.rb

@@ -87,9 +87,13 @@ def self.regexp_value(str, opts = {}, name = nil)
     end
 
     STRING_TYPE = Proc.new { |val, opts = {}, name = nil|
-      v = val.to_s
-      v = v.frozen? ? v.dup : v # config_param can't assume incoming string is mutable
-      v.force_encoding(Encoding::UTF_8)
+      if val.nil?
+        nil
+      else
+        v = val.to_s
+        v = v.frozen? ? v.dup : v # config_param can't assume incoming string is mutable
+        v.force_encoding(Encoding::UTF_8)
+      end
     }
 
     ENUM_TYPE = Proc.new { |val, opts = {}, name = nil|

test/config/test_literal_parser.rb

@@ -240,6 +240,7 @@ def test_falseX
         assert_text_parsed_as("foo1", '"foo#{worker_id}"')
         ENV.delete('SERVERENGINE_WORKER_ID')
       }
+      test('nil') { assert_text_parsed_as(nil, '"#{raise SetNil}"') }
     end
 
     sub_test_case 'array parsing' do

test/config/test_types.rb

@@ -149,6 +149,10 @@ class TestConfigTypes < ::Test::Unit::TestCase
       assert_equal Encoding::UTF_8, Config::STRING_TYPE.call(val, {}).encoding
     end
 
+    test 'string nil' do
+      assert_equal nil, Config::STRING_TYPE.call(nil, {})
+    end
+
     data('latin' => 'Märch',
          'ascii' => 'ascii',
          'space' => '     ',